Solar design tips, sales advice, and industry insights from the premier solar design software platform

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solar design | Solar design tips, sales advice, and industry insights from the premier solar design software platform

One of the challenges of the current economic climate is that solar installers have to do more with less. In the past, a solar sales rep could be responsible solely for door-to-door knocking. Once they secured a lead, they could then set an appointment for the solar designer to visit the home to design the appropriate system.

In today’s solar industry, however, things are moving much faster. In order to compete in today’s market, solar installers need to improve their operational efficiency or they could get left behind by their competition.

Luckily, new tools are rapidly being developed to help both the solar sales rep and the solar designer (who, let’s face it, are sometimes the same person).

In this post we’ll cover three new tools that we’ve developed to help make designing a solar installation faster.

## 1. Battery Storage

According to Aurora’s Technology Benchmark Survey, over 70% of solar installers are selling storage today. While solar + storage is a great way to boost solar sales, it also presents a lot of headaches for solar sales reps.

According to the survey, 92% of installers currently use design, site assessment or shading analysis software, however, most installers don’t have a designated tool to use for backup calculation and sizing recommendations. Many solar installers make highly generalized sales recommendations because they are unable to confidently calculate sizing based on the backup capacity that the homeowner wants.

Aurora’s new battery storage feature will be a game changer for the industry as it’s the only tool on the market that can calculate backup requirements and provide battery storage sizing recommendations. Simply plug in how much backup capacity your customer wants, and Aurora will give you the most compelling backup sizing recommendation. Once the feature launches you'll be able to take your battery storage deal from backup calculation to sales proposal in 10 minutes or less.

You can watch a sneak peek video of the solar storage tool in action here as well as sign up for early access.

## 2. Fit Trees to LIDAR

One of the most difficult pieces of designing a solar system is making sure you account for shading. Most shading analysis tools can do a good job of modeling shading with the correct inputs. The tricky part is getting those inputs right.

One of the most difficult inputs for installers are trees. Aurora’s latest feature, Fit Trees to LIDAR, helps solar designers model trees by automatically modeling the tree height using LIDAR data. All a designer has to do is pick the location and type of tree (conical or round), and the Aurora engine will automatically model the height and crown height. This helps designers cut down project design times so they can spend more of their time on the most important task, designing a great pv system.

Experienced solar installers know that a solar system is only as good as its weakest link. Solar power functions like a system of pipes, if there’s a clog in one pipe it affects the flow of other pipes around it. For example, if one solar panel is covered by shade, it can affect the power generation of the panels around it.

Many solar tools use irradiance mapping to give a general idea of what the power generation will be on the face of a roof. What those tools don’t account for is how much irradiance each panel will experience once placed on the roof. Aurora’s new Irradiance on Panels feature takes into account shading from obstructions, trees, and nearby panels (also known as inter-row shading). This allows sales reps and designers to quickly and confidently troubleshoot a design and present an efficient design that reduces shading on the system.

Solar Storage Feature

Fit Trees to LIDAR Feature

Topics: solar design

Even before social distancing drastically expanded remote work, remote PV system design was a smart choice. According to NREL, remote solar design software can reduce solar costs by up to 0.17/W. However, remotely designing a PV system requires a reliable 3D model to provide an accurate calculation of the system’s potential energy production. Fortunately, you don’t have to do this on your own — or even with just your small (and already busy) team. Today you can instantly expand your design team at any time by using a 3D modeling service with just a click of a button. Using Aurora’s 3D modeling service, you can get an accurate PV system model that shows: • Detailed 3D image of the potential system • Shading analysis for each hour of the year • Sun-path simulation • Energy production estimate • Customer savings estimate And the best part? Aurora’s modeling service is built right into the platform. So, if you start a design and get stuck, you can quickly get help with it from a designer who will have your design ready in as little as 3 hours! But, the benefits of using 3D modeling services go far beyond just saving time. Here are 4 additional benefits to supplementing your 3D modeling: ## 1. Scale Quickly We all know that solar system demand fluctuates seasonally. This can make hiring enough full-time designers to handle peak demand difficult for solar installers. Solar contractors often face a double-edged sword when it comes to staffing. While a larger design team may seem overstaffed during the slower seasons, a leaner design team may struggle to keep up with peak seasonal demand. A 3D modeling service fills this gap by allowing businesses to instantly flex their team’s capacity to meet seasonal demand fluctuations. ## 2. Enhance Your Customer Experience Solar buyers appreciate quick service — as long as it’s quality service too. A solar modeling service provides both. Taking advantage of a short 3 hour turnaround time, a solar consultant can impress a buyer with a realistic 3D system model the same day that they pitch them. And, more importantly, the model can also provide an accurate, detailed estimate of the customer's potential savings, helping close the deal right then and there. Additionally, in a post pandemic world, many customers may be wary of inviting others (such as solar sales consultants) into their homes. Fortunately, solar sales reps can use the solar design service to get around this limitation while still providing the same high level of accuracy and detail as they would with an in-person meeting. ## 3. Save Your Sales Team’s Time In many solar businesses, sales reps often have to spend time learning about 3D modeling to create them for customers. That’s time they could have spent closing more sales instead Using a 3D modeling service enables these businesses to free up their sales teams’ time. Andrew Spalding, a sales rep at Aurora, has noticed an additional benefit for his customers as well: “By using a 3D modeling service, solar installers don’t need to train new salespeople to design systems. This allows them to scale up their sales team much faster and with minimal training.” ## 4. Ensure Accuracy & Reduce Cancellations If there’s one thing solar customers want from a company, it’s reliability. At the prospect stage, this includes an accurate and realistic estimate of their roof’s solar energy potential. A common problem sales reps face is when a proposed solar system design doesn’t actually match up with the home’s structure. When this happens, the solar sales rep has to come back to the customer to make the necessary changes and many customers simply cancel their order instead of dealing with the hassle. Using Nearmap imagery, along with LIDAR, shading and irradiance engines, Aurora’s 3D modeling provides the most accurate design on the market. An added benefit is that once these parameters have been finalized by the designer, they can be locked so that they aren’t modified and don’t lose their accuracy. Since design services allow businesses to provide accurate estimates even for challenging locations, solar customers can feel confident that they’re receiving a reliable PV model and energy savings estimate. ## Takeaways and Next Steps Solar design services allow solar companies to: • Scale instantly • Enhance the customer’s experience • Optimize their sales team’s work time • Ensure accurate estimates • Reduce cancellations Whether you’ve been in the solar business for years or are just starting out, giving a 3D modeling service a try is a great way to see how it works and whether it can help scale your business. Seneca Schachter, a Senior Account Executive at Aurora, sums it up perfectly when he says, “3D modeling services help small and medium sized solar businesses because they can quickly produce professional, accurate designs and quotes for faster lead conversions.” With a fluctuating economy, fluctuating your solar design resources becomes an incredibly valuable tool in any business’s toolkit. If you’d like to see how our 3D modeling service works, you can schedule a free demo using the Demo button above. Topics: solar design While solar softwares can help design the optimal PV system, the components you select will also make a difference in achieving the desired energy production. One particular component type—the smart module—has been increasing in popularity because of its benefits compared to traditional modules. If you haven’t considered smart modules (also known as DC-optimized modules) they’re worth a look. ## What Is a Smart Solar Module? A smart module is a solar panel with an integrated DC power optimizer. Smart modules will have the power optimizers pre-attached to them, and the optimizers help each panel operate at its maximum power level regardless of how the other panels on the same string are performing. This allows for more energy to be harvested from the smart module PV systems. The tradeoff of using smart modules comes down primarily to cost. The price tag might be higher, but the benefits from smart solar modules may be more attractive depending on the situation. ## Top 3 Benefits of Smart Modules 1. Increased energy production: As mentioned earlier, a PV system using smart modules can produce more energy compared to a traditional system. With the embedded DC optimizers, each module is able to correct for its “mismatch” and function independently from one another, resulting in more energy production. 2. Lower soft costs: Smart modules can help streamline purchasing processes and reduce installation time. Instead of having to source a vendor for both panels and DC optimizers and order them, you only need to do it for one hardware. Also, installers won’t need to carry multiple hardwares up to the roof, install and connect them. Faster installation times can lower labor costs, and the savings could be passed down the end customer. 3. Faster troubleshooting: Since smart modules operate independently of one another, you can monitor the performance of each module. If maintenance is required or the system is underperforming, you’ll have a much easier time identifying which panel(s) need attention. ## When to Use Smart Modules Smart modules (or adding power optimizers to your PV system) are typically ideal for situations where shading is a problem or if the PV system will be installed on multiple roof surfaces. For systems on a roof surface with no shade throughout the day, in an area with great weather almost year round (like Southern California), a traditional system may be the ideal choice. Before selecting which components to use, it’s important to have a full understanding of each component and what your options are, and know how much solar energy (or irradiance) is available at the project site. Depending on the situation and what you’re trying to solve for, smart modules may be the best option or there might be another suitable solution at a lower price point. A solar panel spec sheet provides valuable information about the operating parameters of a panel, and can help designers, engineers, and installers determine how to configure a solar PV system. "The panel spec sheet will tell you about the panel's electrical power production, including its efficiency and how it operates with changing temperatures, as well as mechanical information like the dimensions and wind loads,” says Andrew Gong, research engineer for Aurora Solar. "This information is required to get an accurate performance simulation," he adds. ## Understanding the Pmax Rating The first value people should pay attention to is the maximum power point (Pmax) rating. “Maximum power point is a combination of voltage and current,” he says. It’s the combination of volts and amps that creates the highest wattage. “If you lower the current and increase the voltage, you move away from the maximum power point,” says Gong. Typically, solar panels are rated between 250 and 400 watts. Higher wattage generally means a system will be more efficient and require fewer modules. ## Voltage is Important Voltage is also an important consideration. If, for example, a designer decided on 12 panels in a string, it’s important to make sure the voltage doesn’t exceed certain thresholds. “You want to size the system so it doesn’t exceed 600 volts per string,” Gong explains. Above that, the panel won’t operate as well. ## Solar Panel Efficiency Installers, engineers, and designers should consider efficiency ratings. On average, solar panel efficiency ranges from 15% to 20%, with some panels as high as 23%. As cell technology improves, so do efficiency ratings. A spec sheet also provides information about the assumptions used to create a panel’s operating parameters. For example, SunPower's spec sheet provides a range of temperatures, from -40 C degrees F to 85 degrees C. That’s listed under Operating Condition and Mechanical Data. “In colder temperatures, panels operate a bit better,” says Gong. ## In Extreme Weather, Consider Temperature Ranges The temperature ranges of modules generally are between -20 degrees C to +85 degrees C in the U.S. In areas with more extreme temperatures—such as Alaska—installers and designers should be aware of panels’ temperature ranges. Another value is the operating cell temperature, says Gong. “Some panels run hotter than others. This value tells you how modules respond to various levels of sunlight.” It’s also important to understand current in panels. Under the heading of electrical data, a spec sheet provides a rated current. “If you exceed the current, you destroy the panel,” says Gong. “Maximum current depends on the panel and how many parallel strings in the system,” he says. ## Ratings That are Important in Areas With High Winds In areas of extreme weather—those susceptible to high winds or snow—installers should pay attention to the mechanical or static load ratings. The front side rating focuses on the snow load, and the back side rating is about the wind load. The load figures appear in Pascals, a unit of pressure. Higher numbers mean the panel is stronger. ## Warranties Can Vary Spec sheets also mention warranties. Most have 25-year warranties, according to Gong. Some manufacturers offer a 90% warranty for 10 years, and decrease that amount as the panels age. Premium panels have better warranties. Once you’ve gathered this and other data from a spec sheet, you can load the data into Aurora Solar or other software and create a picture of how the panels will fare. Topics: solar design, solar installation For Andy McCarthy, founder of Gippsland Solar, integrating 666 solar panels into the design for the Penguin Parade Visitor Centre in Australia posed a big challenge. That’s because at the time Gippsland Solar was bidding for the project, the Centre’s new building had not yet been built! The new building, which houses 1,800 square meters of interpretation and public spaces, replaced an existing building and featured an unusual roof shape for the internationally renowned center. Using functionality in Aurora Solar software, Gippsland solar won the project. In this article, McCarthy shares the process and insights on how you too can put in place a winning system for designing solar for new buildings. Gippsland Solar’s PV design for the Penguin Parade Visitor Centre in Australia as the building neared completion. Photo Credit: Kane Construction, courtesy of Gippsland Solar. ## The Challenge of Designing Solar for a Building Not Yet Built The challenge: All Gippsland Solar had to work with were the architectural plans. Because the building did not yet exist, it wasn’t possible to physically measure the roof and calculate how many panels would be required, or to measure irradiance to determine how it would affect solar production and where best to place panels. What’s more, it was difficult to communicate to the client what the building would look like once the solar panels were added. With a building as high-profile as the Penguin Parade Visitors Centre, aesthetics were an important issue. “It was an interesting project because of the Centre’s global recognition,” says McCarthy. In addition, without a physical building, it wasn’t easy to calculate how nearby trees or other buildings would shade the roof throughout the year. In the case of the visitor center, the challenge was more difficult than most new construction solar projects. ## A Unique Roof for an Internationally Recognized Visitor Center “The roof almost looks like shards of glass cut in different angles; it’s spectacular,” says McCarthy. “The building has lots of innovation and design and has won sustainability awards.” Viewed from above, the building’s shape is similar to an unwieldy star, with many different roof points and angles. “Due to the architecture of the building, it was a very complex roof to work with,” McCarthy says. At first, McCarthy and his associates tried adding solar panels to the architectural plans. “It didn’t look good,” he says. It was back to the drawing board. McCarthy needed a tool that would communicate to the potential client exactly how the building would look with solar panels. ## Finding a Solution to Design Solar for New Construction: Aurora Solar Software Next, Gippsland Solar turned to Aurora Solar’s solar software and tried the design again. “We took the electronic version of the building plans and uploaded them into Aurora,” he explains. They took the measurement of the longest section of the roof from the architectural plans, then manually entered that measurement into Aurora program. The software is smart enough to take that information and calculate the rest of the dimensions of the roof, McCarthy explains. In fact, from that information, Aurora’s SmartRoof technology created a 3-D model of the roof. Next, based on the information in the roof plans, McCarthy and associates increased the roof pitch to 11 degrees. “That was the pitch of the roof,” he explains. “We didn’t see any financial benefit in using tilt frames to adjust the pitch, and the architects were very clear that they didn’t want the solar array to have a visual impact on the building itself,” he says. What happened next surprised them. In the model, it looked like the building was being built. “I had never seen anything like that,” he says. “It almost looked like paper mache. In the model you see the building rise up.” The model allowed for a 360-degree view of the building. It took about half an hour to build the model using the software, McCarthy says. He’s sure that using the program helped his company get the job. A top-down view of Gippsland Solar’s PV design for the Penguin Parade Visitor Centre in Australia. Photo Credit: Kane Construction, courtesy of Gippsland Solar. ## New Buildings Pose Challenges, Opportunities for Solar Designing solar for new buildings like the Penguin Parade Visitors Centre poses challenges, and more and more solar companies are grappling with this challenge. But it’s not necessarily bad news. Because states and cities are calling for solar panels in new construction, the market for solar is increasing. For example, beginning in 2020, California mandates solar panels on all new homes under the state building code. As a result, solar demand is expected to jump by more than 800 MW between 2020 and 2023. Under the new California solar mandate, builders must either build homes with solar panels, or build a shared solar power system that provides solar energy to a group of homes. Additionally, cities all over the U.S. are calling for solar on new buildings. Watertown, Massachusetts now requires solar on new commercial buildings larger than 10,000 square feet and on all new residential buildings with ten or more units. With the market increasing for new construction solar, it’s a good idea to have a tool that speeds up the process. ## 3 Simple Steps to Designing Solar for New Construction (Buildings Not Yet Built) ### 1. Begin by Uploading Roof Plans When designing a solar installation for a new (not yet constructed) building using Aurora software, the most important step is to upload the roof plans. With that as your starting point, outline the perimeter of the roof—just as you would draw over a satellite or aerial image when using Aurora to design solar for an existing building. You’ll need to include a measure for at least one section of the roof as indicated in the plans. This data allows Aurora to correctly scale the 3D model and ensure accurate measurements for the remaining sections. It’s also important to indicate the pitch of different roof planes according to the architects’ plans, since there will not be 3D LIDAR data for Aurora to match the roof to if the building is not yet constructed. From there, Aurora’s SmartRoof technology will extrapolate the 3D structure of the rest of the building. If your designers need to make tweaks the building model, the program will respond by re-calculating and re-modeling, McCarthy explains. ### 2. Simulate Shading During Different Times of Day, Year Another important feature of the Aurora software is the Sun Path simulation, which can do an interactive shade simulation. “When you play the simulation, you can see how certain parts of the roof will be shaded during certain times of day and can play with the design and move panels to less shady areas,” McCarthy explains. With a colorful irradiance map, the software will tell you how much irradiance will reach the panels at any given point on the roof. Adding trees to see how they will shade the roof of new buildings is also important, he says. By creating multiple versions of your design with different tree heights you can virtually “grow” young trees to see how they will shade the roof as they mature. #### How Will Other Buildings Affect Shading? Along with modeling the effect of trees, designers should simulate how nearby buildings affect shading, McCarthy says. For example, in another new construction solar project, Gippsland Solar added solar to a school that was built in two stages. To do this, the company used Aurora to model the second section of the building and see how it would affect the first section—and vice versa. Company designers did all the modeling before designing the first building. “We ran a shade analysis of both the old and new buildings,” he says. ### 3. Close the Sale with Stunning Visuals Such modeling saves time, impresses clients, and also saves money, says McCarthy. It makes sense to avoid trying to overlay solar panels on architectural designs--and to choose instead design software. “Aurora is a fraction of the cost of 3-D simulations with architects’ software,” he says. “People need to build this into their sales pitches. It helped us get the job.” As the market for solar on new construction grows, so too will the need for scalable, accurate solutions for designing solar for buildings that have not yet been built if your company wants to tap into this market. If you’re a solar salesperson or contractor in the U.S., you know that net energy metering (NEM) policies—which traditionally pay solar system owners the retail electricity rate for the solar energy they produce—play a key role in providing a strong return on a solar investment. But you may also have observed the trend of utilities around the country, modifying and scaling back their net metering rules. We took a close look at this a phenomenon in our recent white paper, Analysis of U.S. Net Metering Policy Changes in the United States, so we could tell you the impact of specific policy changes and how to adapt to them. In our previous article, we shared our findings on how some of these common net metering changes impact solar customers’ solar savings and utility bills. This follow-up blog post provides a quick visual summary of how those rules result in new design rules of thumb to maximize your customers’ solar savings. (In our white paper we provide more detailed recommendations for maximizing NPV under specific utility's policies.) ### Designing Around Export Rules NEM rules that reduce the value of exported solar energy will impact all customers who export energy to the grid. One bright side is that customers who self-consume all of the energy their PV system produces won’t be bothered by the change. Here’s a convenient way to look at the customer’s annual utility bill against their energy offset level, for a household with moderate energy consumption: The important points on this graph are where the chart “bottoms out”—this represents where a customer’s bill is comprised only of minimum or fixed charges. Adding more PV panels after this point won’t increase the customer’s solar savings any further. While some customers might see a small amount of cash credit from net surplus compensation, it doesn’t justify the additional cost to increase the system size. A second important takeaway is that the reduction in exported value—whether it be from a non-bypassable charge, fixed export rate, or percentage reduction—results in needing a larger system (read: greater energy offset) to reach that level. If we look at the Net Present Value of a PV system (essentially the equivalent cash value of all of the costs and savings for the project) it tends to get maximized at the point which the customer’s bill is minimized. Looking at the curves, it’s clear that these value-reduction rules reduce NPV; however, in many cases, they also move the peak of that curve further to the right: customers need a larger system to maximize their NPV. Installers could use this to try to upsize systems creating a win-win for both themselves and customers, but they should also be careful to not exceed sizing limitations of the customer’s utility. For example, NV Energy has a fairly strict 100% offset limit which puts the target 105% out of reach, but other areas do offer the option to go larger. ### Finding the Best Payback Period The payback period of the system is how long it takes for a customer to recoup their investment, in terms of nominal dollars. An interesting case with a tiered rate structure is that a partial-offset system, say around 50%, might offer the minimum payback period because it offsets the more expensive energy in higher price tiers. Adding on more PV after this point is still advantageous in terms of NPV, but it will increase the payback period by a few months to a year. However, in the case of utilities that have implemented a flat export rate for solar customers instead of pricing their exported energy based on their current usage tier, you lose this effect. There’s no longer an incentive to sit at the midpoint of energy offset to reduce payback time. ### Sizing Guidelines Under Disadvantageous Expiration Policies There are several states and utilities that have established expiration times for accrued solar energy credits that are disadvantageous for the solar customer. The seasonal nature of solar makes it so that a credit expiration cycle at the end of summer or early winter forces the homeowner to buy energy in the winter months without the option to offset these costs with credits from their prior solar energy production. We found that customers whose utilities do not allow them to carry net metering credits from one month to the next (or who only get wholesale avoided cost compensation) will start to lose credits if their system offset is greater than 70%. That might be a reasonable threshold to target when designing in regions that have this ruleset. For customers with a specified annual credit expiration cycle, the decision is a little more complex. Customers with an expiration month in June, July, and August will often see credit loss above a 75% offset threshold. If the cycle ends in April, May, September, or October the threshold is around 85%, and November, December, and January expirations might see losses at a threshold of 90%. February and March expiration months are almost equivalent to a utility policy where the credits aren’t reset every year. Finding the optimal solar design for your customer can be challenging and utility changes to net metering rules add additional complexity. However, having a solid grounding in these best practices can help. To see our full findings on this topic, including specific recommendations for how much of your customer’s energy consumption to offset in different utility regions, download the complete white paper. Remote solar design would not be possible without good map data. Map data helps answer basic questions like how many panels can fit on a roof, as well as more complex issues like which areas of the roof are shaded and at what time of day. Aurora has always tried to give our users access to the best possible data, including HD Imagery from Nearmap and our repository of LIDAR data. In that spirit, Aurora recently announced that we are partnering with Google's Project Sunroof to bring better 3D and imagery data to our users. This partnership will get high quality map data into the hands of more solar installers so that designing solar becomes faster, easier, and more accurate in many regions across the US and even across the globe. Project Sunroof uses Google's huge repository of 3D map data to analyze the solar potential of millions of roofs. Their data covers over half of US households, and many cities across the world. Curious homeowners can go to the Project Sunroof website and check the solar potential of their roofs. Local governments can also use their data explorer to look at solar potential on a city scale so they can plan for things like grid management and incentives. This partnership will get high quality map data into the hands of more solar installers so that designing solar becomes faster, easier, and more accurate in many regions across the US and even across the globe. An estimate of solar capacity in Manhattan, courtesy of Project Sunroof. With this new partnership, installers will be able to combine Google's 3D map data with Aurora's CAD, shading, performance simulation and financial analysis engine. This will combine the global reach of Google's data with the accuracy of designing a solar installation in Aurora. This will make installers' jobs easier, and in turn help bring solar to more homes across the country. A sample of the Google 3D data available in Aurora. Aurora users can continue to access our wide coverage of LIDAR in the US, but will now also get access to 3D data through Project Sunroof in new locations such as Reno, Phoenix, California's Central Valley, and Chicago—as well as worldwide locations such as Paris, London, Tokyo, and Berlin. ## How Google Captures Data Using Photogrammetry You may be wondering where all of this data comes from. Google uses planes equipped with custom cameras to fly over cities and capture images from many different angles. The planes capture images from 5 different angles: straight down, forward, back, right, and left. Then proprietary algorithms combine all of these images together into a 3D model. This process is called photogrammetry, from the word photograph and the suffix -ometry, meaning to measure. An illustration of how multiple camera angles can be used to locate points in 3D. These photogrammetry algorithms work by looking for similar points across multiple images, for example the peak of a roof, or the end of a driveway. By combining the location of the airplane when it took the picture and where the point appears in the photo, you can figure out the actual location of the point in 3D. Doing these calculations for a single point requires just some basic algebra. Doing it for millions of points and thousands of images across a city, on the other hand, requires sophisticated algorithms and a substantial amount of computing power. When the processing is finished, you get a full city-scale 3D model. The final step is to add color. Fortunately, since the 3D model was generated from photos, you can get pixel-perfect alignment of the photo to the 3D scan, and you can “paint” the 3D model patch by patch with color data taken from the images, producing the full-color 3D scans that you can see in Google Maps, Google Earth, and now Aurora. A 3D model of Aurora's neighborhood of San Francisco, courtesy of Google Maps. Photogrammetry differs from LIDAR data in several key ways, including offering a number of advantages. Photogrammetry often allows you to see smaller details because pixels are closer together than points are in a LIDAR point cloud. Additionally, photogrammetry camera equipment is cheaper than LIDAR sensors. And even if you have existing LIDAR data, for purposes like solar design, imagery is still needed on top of it, which adds to the cost. When you are trying to operate at a global scale, these cost savings add up and make it easier to expand into more markets. Furthermore, advances in photogrammetry tend to come from algorithms while advances in LIDAR tend to come from better sensors. This fits in well with the philosophy of running smart algorithms on cheap hardware that Google used to be famous for. However, LIDAR still has some advantages. The 3D measurements taken from LIDAR data are more accurate because the distance from the airplane is physically measured instead of inferred. It often takes less computational power to process as well because the data starts out in 3D, closer to the final format. Fortunately at Aurora, there is no need to pick which technique is better—both data sources will exist side by side in our software. Aurora users can continue to access our wide coverage of LIDAR in the US, but will now also get access to 3D data through Project Sunroof in new locations such as Reno, Phoenix, California's Central Valley, and Chicago—as well as worldwide locations such as Paris, London, Tokyo, and Berlin. Topics: solar design, technology, imagery Solar panel wiring (aka stringing), and how to string solar panels together, is a fundamental topic for any solar installer. You need to understand how different stringing configurations impact the voltage, current, and power of a solar array. This makes it possible to select an appropriate inverter for the array and make sure that the system will function effectively. The stakes are high. If the voltage of your array exceeds the inverter’s maximum, production will be limited by what the inverter can output (and depending on the extent, the inverter’s lifetime may be reduced) . If the array voltage is too low for the inverter you’ve chosen, the system will also underproduce because the inverter will not operate until its “start voltage” has been reached. This can also happen if you fail to account for how shade will affect system voltage throughout the day. Thankfully, modern solar software can manage this complexity for you. For instance, Aurora will automatically advise you on whether your string lengths are acceptable, or even string the system for you. However, as a solar professional, it’s still important to have an understanding of the rules that guide string sizing. In this article, we review the basic principles of stringing in systems with a string inverter and how to determine how many solar panels to have in a string. We also review different stringing options such as connecting solar panels in series and connecting solar panels in parallel. Solar panel wiring is a complicated topic and we won’t delve into all of the details in this article, but whether you’re new to the industry and just learning the principles of solar design, or looking for a refresher, we hope this primer provides a helpful overview of some of the key concepts. ## Key Electrical Terms to Understand for Solar Panel Wiring In order to understand the rules of solar panel wiring, it is necessary to understand a few key electrical terms—particularly voltage, current, and power—and how they relate to each other. To understand these concepts, a helpful analogy is to think of electricity like water in a tank. To expand the analogy, having a higher water level is like having a higher voltage - there is more potential for something to happen (current or water flow), as illustrated below. ### What Is Voltage? Voltage, abbreviated as V and measured in volts, is defined as the difference in electrical charge between two points in a circuit. It is this difference in charge that causes electricity to flow. Voltage is a measure of potential energy, or the potential amount of energy that can be released. In a solar array, the voltage is affected by a number of factors. First is the amount of sunlight (irradiance) on the array. As you might assume, the more irradiance on the panels, the higher the voltage will be. Temperature also affects voltage. As the temperature increases, it reduces the amount of energy a panel produces (see our discussion of Temperature Coefficients for a more detailed discussion of this). On a cold sunny day, the voltage of a solar array may be much higher than normal, while on a very hot day, the voltage may be significantly reduced. ### What Is Current? Electric current (represented as “I” in equations) is defined as the rate at which charge is flowing. In our example above, the water flowing through the pipe out of the tank is comparable to the current in an electrical circuit. Electric current is measured in amps (short for amperes). ### What is Electric Power? Power (P) is the rate at which energy is transferred. It is equivalent to voltage times current (V*I = P) and is measured in Watts (W). In solar PV systems, an important function of the inverter—in addition to converting DC power from the solar array to AC power for use in the home and on the grid—is to maximize the power output of the array by varying the current and voltage. For a more technical explanation of how current, voltage, and power interact within the context of a solar PV system, check out our article on Maximum Power Point Tracking (MPPT). In it, we discuss current-voltage (IV) curves (charts which show how the panel output current varies with panel output voltage), and power-voltage curves (which show how panel output power varies with panel output voltage). These curves offer insight into the voltage and current combination(s) at which power output is maximized. ## Basic Concepts of Solar Panel Wiring (aka Stringing) To have a functional solar PV system, you need to wire the panels together to create an electrical circuit through which current will flow, and you also need to wire the panels to the inverter that will convert the DC power produced by the panels to AC power that can be used in your home and sent to the grid. In the solar industry. This is typically referred to as “stringing” and each series of panels connected together is referred to as a string. In this article, we’ll be focusing on string inverter (as opposed to microinverters). Each string inverter has a range of voltages at which it can operate. ### Series vs. Parallel Stringing There are multiple ways to approach solar panel wiring. One of the key differences to understand is stringing solar panels in series versus stringing solar panels in parallel. These different stringing configurations have different effects on the electrical current and voltage in the circuit. #### Connecting Solar Panels in Series Stringing solar panels in series involves connecting each panel to the next in a line (as illustrated in the left side of the diagram above). Just like a typical battery you may be familiar with, solar panels have positive and negative terminals. When stringing in series, the wire from the positive terminal of one solar panel is connected to the negative terminal of the next panel and so on. When stringing panels in series, each panel additional adds to the total voltage (V) of the string but the current (I) in the string remains the same. One drawback to stringing in series is that a shaded panel can reduce the current through the entire string. Because the current remains the same through the entire string, the current is reduced to that of the panel with the lowest current. #### Connecting Solar Panels in Parallel Stringing solar panels in parallel (shown in the right side of the diagram above) is a bit more complicated. Rather than connecting the positive terminal of one panel to the negative terminal of the next, when stringing in parallel, the positive terminals of all the panels on the string are connected to one wire and the negative terminals are all connected to another wire. When stringing panels in parallel, each additional panel increases the current (amperage) of the circuit, however, the voltage of the circuit remains the same (equivalent to the voltage of each panel). Because of this, a benefit of stringing in series is that if one panel is heavily shaded, the rest of the panels can operate normally and the current of the entire string will not be reduced. ### Information You Need When Determining How to String Solar Panels There are several important pieces of information about your inverter and your solar panels that you need before you can determine how to string your solar array. #### Information About Your Inverter You’ll need to understand the following inverter specifications which can be found in the manufacturer datasheet for the product: • Maximum DC input voltage (Vinput, max) - the maximum voltage the inverter can receive • Minimum or “Start” Voltage (Vinput, min) - the voltage level necessary for the inverter to operate • Maximum Input Current • How many Maximum Power Point Trackers (MPPTs) does it have? • As noted above, a function of inverters is to maximize power output as the environmental conditions on the panels vary. They do this through Maximum Power Point Trackers (MPPTs) which identify the current and voltage at which power is maximized. However, for a given MPPT, the conditions on the panels must be relatively consistent or efficiency will be reduced (for instance, differences in shade levels or the orientation of the panels). However, if the inverter has multiple MPPTs then strings of panels with different conditions can be connected to a separate MPPT. #### Information About Your Solar Panels In addition to the above information about your selected inverter, you’ll also need the following data on your selected panels: An important thing to understand about these values is that they are based on the module’s performance in what is called Standard Test Conditions (STC). STC includes an irradiance of 1000W per square meter and 25 degrees Celsius (~77 degrees F). These specific lab conditions provide consistency in testing but the real world conditions a PV system experiences may be very different. As a result, the actual current and voltage of the panels may vary significantly from these values. You’ll need to adjust your calculations based on the expected minimum and maximum temperatures where the panels will be installed to ensure that your string lengths are appropriate for the conditions the PV system will encounter as we’ll discuss below. ## Basic Rules for How to String Solar Panels ### 1. Ensure the Minimum and Maximum Voltage Are Within the Inverter Range When stringing your solar array, one of the basic considerations is to ensure that the voltage of the strings you are connecting to the inverter is not going to exceed the inverter’s maximum input voltage or fall below its minimum/start voltage. You’ll also need to avoid exceeding its maximum current. You’ll also need to ensure that the maximum voltage complies with code requirements in the area where you are designing. In the U.S., the National Electrical Code caps the maximum allowable voltage at 600V for most residential systems. In Europe, higher voltages are allowed. We know that voltage is additive in series strings while current is additive in parallel strings. As such, you might intuitively assume that you can determine the voltage of our proposed PV system design and whether it falls within the recommended range for the inverter by multiplying the voltage of the panels by the number in a series string (as illustrated in the example in the green box below).  Voltage Maximum and Minimum Calculations based on STC Values (not temperature adjusted): Assumptions: I am using 300W panels with an open circuit voltage (Voc) of 40V. The inverter I plan on using has a maximum voltage (Vmax) of 600 V and a start voltage (Vstart) of 150 V. I can get an initial rough understanding of the maximum number of panels that can be included on a string in series by dividing the inverter’s maximum input voltage by the Voc of the panels: 600 V / 40 V = maximum of 15 panels on a string I can follow the same process, but using the start voltage, to determine the minimum number of panels I can include on a string. 150V / 40 V = minimum of 3.75 panels → therefore minimum of 4 panels on a string BUT, as we discuss below, this doesn’t give the entire picture. You’ll need to adjust based on temperature. You might also assume that you could determine the current of the system by adding the current of each parallel string (which would be equal to the current of the panels multiplied by the number in the parallel string). However, as we discussed above, since STC values reflect the modules’ performance under very specific conditions, the actual voltage of the panels in real-world conditions may be quite different. Thus the simplified calculations above only give you an initial rough estimate; you must account for how the voltage of the system will change depending on the temperatures it may experience in the area where it is installed. At colder temperatures, the voltage of the system may be much higher; at higher temperatures, it may be much lower. To ensure that the temperature-adjusted string voltage is within the input voltage window of the inverter, the following formulas can be used: Aurora solar design software automatically performs these calculations and alerts you as you are designing if your string lengths are too long or too short given the expected temperatures at the site. (For more information on stringing in Aurora, see this help center article.) Aurora also performs a variety of other validations to ensure that the system will operate as expected and not violate codes or equipment specifications—this can prevent costly performance issues. (For a detailed overview of these validations see this page in our help center.) For a real-world example of why it is so important to accurately account for how environmental conditions will impact the voltage of your PV system, read our analysis of an underperforming system in Cathedral City, California. In that case, a solar designer’s failure to account for the presence of shade resulted in the system frequently falling below the inverter’s start voltage and therefore producing significantly less energy than forecasted. ### 2. Ensure Strings Have Similar Conditions—or Connect Strings with Different Conditions to Different MPPT Ports Once you’ve determined that your strings are acceptable lengths for the inverter specifications, another key consideration is to ensure that the strings to have the same conditions (e.g. same azimuth/orientation, same tilt, same irradiance) if they are connected to the same inverter MPPT. This is because mismatches in the conditions on the strings will reduce the efficiency and power output of your solar design (for a discussion of why mismatches in shading, orientation, or azimuth result in lost power output see the fourth article in our PV system losses series). If you are designing for a site where it’s necessary to have panels on different roof faces, or some areas of the array will get more shade than others, you can ensure that the panels with different conditions are separated into their own strings, and then connect those strings to different MPPTs of the inverter (provided your chosen inverter has more than one MPPT). This will allow the inverter to ensure each string operates at the point where it produces the maximum power (its maximum power point). ### 3. Advanced Considerations to Optimize Your Design The above rules will ensure that your stringing configuration will comply with the specifications of your inverter and that the energy production of the system won’t be negatively affected by mismatches in the conditions on the panels. However, there are additional factors that a solar designer can consider to arrive at the optimal design (that is, the design that maximizes energy production while minimizing cost). These factors include inverter clipping, the use of module-level power electronics (MLPE)—devices which include microinverters and DC optimizers, and design efficiency provided by software tools. #### Inverter Clipping Sometimes it may make sense to oversize the solar array that you are connecting to the inverter leading to a theoretical maximum voltage that is slightly higher than the inverter max. This may allow your system to produce more energy (because there are more panels) when it is below its maximum voltage, in exchange for reduced (“clipped”) production during the times when the DC voltage of the array exceeds the inverter’s maximum. If the production gains exceed the production lost to inverter clipping, then you can produce more power without paying for an additional inverter or one with a higher voltage rating. Of course, this decision should be made with care and a clear understanding of how much production will be clipped compared to how much additional production will be gained at other times. In its system loss diagram, Aurora indicates how much energy will be lost to clipping so that you can make an informed decision about whether this makes sense. For a detailed explanation of inverter clipping and when a system with inverter clipping makes sense, see our blog article on the subject. #### Module-Level Power Electronics (MLPE) String inverters are not the only inverter option. Microinverters, which are inverters that are attached to each individual panel (or a couple), allow each panel to operate at its maximum power point regardless of the conditions on other panels. In this arrangement, one need not worry about ensuring panels on the same string have the same conditions. Microinverters can also make it easier to add more panels in the future. We discuss MLPE in more detail in this article. #### Explore a Few Different Options to Find the Best One As you can see, there are many considerations when it comes to stringing your panels and finding the inverter and stringing configuration that are best for the customer. You may not arrive at the optimal design the first time around so it can be helpful to evaluate a few different options. In order for this to be efficient, however, you’ll need a process where you can evaluate multiple designs quickly, as Aurora co-founder Christopher Hopper explains in this blog post. This is where solar software can be particularly valuable. #### Let Solar Software Do the Stringing For You Finally, new technology developments like Aurora’s autostringing functionality (discussed here) can actually do the stringing for you! It will take into account the considerations discussed here and present you with an ideal stringing configuration. Understanding the principles of solar panel wiring will enable you to ensure optimal designs for your solar customers. We hope you found this introductory primer helpful! When designing a solar project for a prospective customer, you know it’s important to get the details right. That helps ensure that the design you propose to them is the design that actually gets installed—without the need for costly and time-consuming design changes, as might be the case if you thought that more panels would fit on a particular part of their roof, for instance. But, in the increasingly competitive solar industry, speed is also of the essence. You need to follow up as soon as possible to maximize your chances of winning the customer’s business. That means that driving to the site and taking manual measurements may not be practical, particularly if the customer is far away. (Not to mention, you could save time and money by avoiding the trip.) It’s this very challenge that Aurora was founded to solve, and we’ve been hard at work developing many new software technologies that make it possible for solar contractors to accurately design solar installations without the site visit, from NREL-validated remote shading analysis to providing access to LIDAR data and crisp aerial imagery to cutting-edge roof drawing tools. This month, Aurora is excited to announce a new tool that gives solar contractors another way to get accurate measurements of elements of the project site: Street View Ruler. Aurora’s Street View Ruler makes it easy to take site measurements without actually being at the site, so you can ensure that you can fit as many panels as expected and that the pitch of the roof is what you think it is (this can affect how much energy your PV system produces). ## Street View Ruler The Street View Ruler leverages computer vision, or the use of computers to interpret images. As we discussed in our overview of computer vision and how Aurora uses it to improve the solar design process, one application of computer vision is to calculate measurements using multiple images of a site. This new tool, which builds upon prior advances by the Aurora computer vision team, offers a simple and easy-to-use method for taking accurate measurements of the project site from the comfort of your desk. Behind the scenes, the computer vision approach that the Street View Ruler uses is the mathematical process of triangulation. Commonly used in nautical navigation, triangulation allows you to determine the distance to an object if you know the direction from two known locations. In this case, satellite imagery and Street View imagery provide the two different views of a site. Because these imagery sources include the camera positions and angles, measurements can then be extracted from the images. With this tool, solar designers can measure distances—like the height of a tree or width of a roof face—and slopes—like the pitch of a roof. To do so, the designer identifies the points they want to measure, in two different images of the site: the Street View image and a top-down satellite or aerial image. By indicating to Aurora which points correspond to each other in the images from two different angles, Aurora’s computer vision engine can perform triangulation and generate an accurate measurement. ## Key Features Several teams worked together to develop this tool. Our UI/UX (user interface/user experience) team worked to create a workflow that would be intuitive and minimize chances for confusion, while our Front End engineers Carl Olsson and Kelly Stevens worked to create the tool using the computer vision measurement functionality that our computer vision team had developed. ### In-App Instructions As you use the Street View Ruler, prompts on the screen guide you through the process. This makes it faster to learn and helps to minimize the chance of missing a step that would impact your measurement. As you use the Street View Ruler, prompts guide you through the process to ensure correct usage. ### Numbered Points to Match Street View and Top-Down Measurements Numbered points make it easy to ensure that you’re lining up the points correctly between the Street View image and the top-down satellite/aerial view of the site. To allow Aurora’s Street View Ruler to take measurements using triangulation, place each numbered point on the spots you would like to measure in both top-down and street-level views of the project site. ### Camera Animations Offer Enhanced Visualization Another feature of the tool is camera animations in which Aurora automatically aligns the 3D view of your site model with the perspective of the Street View camera once you’ve taken your measurements. Once the measurement is complete, Aurora automatically rotates the view of your project site to match the street-level view, allowing you to get a better sense of the area you measured. As Carl Olsson, one of the software engineers who built the Street View Ruler, explains, “Once you're done creating a measurement, the top-down camera view will rotate to the direction of the street view camera. I think that makes it easier for users to understand the measurement they've just created and how it correlates with the Street View.” Street View Ruler is another tool in your toolkit for ensuring accuracy and precision in your solar designs for customers while saving time by minimizing the need for time-consuming and costly visits to the site during the design stage. Let us know in the comments below how you’re using the Street View Ruler! Traditionally, for rooftop solar installations, solar is added on to an existing building. But a vast new solar market is emerging in recent years: solar for new construction. In fact, in California alone—where the state building code will require solar on all new homes starting in 2020—solar demand is expected to increase by over 800 MW from 2020-2023 due to this market. This regulatory trend is not just limited to California, however. Cities from Arizona to Florida have made similar solar requirements. Watertown, Massachusetts moved to require solar on new commercial buildings larger than 10,000 square feet and all new residential structures with ten or more units. Other jurisdictions may roll out similar policies as cities and states around the country make increasingly aggressive commitments to clean energy. This is great news for solar contractors. But to access this new class of customers, solar contractors need new solar design and sales strategies. Traditional methods tailored to existing buildings fall short in several key ways. In this article, we highlight the ways that solar design for new construction differs from traditional solar design. We also share real strategies and tools for designing and selling stunning solar arrays for new buildings—whether residential or commercial—so you can confidently pursue opportunities in this new market segment. ## How is Solar Design for New Construction Different from Traditional Solar Design? Designing solar for a building that’s not yet built differs from traditional solar design in three key ways. 1. Without an existing building, it can be difficult to know how many solar panels will fit on the roof or other parts of the site and determine the best location for the array. 2. To determine how much energy the solar installation will produce—and whether solar is even a viable option—it is critical to understand how much shade will fall on different parts of the site. This assessment is complicated by the lack of an existing building. 3. Finally, without imagery of an existing building, salespeople need new options to communicate to the customer what the solar design will look like. Fortunately, there are solar software tools contractors can utilize to overcome these barriers. ## Designing Solar for New Construction: Overcoming the Challenges Let’s explore the three critical differences in solar design and sales for new construction versus existing buildings, and the solutions solar contractors can employ to enter this new market. ### Challenge 1: Determining the Appropriate PV System Size and Location How do you determine the best locations for solar panels and the number that will fit on a roof when the building you’ll put them on doesn’t exist yet? Naturally, traditional approaches based on on-site measurements or remote site assessment using satellite imagery are not an option. Fortunately, with the right solar software solar contractors can import roof plans or blueprints to serve as the basis of creating a virtual 3D model of the project site. With an accurate site model, contractors can easily determine how many solar panels will fit on different roof faces and get a better sense of where it would make sense to locate an array. Aurora Solar allows you to import roof plans of a future building, scale them to an accurate size, and situate them on the property. From there, it’s easy to create an accurate 3D model of the building on which to design a solar installation and accurately estimate it’s energy production. This allows solar contractors to enter the fast-growing market of solar for new homes and buildings. In Aurora’s solar software, solar contractors can upload the roof plan as an image and then scale it to the correct size based on the specified dimensions in the building plan. Since there is not yet an address for most of these new construction sites, the contractor can input the geographic coordinates of the project to situate it in the actual location where it will be built. One of the things Aurora Solar has pioneered that makes this process much simpler is SmartRoof, a design tool that infers the 3D structure of a building based on the 2D outline of the roof. Adjustments can be made to ensure the inferences match the roof plan, but the manual work needed to create an accurate 3D model on which to design the solar array is significantly reduced. Aurora’s SmartRoof tool infers the 3D structure of a roof based on its perimeter, streamlining the solar design process. Additionally, Aurora’s ruler tool—which provides measurements of different parts of the project and site model—makes it easy to double-check that the site model matches the construction plans. ### Challenge 2: Assessing shading and solar access values Perhaps the biggest challenge of designing a solar installation for a building that has not yet been constructed is getting an accurate understanding of how much solar energy will be available on different parts of the roof or surrounding property. As we explain in our blog post on how irradiance is calculated, any structure that may cast a shadow at any time throughout the year—from a chimney to a nearby tree—can impact the solar irradiance on the site. Without accurate solar access values and shade measurements, you cannot accurately estimate how much energy the solar installation will produce. Fortunately, Aurora makes it simple to accurately calculate all of these values. An example of an irradiance map, generated by Aurora. Brighter colors indicate greater solar irradiance. Because geographic coordinates are used to situate the site model in its real future location, you can review satellite imagery of the property to identify and model trees and surrounding objects that may impact the amount of sunlight that reaches the roof. Additionally, actual local weather data is used in simulating how much energy the system will produce. With the creation of a precise 3D model of the future building and other features of the project site, Aurora can simulate the movement of shadows on the site for every hour of the year and give precise irradiance values for each part of the site. This approach allows you to be confident in the accuracy of your energy production and utility bill savings estimates for the project. ### Challenge 3: Visually showcase the solar design for the buyer A further challenge of designing solar for new construction applies at the sales stage. How do you show the customer what the design will look like? The aesthetics of the solar design are likely to be a significant concern for the prospective customer, especially in the residential market. An example of a 3D model of a future home as rendered in Aurora solar software. These kinds of visuals can help the customer understand what your solar design will look like and feel more comfortable knowing how it will impact the aesthetics of the building.  As the home construction and solar markets intersect in California—where new homes will be required to have solar starting in 2020—other players like architects and home builders will also need tools to present solar information including the appearance of the building. To see how Aurora makes this easy, sign up for a free demo to see the software in action! Without being able to visualize how solar will affect the appearance of their future building, the customer may be more hesitant about a solar purchase. Fortunately, creating a realistic 3D model of the project and site makes it easy to showcase and sell your solar design. Aurora offers a variety of compelling and customizable solar sales proposal templates. You can include a variety of different views of the solar project to help them feel at ease with the appearance of the project you’ve designed. Building upon the approaches we pioneered to enable accurate remote solar design, Aurora Solar is delivering solutions that let solar contractors effectively serve the emerging solar market for new buildings. To learn more about solar design for new construction, with live demonstrations of the processes discussed above, join our webinar with PV Magazine on March 20, 2019 at 10AM Pacific Standard Time/1PM Eastern Standard Time! You can also check out our past webinar with Solar Power World, which explores this topic from the perspective of California’s Title 24 mandate of solar on new homes. An underperforming solar PV system is a solar customer’s nightmare. With a big investment like solar, customers want to know that their PV system is producing as much energy as forecasted and they’re getting their money’s worth. Unfortunately for a residential customer in Cathedral City, California, for unknown reasons, their system was consistently producing less energy than expected. Fortunately, their system was monitored by Omnidian, a solar operations and maintenance (O&M) firm that is dedicated to managing the performance of solar systems. Omnidian remotely monitors solar system performance and interprets the data with its proprietary software to identify systems that are experiencing problems–as it did in this case–and coordinates field service work with local service partners where needed. To determine what has gone wrong in these cases, “the industry often responds with an initial truck roll to go out to the site to investigate what's going on,” explains Omnidian Chief Operating Officer David Kenny. But truck rolls can be costly, so if there were a way to remotely identify the problem and determine the necessary service before sending someone out, reaching a resolution could be more efficient and affordable. To this end, Omnidian turned to Aurora’s simulation tools to determine if it would be possible to remotely diagnose the cause of this system’s underproduction. In this article, we explore how Aurora’s software allowed Omnidian to identify design flaws and make adjustments that significantly increased energy production. ## Remote Diagnostics with Aurora Most users know Aurora for solar design and sales software that makes it possible to remotely design a solar system, accurately forecast its energy production, and estimate the monetary value of that production. In this case, however, Aurora’s simulation engine–which calculates how much energy a PV system will produce based on its design and location–would be used to retroactively determine why there was such a discrepancy between actual and predicted production. To do this, the project site was first modeled precisely in Aurora. An accurate 3D model of the project site is essential to determining how much energy a PV system will produce because it provides the basis for determining the amount of shade that will fall on the modules at different times throughout the year. The PV system was then recreated in Aurora according to how it was installed–with the same module and inverter specifications, panel placement, and stringing configuration. The existing system consisted of 30 modules and two string inverters, each of which were connected to three strings of five modules in series. The underperforming solar installation as originally designed, recreated in Aurora for modeling purposes. Recreating the existing system design made it possible to simulate how much energy the system “should” be producing and identify factors that were reducing power output. Aurora calculated that the existing design would produce approximately 12,000 kWh per year. A preliminary comparison of Aurora’s simulation results to recorded production data from the system revealed that Aurora’s simulation was within 1% of the system’s actual annual production. Aurora’s simulated system performance (monthly values in blue) compared to the actual system performance. Aurora’s simulation was within 1% of the actual annual production of the system. From there, a review of Aurora’s simulation warnings helped to determine why production was less than it could have been. Aurora performs a wide array of checks on every system design, testing to see if there are any violations of engineering principles, the National Electric Code, or the capabilities of the components used. Aurora’s performance simulations, which forecast how much energy a PV system will produce, also include alerts about potential design errors and other factors that will limit energy production or violate codes. (Note that the customer’s energy usage was not modeled in this diagnostic exercise, which is why there is no energy offset data.) One alert in particular raised a big red flag about the system design: 72% of the time the string voltage for the system was falling below the inverter’s minimum operating voltage! This information provided a helpful starting point for determining what needed to be fixed for the system to perform optimally. ## Pinpointing the Performance Problem Further exploration revealed that shading was part of the issue; the shading from two neighboring palm trees at the site frequently caused the string voltage to be too low for the inverter. Another contributing factor was the fact that the strings were short (voltage is additive when panels are connected in series, so longer strings result in higher voltage). Because the voltage was frequently falling below the inverter’s minimum starting voltage due to these factors, there were periods of time when the system wasn’t exporting any energy at all. As the Aurora team member who led the diagnosis explains, “The shade [at this site] plays a big part in the performance issue since the strings are at the very lower limit of the acceptable range. This means any shade will drop the string out of the voltage range and stop production. In a heavily shaded situation like this, it is imperative that strings as long as possible are used with a traditional string inverter.” With the cause of underproduction identified, it was determined that it would be necessary to restring the system, making the strings longer so that they wouldn’t drop out of the voltage range of the inverter when shade was present. ## Finding a Solution Once it was determined that the system needed to be restrung with more modules on each string in order to keep the voltage within the inverter’s operating range, Aurora was used to model possible solutions. Simulating new potential stringing configurations made it possible to quantify the resulting production changes and ensure that there were no design flaws before service work was initiated. The new proposed stringing configuration with longer string lengths to increase string voltage; it consists of two strings of seven panels in series connected to the first inverter and two strings with eight panels in series on the second inverter. The stringing configuration proposed for the repair of the system included two strings of seven panels in series connected to the first inverter and two strings with eight panels in series on the second inverter. Aurora’s performance simulation revealed that the redesigned system would produce 3,433 kWh more per year than the existing design! A key reason for this is that the string voltage would only fall below the inverter limit for 0.91% of daylight hours throughout the year under the new stringing configuration, compared to 72.39% of daylight hours when this occurred with the installed design. Aurora’s performance simulation results for the new proposed stringing configuration, showing monthly and annual production, as well as alerts. (Note that the customer’s energy usage was not modeled in this diagnostic exercise, which is why there is no energy offset data.) ### Accounting for Inverter Clipping Once a restringing solution was identified, there was another question to resolve: whether the stringing configuration was compatible with the existing inverters. The new, longer string lengths meant that the DC voltage was oversized compared to the inverter rating and could sometimes exceed the max DC power of the inverter during times of high irradiance. This raised a potential red flag because it could limit energy production as a result of inverter clipping. However, because Aurora models the expected impacts of inverter clipping based on local weather patterns and shading at the site, it was possible to determine that inverter clipping impacts would actually be very limited (1% of annual production, as noted in the simulation results above). As a result of this insight, the costly need to replace one or both of the inverters was avoided. ## Achieving Performance Gains With a resolution identified remotely, Omnidian coordinated service work to restring the system with the new stringing configuration. Initial production data showed marked improvements in performance: comparing three sunny days before the service work to three sunny days after the service work, the max power (kW) increased 16% and kWh generation increased 24%! This solar customer was fortunate to have Omnidian monitoring their system, to identify the performance problems with their PV system and find a resolution without the need for the customer’s involvement. With Aurora’s top-of-the-line performance simulations, it was possible for Omnidian to diagnose the problem without a site visit, and then coordinate service to resolve the underproduction issue. Although not a typical use of Aurora’s solar design software, this initiative highlighted the value of Aurora’s accurate performance simulations. It also shows how solar contractors can avoid design flaws through the use of robust design and performance simulation software. Had the installer of this system used Aurora they would have been alerted that the string voltage would frequently fall below the inverter’s operating voltage range, avoiding production losses for the customer and the need for system repair. Thankfully, the resolution Omnidian arrived at with Aurora restored the system to its optimal performance, allowing the customer to generate thousands more kilowatt hours each year! Topics: solar design When you sit down to design a solar installation for a prospective customer, probably one of the first things you consider is how much solar energy (irradiance) is available in different locations. If you’re using remote solar design software, rather than relying on manual measurements at the project, all you have to do is click a button and the software generates an irradiance map showing the solar irradiance at every point on the roof of your site model. But what’s happening behind the scenes in your solar software to deliver that irradiance map? Do you understand the diverse components that go into the calculation of solar irradiance? While one of the benefits of solar software is that you don’t need to think too much about these calculations, it can be helpful to have an understanding of how solar irradiance is calculated to answer customer questions. Here at Aurora, we think about these calculations a lot, and recently our engineers have been working hard on updates that increased the speed of irradiance calculations by 30 times! Today’s blog post explains the principles of calculating solar irradiance and discusses some of the computation approaches we employed to make this critical process faster for you. An example of a solar irradiance map generated by Aurora solar software. ## The Basics of Irradiance Calculations While you might think that solar irradiance is just based on the rays of sunlight that directly reach a surface, there are actually several sources of irradiance that go into the calculation. The first of these is that direct “beam” irradiance that you might intuitively associate with irradiance. This involves determining whether there are any objects that would block rays of the sun from reaching the solar panel (i.e., cause shading), in order to determine if this component should be included in the total irradiance. In addition to this, there are two types of “diffuse” or indirect irradiance that need to be accounted for: sky diffuse irradiance–the light reflected from the atmosphere, separate from direct rays of sunlight that fall on the panel, and ground-reflected diffuse irradiance, light that is reflected back up from the ground. In order to calculate these three broad types of irradiance, it's also necessary to take into account the angle of the array and the direction to the sun relative to the panel. There are three broad types of solar irradiance that must be included in calculations of the irradiance on a particular surface; these include direct irradiance from beams of the sun, as well as diffuse irradiance from both the sky and the ground. Of these calculations, determining whether or not direct beams from the sun can reach the panel requires the most processing power. This is because shading from surrounding objects must be calculated based on the location of the sun at every daylight hour of the year–these calculations can quickly add up! ## Determining Sunbeam Intersection In order to determine whether the rays of the sun will directly hit a particular surface, one must first have an accurate understanding of the surroundings–including objects like trees, surrounding buildings and roof planes, and obstructions like skylights, vents, and chimneys. This is why the starting point for creating a solar design in Aurora is to construct a 3D model of the project site. Aurora’s irradiance engine translates the fully modeled project site into simpler shapes, which are more conducive to computational processes by computers. Aurora translates the 3D model of the project sites into simpler shapes. Aurora then computes whether any of these component shapes will block the rays of the sun during each daylight hour of the year, one key component of calculating solar irradiance. From there, Aurora’s irradiance engine computes the location of the sun, relative to the panel, for every daylight hour of the year; for each hour, it tests whether a beam from the sun to the panel hits any object in the scene. If the beam intersects with an object, that means it cannot reach that point on the surface and the direct beam irradiance component should not be included in the irradiance calculation (in other words, that location is shaded at that hour of the day). To generate an irradiance map, Aurora intelligently samples different points on the roof. For performance simulations, Aurora computes the irradiance at specific points on each panel or cell string. Aurora solar software calculates whether any objects at the solar project site would block the rays of the sun at any given hour. ## Making Our Irradiance Calculations 30 Times Faster Because a project site can contain thousands of objects, and intersections with solar rays have to be calculated for every daylight hour of the year, the number of calculations that need to be computed can be significant. There are generally over 5,000 daylight hours for a given location. This means that, for each point on the roof, over 5,000 potential sun locations must be simulated, and a complex project site could require irradiance calculations for as many as 100,000 to 500,000 points! As you can imagine then, running these processes one at a time could sometimes be a lengthy process–especially for very large or complicated sites. Computing whether rays of the sun (direct beam irradiance) will reach a given point requires significant processing power, especially for complex sites like this one. By computing the many component processes in parallel (i.e., at the same time) Aurora solar software was able to deliver 30x improvements in the speed of irradiance map generation. That’s why Aurora’s computation team set about developing an approach to enable Aurora to run many of these computations at the same time. This was done by utilizing Graphics Processing Units (GPUs). In contrast to Central Processing Units, or CPUs, which you might be familiar with as the devices that perform most of the computing processes in your computer, GPUs are much better at performing thousands of calculation-heavy operations in parallel. This made it possible to dramatically speed up shading calculations. By computing the intersections of the sun’s rays with thousands of objects in the scene in parallel (at the same time) rather than sequentially (one after the other), Aurora has been able to deliver 30x speed increases. To put this in context, irradiance for a large commercial project site of 7 MW PV system can now typically be calculated in under 20 seconds. And, of course, this is done while still maintaining the high shading accuracy that Aurora is known for. Aurora's advanced solar design software has made it significantly easier for solar contractors and designers to determine how much solar energy is available to the solar arrays they design. Instead of having to visit the home or business of every prospective customer and take manual measurements from the roof or ground where the array would be located, this can now be done accurately with the click of a button. The National Renewable Energy Lab calculates this could save solar installers over800 per system.

The next time you press “simulate” in Aurora, not only will you notice that the irradiance map generates much faster than you might expect, you’ll also have a better sense of what’s going on “under-the-hood” in the software. As we discussed in a recent post, being able to explain the power of your solar software tools is one way to help prospective customers understand the quality of your solar design processes–and feel more confident choosing your company for their solar installation.

Using cutting-edge solar software like Aurora gives you an advantage when it comes to the quality of your solar designs for your customer. But for prospective solar customers who may be unfamiliar with the solar design and installation process, it’s not always easy to understand how your solar design software sets you apart from competitors.

It doesn’t have to be that way, however. When you can clearly communicate the benefits of your advanced design tools, you can help the customer see the value your company brings to the table–and ultimately close more sales. These five strategies make it easy for prospective solar customers to understand how Aurora sets your company apart.

## 1. Educate the Client with Stunning 3D Visuals

They say a picture is worth a thousand words and that’s certainly true when it comes to solar sales. One of the easiest and most powerful ways to help the customer understand the quality of your design process with Aurora is to show them.

Aurora generates beautiful and accurate 3D representations of the project site and your solar design, letting the customer see exactly what their home or business will look like with your installation. These visuals can help them feel confident that they’ll be happy with the aesthetics of the PV system–a crucial consideration for an investment that will likely be with their property for the next 25 years.

A solar design in Aurora (right) with an irradiance map showing solar access, compared to aerial imagery (left). Accurate visuals give customers a realistic sense of how their solar installation will look.

Aurora visuals can also be helpful in educating the client about different solar design considerations. For instance, the sun path simulator, which shows the sun’s movement during every daylight hour of the year, can help illustrate how shade moves across the property at different times.

Similarly, Aurora’s irradiance engine calculates the available solar energy at every point on the roof surface and generates beautiful irradiance maps that show differences in solar access. These are great ways to help the customer understand why particular array locations are better than others.

Aurora simulates the sun’s movement, and resulting shadows, during every hour of the year. The sun path animation provides a handy visual representation of this.

You can also use these tools to demonstrate options the customer might want to be know about. For instance, if trees cause a lot of shading, you could provide irradiance maps and production data for different scenarios, such if trees were pruned or removed.

## 2. Demonstrate Accurate Solar Sizing and Production Estimates with Industry-Leading Algorithms

Of course, even more than stunning visuals, the customer wants to know they can trust your expertise–particularly when it comes to the amount of energy that their system will produce and how much of their energy usage it will offset. Aurora has developed proprietary algorithms that allow you to estimate the customer’s energy usage and forecast solar production with confidence.

Aurora gives you a variety of ways to estimate how much energy the customer uses at different times, such as inputting their electric bills or uploading data from their utility. This provides a strong starting point for determining how much solar energy the customer's needs.

From there, Aurora makes it easy to precisely calculate how much energy the system will produce. The National Renewable Energy Laboratory (NREL) has validated the accuracy of Aurora’s shading engine, finding its estimates of available solar energy to be statistically equivalent to manual, onsite measurements.

Aurora helps solar contractors accurately determine the customer’s energy consumption and future solar energy production throughout the year.

Additionally, our algorithms for calculating solar energy production take into account a number of considerations other solar software programs don’t. For example, Aurora is the first solar software that can model electrical behavior within each module, accounting for the locations of bypass diodes. This also us one of the only softwares that can model panels with integrated cell-string optimizers like Maxim’s.

Likewise, many solar software programs do not model how different stringing configurations change energy production, such as if shaded modules are grouped together in a separate string. We also model whether the selected inverter performs local or global maximum powerpoint tracking.

While customers may not understand all of the technical details that impact how much energy their solar installation will produce, highlighting that you’re using one of the industry’s most advanced software programs tools for system sizing and energy production modeling can help close more solar sales.

## 3. Showcase Tools for Accurate Post-Solar Rates and Financial Returns

Most likely, one of the main reasons your prospective customer is interested in solar is to save money on their utility bills. That means the accuracy of the bill savings you present to them is of the utmost importance. Explaining how Aurora produces accurate estimates of their solar savings can help the customer be confident your design will deliver the savings they seek.

Aurora has an extensive database of utility rates–covering over 3,000 utilities and over 17,000 utility rates around the world–so you can accurately model your customer’s electricity bill and how it will change with solar. Aurora even models bill savings under time of use rates, in which the value of electricity varies depending on time of day. Utilizing accurate pre- and post-solar utility rates provides the client with a predictable future monthly bill and overall lifetime savings.

Aurora also offers financial modeling tools that allow you to show the customer key metrics like the Net Present Value (NPV), Internal Rate of Return (IRR), and Levelized Cost of Electricity (LCOE). Plus, Aurora has an extensive database of financial incentives, so you can take into account any applicable grants, tax rebates, or production based incentives (PBIs) like SRECs when presenting financial metrics to the customer.

## 4. Explain How Aurora Reduces Change Orders by Up to 100%

Your prospective customer probably also wants to know that the installation process will go smoothly–without unexpected errors, changes, or delays. You can highlight the wide variety of tools Aurora gives you to ensure design accuracy and avoid time-consuming change orders (revisions to the design) at a later date.

Aurora makes it easy to accurately model the project site–from the height and pitch of the roof to the presence of obstructions like skylights and vents. Aurora’s ruler tool makes it easy to confirm site dimensions. The ruler snaps to objects like building edges, obstructions, solar panels, carports and groundmounts and indicates their length. Additionally, Aurora allows you to specify required setbacks so that your panel placement doesn’t violate fire codes or jurisdiction requirements. Aurora will alert you of any violations.

Aurora's ruler tool snaps to objects like roofs or solar panels making it easy to ensure the accuracy of your site model.

If you have a premium account, you have even more cutting-edge tools to ensure accuracy, such as LIDAR, computer vision measurements, and even National Electrical Code (NEC) validation to ensure that your design doesn’t violate any electrical or mechanical constraints or industry best practices.

For the customer, all of this means that you are less likely to have to make design changes (change orders) later that add time and cost to the project. In fact, California contractor Solarponics reports that they have completely eliminated change orders since switching to Aurora!

## 5. Highlight How Aurora Makes It Easy to Find the Best Design

Ultimately, your customer wants to know they’re getting the best solar design. Aurora’s solar software helps set your company apart by giving you an efficient design workflow that allows you to quickly and cost-effectively explore a variety of design options to find the best one.

For example, in Aurora, you can copy existing designs you’ve created and then make adjustments, letting you quickly iterate through different options, like incorporating microinverters or DC optimizers or using different panels. From there, you can quickly assess the energy production and financial returns of each design to find the best choice.

Companies with less efficient design processes may not have the time to explore multiple design options and find a custom solution. Highlighting this difference can give you a solar sales advantage.

You’ve made an investment in top-notch solar design tools that help you deliver high-quality solar installations to your customers, so why keep those tools under wraps? Discussing your design process can help the customer see what sets you apart from the competition.

Do you have other strategies for highlighting the advantages of your solar design software in solar sales conversations? Let us know in the comments below!

Topics: solar design, Solar Sales

Solar contractors face many decisions when it comes to finding the best solar design. One important consideration is determining whether to use module-level power electronics (microinverters or DC optimizers).

Once costly specialty products, module-level power electronics have made great strides in the last decade and are rapidly growing in popularity. And there’s good reason for that! Incorporating these devices can offer a number of design benefits.

In today’s article, we explore some of the benefits of module-level power electronics and take a closer look at each type and where they fit within a PV system design.

## What Are Module-Level Power Electronics (MLPE)?

Module-level power electronics (MLPE) are devices that can be incorporated into a solar PV system to improve its performance in certain conditions (especially where shade is present) and to achieve a number of other solar design benefits. MLPE include microinverters and DC power optimizers. They perform some of the same functions as a string inverter or central inverter, but are typically coupled to just one (or a few) solar modules rather than many, and offer additional features.

Figure 1. Even partial shade, as shown here, can significantly reduce the power output of a solar array; MLPE–including microinverters and DC optimizers–can mitigate these performance losses, among other benefits.

## Why Use MLPE?

There are a number of reasons why incorporating MLPE into your solar designs can be a good option. One of the primary reasons is to improve the energy production of the system. MLPE can help mitigate production losses from a variety of different factors such as shading, module mismatch losses, and orientation mismatch losses (for instance, if you have panels on different roof planes).

The U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy explains that MLPE can reduce energy losses due to partial shading of modules by 20%–35% and they completely eliminate losses due to orientation mismatch of PV modules.

Additional benefits of MLPE include providing compliance with module-level rapid shutdown requirements under the National Electrical Code (NEC), safety benefits, and typically longer warranties than for traditional inverters. Most MLPE products also come with performance monitoring and diagnostic functionality, which can be valuable in making sure the system is producing as expected or pinpointing technical issues.

Solar contractors may want to weigh these benefits against possible higher up-front costs and increased installation labor.

## How Do MLPE Improve PV System Performance?

MLPE can improve the energy production of a solar PV system by performing maximum power point tracking at the module level, rather than at the array level as would be the case with a string inverter. Maximum power point tracking (MPPT) refers to how inverters (and MLPE) instruct a solar panel or array to operate at a specific current and voltage combination that maximizes power output.

Inverters and DC optimizers perform maximum power point tracking by responding to changes in the current and voltage of the solar installation (for example, a decrease in current resulting from shade falling on the panel). They respond to these changes by adjusting the voltage to maximize power output. (For a deeper discussion of this process, and the relationship between current, voltage, and power, see our article on global MPPT.)

In a system with a string inverter and no MLPE, shade or soiling on one module can decrease the power output of the entire string. This is because, as detailed in our overview of shading losses, the current through the string is limited to the current of the lowest-producing module. In contrast, in systems with microinverters or DC optimizers, each module produces at its maximum level regardless of shading on other modules on the string because these devices offer module-level MPPT functionality.

## DC Power Optimizers

DC power optimizers, commonly called DC optimizers, are attached to the junction box of individual solar modules, or in the case of some “smart modules” may be integrated directly into the module. These devices maximize the module’s DC power output before that power is converted to AC power by an inverter. As discussed above, they achieve this by providing MPPT at the module level, so that each module produces at its maximum level regardless of shading on other modules on the string.

When using DC optimizers, a string inverter is still required to convert the energy produced from DC to AC (see Figure 4 below for a comparison of system configurations with DC optimizers, microinverters, and traditional string inverters).

Figure 2. An example of DC optimizer products. Source: Tigo. The products pictured are part of Tigo’s TS4 Platform. Pictured on the left is the back of an integrated smart module in which a DC optimizer is installed before the module leaves the factory. On the right is an add-on optimizer which can be fitted to a standard module. Click on the image to view Tigo’s video guide to optimizer installation.

Discussing the benefits of her company’s DC optimizers, Gal Bauer, Director of Customer Care at Tigo, a leading MLPE manufacturer, explained that “Tigo’s DC-DC optimizers–the integrated TS4-O and the retrofit/add-on TS4-R-Oincrease solar production, reduce shade impacts, prevent burnt diodes, and delay other aging effects that degrade a system’s performance over time. Tigo’s optimizers also include matched module warranties as well as a built-in UL-certified rapid shutdown solution and module-level monitoring with sophisticated alerts. These unique features purposefully keep costs of ownership at record lows and revenues at record highs for our customers.”

## Microinverters

As their name implies, microinverters are similar to traditional inverters but operate just one or, in some cases, a few modules rather than the full array. Like a string inverter or central inverter, they convert the DC power produced by the panels to AC power that can be sent to the grid and used in the home.

In addition to the benefits of MLPE discussed above, such as improving performance through module-level MPPT, microinverters can offer increased design flexibility. For instance, systems with microinverters can more easily be expanded at a later date if that is something the customer is considering (such as if they purchase an electric vehicle). Whereas string inverters have specific string length requirements, those considerations are avoided in systems with microinverters. Additionally, while not something you would commonly design, microinverters would allow for different types of modules to be used in the same system.

Figure 3. An example of a microinverter. Source: Enphase. Click on the image to view an Enphase instructional video on the installation process for their microinverters.

## How Do MLPE Fit Into Your Solar Design?

Both microinverters and DC Optimizers are attached to individual modules in your solar array (though as referenced above, there are some microinverters that operate multiple panels). If using microinverters, you will not need a string inverter for the system. If you are using DC optimizers, the panels will be connected in series to a string inverter. The figure below compares the installation configurations for these two options to a design without MLPE.

Figure 4. An illustration of PV system configurations depending on whether MLPE options like DC optimizers or microinverters are used. As you can see, DC optimizers still require a string inverter, while microinverters do not. Both options are typically connected to individual solar panels. Source: Aurora.

In contrast to systems with microinverters, in which every panel must be connected to a microinverter, DC optimizers can sometimes be deployed selectively. This is the case for Tigo’s selective deployment capabilities, in which MLPE devices that perform different functions can be attached to specific modules as needed. For instance, if shading only affects selected modules in your system, DC optimizers could be added to those specific modules so that they will not bring down the power output of the rest of the string.

Finding the optimal PV design for your customer can be a challenging proposition, but being aware of the diverse benefits of different components can help. Module-level power electronics can be a great option to maximize system performance, enable greater design flexibility, and capture other benefits. As with all design considerations, being able to quantify the performance impacts with accurate solar design software like Aurora can help ensure that you’re making the best design choices for the customer.

With integrated financial analysis tools, Aurora can also help you to understand if a potential increase in the up-front cost of the system is justified based on the value of the additional energy that the system will produce. Aurora models the precise impacts of DC optimizers and microinverters based on manufacturer specifications and is a leader in accurate modeling of complex MLPE functionality. For instance, we were the first software to simulate Selective Deployment of Tigo’s optimization.

The next time you confront solar design challenges like shade, modules on different roof faces, or the need to support future expansion of the PV system, consider MLPE as a possible solution.

Topics: solar design

In 2011, grad school classmates Sam Adeyemo and Chris Hopper discovered a shared interest in advancing solar energy in emerging markets and teamed up to design and install a solar installation for a boarding school in Kenya. Designing a PV system for a site on another continent made it clear how challenging solar design can be–and how how much the design process could be improved with the right tools.

With the idea of building the solar design software they wished they’d had, one that offered the accuracy to confidently design without site visits, Sam and Chris launched Aurora Solar in 2013. In the five years since that time, Aurora has grown from a small company whose entire team fit at one table to an industry-leading solar design company trusted by top solar firms around the world. We’ve achieved a lot that we’re proud of, from creating the first solar design program to model the electrical behavior of a solar installation down to the cell-string level to bringing new technologies like computer vision and solar design automation to the solar sector.

We’ve also learned a lot along the way, listening to customers to understand how we could better serve their needs. As we looked toward the future of the solar industry and how we could help the industry grow, we realized there were opportunities to serve solar contractors better if we reimagined our design tools from the ground up. To deliver a best-in-class solar design experience, we set about rewriting the very code our design software is built on.

After nearly two years of development, Aurora is thrilled to release its most significant update ever–a new version of our software that hits the sweet spot between accuracy, speed, scale, and simplicity.

## Simplicity

We’ve heard from customers that they love the accuracy Aurora enables–from constructing a representative model of the project site to precisely determining irradiance and solar energy production, as well as its compelling visuals. But sometimes a high-level of precision can make the design process complex. As we redesigned Aurora, we focused on approaches to maximize simplicity and ease of use. We worked closely with designers to streamline the software interface and improve user experience.

Drawing from some of the same approaches that enable video games to render incredible 3D visuals, we built a fully 3D design experience that allows solar designers to seamlessly transition from 2D views to 3D views of the project site model and PV design. In addition to viewing the site model and solar installation from any angle, designers can make modifications in 3D making accurate design easier. For instance, you can easily see the height of the roof in comparison to surrounding features like trees, and adjust accordingly, without having to toggle between 2D and 3D tools.

With integrated site model and system design tools, as well as the ability to edit both in 3D and view the project from any angle, the latest version of Aurora offers greater simplicity for solar design.

We also combined our tools for creating a model of the project site and designing the PV system into a single section of the application. This reduces the need to switch between tools if you need to adjust the site model or the design.

Finally, recognizing that the process of stringing panels to inverters can be quite complicated, with many different stringing configurations to choose from, we developed new tools to simplify the process. With automated stringing functionality, solar designers no longer need to ponder the optimal stringing configuration that will match inverter input requirements (acceptable string lengths and number of inputs) while maximizing the number of panels and minimizing costs.

Simplicity highlights of Aurora reDesigned:

• Seamlessly transition between views of the project, including moving from 2D to 3D
• Site model and solar design tools combined into one streamlined section
• New automated stringing functionality saves designers the headache of identifying the optimal stringing configuration

## Speed

Another key focus for us was delivering speed upgrades to our customers. It takes significant computing power to generate and manipulate hundreds or thousands of elements–like roof obstructions, solar panels, and inverters–while also maintaining accuracy. Yet speed is key to enabling efficient design, particularly when designing large, multi-megawatt commercial solar installations.

By rebuilding our CAD functionality and incorporating state-of-the-art graphics technology, we were able to deliver 10x performance upgrades for large solar projects. Discussing the new updates, Matthew Gschwend, Senior Solar Analyst at NRGTree in Boston, says “Even more impressive than all the design tools is the processing power, which allows you to create a site model, lay out your system, and run production simulations quicker than ever.”

Another change we implemented to reduce design time was integrating Aurora’s performance simulation tools–which precisely calculate the expected solar energy production of the PV system–into the design stage. You can now simulate the energy production of your design as you’re designing, allowing for real-time understanding of the performance implications of different design approaches.

One way we’ve helped solar designers speed up their workflows in Aurora reDesigned is by making it possible to assess the energy production of a design from within the design tool.

Speed highlights of Aurora reDesigned:

• 10X performance upgrades for multi-megawatt, commercial-scale solar projects
• The ability to simulate solar energy production while designing the PV system, allowing real-time assessment of the performance impacts of different design choices

## Scale

When we first started building our software in 2013, we began with a focus on the residential solar market. As we grew, we added both commercial solar design functionality as well as financial analysis tools for commercial customers, allowing us to serve the needs of C&I contractors as well. However, designing massive systems on a platform originally built for smaller projects could sometimes be challenging.

By rewriting our software code to utilize a new approach optimally suited for rendering 3D graphics on the web, we created a solar design platform that supports the creation and manipulation of large, multi-megawatt solar designs as easily as for smaller residential designs.

An example of the multi-megawatt projects easily supported in Aurora reDesigned.

We also built out a number of new, cutting-edge tools specifically designed for the challenges of large-scale solar designs. For instance, we’ve enhanced Aurora’s automatic obstruction detection, which automatically identifies similar obstructions on a roof and builds them into the site model. Already a significant benefit for sites with hundreds of vents and skylights, we beefed up the power of this tool, allowing it to now quickly detect and model thousands!

Additionally, we enhanced Aurora’s “fill zone” tool, which makes it possible to specify an area of the project site for Aurora to fill with panels according to the designer’s specifications (row spacing, panel tilt and orientation, etc.). Aurora’s fill zones can optimize panel location to maximize the number that fit within the available space–rapidly producing panel configurations even for massive projects.

Scale highlights of Aurora reDesigned:

• Support for significantly larger, multi-megawatt solar projects
• Enhanced “fill zone” functionality which automatically optimizes solar panel locations to maximize the number that fit within an available space

Aurora was founded to give solar contractors the tools to easily accurately design solar installations without site visits; but on a larger scale, our goal is to make solar energy more accessible by driving down the cost of delivering a quality system. In the five years since Aurora started, we’ve pioneered accurate remote solar design and developed new tools for solar designers–from 3D measurements with computer vision to solar design automation. But while we’re proud of what we’ve achieved to date, we’re always considering how we can do better.

Rather than continuing to build upon the same CAD tools we built in the beginning, we saw an opportunity to deliver an order of magnitude increase in simplicity, design speed, and the scale of projects Aurora supports by incorporating new approaches in web graphic technology. This new version of Aurora–Aurora reDesigned–not only helps us deliver on our mission to bring solar contractors the best design tools, but also provides a more scalable platform on which to continue our work to bring about a solar-powered future.

Topics: solar design, technology

As a solar contractor, you’re on the front lines of the incredible transition to cleaner energy–bringing your customers more control over their energy bills and the peace of mind that their energy is sourced responsibly.

But, as you no doubt know, running a solar contracting business isn’t always easy. You have to be able to roll with the punches of things beyond your control, like the imposition of tariffs and uncertainty in solar policies and incentives (for instance, decisions by Connecticut and Michigan to eliminate net metering this year).

But there’s one common solar contracting struggle that you can control–the efficiency of your site assessment and solar design processes. Here at Aurora Solar, we’ve encountered these challenges firsthand. That’s why we’re passionate about finding ways contractors can work smarter and more efficiently, saving time and money on their design and sales processes. In today’s article, we explore some of the ways solar design software makes that possible.

Aurora co-founder Samuel Adeyemo installing a commercial solar installation on a school in Kenya. In the process of designing the system from across the world, he and co-founder Christopher Hopper realized the barriers to remote solar design without effective software. They founded Aurora to address that need.

When you get an inquiry from a prospective customer, where do you start when it comes to determining if their home is suitable for solar and putting together a quote?

If, like many solar contractors, you set up a time to visit the site, climb on the roof, and take solar access measurements before compiling a proposal, your time-consuming approach could be costing you sales. Cascadia Solar learned this the hard way.

A family business serving Washington state’s Olympic Peninsula, Cascadia Solar prided themselves on their exceptional customer service and detail-oriented solar design process. But over time, they started to find that companies with faster turnaround times were beating them to the punch. Sometimes, by the time Cascadia arrived to conduct their site visit, the customer would already have several quotes from companies that used remote site assessment.

When Cascadia Solar learned about Aurora Solar design and sales software and how it could enable them to develop a proposal that was just accurate as their previous process without time-consuming site visits, the choice was easy.

Since switching to Aurora, Cascadia’s solar sales have doubled month over month, and more than doubled year over year! In addition to being able to send a proposal quickly (getting back to the customer while they’re most engaged is key to closing sales), they can now pursue leads that would have been too costly to target before.

## 2. Save time and money on site visits

Not only can a more efficient solar design process help you close more sales by responding to inquiries faster, the time and money saved by reducing your site visits and manual measurement processes can be significant.

In a low-margin industry like solar, where every dollar counts, adopting an accurate remote solar design software like Aurora is a powerful way to put more money back in your pocket. NREL has estimated that installers can save ~$850 per 5-kW install with remote site assessment software (savings of$0.17/W).

For Solarponics, a residential installer in California serving San Luis Obispo county, switching to Aurora allowed them to cut initial site visits by 90% while doubling installs.

## 3. Achieve superior accuracy with state-of-the-art technologies

Of course, these benefits of software-based remote solar design are only meaningful if the results are as accurate as traditional methods rooted in on-site assessment. That’s the beauty of the technological advances that enable remote solar site assessment and design.

NREL has found that Aurora’s shading engine (which allows us to precisely calculate irradiance on the roof) produces results that are statistically equivalent to onsite measurements. But we haven’t stopped there. Commitment to developing and incorporating the latest technologies is at the core of our company culture.

One key technology we offer customers to help improve design accuracy is LIDAR. If you’re not familiar with it, LIDAR is a lot like SONAR but instead of sound pulses it uses laser beams to create a detailed topographical map. This data is perfect for ensuring that you’ve accurately modeled the height of a tree or the pitch of the roof, which could affect the solar access and energy production of your design.

Additionally, we've partnered with HD imagery provider Nearmap, to make the most up-to-date and crisp imagery accessible to our customers for purchase in small, affordable bundles within the Aurora app. This way, if the Google or Bing satellite imagery for your project site is not recent enough or lacks clarity, HD imagery is just a click away.

We’ve also pioneered the use of computer vision for solar design. This field of computer science teaches computers to interpret visual images. At Aurora, we’ve developed computer vision approaches that allow you to take precise measurements of the project site using a combination of street-level and aerial images.

Aurora’s computer vision tools give solar designers the ability to take measurements
of a project site using aerial and street-level imagery.

Our computer vision tools also make it possible to automatically detect similar roof obstructions. This can save considerable time, especially on commercial projects where there might be hundreds of repeating skylights or vents that would otherwise have to be drawn out by hand.

## 4. Build trust with customers

Being able to demonstrate to your customers that you’re using the latest technologies to develop a personalized solar design for them is also a great way to help build trust and stand out from the crowd of competitors.

Scott O’Hara, Solar Energy Consultant at Baker Home Energy, a San Diego area solar company (twice ranked the #1 solar electrical subcontractor in Solar Power World’s Top 500 Solar Contractors list), can attest to this.

“Aurora’s software has given me a significant advantage in an extremely competitive market. It allows me to show customers why we are proposing a specific panel layout with the help of the sun path simulator.”

Aurora models the sun’s movement, and resulting shadows, at every hour of the year.
Showing the sunpath animation to your customers can help explain design decisions.

Numerous other companies have found it helpful to show off their Aurora design processes during the sales process–such as Sunworks, which operates a solar design showroom where they create personalized designs in Aurora with the customer.

Another key to building trust with customers is the accuracy of your energy production and bill savings estimates. According to O’Hara, “[Aurora] also increases consumer confidence, because they know we are using the best technology available today to accurately project the performance of the system.”

Unlike other solar software programs on the market, Aurora takes into account the exact stringing configuration of your system as well as the capabilities of the components you’ve selected, such as whether your inverter performs global maximum power point tracking. Aurora also pioneered the approach of simulating PV production at a submodule level, adding another layer of precision.

Aurora even details the causes of reduced system performance in it’s system loss diagrams, allowing you to understand the impact of factors like inverter clipping. These insights can help you arrive at the best design approach for your customer (as we discuss in more detail below).

(For a deeper discussion of some of the key factors for accurate performance simulations, see our article in Solar Power World.)

Aurora’s system loss diagrams indicate how much different factors are impacting energy production.

## 5. Deliver the best design for the customer’s goals

A final, powerful reason solar design software can improve your design processes is that this streamlined approach makes it considerably easier to compare multiple designs, in order to arrive at the one that best meets the customer’s goals.

We all have a limited amount of time, so without an efficient process for iterating through different designs it may not be feasible to evaluate many options and find the best (as Aurora co-founder Christopher Hopper discusses in his article, “Four Steps to Optimize PV System Performance in Shaded Conditions.”)

One key factor on which to evaluate solar designs is how much they will save the customer on their electricity bills. Aurora has an extensive database of utility rates (and makes it easy to add new rates) so you can assess the bill savings impact of different designs given the customer’s utility rate.

For instance, if the customer is on a time of use rate, a design that produces more energy during hours when electricity is most expensive might save them more than a design that produces more total energy.

Aurora’s AutoDesigner tool takes design iteration to the next level, applying approaches from the field of mathematical optimization to create an automated process that mimics natural selection to arrive at the ideal design given different objectives.

A depiction of how Aurora’s AutoDesigner iterates through potential
designs to arrive at the optimal one for the customer’s goals.

As a solar contractor, you’ve got a lot of demands on your time. Advanced solar software for remote site assessment and solar design can cut the time and cost of site visits, freeing you up to focus on quality installations and satisfying your customers.

Topics: solar design

Regular readers of this blog will know that we recently launched an integration with Nearmap, a provider of high definition aerial imagery. Integrating with Nearmap offers many benefits to solar installers, including allowing them to accurately design PV systems and to impress their clients with the crisp imagery in their proposal. As Nearmap CEO Dr. Rob Newman mentioned in a recent blog article, Nearmap “capture[s] the truth on the ground… [with] camera systems in planes flying over approximately 400 cities in the U.S. capturing highly accurate aerial imagery.”

As excited as the industry has been about the sales benefits of high quality imagery, little attention has been paid to the economic impact of its potential for reducing change orders.  A change order is defined as “a written order from the owner, architect, engineer, or other authorized person to depart from previously agreed upon plans and specifications for construction.”

In tangible terms, a change order can range from moving modules from one part of the roof to another because the customer had a change of heart, to realizing that you cannot fit as many modules on the roof as you wanted to due to obstructions you could not see on the roof.

For a term that is commonly used in the industry, there is precious little research that has gone towards quantifying the effect of change orders. A search of NREL’s website and database of publications does no more than acknowledge they exist and are important to manage, while looking through the archive of solar industry publications fails to unveil any research. Given that change orders are largely within the control of the solar installer, could it be that the solar community is unwilling to acknowledge that some of our own processes are the biggest impediment to our own success?

If so, it is time to talk about the industry’s dirty little secret if we are to have a hope of changing things.

To help us assess the significance of change orders, we conducted a simple poll of solar professionals who attended a recent Aurora webinar, which yielded responses from 107 individuals. The job functions of the survey group ranged from designers to salespeople and from c-level suite executives to entry-level employees.

As we suspected, change orders are pervasive in the industry. Of 76 individuals who responded to our question about how prevalent change orders are at their companies, 47% reported that change orders impact between 10 and 30% of their projects. Nearly 7% of respondents indicated that change orders are needed for over half of their projects.

What about the financial impact of change orders?

It is important to note that not all change orders are created equal. Pey Shadzi, Operations Manager at Cosmic Solar, a family owned installation company in Southern California, explains that “a change order can range from a major redesign of the installation after the deal has gone into contract to a slight modification as the customer is evaluating different options.” Shadzi notes that, for Cosmic Solar, change orders typically involve only minor changes such as slight adjustments based on customer input.

To help account for the range of change order types, we looked at how much a change order costs. We assumed that a smaller modification would cost very little, whereas a significant redesign could run thousands of dollars.

While the greatest number of respondents (34%) indicated that their change orders cost on average less than $250, a similar number (31%) indicated that change orders can cost up to$750. Twenty-one percent of respondents reported that their average change orders cost between $750 and$1250. Thirteen percent reported change orders costing as much as $1750. A weighted average1 generated from these results yielded an average change order cost of$583.

A lot of change orders are not within the installer’s control. Anecdotally, a customer changing their mind is a frequent cause of change orders. However, there are a lot of factors that the installer can control. Victor Ionin, a customer success specialist with Aurora, notes that many change orders result from a solar designer missing something about the site.

In our survey results we found that 88% of solar installers perform some degree of remote system design—meaning that they use some form of imagery in the development of their proposed solar PV system. It stands to reason that the more accurately that imagery communicates the conditions of the project site, the less likely they will have to change the design in the future.

This is where HD imagery comes into play; being able to get accurate measurements ensures that you will not over or underestimate the number of solar panels that can fit on a client’s roof. Crisp imagery allows Aurora’s computer vision algorithms to more accurately detect all the obstructions on a roof. Again, this allows solar installers to accurately forecast how many modules will fit on their roof, helping to reduce change orders.

Pey Shadzi remarks that using Aurora design software helps Cosmic Solar minimize the occurrence of change orders “because it allows us to measure the roofs with more accuracy. This allows us get our customers’ systems up-and-running sooner than if we had to make a change.”

1. Because respondents answers provided a range of costs that their change orders typically fall within, rather than exact costs, the weighted average was generated by randomly generating specific values for each respondent within the cost range they had specified. These values provided a basis from which to create a weighted average.

Topics: solar design

Software tools that enable remote solar design are transforming the solar industry—cutting industry soft costs by eliminating the need for truck rolls and reducing design time from days to minutes. However, remote design tools are developing rapidly, aided by advances in fields like mathematics and computer science, and it can be hard to keep up with all of the new technologies available to increase design speed and accuracy.

Many of these technologies once required a supercomputer to access, but today they are becoming accessible to everyone. This means that small and medium-sized solar sales, design, and installation companies—those without million-dollar budgets—can now access these technologies to improve the efficiency and quality of their design process and, ultimately, serve more customers.

As the solar industry becomes increasingly competitive, contractors need to take advantage of every tool at their disposal to produce the best designs as quickly and easily as possible. In today’s article we examine the practical implications of key technology advances that fundamentally change the solar design process.

# What technology developments are most important for remote solar design?

• New imagery tools, including LIDAR and drone imagery, enable more accurate remote solar design.
• Computer vision, using computers to interpret images, enhances accuracy and reduces design time.
• New applications of mathematical algorithms—“Optimization algorithms” are enabling software to automate solar design (as detailed by Cornell University Professor Madeleine Udell ), and enhancing the process of creating a 3D site model.

Many of these advances are not widely understood outside of their respective fields (particularly mathematics and computer science), yet they can be transformative for solar contractors who take advantage of them. Let’s explore how:

Imagery is one of the main areas in which technological advances have transformed solar design. The increased availability of diverse types of imagery, such as satellite imagery and LIDAR, makes it possible to accurately design a solar installation without physically visiting the site.

## Satellite Imagery

Although satellite imagery has been readily accessible for some time, through tools like Google Earth, it is worth acknowledging because this technology is at the heart of remote solar design. Combining this imagery with software solutions for solar design, it is no longer necessary for installers to visit each project site to measure solar access values and the available roof area.

With imagery of sufficient resolution to clearly identify buildings, trees, and other structures, it is possible to remotely assess the suitability of a project site for solar. This also supports the creation of representative 3D models of project sites, which enable highly accurate estimates of solar energy production by taking into account the shading impacts of trees and other obstructions.

## LIDAR

LIDAR data adds greater accuracy to remote solar design. This is because LIDAR data provides a means to verify the height and position of different parts of a building or surrounding objects like trees.

An example of LIDAR data for a solar project site, which can help verify the accuracy of a site model.

LIDAR (an acronym for Light Detection and Ranging) operates much like similarly-named SONAR and RADAR. But instead of pulses of sound or radio waves, a LIDAR scanner emits laser beams and measures the time that they take to return in order to map the location and elevation of objects in the surrounding area.

In the case of the LIDAR data used in solar design, the scanner is typically outfitted on a plane to map the topography of the land below, but LIDAR has other applications as well. For instance, LIDAR is what allows self-driving cars to “see” what’s around them.

## Drone Imagery

The emergence of consumer-affordable drones offers yet another valuable imagery source. Where high resolution satellite imagery is unavailableor not current enough to show recently constructed buildings, drones offer an option for solar contractors to access useful imagery for remote solar design.

Drones now offer an additional option for solar designers to access improved imagery of project sites. Software like Aurora allows solar contractors to upload their own imagery to take advantage of these options.

# Computer Vision

Computer vision is the use of computers to interpret images. There are many applications of computer vision, but in the field of solar design it offers a number of ways to make solar design faster and more accurate.

Computer vision can dramatically speed up the design process by automating the process of modeling obstructions on a roof. In Aurora, a designer can identify one obstruction, like a skylight or a vent, and then computer vision can be used to automatically find all of the other obstructions of the same type. The resulting time savings can be significant, particularly for commercial sites with many repeating obstructions.

Satellite imagery showing obstructions on a commercial roof (left) and Aurora’s automatic identification of similar obstruction instances (right).

Computer vision can also enable solar designers to measure distances and angles on the project site, such as the height of a tree or the pitch of a roof, with just an image. This ensures that models are true to life so the design and energy production estimates will be error-free.

Aurora’s 3-D Metric Estimation tool gives solar designers the ability to take measurements of a project site using aerial and streetview imagery. Click on the image to be directed to a video of this feature in action.

Algorithms Helping to Automate Solar Design

Computer science and mathematics are providing a number of other technological advances that are making remote solar design more automatic, while offering improvements in accuracy.

## Optimization Algorithms

Particularly exciting for any solar contractor who’s ever struggled to find the optimal design configuration for a particular location is the emergence of tools that can automate the solar design process.

Drawing from the fields of optimization and computational mathematics, Aurora developed an algorithm that iterates through thousands of potential solar designs to find the most cost-effective design that achieves a particular energy offset or bill savings target.

Aurora's "AutoDesigner" feature evaluates thousands of potential solar designs to recommend the best solution.

There is significant value in automating the solar design process. The number of possible designs for a site is vast—in fact, if every possible design configuration were accounted for it would take a human many lifetimes to evaluate them all! Relying on a computer program to do the heavy lifting of evaluating the multitude of designs can reduce error while freeing up time time for other responsibilities, like ensuring customer satisfaction.

## Geometric Modeling Algorithms

Another area where mathematical approaches provide advances in remote solar design is in the process of creating a 3D site model. Creating an accurate model of a customer’s roof can be very challenging, depending on the site, presenting a common trade-off between developing a site model quickly and getting every detail right.

With recent algorithmic advances, however, solar design software can make smart inferences about the structure of the site. For instance, SmartRoof, a roof modeling tool released by Aurora in 2017, can use just the perimeter of a roof to infer the internal structure of the roof and how the planes of the roof intersect. The designer can then make slight adjustments, such as removing or adjusting certain roof planes, but is saved significant time in creating the model.

"SmartRoof" infers the internal lines and planes of a roof based on its perimeter.

Yet another computational technique being integrated into solar design software draws from geometric modeling approaches to enable the creation of complex shapes through the merging of simpler shapes. SmartRoof includes this functionality to allow designers to draw a house in multiple parts and have them automatically integrated into a single building model. This makes complicated buildings much less daunting to model.

While the science behind many of these tech developments is complex, the integration of these innovations into software programs means anyone can access them without special knowledge. With these tools, it is easy to remotely design a solar installation, which the National Renewable Energy Laboratory found can save as much as $850 for a 5kW system. These advances are also lowering barriers to solar design, so anyone on your teamfrom engineers to salespeoplecan create an accurate site model and design. In the fall of 2017, California became the first U.S. state to require the use of advanced, or “smart,” inverters in solar projects (and other forms of distributed electricity generation). These changes, implemented through updates to “Rule 21,” require that inverters have certain capabilities to help ensure proper operation of the electric grid as more and more renewables are connected. While these requirements are specific to California for now, the changes are representative of approaches other states are likely to consider in the future. So, if you’re a solar professional, it's a good idea to get familiar with these changes no matter where you’re based. In today’s post, we explain the new inverter requirements under Rule 21 and what they mean. ### Why Are These Changes Being Implemented? The significant expansion of solar and other renewable energy sources is a huge opportunity—for tackling climate change, improving public health, delivering cost savings to consumers, and much more. However, it also presents new challenges for the management of the electric grid, which was originally built for one-way flows of power from power plants to the grid and then to consumers. Customer-sited “distributed energy resources” (DERs)—like solar—introduce two-way power flow, as systems feed excess energy back to the grid. The variable nature of energy sources like wind and solar, which fluctuate depending on weather conditions, adds additional complications for grid managers. California has led the nation in the deployment of solar and is likely to continue as the state works toward achieving its target of sourcing 100% of its electricity from renewable sources by 2045. As the proportion of renewables reaches unprecedented levels, there is a need for grid operators to have additional tools at their disposal to manage these resources and keep the grid running smoothly. As the “brains” of solar projects, inverters can support grid management, but to date regulations have prevented the use of the full range of inverter capabilities. Smart inverters, now mandated under California’s Rule 21, can help support management of the electric grid. Beginning a few years ago, California utilities warned that advanced inverter capabilities would be needed to avoid potential grid disruptions. With more nuanced capabilities for determining when and how solar systems disconnect from and reconnect to the grid in the case of a power outage or other disturbance, smart inverters can help ensure that solar and other DER systems don’t make grid disturbances worse. For instance, during and after a disruption on the grid, variations in voltage and frequency may occur. Historically, PV systems have been required to immediately disconnect when these conditions are detected; however, if a large amount of DER capacity disconnects at once this could further destabilize the grid. Similarly, the grid could be stressed if many solar installations reconnect to the grid at once after an outage, or increase their power output at too steep a rate. Smart inverter functions allow systems to remain connected to the grid under a wider range of voltage and frequency levels. Requiring these changes now also has cost-saving benefits, because they may prevent the need for costly retrofits to the inverter fleet. These issues—both grid instability and the need for expensive inverter retrofits—occurred in Germany, where solar capacity expanded very rapidly over the span of ten years. Beyond preventing grid disruptions, the use of advanced inverter functions has the potential to improve the stability of the grid. For example, dynamic volt/var operations (also called dynamic reactive power compensation) of smart inverters allow systems to help counteract voltage deviations on the grid. Furthermore, eventually, remote communication capabilities will be rolled out that allow grid operators to remotely adjust the operation of inverters to support the grid. The Smart Electric Power Association and the Electric Power Research Institute note that smart inverters may be one of the most cost-effective mechanisms for addressing many grid management challenges, and in some cases, “could help defer or avoid certain distribution, transmission, and electric supply upgrades.” Craig Lewis, Executive Director of the Clean Coalition , a nonprofit that works to accelerate the transition to renewable energy and a modern grid, notes that “enabling the full suite of advanced inverter functionality is essential to bring high-levels of distributed generation online quickly and cost-effectively – in California and every other leading market around the world.” On September 9, 2017, new requirements for inverters used in solar projects came into effect in California. These changes were implemented by the California Public Utilities Commission through significant updates to its Electric Tariff Rule 21 (or “Rule 21”), a set of existing interconnection requirements. ### What’s Changing Under Rule 21? The revisions to Rule 21 are being implemented in three phases. Phase One, which went into effect on September 9, 2017, requires that any solar project which applies for interconnection to the grid must use an advanced inverter capable of performing seven autonomous grid support functions. Inverters that are eligible for use under Rule 21 are those that have been tested and certified under the new UL testing protocol known as UL 1741 Supplement A (SA). A complete list of eligible inverters can be found on the California Energy Commission (CEC) website . The list—which is updated monthly—contains over 3,200 eligible inverters. One of the main changes under UL 1741-SA is that inverters are now allowed to operate under a wider range of voltage and frequency levels. As Solar Power World explains , under the previous testing protocol, UL 1741, “the old interconnection requirements only allowed inverters to operate within a narrow range of... frequency and voltage requirements.” This meant that the use of many commercially available inverter functions, including those that offer grid support benefits, was prevented. Phase Two will establish communication requirements for inverters , setting standards for how inverters communicate with each other and utility systems. This will be important for enabling grid managers to eventually make remote adjustments to inverter operations to keep the grid running smoothly. Phase Two will also require that inverters have the capability to communicate over the internet. (However, internet connections for solar systems will not be required at this stage, because it has not yet been determined whether utilities or solar customers will be responsible for paying for internet connections.) The exact date that Phase Two will go into effect is not yet determined, but it will be either March 1, 2018, or nine months after the release of an industry-recognized certification test standard for inverter communication protocols, whichever is later. Finally, Phase Three will require additional advanced inverter functions , “like data monitoring, remote connection and disconnection, and maximum power controls.” The specific requirements and timing of this phase have not yet been determined, although the Smart Inverter Working Group , which has been instrumental in establishing the details of Rule 21 revisions, has released recommendations (available here ). ### How to Comply with Rule 21 To comply with the current phase of Rule 21, the main thing you need to know is that the inverter you select for your solar design must be one that has been certified under UL 1741-SA ; consult the CEC database to be sure. After choosing a certified inverter, some setup may be required to ensure that the inverter operates under the default parameters of Rule 21. As Solar Power World explains, the necessary settings can be determined during the interconnection process with the local utility and set up either remotely or through the inverter interface. ### Coming Soon to a State Near You? While California is the first state to take these steps, as a solar contractor it’s a good idea to be aware of these changes wherever you work, because other states are likely to be considering similar moves in the future. Hawaii, Nevada, Arizona, Vermont, and Massachusetts are among states that may soon follow California’s lead. Quoted in Solar Power World, John Drummond, applications engineer at inverter company Chint Power Systems, says his company “expect[s] these kinds of advanced inverter functions to be required in the entire country in the next few years.” As we work towards a future where clean, renewable energy is the norm, smart inverters will play an important role in managing the modern grid. We hope this article has given you a better understanding of how regulations are changing to manage rising levels of renewable energy and the details of Rule 21’s new inverter requirements for solar systems in California. Editor's note: This article was updated in September 2019 to reflect California's passage of SB100 which sets a target of sourcing 100% of the state's electricity from clean energy by 2045. Two weeks ago, during the Solar Decathlon 2017 Competition , we explored the solar powered house designs from participating university teams. The designs showcased many creative and resourceful strategies—and presented a fun challenge for modeling in Aurora. With the competition now complete, today’s post takes a closer look at the top three teams to identify some of the solar design lessons from their success. The Solar Decathlon 2017 competition houses, modeled in Aurora. ### The Solar Decathlon Contests and Winning Teams The Solar Decathlon is comprised of ten equally-weighted contests, each with a total of 100 available points. Six of the contests—Architecture, Market Potential, Engineering, Communications, Innovation, and Water—are juried contests in which industry experts tour each house and assign it a score. Performance in the last four contests—Health and Comfort, Appliances, Home Life, and Energy—is based on measurements by sensors connected to each home. (For more information on the criteria of each competition, see the end of this article.) The winning teams this year featured a few common characteristics: appealing layout and appearance, energy and water efficiency through cutting-edge design practices and innovative methods, and excellent operation of the house during the contest week. Here’s a breakdown of the scores of the top three teams: 1. Swiss Team - 872.910 points 395.4 out of 400 measured contest points (#1) 478 out of 600 juried contest points (#2) 2. University of Maryland - 822.683 points 348.7 out of 400 measured contest points (#4) 476 out of 600 juried contest points (#3) 3. UC Berkeley / University of Denver - 807.875 points 394.6 out of 400 measured contest points (#2) 414 out of 600 juried contest points (#9) The top three house designs from the 2017 U.S. Solar Decathlon, left to right: NeighborHub by the Swiss Team, reACT by Team Maryland, and RISE House by UC Berkeley and the University of Denver. Photo Credits: (left) Dennis Schroeder/U.S. Department of Energy Solar Decathlon; (center and right) Jack Dempsey/U.S. Department of Energy Solar Decathlon. Both the Swiss Team and UC Berkeley/University of Denver did exceptionally well in the measured competitions, losing just a few points across the Health & Comfort, Appliances, Home Life, and Energy contests. In the juried contests, the Swiss Team took second place and Maryland tied for 3rd (with the Northwestern house). ### Lessons from the Energy Contest The Energy Contest evaluates each team's energy production (kWh) and the value ($) of that energy based on a theoretical utility rate structure. Of the total 100 points for the Energy Contest, Energy Production accounts for 60 possible points and Energy Value accounts for 40.

Each team’s house both could both contribute energy to and take energy from the Solar Decathlon electricity grid (a microgrid created for the competition), just as would be the case for net metered customers on the U.S. electricity grid. Additionally, for the first time, this contest included time of use energy pricing.

Let’s take a quick look at the Energy Contest and how the top teams fared:

Graph of teams' cumulative energy production and energy value, the two components of the Energy Contest. Credit: U.S. Department of Energy Solar Decathlon 2017 .

The above graphs show the top three teams’ Energy Production and Energy Value throughout the competition week. In the Energy Production segment, teams receive the full 60 points if they have an energy surplus for the competition; if they have an energy deficit, they can receive partial points depending on the size of the deficit, between 0 and -50 kWh. For the Energy Value segment, teams get the full 40 points for having at least $10 in energy credits by the end of the competition, with prorated points for having between$10 in credits and -$10 in energy charges. Both the Swiss Team and UC Berkeley/University of Denver achieved the$10.00 credit threshold, and Maryland managed their house energy demands at the end of the contest to keep a small energy surplus despite inclement weather that reduced energy production.

#### Designing for the Local Weather

October 9th was the first time in all of the Solar Decathlon contests that snow fell on the competition site, presenting a new challenge for the competitors. Most of the Solar Decathlon teams had PV systems sized to handle inclement weather, as is evident in the growing energy surplus for all three teams during the in the first few (sunny) days of the competition. This surplus proved very valuable when snow arrived mid-week. During the snowfall, we can see that each of the houses experienced a decline in their net energy balance, a result of powering their homes for the contests while there was minimal production from the PV arrays.

While several teams had to sweep snow off their solar panels to keep the systems up and running, the Swiss Team simply left the facade of the NeighborHub closed. This prevented snow from accumulating in the first place, contributing to their strong performance. Not all systems were designed with snow in mind, but rather reflected the climate of the house’s target market.

A model of NeighborHub in Aurora, showing the house’s ability to adjust pitch of its panels.

#### Benefits of Module-level Power Electronics

Many teams came in with some sort of module-level performance control, either a set of optimizers or microinverters. In some cases they served mostly to help monitor individual module health, but the Swiss Team’s winning design took it a step further by using optimizers to connect modules with different orientations without taking mismatch losses in production. It also provided an additional benefit when a muddy bird walked all over the array, seen here:

Photo credit: Joe Simon/U.S. Department of Energy Solar Decathlon.

Hungry for more inspiring solar designs? You can check out our Solar Landmark blog series—as well as future Solar Decathlon events! The program now has multiple international events, with five more planned before the next U.S. competition in 2020:

You can also check out some of the innovations that have come out of the Solar Decathlon competition in their latest blog post .

What solar design lessons did you take away from the U.S. Solar Decathlon 2017? Let us know in the comments below!

Solar Decathlon Contest Details
Curious about what goes into each of the ten contests that comprise the Solar Decathlon Competition? Here’s an overview of how each is judged:

1. Architecture: A jury of architects evaluates each team's architectural concept and design approach; the implementation of the design and its innovative features; and required documentation for the project.

2. Market Potential: Teams design a primary residence for year-round occupancy for a specific target client. A jury of professionals from the homebuilding industry evaluates the overall attractiveness of each team’s design to its selected target client and the market impact potential of the house.

3. Engineering: A jury of engineers evaluates the engineering design and implementation of each team's house based on the engineering approach, design, efficiency, and performance.

4. Communications: A jury of communications professionals evaluates each team's communication strategies, materials, and efforts to educate, inform, and interest the team’s local communities, visiting public at the event, and diverse online audiences.

5. Innovation: This is a new contest for Solar Decathlon 2017. A jury of industry professionals will evaluate each team's research, approach to sustainability, innovations for the target client, and durability and safety of innovative elements, while also evaluating whether the price is right for the target client.

6. Water: Solar Decathlon 2017 is rewarding smart water solutions for the first time. A jury of industry professionals evaluates each team's approach to water conservation, water use and reclamation, and landscaping water impacts.

7. Health and Comfort: Team houses must minimize the flow of cooled air in summer or heated air in winter to the outdoors, operate heating and cooling systems that keep temperature and humidity steady, all while maintaining healthy indoor air quality.

8. Appliances: The Appliances Contest is designed to mimic the appliance use of an average U.S. home. Teams earn points for operating their refrigerator and freezer, washing and drying laundry, and simulating cooking tasks and hot showers.

9. Home Life: Teams are required to engage in common household activities that use electricity. They cook and share meals with friends and neighbors, watch television, use computers, and host game nights. And, for five days, they “commute” at least 25 miles in an electric vehicle charged by the house solar electric system.

10. Energy: The Energy Contest evaluates each team's energy production and a theoretical value to a utility of the energy each team both contributes to and takes from the Solar Decathlon electricity grid. For the first time, this contest includes real-time energy pricing.

Background Image Credit: Jack Dempsey/U.S. Department of Energy Solar Decathlon.

Topics: solar design

The U.S. Department of Energy Solar Decathlon is a great opportunity for college students to get hands-on experience with the design and construction of houses and solar PV systems. The collegiate competition—happening in Denver, Colorado at the time of publication—challenges student teams to design and build full-size, energy-efficient houses powered exclusively by solar energy.

The Solar Decathlon is a biennial competition that has been running since 2002, and has involved over 35,000 participants across 274 teams thus far. For each competition, up to twenty university teams are selected from a pool of applicants. Once selected, each team has a year and a half to design and build their house before bringing it to the competition site. Previous Solar Decathlon contests have taken place in Washington, D.C. and Irvine, California.

During the contest week, each team works through 10 competitions that evaluate their houses on different criteria, including hosting their rivals for a dinner party, washing loads of laundry, and taking a commute in an electric vehicle charged by their house’s solar installation. The winning team is the one that best blends design excellence and smart energy production with innovation, market potential, and water and energy efficiency. The Solar Decathlon as a whole fosters collaboration between students of different disciplines and an emphasis on sustainability.

I had the good fortune to participate in two previous U.S. Department of Energy Solar Decathlon competitions—once in 2011 as a student, and again in 2013 as a project manager. So naturally, I was excited to take a look at the designs from this year’s competition.

In this installment of our Solar Landmarks Series, we examine all 11 of the Solar Decathlon 2017 houses, what makes them special, and how they can be designed in Aurora.

The Solar Decathlon is also a unique chance to interface with industry leaders—here's me (center) chatting with then-Secretary of Energy Dr. Steven Chu about some of the energy efficiency measures in our Solar Decathlon 2011 house, CHIP. Photo Credit: Stefano Paltera/U.S. Department of Energy Solar Decathlon

### New Themes

In this year’s competition, I picked up a few themes. The contest has brought back electric vehicle driving which had been absent for several iterations of the competition, and battery-powered cars are all on display. The Energy contest has also been upgraded, now featuring net energy metering (NEM) which has encouraged concurrent energy production and usage as well as energy storage systems. The Health and Comfort contest has asked teams to bring in more plants and materials that emit fewer VOCs (a form of air pollutant). And finally, several teams came in with the modular design approach, where the prototype house brought to the competition could be scaled into a larger house in the future.

### Las Vegas - Sinatra Living

The University of Nevada, Las Vegas’s Sinatra Living house features a combination of photovoltaics and thermal heating, plus a battery pack. Deep overhangs and adjustable patio shade are great for managing the intense desert sunlight, and the inclusion of energy storage is helpful given Nevada’s less favorable net energy metering policy.

Photo Credit: Jack Dempsey/U.S. Department of Energy Solar Decathlon

To design this house in Aurora, the user should start with our SmartRoof tool and select the Flat Roof option before drawing (as illustrated below). Once the roof has been outlined, simply select one of the bottom wings and set it to “pitched,” which will tilt the whole roof up from that edge.

### Maryland - reACT

Back in 2011, the SCI-Arc/Caltech team I was on took sixth place in the Solar Decathlon on the strength of heavy insulation, a creative custom smart home app that included a complete power-down button, and some thorough weather analysis that resulted in a PV design that got us through a rainy competition week with energy to spare. The team that took first place overall that year was the University of Maryland team, which not only had a beautiful house, but a custom dehumidification system that worked with just heat from the sun and a large amount of greywater recycling.

This year, Team Maryland brings the reACT house, a self-sufficient design that also features a large amount of plant life and a central courtyard that helps collect thermal heat. The PV system is mounted on two wings of the house, and uses a combination of DC optimizers and energy storage to manage energy usage. With half the array pointed west and half the array pointed east, the system’s peak production is spread out through more of the day.

Photo Credit: Jack Dempsey/U.S. Department of Energy Solar Decathlon

To design reACT in Aurora, we need four SmartRoof structures: one for the east wing, one for the west wing, and two gable-style roof structures—one for the center of the house and another for the enclosed courtyard. The deck is optional, but I made it using a flat roof.

### Missouri S&T - SILO

Missouri University of Science and Technology is taking part in their seventh Solar Decathlon competition, this time bringing in the sleek SILO house. Large glass walls bring in plenty of diffuse light, and the 24 PV modules are more than enough to power this house through the contest. Like many other Solar Decathlon 2017 teams, Missouri S&T elected to use energy storage to manage the TOU energy pricing and the fact that exported energy is valued at a lower rate than energy bought from the grid. Both of these aspects are new to the Solar Decathlon Energy contest this year and are typical of most utility NEM rates.

Photo Credit: Dennis Schroeder/U.S. Department of Energy Solar Decathlon

SILO takes three SmartRoof pieces to design in Aurora, one for the south face with PV, one for the sloped north roof, and one for the arched middle segment. Curves take a little bit of time to model and aren’t optimal for PV installations, but it’s possible to make one in Aurora by using pitched folds with SmartRoof. After creating an outline of the curved roof face, I made only the south edge “pitched” and then inserted several pitched folds. By setting these in progressively smaller tilts, I was able to create a shape similar to the curved roof.

### Netherlands - Selficient

The Selficient house, by HU University of Applied Science Utrecht in the Netherlands, is one of the few cases we’ve seen with dual tilted systems in the Solar Decathlon, although the team from Washington University in St. Louis is also using them this competition. One cool part of this house is the modular design, which lets the installer fit different pieces of wall, floor, and roof to create different floor layouts.

Photo Credit: Jack Dempsey/U.S. Department of Energy Solar Decathlon

In Aurora, dual tilt systems can be created using the Fill Zone feature. This house appears to use a tilt of around 30 degrees, with very small row spacing. Stringing with Aurora fill zones connects modules with the same orientation to avoid mismatch in light availability.

### Northwestern - Enable

The Northwestern University team’s Enable house sports a nicely tilted PV array, a sunroom, and—a rarity in Solar Decathlon designs—a garage for an electric car. The integrated energy storage system pairs well with EV usage, which will allow the car to charge up during the night when electrical rates are more favorable.

Photo Credit: Dennis Schroeder/U.S. Department of Energy Solar Decathlon.

To create a 3D model of Enable in Aurora, we used four separate roof segments: one for the south-tilted section, a flat segment for the middle of the house, a third roof for the sunroom, and one for the back of the house. One way to ensure azimuth alignment is to copy-paste the same rectangle twice and then resize the pieces. The PV array is nicely-sized and sits at a good tilt for the intended latitude.

### Swiss Team - NeighborHub

The NeighborHub from the Swiss team (a team comprised of students from École Polytechnique Fédérale de Lausanne, the School of Engineering and Architecture Fribourg, Geneva University of Art and Design, and the University of Fribourg) has a central core surrounded by an unconditioned flexible-use space. Some other unique features include a zero-water toilet and exterior wall sections that can be folded upwards to open up the flexible space to the outside. The folding wings hold the PV modules used in this house. Most power is drawn from a series of monocrystalline panels, and a small amount of power is generated from a series of semi-translucent thin-film dye-sensitized modules. The effect is truly building-integrated PV.

Photo Credit: Dennis Schroeder/U.S. Department of Energy Solar Decathlon

The structure of the Swiss Team's house is straightforward—it just needs a single roof structure. However, the modules are not placed on the rooftop, so this design calls for roof racks to hold the modules in space, rather than placing them on the structure. I used ground mounts at tilts of 15 degrees for the folded-up section and another piece at 89 degrees for the vertical walls, in order to place the modules. Aurora’s stringing tool also permits us to connect modules in different orientations like we see in this design when the wings are opened.

### Team Alabama - surviv(AL) house

The surviva(AL) house by Team Alabama (comprised of students from the University of Alabama at Birmingham and Calhoun Community College) has a nice large south-facing roof that sports a 9.9 kW array. Each of the modules is attached to a microinverter, which will minimize potential shading losses. It also has a series of 14 clerestory windows (small windows along the top of a structure's wall, near the roofline) and a porch with a translucent overhang, which lets in more light while keeping the elements out.

Photo Credit: Dennis Schroeder/U.S. Department of Energy Solar Decathlon

Modeling surival(AL) in Aurora takes two roof sections: one for the large south face and one for the smaller north face. Each roof piece just needs one edge to be pitched, and they can be set to the same height and tilt which results in the south roof reaching a greater vertical height than the north segment.

### Team Daytona Beach - BEACH House

Team Daytona Beach (comprised of students from Embry-Riddle Aeronautical University and Daytona State College) brings in the accessible BEACH House, designed for Florida’s climate. Like the surviv(AL) house, BEACH House can be modeled with two segments, a north-facing roof and a south-facing roof. To create the extended overhang over the west portion of the house, create the 2D outline as a flat roof, and then change only the bottom-most edge to “pitched” to base the tilt of the roof off of that edge.

Photo Credit: Jack Dempsey/U.S. Department of Energy Solar Decathlon

BEACH House also features two different types of PV modules, all of which are connected to a central inverter. Aurora lets strings with different modules connect to the same inverter on different MPPTs, so there is no difficulty in modeling this design. Aurora’s module snapping functionality even snaps the different model types together without issue.

### UC Berkeley / University of Denver - RISE

The RISE House by UC Berkeley and the University of Denver is intended as a modular design, with stackable stories and communal living spaces. Only the top level is present at the Solar Decathlon due to 18’ height restrictions, but it gives a good sample of the house’s design philosophy.

Photo Credit: Jack Dempsey/U.S. Department of Energy Solar Decathlon

Modeling any version of RISE is a straightforward task in Aurora, using individual rectangles for each level of the house. We also modeled the stairs using a 45-degree sloped roof, but this has no effect on the site performance. There are also railings on the house, which can be modeled using a thin rectangular obstruction if desired.

### UC Davis - Our H2Ouse

UC Davis brings in Our H2Ouse, an incredibly water-efficient house that uses smart systems to display homeowner’s water usage. The array is segmented into two systems, one of which feeds directly to the load panel and another that connects to an energy storage system. We think the bicycle wheels that provide deck shade are also a nice touch.

Photo Credit: Dennis Schroeder/U.S. Department of Energy Solar Decathlon

Our H2Ouse can be modeled in a single polygon using SmartRoof, with the south-most edge set to a slight tilt for the whole structure.

### Wash U - St. Louis- CRETE

The team from Washington University in St. Louis brings in CRETE, a storm-proof precast concrete house with vertical planters that connect the exterior to the interior. The precast modules also have a core of insulation that helps minimize heat losses. Building the main structure of the house in Aurora is as easy as drawing a rectangle.

The PV system for CRETE is row tilted, which can be completed easily by using the standard Aurora module layout tool or a fill zone.

Photo Credit: Jack Dempsey/U.S. Department of Energy Solar Decathlon

Aurora’s CAD tool does not model overhangs so, for aesthetic purposes, I created a dummy module with a deep z-dimension to show a fake gutter piece. To enable an accurate performance simulation with these fake modules present, they are attached to a 0% efficiency inverter. An actual proposal wouldn’t need to go into as much detail, but it was fun to model the house as close as possible to the real deal.

I'm glad to see that the Solar Decathlon is still going strong in its eighth iteration (not counting the international events). Each year it seems that the houses become more innovative and competitive. There is also more emphasis on energy-efficient house design, especially important given the 10 kWdc PV system size limit, making these homes truly designs of the future.

~~~

What do you think about the houses? Comment below to tell us which one is your favorite!

The winners have just been announced, so check out our follow-up post in which we highlight lessons from the winning designs.

The Solar Decathlon 2017 competition site and all of the team's houses, modeled in Aurora.

Top photo credit: Jack Dempsey/U.S. Department of Energy Solar Decathlon

This blog post is not affiliated with the U.S. Department of Energy Solar Decathlon or any of the competing teams.

Topics: solar design, Solar Landmarks

Six years ago, business school classmates Sam and Chris discovered their common passion for improving people’s lives with affordable access to solar energy. During their first year at Stanford’s Graduate School of Business, they joined forces to develop a 50kW solar installation for a school in East Africa—reducing its electric bill and providing uninterrupted access to clean energy.

But while the installation took just a couple of weeks to install, they were struck by how long it took to plan and design. Designing a system on the other side of the world, conducting financial analysis, and planning its installation took months!

Realizing how much time and money solar installers could save if they had a way to create accurate solar designs remotely, Chris and Sam founded Aurora Solar in 2013 to make that vision a reality. Since then, the desire to make remote design accessible and intuitive to solar installers—while being as accurate as on-site assessment—has been the driving motivation for the team, and is why we continually focus on releasing new features and functionality. Aurora has pioneered remote solar design, becoming the industry’s most validated and feature-rich solar software.

However, while building an accurate 3D model of a project site is vastly faster and easier than on-site assessment, this process can still be challenging and time-consuming.

Even with cutting-edge tools, like LIDAR and computer vision, there can be trade-offs between speed and accuracy. Getting every detail perfect, in spite of factors like skewed satellite imagery or irregular roof structures, can require additional time or skill, and creating a quick, simplified design might sacrifice accuracy. But what if there was a way to eliminate these trade-offs?

To create the industry’s most intuitive solar design program, Aurora set out to reinvent the process of constructing a roof model, rethinking it from the ground up. This is the story of Aurora’s invention of SmartRoof, a tool that reimagines solar design.

Figure 1. An example of the kind of complex solar project site model and design that Aurora’s new approach to remote site design makes possible in just a few minutes.

### Rethinking Remote Modeling

How do you make roof modeling dramatically easier without sacrificing accuracy and functionality? Co-founder Chris Hopper has been contemplating this question since Aurora’s earliest days, and for over a year our team has been building a new feature to make this vision a reality.

We wanted to not only make the process of building a site model faster and simpler, but also reduce human error, such as model inaccuracies resulting from confusing or skewed satellite imagery.

Additionally, we wanted to create a tool that would make modeling unusual and complex roofs straightforward. If you’ve been designing solar installations for a while, you know that residential roofs come in a vast array of forms (for definitions of some of the roof terms we use in today’s article see our examples below).

Figure 2. An example of a gable roof (2D left and 3D right) as modeled in Aurora. One of the simpler roof types to model, gable roofs are defined by having just one central ridge line.

The diversity of roof types presents many modeling challenges for solar designers—from basic gable roofs (Figure 2), to hipped roofs (Figures 3 and 4), roofs with dormers (Figure 5), roofs with folds (Figures 6 and 7), and roofs where the ridge line is off-center (Figure 8).

Figure 3. An example of a hip roof modeled in Aurora. In contrast to a gable roof, hip roofs have diagonal ridge lines extending from the corners to the center of the roof.

Figure 4. Hip roofs come in many variations, such as this cross-hipped roof modeled in Aurora.

Figure 5. A house with a dormer (circled in green) modeled in Aurora. Dormers are common roof features that have traditionally presented a challenge when creating a site model.

Figure 6. An example of a Dutch gable roof modeled in Aurora. Also referred to as “attic overhang dormers,” Dutch gable roofs are defined by folds (circled in green) that create the appearance of a dormer.

Figure 7. Another type of roof with folds is a gambrel roof, such as the one above modeled in Aurora.

Figure 8. Saltbox roofs, like this one modeled in Aurora, are defined by an off-center ridge line.

Recognizing the complexity created by the great variety of roof types, we arrived at the idea of a software tool that would be able to infer a roof's internal lines just from its perimeter. In this way, much of the time-intensive work would be done for the designer—eliminating sources of human error, and making site modeling easy and (dare we say it?) even fun.

After over a year of development and extensive user testing, SmartRoof has arrived.

### What Makes SmartRoof Different?

SmartRoof introduces several completely new innovations for remote solar design. SmartRoof’s defining breakthrough, never before achieved in solar design software, is its ability to infer the internal roof structure (how different planes and roof sections intersect) just from the roof perimeter and a few inputs from the designer (Figure 9).

Figure 9. SmartRoof infers the internal lines and planes of a roof based on its perimeter.

SmartRoof makes the process of drawing the roof perimeter easier by providing guides and snap functionality to get perfect 90º angles, so inaccuracies in satellite imagery don’t translate into inaccuracies in the 3D model. Additionally, SmartRoof makes modeling multilevel roofs and other complex structures easier by allowing the designer to draw roofs in multiple parts, which are then seamlessly combined.

SmartRoof also makes it much easier to account for dormers and folds, two common but difficult-to-model roof features. With special dormer functionality (Figure 10), you can drag and drop a dormer onto your roof drawing and SmartRoof will incorporate it into the 3D model. With the ability to copy and paste dormers onto different roof planes, designers can save even more time. Similarly, folds—where a roof plane with a certain pitch intersects with a roof plane at a different pitch—have historically been difficult to add when building a 3D model. With SmartRoof, you can easily insert folds (such as the ones in Figures 6 and 7 above) and adjust their location as needed.

Figure 10. SmartRoof’s dormer feature allows designers to drag and drop dormers onto the roof, as well as copy and paste them, for easy integration into the site model.

### Building SmartRoof

In addition to Aurora co-founder Chris Hopper, who first envisioned SmartRoof, the core project team included Computer Vision Engineer Matt Stevens and Front-End Engineer Kelly Stevens. After conceiving of the initial idea for SmartRoof and identifying mathematical approaches that could enable this functionality, Chris developed the initial prototype of SmartRoof. From there, Matt worked to refine the underlying algorithm, and Kelly built the functionality into Aurora. Matt and Kelly also worked together to incorporate approaches for modeling dormers and combining different roof sections.

After SmartRoof was developed, extensive user testing was done to ensure that this new approach to roof modeling was accurate, intuitive, and met the needs of both solar designers and salespeople. Among the modifications made based on user feedback were the ability to drag interior edges and folds and pop-ups to make it easier to make adjust the properties of different parts of the roof, like dormers (see Figure 11) or roof faces (Figure 12).

Figure 11. SmartRoof has an inspector function to allow the user to modify the characteristics of dormers.

Figure 12. SmartRoof users can adjust the pitch roof faces or change the height of a roof (particularly helpful when creating models of houses with roofs at different levels).

Judging from preliminary user responses, the final product is already reshaping how solar designers work for the better. Discussing how SmartRoof has impacted his work, Ivan La Frinere-Sandoval of First PV Solar, says:

"SmartRoof speeds up the solar design process tremendously. Instead of drawing the entire detailed roof structure we just trace the perimeter outline and the software detects the interior roof edge details. Incredible!"

Aurora has come a long way since we first started our journey in 2013, but Chris and Sam’s vision of a software program that would make exceptional remote solar design faster, easier, and more cost-effective remains our guiding light. SmartRoof is our latest—but certainly not last—push to expand what is possible in remote solar design.

Interested in learning more about how to integrate SmartRoof into your workflow?

Pamela Cargill is Principal of Chaolysti , a consulting firm that helps residential solar contractors succeed and reach profitability. With over ten years in the industry, she has built an impressive track record of helping solar businesses grow.

In the first of two articles from our conversation with Cargill, we shared her advice for practices contractors can put in place to operate more effectively. Today, we’re pleased to share her observations on how the industry is evolving and what trends contractors should be keeping an eye on.

[Please note that this interview has been edited for brevity and clarity.]

## As someone who works closely with many different players in the industry, what can you tell us about the current state of the solar market and how it may be evolving?

I would say that we're going to continue to see small contractors take a larger and larger percent of the overall share of the market.

This whole idea of having a "long-tail" is going to become irrelevant because there are just going to be small contractors.

I really see that we're on track as an industry—as a specialty contracting industry—to look a lot more like HVAC. For instance, HVAC has somewhere around 450,000 to half a million contractors all over the nation and these are all small local businesses. There are some regionally focused enterprises, but there's really no such thing as a national, multi-state contracting business in HVAC.

Because the solar industry is a specialty contracting space that's still so small, we have a long way to grow. According to some of the numbers I've looked at from The Solar Foundation, we have somewhere between 6,000 to 8,000 contractors nation-wide. So there's a huge difference between what our industry looks like and what HVAC looks like. But then again they also have about a 100-year head start on us.

This creates some interesting dynamics. I think that as the overall growth and net profit margins of solar contractors start to look more like other traditional trade spaces, it's probably going to become less interesting for some businesses that are involved now to continue to be involved.

This comes back to the importance of having that sense of why [you’re running your business]. If a contractor doesn't have a long-term vision for why they are in this business or plans for how they're going to be there in the long-term for the customers in their portfolio, I don't really see a compelling reason why they'll be in this business.

This is not a sales business, it's a contracting business. And I think we're at a juncture right now where that needs to split. Yes, we still do need to have better sales and marketing practices, but we need much more focus on running a good contracting business. That's really what a lot of this is going to come down to:

The more we're focused on running contracting businesses, the more we're going to start looking like other traditional trades.

## Recognizing that a focus on efficiency will be needed as the industry matures and profit margins become tighter, can you speak to the role of automation in solar contracting? What elements in the process of taking a solar installation from conception to project completion do you think are best suited to automation? Are there areas where you think automation can be counterproductive?

The parts of the process that I see as most suitable for automating are anything that helps you track how often you follow up with a customer. During the sales process as you're continuing conversations with the customer, and you're going back and forth with them—that cadence of follow up is ripe for automation.

I would be careful, though, about over automating that.

You want to build a genuine relationship with the customer that you're working with. You don’t want to over send automated emails in a way that isn't personal and genuine.

Automations should help you track when you had a conversation with a customer and remind you to follow up at a specific cadence, say a 5-day window. That's a good automation. Then you should personally shape that follow up. You may have a template you work from, or a content library that you send some articles from, but ensuring that the touch is really personal is critical.

Another area well suited to automation is the design process. There are a lot of aspects of the initial design that can and should be automated. I can say for a fact, based on my early experience in the industry doing a lot of this work by hand—going into a string sizing website, and then going to PV WAtts, and then going to an Excel workbook for pricing, and then going to another Excel workbook for material take-off—that was not particularly effective. It took a long time, and if I got interrupted in the middle of it, it was difficult to come back to and figure out where I was. That I think is where we've made a lot of progress.

Software that automates more routine aspects of the design process, so that the designer can stay more focused on ensuring that the design is meeting the objectives that the customer has stated, that I think has a ton of value.

## Any final thoughts you'd like to share?

I would close by noting that the easy days of floundering around to be a solar contractor in this business are behind us now.

My old boss called me the other night and we were catching up about the changes in the industry. We've both been in the industry for a long time and we were reflecting on how easy it was for us in those really early days to just kind of make it up as we were going along and not really have the tightest processes in place, because there was so much margin to work with.

While we both had skills in construction, we hadn't worked at an HVAC company where you live and die by very small percentage points on your margin and you have to be constantly focusing on the operational effectiveness of your business. In solar, we've had [some] time to muddle through and not really focus on process.

I think as we're moving into the future, it's really going to be worthwhile for us to look much more at how are other contracting businesses operate. What are the best practices from those spaces that we could bring over?

Whether it be in terms of project management, scheduling and dispatching, long-term customer support, service plans, keep in touch, re-marketing, etc. That's really what's going to start driving excellence in this business in the very near future and going forward.

We only have growth ahead of us in this space. It’s definitely going to be tough and there's going to be some weeding out, but I'm bullish on the growth of rooftop solar and I'm sticking with it!

For many new entrants to the solar industry, coming up with the best solar design for a homeowner is a daunting process. You have to take into account environmental conditions like the site location, available roof area, and shading considerations. You also have to make sure you have the right number and combination of modules and inverters to hit your energy target. Try doing all of this live at the kitchen table in front of a homeowner and it can be a nightmare.

Historically, every PV system has had to be designed manually. But the multitude of factors to be considered makes this design problem difficult and time-consuming for humans to solve. For instance, a proposed design might include an inverter that is too small to handle the current of an array or panels might be situated in a way that violates fire codes or setback requirements.

Even in the absence of violations like these, the proposed design may not be the best design. For example, designers might not consider that just by changing their stringing configuration, they could substantially boost the energy production of their array (our analysis of a shaded site found improvements of over 17% annually).

But what if this fundamental question in solar design—“What is the best system design to meet a customer’s goals?”—could be answered by a computer?

Not only could you ensure consistently optimal designs for customers, but hours of design time and associated costs could be saved. Beyond the benefits for individual designers and companies, this kind of automated design could dramatically reduce the cost of solar, making sustainable solar energy available to more people.

Figure 1: Comparison of an 80% energy offset solar design created by Aurora’s AutoDesigner (left) and one created by a human designer (right).1 Note that in the AutoDesigner’s arrangement, no module was placed near the roof obstruction, and that in the human design there are two isolated (“islanded”) modules and a module that overlaps with a ridge.

Solving these pressing needs in the solar industry was at the forefront of our minds, when Aurora set about developing the “AutoDesigner”—to make it possible to find the best solar design with just the click of a button. Nothing like this had ever been done before, however, and the scope of the challenge was vast.

Given all the design variables, the number of possible designs for a site is often upwards of one quadrillion. To put this into perspective, if a human could evaluate a design per second, it would take them over four hundred thousand lifetimes to get through them all!

In today’s article, we dive into how Aurora solved this challenge, and explain the inner workings of how the AutoDesigner finds the optimal solar system for a particular site.

## The Aurora AutoDesigner Team

With such a difficult undertaking ahead of us, we needed to get the right people and resources in on the process. In 2014, Aurora was honored to receive a Sunshot Grant for this undertaking. Over the course of two years, the Aurora team worked with top scientists in the fields of optimization and computational mathematics to develop the algorithms and infrastructure that drive the AutoDesigner.

Leading the development of our AutoDesigner feature are Oliver Toole, Dr. Madeleine Udell, and Mitchell Dawson. Oliver Toole is a Quantitative Engineer at Aurora Solar. Drawn to the opportunity to contribute to this ground-breaking undertaking, he joined the Aurora team in 2014 as one of the original six members of the company, after completing his B.S. in Electrical Engineering from Stanford University.

Consulting Scientist Dr. Madeleine Udell is Assistant Professor of Operations Research and Information Engineering and Richard and Sybil Smith Sesquicentennial Fellow at Cornell University. She completed her Ph.D. at Stanford University in Computational & Mathematical Engineering in 2015, and a one-year postdoctoral fellowship at Caltech in the Center for the Mathematics of Information.

Quantitative Engineer Mitchell Dawson joined Aurora in 2016. He completed his B.S. in Computer Science in June 2017 with an emphasis in Artificial Intelligence, and is currently working towards his M.S. in the same field.

## Defining the Challenge of Automated Solar Design

To create a computer program capable of finding the optimal solar design, we had to articulate the design question in mathematical terms. Specifically, we had to formulate equations that characterize the mathematical relationships between various aspects of the design question. We started by defining the pieces of information that must be provided and what variables the equation would solve for.

### Required Inputs

We had to start by considering what information must be known to create the optimal design. The key inputs include: an accurate 3D Site Model, the available hardware components, weather data, utility rates, and especially the customer’s objectives for the design.

Figure 2: An example of an accurate 3D site model, including trees and other obstructions, created in Aurora.

An accurate 3D Site Model—including trees and obstructions which dramatically impact the shading on some roof faces—provides the starting point for finding an optimal design for a specific site. This determines the spatial limitations on where panels can be placed, and how much energy they will produce.

It is also essential to provide the AutoDesigner with the customer’s objectives for the solar system. For instance, a customer may want to offset a specific amount of their energy consumption, or they may want to maximize bill savings. In the AutoDesigner system, Design Targets can be entered as either a desired percentage of the customer’s energy consumption they would like to offset or a target amount of bill savings.

Figure 3: In the AutoDesigner, design targets may be specified in terms of energy or bill savings.

Other vital pieces of information are the components the AutoDesigner can choose from, local weather data for the site, and the relevant utility rates. Once available components—including panels, string inverters, microinverters, and DC optimizers—are specified, the AutoDesigner will evaluate designs containing some or all of the selected components to find the best ones for the particular site. Local weather data, which will impact expected energy production, must also be provided. The AutoDesigner obtains this data from local weather stations to simulate the energy production of each design on an hour-by-hour basis.

Figure 4: A user can specify the hardware components that are available for the AutoDesigner to consider in designs.

Finally, if a customer’s objective is a bill savings target, we must provide the pre- and post-solar utility rates. Using Aurora’s financial analysis capabilities, the AutoDesigner performs a full financial analysis for each candidate design to find the approach that maximizes savings. The financial simulation is compatible with diverse utility rate structures including tiered rates, time of use (TOU) rates, and even California’s NEM 2.0 rate.

### What Variables Does the AutoDesigner Solve for?

The primary variables that the AutoDesigner solves for are panel locations and inverter configurations, though other elements are ultimately considered to arrive at an optimal design.

Given the 3D site model, the AutoDesigner assesses all potential placements of solar panels, with some limitations on how the arrays can be arranged. Modules cannot overlap, nor should they be spaced out randomly across the roof face. Additionally, designs with rectangular arrays, that are located in high energy locations, are preferred.

Figure 5: Even if energy production is not considered, panel location can have a significant impact on a design’s installation cost and aesthetic value. While these designs differ by only one panel, the design on the right is much worse. The “islanded” panel may increase the number of roof penetrations needed, and reduces the aesthetics and practicality of the design.

The second key variable that the AutoDesigner solves for is inverter configuration, or the way that panels are connected to inverters. The AutoDesigner considers how many of each inverter type are needed, as well as the engineering specifications that dictate how they may be connected. In the case of microinverters, this is a relatively simple process; each panel is assigned a unique inverter. However, for string inverter and DC optimizer designs, panels must be strung to an inverter. String lengths must be compliant with the latest NEC rules and obey the inverter’s voltage, current, and power limits.

Additionally, the performance implications of different inverter configurations must be considered. For example, in the case of string inverters, if a single panel is shaded then the energy output of the entire string of panels will be reduced. Finally, panels should be strung in such a way that reduces wire cost and installation time for the design.

## How the AutoDesigner Arrives at the Optimal Design

The AutoDesigner was developed to work via a two-part process. First, the design problem is solved mathematically to arrive at a preliminary design for the site. Then, a “genetic algorithm”—which mimics the evolutionary process in nature—iterates through potential combinations, to arrive at an optimal design.

### The Optimization Problem

To start with, the AutoDesigner uses a mathematical optimization algorithm (based on linear programming) to solve the problem (i.e., panel locations and inverter configurations) exactly.

Another way of asking “what is the optimal design for a particular site?” is:

“What design will minimize cost, a) without violating electrical constraints (e.g. string length and voltage/current/power requirements of inverters) and b) while meeting the customer’s design targets (producing the desired amount of energy or bill savings)?”

This statement provides the basis for the optimization algorithm.

If the customer’s design target is to offset a set amount of their energy consumption, potential panel locations are evaluated based on the amount of energy a particular location would produce. Alternatively, if the customer’s design target is reducing their bills by a set amount, this evaluation is based on how much a panel in that location would contribute to overall bill savings.

Figure 6: A simplified representation of how the AutoDesigner selects panel locations. All potential panel placements are identified, then the locations that will be used in a design (represented by 1s) are selected based on the energy production or bill savings contributions each will provide within the context of the customer’s goals.

This approach reaches a solution in a purely mathematical sense, without taking into account aesthetics or other design subtleties. This provides a starting point for evaluating potential designs.

### Simulating Evolution to Reach the Optimal Design

Next, a genetic algorithm, which simulates the evolutionary process, is used to iterate through thousands of potentially desirable design variations and move towards the most “fit” variations.

Figure 7: Depiction of the AutoDesigner's process of iterating through potential designs. Click on the GIF to see a longer video of the AutoDesigner in action.

Given the complexity of the problem, we didn’t want to reinvent the wheel. Instead, the Aurora team looked to nature for a solution. A genetic algorithm that models the evolutionary process of natural selection provides a powerful way of reaching an optimal design. In this process, a group of solar designs is the equivalent of a population of individuals in nature.

Each design has certain characteristics that make it distinct, just like any individual. The genetic algorithm programmatically simulates many generations, where designs (i.e., “individuals”) pair off and combine their traits to produce new designs, or “offspring.” Algorithms like this one rely on powerful computers to simulate the recombination and mutation of thousands of individuals in a fast way.

Figure 8: The AutoDesigner’s genetic algorithm simulates the evolutionary process to arrive at an optimal solar design.

To initiate the process, AutoDesigner creates a diverse set of potentially good designs to make up its population. It then combines these designs to create diverse “offspring” and evaluates the fitness of each resulting design (scoring them based on a variety of factors including: energy production, bill savings, aesthetics, hardware costs, and installation costs). Unfit designs are eliminated at each “generation” and the process continues until an optimal design is reached.

## What Does Automatic Design Mean for the Solar Industry?

Aurora’s consulting scientist, Dr. Madeleine Udell, states that “the AutoDesigner solves a major problem in the residential solar industry: automated design of cost-effective, efficient rooftop photovoltaic PV installations.” The AutoDesigner is a powerful tool for seasoned solar designers as well as those new to the industry, whether you are trying to minimize shade losses, or impress a prospective client with a customized design to meet their goals. In addition to saving for individual designers and solar companies time and money, the AutoDesigner can help lower the soft costs of solar, making this clean energy source cheaper and more accessible.

The U.S. Department of Energy’s National Renewable Energy Laboratory analyzed Aurora’s AutoDesigner to see how its proposed designs compared to those designed by human designers—in terms of project cost and meeting energy production or bill savings targets. In more than 70% of tests, the AutoDesigner’s designs performed better than those produced by the designer.

While there is still work to be done, the AutoDesigner provides a strong foundation for allowing any solar professional to create faster, cheaper, and more efficient installations, all with just the click of a button.

Acknowledgments: Special thanks to Oliver Toole and Mitchell Dawson for their advice on the development of this article and providing substantial content.

Notes:

1. Figure 1 depicts a simplified design challenge for a house that did not require fire code setbacks. For a detailed overview of NREL's analysis and Aurora's AutoDesigner, see "Optimal Design of Efficient Rooftop Photovoltaic Arrays."

Here at Aurora, one of our primary goals is to reduce the cost of solar by providing installers with tools to make their work more efficient. By developing techniques to design PV systems quickly and accurately without having to visit the site, we eliminate the time and costs associated with truck rolls. Remote system design has the potential to reduce the cost of solar by as much as $0.17/W, according to the U.S. National Renewable Energy Laboratory (NREL). Designing a solar installation remotely requires an accurate 3D model of the roof and its surroundings. This ensures that the system is appropriate for the site and enables accurate modeling of the energy it will produce. There are multiple ways to create a representative 3D model of a site, including the use of LIDAR data, which is gathered by scanners that emit pulses of light energy (using a laser) at buildings and other objects in an area, and measure how long it takes for the pulse to return. The use of LIDAR data is one important element of Aurora’s work to improve the solar design process through remote site modeling. "The high accuracy, high resolution, three-dimensional information inherent in a LIDAR dataset has been game-changing on so many levels, and to be honest I believe we're still on the front end of the adoption curve,” says Jason Stoker, U.S. Geological Survey Physical Scientist and Chief Elevation Scientist for the National Geospatial Program. However, LIDAR data is not available for all areas, and not always current where it is available. Computer vision—the use of computers to interpret visual images—provides additional ways to remotely model a solar project site. With computer vision, widely available aerial and street view imagery can be used to extract information about the scene. Because of this, computer vision has the potential to transform the solar design process. Aurora has invested in developing these cutting-edge tools with our team of experienced computer vision engineers. In today’s article, we delve into current applications of computer vision in solar design and how they work. In future articles, we’ll take a broader look at how this technology enables industry-level changes. ## Aurora’s Computer Vision Team Aurora’s Computer Vision research and feature development is led by Computer Vision Engineers Matt Stevens, Ganesh Nunnagoppula, Maxwell Siegelman, Adriel Luo and Consulting Scientist Dr. Amir Zamir. From left to right, Aurora's Computer Vision Engineers Matt Stevens, Ganesh Nunnagoppula, Maxwell Siegelman, and Adriel Luo. Matt received a B.S. in Computer Science from Stanford University with a concentration in Artificial Intelligence in 2016. Matt joined Aurora in 2014. Ganesh received a Master's degree in Electrical and Computer Engineering from Carnegie Mellon University in 2015 and his B.Tech (Bachelor of Technology) degree from the Indian Institute of Technology Kharagpur (IIT Kharagpur) in 2016. Maxwell received a B.S. in Symbolic Systems from Stanford University, followed by a Master's in Computer Science from Stanford in 2017. He joined Aurora in 2017. Adriel Luo received his B.S. in Computer Science from Carnegie Mellon University in 2018. He interned with Aurora in the summer of 2017 and joined the team full-time in of 2018. Amir is a Postdoctoral Researcher in Computer Science at Stanford University, where he works in the Computational Vision and Geometry Lab. He received his Ph.D. from the University of Central Florida’s Center for Research in Computer Vision in 2014. ## Making Remote Solar Design More Accurate One exciting application of computer vision in remote design is the ability to accurately measure distances using images of a site. This is made possible by the mathematical technique of triangulation. Think back to your high school trigonometry class—you might recall that if you know the length of one side and two of the angles of a triangle, you can easily calculate the remaining two sides and angle. This process is based on the same rules. Triangulation, commonly used in nautical navigation, allows you to determine the distance to an object if you know the direction from two known locations. With this approach, computer vision can reconstruct the 3D shape of objects using images from multiple angles of a scene. If you form two rays extending out from the viewing locations, the rays will intersect at the location of the object. An illustration of how computer vision uses triangulation from two different perspectives to determine distances. In this example, the distance between the two points on the house (indicated by red dots) is calculated. Aurora's 3D measurement tool uses any satellite or aerial imagery (such as Google, Bing or even aerial imagery captured from a drone) and Google Street View imagery to provide those two different viewpoints needed to use triangulation. These images also provide information on the camera position that is accurate within a few feet. With this data, computer vision allows project designers to extract 3D measurements from the scene—such as the slope of a roof or the heights of chimneys or trees—ensuring the accuracy of the site model. Aurora’s 3-D measurement tool gives solar designers the ability to take measurements of a project site using aerial and streetview imagery. Click on the GIF above to see a longer video of this feature in action. NREL has analyzed Aurora’s 3D measurement tool and validated its accuracy; roof slopes can be measured to within 2 degrees and distances to within six inches. Two thousand measurements per week are taken using Aurora’s 3D measurement tool, each one serving to enhance the accuracy of the design. ## Speeding Up the Design Process Computer vision can also be used to speed up the tedious process of drawing a 3D model of a site. One of the most repetitive tasks when modeling commercial roofs is placing obstructions. Often, these roofs will have the same kind of obstruction in many places—such as skylights, vents, or pipes. Using an approach called template matching, computer vision can automatically detect these instances in the imagery. Satellite imagery showing obstructions on a commercial roof (left) and Aurora’s automatic identification of similar obstruction instances (right). With Aurora's Automatic Obstruction Detection tool, the user can select a particular obstruction as a template to guide the identification of other similar instances. Aurora then sweeps over the image looking for similar obstructions. For every possible location of the obstruction a score is generated based on how similar it is to the template. Then Aurora places obstructions at the highest-scoring locations. In this way, a time-consuming process can be reduced just a few clicks. “Aurora’s automated obstruction detection feature has been a huge help. We used to spend hours drawing out each individual skylight and AC unit, particularly on large data centers and warehouses, and this feature has easily cut our rooftop design time to a fraction of that,” says Douglass Jordan, Project Manager, Pre-Construction Services at SunPower Aurora’s obstruction detection features make it possible to automatically identify and model in 3-D all occurrences of similar obstructions instead of having to draw each by hand. Click on the GIF above to see a longer video of this feature in action. As you can see, computer vision has huge implications for cutting costs in the solar industry. As a solar contractor, being able to accurately model a customer’s home or commercial site remotely saves your team time-intensive site visits. It can further speed up the remote design process by automating repetitive tasks, like identifying obstructions. Aurora recently completed a$500,000 grant from the Department of Energy’s SunShot Incubator program to develop these features as a means to reduce soft costs and advance the growth of the solar industry. And this is just the beginning.

As the applications of computer vision evolve, the Aurora computer vision team will continue to bring the latest innovations of the field to the industry, helping installers create PV projects quickly and accurately.

## Key Takeaways

• Remote solar design can help save solar companies time and money by eliminating the need for onsite measurements. NREL has estimated this can reduce the cost of solar by as much as $0.17/W. • Remote design requires the development an accurate 3D model of the project site; computer vision—a field of computer science that teaches computers to interpret visual images—enhances accurate remote site modeling in multiple ways. • One way that computer vision can increase the accuracy of 3D models of a solar installation site is by making it possible to take accurate site measurements from photos, including heights and roof slopes. This is made possible by using the mathematical technique of triangulation. • Computer vision can also dramatically speed up the process of modeling a site by automatically detecting obstructions on the roof, eliminating the need for the designer to draw each one by hand. • Aurora is continuing to invest in Computer Vision and Artificial Intelligence applications to make solar more ubiquitous. Assessing the impact of shading on system performance is an essential step in solar design. Especially in the residential market, solar designers often deal with shading issues like trees, chimneys, and other obstructions. The question designers often face then is: given these conditions, how do I maximize system performance? This is not an easy question to answer because shading can affect performance in a nonlinear way. However, an optimal solution can be found by following four steps. 1. Quantify. What’s the best way to quantify the impact of shading? Solar Access measurements are useful as a guide but have limitations because they do not account for system configuration. Thankfully, modern, module-level simulation engines can accurately model the impact of shading on performance. (Simulation engines that model system performance at a submodule level offer even more accurate estimates of energy production when modules are partially shaded.) Aurora’s performance simulation feature quantifies energy losses from shade and other sources. 2. Explore. Systems come in countless combinations of size, location, and configuration. Designers have several options to mitigate shading losses: • When using string inverters, string the modules in a manner that minimizes shading losses. In some cases, simply changing the stringing configuration of a system can result in energy boosts of over 10%. • Use module-level power electronics (microinverters or DC optimizers). In addition to mitigating the impact of shading by performing maximum power point tracking (MPPT) on a module-by-module basis, they eliminate module mismatch losses (which occur when one shaded module causes the current through an entire string of modules to drop). • Use modules with integrated cell string-level power electronics. These replace the bypass diodes inside modules with DC optimizers that perform MPPT at the cell string-level. • Increase the DC-to-AC ratio to reduce balance of system costs (the costs of all components of a PV system other than the PV panels, such as wiring, racking, and inverters). Shading results in lower DC power, thus more panels can fit on an inverter without causing significant clipping. • Explore the use of higher efficiency modules or modules with a higher open-circuit voltage (or Voc — the maximum voltage available from a solar module). A higher power density allows you to make better use of low-shade areas, whereas shorter strings are impacted less by shading. • Vary the location and size of the system. Energy produced at different times of the day can have different values to the client. 3. Assess. Cost-benefit analysis ultimately leads to the “optimal” system design. But value is not always easy to determine. With Time of Use and tiered rates, the compensation for each kWh produced by the system can vary greatly. It can sometimes be better to place a system where there is more shade overall, but the system remains unshaded during high-value times. A detailed financial model that can handle these nuances is essential. An example of a Time of Use rate, with higher energy prices at times of higher energy demand. 4. Automate. A detailed site assessment takes time. Without the ability to quickly assess a variety of design variants, how many iterations can you afford to do? And how do you know if your design is really the optimal solution? Putting a streamlined process in place is crucial. We believe software can empower solar designers to make these critical design decisions in an efficient manner. That is why we built Aurora to streamline the design process from remote shade measurements and module-level performance simulations, pricing and detailed financial analysis, all the way to proposal generation — and Aurora’s AutoDesigner even generates an optimal system design for you at the click of a button. Green Button data — if you’re not familiar with it, it might sound like something that a Marvel comic book villain would enjoy reviewing. But, in fact, Green Button data is actually a very valuable tool for understanding a home or business owner’s energy usage. In this post, we’ll explore what Green Button data is and what benefits it provides for solar designers and customers. Green Button data gives utility customers — both residential and commercial — timely access to energy use data in a standardized, computer-friendly format. #### What is Green Button Data? Green Button data refers to an option provided by some utilities that enables customers to download detailed data on their electricity usage with just the click of a (green) button from the utility website. Specifically, Green Button data gives utility customers — both residential and commercial — timely access to energy use data in a standardized, computer-friendly format. The Green Button Initiative emerged as a voluntary, industry-led response to a 2011 call-to-action from the White House to make energy data more accessible to consumers. Beyond showing how much energy a consumer uses, one of the greatest benefits of Green Button data is that it also provides insight into when energy is being used. Historically utility bills have only shown how much energy was used over a monthly period. However with the increased deployment of “smart meters,” which track energy usage at intervals of one hour or less, much more granular energy use data is becoming available. If a customer has a smart meter, Green Button data will allow a customer to see exactly how much energy they use at specific intervals. The measurement interval available to customers depends on what their utility offers, but many utilities — especially in California and Texas, where utilities are required to provide customers with their energy usage data — provide this information in 15-minute increments. Currently, more than half of American households have smart meters and they are increasingly being deployed by utilities around the country as part of utility efforts to modernize the electric grid. Smart meters and Green Button data go hand in hand as methods to give customers’ greater insight into and control over their energy use. The Green Button program is helping to make the improved data from smart meters more easily accessible. Beyond showing how much energy a consumer uses, one of the greatest benefits of Green Button data is that it also provides insight into when energy is being used. #### Why Is Green Button Data Important? Green Button data offers numerous benefits to energy consumers and for solar professionals looking to design and sell high quality solar installations. Green Button data helps consumers better understand when they are consuming energy, and save on their utility bills. For instance, for residential customers in areas where Time of Use (TOU) rates are standard (like California), Green Button interval data can show how changing the timing of certain energy-intensive activities can result in reduced energy bills. Green Button data is particularly useful for customers who are considering solar, because it makes evaluating projects and savings faster and more accurate. Green Button data offers additional value for commercial customers. Beyond the insights it provides with regard to Time of Use rates (which are more common for commercial customers), Green Button data can also help commercial customers better understand demand charges, which are fees a utility charges based on the maximum amount of power a commercial customer consumes over a given time period. An example of a customer's hourly energy usage based on Green Button Data uploaded in Aurora. #### Green Button Data and Solar: A Perfect Combination Green Button data is particularly useful for customers who are considering solar, because it makes evaluating projects and savings faster and more accurate. Having a clear picture of a household’s energy consumption is critical to determining the appropriate size of a solar array. Furthermore, precise data on energy consumption at different times throughout the day is important in enabling accurate evaluation of the financial returns of the solar design. For instance, if the customer is billed under Time of Use rates, in order to understand how much a solar installation will reduce their utility bill, it is essential to understand how much energy they consume during peak demand times when energy is more expensive, and how those usage patterns intersect with the amount of energy their solar array is likely to be producing at different times. A customer’s savings will be greater if the energy produced by their solar installation coincides with and can offset much of their electricity consumption during hours when electricity is most expensive (typically in the afternoon). Furthermore, this consideration might influence the ideal location or orientation of a solar design (such as siting the design where it will get more afternoon light, and thus offset energy when electricity prices are higher, rather than where it would produce the most energy overall). For commercial customers, whose utility bills include demand charges, the benefits of using Green Button data in the solar design process are a little more nuanced, so we will cover them in a later post. With a customer’s Green Button data, you can save time by automatically importing the exact details of the customer’s energy consumption and Aurora will use that to model the customer’s electricity usage throughout the day and throughout the year (their load profile). Combined with Aurora’s simulations of the solar design’s energy production (the industry’s most accurate), you and your solar customer can be confident in the expected financial return on the installation. #### Key Takeaways: • The Green Button Initiative is a program through which participating utilities provide customers with detailed data on their energy usage, in a standardized, machine-readable format. • Green Button data gives utility customers greater insight into the amount and timing of their energy consumption, helping them to understand how they can save energy and reduce their utility bills. • Green Button data is particularly useful in helping potential solar customers accurately evaluate the financial return on a solar installation. • Aurora’s software can automatically import and interpret Green Button data enabling faster and more accurate development of detailed solar sales proposals. Are you using Green Button data? How has it impacted your solar business? Join the conversation on Twitter , Facebook , and LinkedIn with the hashtag #GreenButtonData. ~~~ Want to be in the loop on our latest articles? Click here to subscribe to our blog! When modeling how much energy a solar design will produce, there are many features of the components that must be taken into account to ensure an accurate estimate. One important factor that modeling software must account for in order to avoid over- or under-estimating the system’s energy production is whether or not the inverter(s) used are capable of “global maximum power point tracking.” In this post, we will examine what global maximum power point tracking means—and why accounting for it is so important. #### Understanding Current-Voltage and Power-Voltage Curves The datasheet of a solar panel includes a variety of data that allow one to understand the basic parameters of the device and to mathematically model its behavior within an electrical circuit. Typically, this will include graphs that illustrate the panel’s “current-voltage curve”—also known as an IV curve, for the standard abbreviations for current (I) and voltage (V) in mathematical equations—and “power-voltage curve.” Looking at the power-voltage curve allows us to see the point (or points) at which the panel’s power output is maximized. These graphs illustrate relationships between three electrical characteristics: current, voltage, and power. Power—which we intuitively understand as the energy produced by the panels—is defined as the rate, per unit time, at which electrical energy is transferred by an electric circuit. Current (I) is the rate at which charge is flowing through the circuit, while voltage (V) is the difference in electric potential energy between two points (e.g., the output wires of a solar panel) per unit electrical charge. A common example used to explain these principles is to think of electricity like water in a tank; the pressure in the tank is analogous to the voltage, while current would be the flow of water out of the tank (Figure 1). The IV curve shows how the panel output current varies with panel output voltage. The power-voltage curve shows how panel output power (the product of the output current and output voltage) varies with panel output voltage. Figure 1: The concepts of voltage and current as illustrated by the example of water in a tank. Looking at the power-voltage curve allows us to determine the point (or points) at which the panel’s power output is maximized. On the IV curve, two values that are often indicated are “Vmp” and “Imp” — which indicate the levels of voltage and current at which the solar panel’s output power is maximized under standard test conditions (STC). Nothing about the panel itself dictates it must operate at maximum power, however; any point along the IV curve is a valid operating point. In designs using string inverters, it is the inverters that “choose” the operating point. The ability of the inverters to locate the operating point of a solar array at which output power is maximized is referred to as maximum power point tracking (MPPT). If the solar array comprises identical solar panels operating under the same irradiance and at the same temperature—such that each constituent module has the same IV curve and maximum power point—the net IV curve of the entire array (which takes into account the IV curves of each individual module) will have a shape like the blue curve in the left half of Figure 2 below. The green curve shows the output power of the array as a function of output voltage; note that there is a single peak in power, occurring at the “knee” of the IV curve. The inverter will seek out this one point at which array power is maximized. #### Accounting for Shade: The Role of Bypass Diodes When parts of the array are shaded, however, the IV curve is much more complicated. The IV curves of the shaded modules are different than those of the unshaded modules, especially in regard to how much current the shaded modules can output. When the amount of irradiance on a module is low, the power of the entire string connected to the module can drop. This is due to the fact that the current through the string can only be as high as the current through the most shaded module. Because bypass diodes allow the inverter to “skip over” shaded panels instead of operating at their lower current, the IV curve of an array that is partially shaded will look different than that of an unshaded array. To help mitigate these effects, manufacturers integrate bypass diodes into their modules. A bypass diode can be thought of as an on/off switch, which conducts any amount of current when it is “on” and, conversely, cannot conduct current when it is “off.” When the diode is turned on, it effectively shorts out the shaded module by routing the string current through the diode (and around the module) rather than through the shaded solar cells. Because bypass diodes allow the inverter to “skip over” shaded panels instead of operating at their lower current, the IV curve of an array that is partially shaded will look different than that of an unshaded array. The resulting IV curve may look like the blue curve on the right in Figure 2, with a corresponding power-voltage curve shown in green. As you can see, there are two distinct operating points at which power is “maximized” - a global maximum where the array operates at a higher current and lower voltage, and a local maximum where the array operates at a lower current and higher voltage. The global maximum occurs when the shaded modules are bypassed, and the local maximum occurs when the shaded modules are not bypassed. Figure 2: (left) Current-voltage (blue) and power-voltage (green) curve of a solar array with no shading; (right) current-voltage (blue) and power-voltage (green) curve of a solar array with shading, where the activation of bypass diodes results in multiple possible maximum power points. Global MPPT refers to the ability of an inverter to sweep the IV curve of the solar array (within the operating voltage limits of the inverter) and find the array voltage at which the global maximum power point occurs. How often the inverter sweeps the curve, and the resolution at which it does so, is generally manufacturer- and model-specific. Importantly, not all inverters perform global MPPT. Some inverters are limited to only search for the maximum power point in a local region where it “usually” lies, a high voltage solution where no modules are bypassed. This can be beneficial for sites where there is no shading, because whenever the inverter is sweeping the IV curve searching for the maximum power point it is not actually operating at the maximum power point, and thus not producing as much energy as it could. If the maximum power point is not going to vary much because there is no shade and no reason to activate bypass diodes, then there is no reason to sweep the entire IV curve. Most modern residential inverters are capable of global maximum power point tracking because shading due to trees and obstructions is common and expected. Large commercial inverters and central inverters, however, may not have this functionality because it is generally assumed there will not be much shading. Importantly, not all inverters perform global maximum power point tracking. Some inverters are limited to only search for the maximum power point in a local region where it “usually” lies, a high voltage solution where no modules are bypassed. #### Modeling Global Maximum Power Point Tracking If your design includes a string inverter with global MPPT functionality, it is critical that the simulation tool you use to model the system accurately represents that behavior. Consider the residential design in Figure 3, which includes two parallel strings connected to an input of an inverter and a third string connected to another input. The irradiance map (left) and 3D model (right) clearly show the effects of shade on this site. Of particular concern are the chimney on the southeast-facing roof plane and the large tree to the west of the house, both of which cast shade on several panels in the design at various times throughout the year. If we simulate this design without global MPPT, the annual production is 5.94 MWh. However, if the inverter actually does perform global MPPT, and we simulate it accordingly, the production estimate increases to 6.25 MWh (Table 1). Figure 3: 2D view and irradiance map (left) and 3D view (right) of a residential design with shading from a chimney and tree, produced by Aurora Solar's software. Annual Production Without Global MPPT Annual Production With Global MPPT Percent Difference 5.94 MWh 6.25 MWh 5.09% Table 1: Annual energy production for a residential design with and without global maximum power point tracking. Given the results shown in Table 1, it is clear that knowing when to model global MPPT is just as important as being able to model it at all. Assuming every inverter has this functionality is dangerous, because it could lead to severely underperforming systems post-install. Assuming no inverter has this functionality can be a costly mistake as well, because it may lead the designer to install a larger system size than necessary. This is why Aurora has contacted leading inverter manufacturers to confirm exactly which inverter models perform global MPPT. If a design includes an inverter with this functionality, Aurora will automatically model it. Aurora will even model global MPPT and bypass diodes down to the cell string-level, including the power losses in the diodes themselves. If Aurora has not confirmed the inverter has global MPPT, or that the inverter only performs local tracking, this behavior will not be modeled. The performance simulation logs will indicate whether or not the simulation applied global MPPT. In this way, designers can be sure they are getting simulation results that are as accurate as possible given what is known about the equipment in their designs. Takeaways • Global MPPT allows an inverter to sweep the IV curve of a solar array to find the point at which output power is maximized, even under partial shading. • We found a difference of over 5% in annual production when simulating a design with an inverter that has global MPPT versus one without it. • Aurora has worked with leading inverter manufacturers to confirm which models apply global MPPT and automatically simulates this behavior for those inverters. ~~~ Want to be in the loop on our latest articles? Click here to subscribe to our blog! Cover photo credit: NREL/DOE As you likely know, solar cells produce direct current (DC) electricity, which is then converted to alternating current (AC) electricity by an inverter. Converting energy from DC to AC allows you to deliver it to the grid or use it to power buildings, both of which operate with AC electricity. When designing a solar installation, and selecting the inverter, we must consider how much DC power will be produced by the solar array and how much AC power the inverter is able to output (its power rating). In this article, we’ll discuss some important considerations for solar projects to ensure that the inverters in your designs are appropriately sized. Specifically, we’ll examine the relationship between the amount of energy your solar array produces and the amount of power your inverter can output, and we’ll introduce the concept of inverter clipping. ## Understanding the DC-to-AC Ratio The DC-to-AC ratio is defined as the ratio of installed DC capacity to the AC power rating of the inverter. It often makes sense to oversize a solar array, such that the DC-to-AC ratio is greater than 1. This allows for a greater energy harvest when production is below the inverter’s rating, which it typically is for most of the day. Consider the graph of energy production as a function of time of day in Figure 1. The purple line shows a typical bell curve of AC output power peaking at noon, just below the rating of the inverter indicated by the dashed line. If we increase the size of the solar array by adding more panels, thereby increasing the DC-to-AC ratio of the system (as illustrated by the green curve), we can harvest more energy throughout the day. The area between the green and purple curves is the energy that is gained by increasing the DC-to-AC ratio. Figure 1: Inverter AC output over the course of a day for a system with a low DC-to-AC ratio (purple curve) and high DC-to-AC ratio (green curve). The chart represents an idealized case; in practice, power output varies considerably based on weather conditions. ## Inverter Clipping While oversizing the solar array relative to the inverter’s rating can help your system capture more energy throughout the day, this approach is not without costs. What Figure 1 also shows is an effect called inverter clipping, sometimes referred to as power limiting. When the DC maximum power point (MPP) of the solar array—or the point at which the solar array is generating the most amount of energy—is greater than the inverter’s power rating, the “extra” power generated by the array is “clipped” by the inverter to ensure it is operating within its capabilities. This leads to a flatline in the green curve, and thus lost energy production, during peak production hours. The inverter effectively prevents the system from reaching its MPP, capping the power at the inverter’s nameplate power rating. It is crucial to model inverter clipping in order to properly design a system with a DC-to-AC ratio greater than 1, as well as in regions that frequently see an irradiance larger than the standard test conditions (STC) irradiance of 1000 W/m2 (because higher levels of irradiance lead to higher power output). Consider a south-facing, 20°-tilt ground mount system in North Carolina (35.37° latitude) with a 100 kW central inverter. If we design the system with a DC-to-AC ratio of 1, it will never clip; however, we will also not fully utilize the AC capacity of the inverter. If we want a larger system size, we could place another 100 kW block (a section of solar panels connected to an inverter), or we can pack more DC power generation onto our first inverter. The latter allows us to save cost by not purchasing another inverter and, like we saw in Figure 1, we can still harvest more energy during off-peak hours. If we choose a high DC-to-AC ratio, we will also sacrifice some amount of energy to inverter clipping. The inherent design trade-off is between the cost of purchasing and installing a new inverter and the value of the energy lost due to inverter clipping. Table 1 summarizes energy production results for three DC-to-AC ratios, as well as how much energy is clipped, for the aforementioned ground mount system. If a simulation tool does not properly model clipping, the designer may be led to believe that, for example, the 100 kW inverter can fully handle the DC-to-AC ratio of 1.5 and output 228.24 MWh, whereas in reality 11.0 MWh would be lost to clipping. This could lead to a system that underperforms relative to the expected result. Knowing how much energy is clipped allows a designer to understand how effective the oversizing scheme is at increasing energy harvest and determine what system configuration is the most cost-effective, in order to make an informed decision about how much DC power to connect to the inverter. DC-to-AC Ratio Annual AC Energy Production Energy Lost to Clipping 1.0 163.06 MWh 0.0 MWh 1.3 193.86 MWh 1.8 MWh (0.9%) 1.5 217.24 MWh 11.0 MWh (4.8%) Table 1: Annual energy production out of a 100 kW inverter as a function of DC-to-AC ratio. As the DC-to-AC ratio increases, so does the AC output and clipped energy. Aurora’s solar design and sales software automatically takes inverter clipping into account in its performance simulations. The amount of energy that is clipped throughout the year, and the percentage of total energy that amount represents, is presented to the user as a simulation warning and in our system loss diagram. Combined with Aurora’s NEC validation report, which ensures designs do not violate any electrical or mechanical constraints or rules of the National Electric Code (NEC), this feature allows users to be confident that the systems they design are appropriately-sized and code-compliant. ## Key Takeaways • Oversizing a solar array relative to an inverter’s rating (DC-to-AC ratio greater than one) allows for increased energy harvest throughout most of the day, especially in the morning and late afternoon. • When a DC array produces more energy than the inverter is rated to handle, the inverter clips the excess power and caps its output at its rated power (an effect known as inverter clipping). • An alternate approach to increase energy production while avoiding inverter clipping would be to include another inverter. When deciding what approach to take, designers must consider the trade-off between the cost of purchasing and installing an additional inverter compared to the value of the energy that will be lost due to inverter clipping if they oversize the solar array. • When estimating the energy production of a solar project design, it’s important that your performance simulations take inverter clipping into account (as Aurora does automatically), in order to ensure production results accurately reflect the system size of the design. ~~~ Want to be in the loop on our latest articles? Click here to subscribe to our blog! Topics: solar design, solar engineering Community solar programs have the potential to greatly expand the market for solar energy and make the benefits of solar more accessible. However, growth of this sector is currently inhibited by uncertainty in project delivery costs. We sat down with Dr. Joseph Goodman of the Rocky Mountain Institute to understand this challenge—and how detailed design modeling capabilities can help overcome this barrier. #### What is Community Solar? By now you've likely heard about community solar – also known as shared solar or solar gardenone of the solar industry’s fastest-growing sectors in 2016. Community solar provides a way for customers to share in the energy produced by a solar installation in their community. The solar installation, which may be community-owned or third-party owned, provides electricity to community members who choose to participate. An important appeal of community solar programs is that, if designed correctly, they save participants money compared to what they would otherwise pay their local utility. Community solar allows homeowners that do not have ideal building conditions to enjoy all the benefits of solar ownership, such as lowered utility bills and the knowledge that they are contributing to a cleaner environment. Factors like having a shaded roof, being a renter, or living in an apartment building, may limit one’s ability to switch to solar. In fact, the National Renewable Energy Laboratory (NREL) has found that these issues affect 49% of households and 48% of businesses! Accordingly, community solar has a critical role to play in the development of the solar industry and in ensuring that the clean energy economy is inclusive and equitable. #### How Does Community Solar Work? The Solar Energy Industries Association (SEIA) identifies four different models for community solar. A utility may provide its customers with the option to purchase a set amount of solar energy from a shared facility- typically at a fixed rate for a long term, such as 20 years (a utility-sponsored model). An on-bill crediting model allows residents and businesses to invest in a portion of a shared solar installation and receive a proportional credit on their utility bill. Individuals can create a business entity to develop a shared solar project, a Special Purpose Entity (SPE) model. Finally, in a non-profit (or “buy-a-brick”) model, donors may contribute to support the development of a shared solar installation that will be owned by a non-profit. The availability of community solar projects depends on state-level policies; the option is not yet available everywhere but 26 states currently have community solar projects. Four different business models for shared solar. Photo Credit: U.S. Department of Energy. #### Cost Certainty: The Secret Ingredient for Community Solar Success? The Rocky Mountain Institute was founded in 1982 to transform global energy use to create a clean, prosperous, and secure low-carbon future. RMI engages businesses, communities, institutions, and entrepreneurs to accelerate the adoption of market-based solutions that cost-effectively shift from fossil fuels to efficiency and renewables. They are pioneers of community solar, developing innovative community-scale solar pilot projects to make solar energy affordable and accessible for all. Their analysis looking at community-scale solar (both shared solar systems and other mid-size arrays), estimates that the community solar market could reach 30 GW by 2020! Dr. Joseph Goodman, Principal with Rocky Mountain Institute’s electricity practice. Dr. Joseph Goodman is a Principal with Rocky Mountain Institute’s electricity practice. He leads RMI’s work to accelerate the deployment of community solar, with a focus on providing practical support to communities transitioning to shared solar. We sat down with him to understand what it will take for community solar to reach its full market potential, based on his work with community stakeholders. We asked Dr. Goodman about some factors that affect the expansion of community solar. He highlighted uncertainty when evaluating the cost of a potential project as a major issue. Even among otherwise comparable community solar projects from the same company, there is often significant variation in what it costs to develop a community-scale solar project. This ambiguity in actual delivery costs means that companies must price projects on the higher end of the spectrum to avoid losses. “[Community solar projects] basically live or die based on... incremental costs in the way the system is developed, designed, sourced, and deployed.” Why is this so significant for community solar in particular? While uncertainty in project cost exists across solar project types, the impact on project viability is particularly significant for community solar. Slight variations in project cost can make the difference between whether or not a project will save members money compared to utility rates, and thus whether communities see it as a good option. As a result, the expansion of community solar on a large scale hinges upon increased certainty and transparency in project costs. As Dr. Goodman explained, “[community solar projects] basically live or die based on those incremental costs in the way the system is developed, designed, sourced, and deployed.” Additionally, he noted that when people don’t have the right information to make a decision, the common reaction is to do nothing—so until there is greater transparency in these costs, community adoption is likely to be slow. There is a great potential to reduce this uncertainty, however, and RMI is working to provide solutions. “Based on the analyses that we’ve been able to conduct, there is tremendous opportunity to reduce the cost of installation and improve total cost of [community solar] ownership. There’s also room to decrease your construction project cycle, and to eliminate much of the variance of projects…” #### Delivering Cost Certainty with Prototyping One solution that Dr. Goodman and the Rocky Mountain Institute have been working on is the use of standardized project design prototypes to eliminate this uncertainty. The development of prototype designsfor which the total cost of ownership has been analyzed and established with certaintyallows communities considering shared solar projects to make informed decisions. “There are other variables at play in finance, but I think the two dominant ones are: ‘Will this asset produce what you said it will produce?’ And ‘Will you be able to sell the energy it produces at the rate that we’re banking on?’” But how do you arrive at a trusted cost evaluation for a particular solar project prototype? One option would be to actually build out a particular design, documenting the costs in detail. Of course, that’s a significant investment! But, as Dr. Goodman explained, “Before you’ve got that luxury, you’ve got to [do this] through more efficient means- and Aurora’s enabled that.” With a solar software design platform that can make accurate projections of project costs and performance, researchers can develop hypotheses on how to effectively reduce project costs and test them without physically developing the projects. These experimental capabilities have the potential to be a major game changer for the community solar sector. Dr. Goodman and his team use Aurora’s design capabilities to run experiments evaluating how different community-scale design scenarios perform based on total cost of ownership. “We’ve found huge savings, savings that are so significant that the total cost of ownership goes from being higher than buying from—either wholesale or retail, depending on the customer—to below.” Aurora’s application enables the development of detailed designs for solar installations, including industry-leading energy performance simulations. Being able to evaluate multiple design solutions that meet diverse project needs provides great value to the industry. “I want to really underscore the magnitude of it…. with a software tool that allows us to search the design space, we can have a step change in the value proposition. It goes from ‘out of the money’ to ‘in the money.’” Dr. Goodman also discussed how this change in the value proposition will expand access to financing for community solar. “There are other variables at play in finance, but I think the two dominant ones are: ‘Will this asset produce what you said it will produce?’ And ‘Will you be able to sell the energy it produces at the rate that we’re banking on?’ And that’s a much more believable story when you’re providing real savings- rather than marketing against inflated utility costs...” An example of a ground mount typical of a community solar project. Photo credit: John Thornton / NREL. #### A Bright Future for Community Solar Despite the current challenge that cost uncertainty creates, Dr. Goodman is optimistic about the growth of community solar across the U.S. "We... foresee getting to play a significant role in the creation of this industry at RMIthrough working with industry, and with [community stakeholders] who are really willing to represent the best interests of their communities.” His outlook is echoed by NREL estimates that community solar could comprise up to 49% of the U.S. distributed PV market by 2020 with supportive policies. Goodman stressed that we are at an exciting time for the growth of community solar: not only do we have the right technologies and business models, but there is growing political will within communities at all scales, from local to international, to reduce carbon emissions through the expansion of renewables. ~~~ Want to be in the loop on our latest articles? Click here to subscribe to our blog! Background Photo Credit: U.S. Department of Energy. [This article was originally published in Solar Power World. ] It isn't easy keeping up with the solar industry. Every few months new products, financing mechanisms, policies, and organizations pop up and change how you design and sell solar. This article will bring you up to speed on some of the industry’s most frequently used acronyms, and keep you up to date on important emerging solar design and financing trends. ## 1. PACE - Property Assessed Clean Energy Infographic on how PACE works. What it is: PACE is a mechanism by which homeowners can finance solar and energy efficiency projects via their property taxes. Local or state governments, working with traditional financiers, fund the upfront cost of the solar installation or energy improvement. Homeowners pay back their local authority via an increased property tax bill, usually over a period of 20 years. Why you need to know about it: PACE has been around since 2001, but for the first 10 years of its life it had a limited impact on the industry. PACE programs received a big boost in August 2015, when the Obama administration issued a new directive to implement legislative changes making it easier to buy and sell properties that have solar installations financed by a PACE loan. PACE offers low financing rates, tolerant credit requirements, but most importantly, local governments are incentivized to promote the product since they keep a portion of the PACE payment. What’s in store: Over the next few years, I predict PACE-based financing will be the fastest growing financing option in the solar market. ## 2. LIDAR - Light Detection and Ranging What it is: LIDAR is a method of obtaining information about objects or areas remotely by using light pulses emitted from a device to measure distances. The device combines GPS data with the distances it measures, constructing precise three-dimensional information about the shape of the environment. Why you need to know about it: LIDAR is slashing solar design costs by helping the solar industry avoid truck rolls. With LIDAR, a solar salesperson or engineer can quickly generate 3D models directly from their office. They can precisely calculate building, tree, and obstruction heights as well as roof slopes. LIDAR data can be used to generate bankable shade reports, which are accepted for rebate purposes by rebate authorities and private lease financiers. What’s in store: As the cost of acquiring LIDAR falls and its benefits become more accessible, I predict that LIDAR will continue to reduce the soft costs of residential solar. NREL estimates that remote site assessment has the potential to reduce industry soft costs by$0.17 per watt -- that’s the equivalent of half the cost of an average string inverter!

LIDAR data is used to improve the accuracy of remote site design in Aurora.

## 3. LCOE - Levelized Cost of Energy

What it is: The LCOE is the average cost per unit of energy that your solar project generates over its lifetime. Mathematically, it is the lifecycle cost of the solar project divided by the amount of energy it produces. The lifecycle cost of a solar project includes the initial cost to purchase it, financing costs (such as loan payments), and operations and maintenance costs (such as inverter replacement costs) over the life of the project.

Why you need to know about it: LCOE is one of the oldest metrics in the solar industry. It offers an “apples-to-apples” way of comparing different financing options. If your client wants to compare the financial returns of going solar via a loan, lease, PACE, or cash purchase, LCOE is one of the best ways to determine their best option. Additionally, knowing your LCOE also has implications for solar design.

What’s in store: Over the next few years there are going to be more and more options for solar design and financing, so knowing how to calculate LCOE offers you the ability to evaluate them on an equal playing field and determine the best option for your customer.

## 4. LACE - Levelized Avoided Cost of Energy

What it is: The LACE is the average revenue per unit of energy that your solar installation generates over its lifetime. Mathematically, it is the lifecycle revenue (or avoided cost in the case of net metering or other similar compensation schemes) divided by the lifetime energy production. Lifecycle revenue includes revenue earned from feed-in tariffs, avoided cost from net metering schemes, and production-based incentives.

Why you need to know about it: One of the drawbacks of an LCOE calculation is that it does not explicitly take into account the revenue or avoided cost of a solar project. LACE, on the other hand, accounts for that. Since utility rates often vary by time of day, it is important to not only know how much energy you are offsetting, but at what times you are offsetting it. Without knowing the value of the energy you are saving, it makes it hard to compare two different solar designs that cost the same, but have different production profiles.

Furthermore, LACE allows you to easily compare a solar installation to an energy efficiency retrofit, for example. This has made LACE popular in government and utility planning circles. For example, a utility can compare the avoided cost of purchasing LED light bulbs versus installing solar (spoiler alert: it partially depends on the differential between daytime and nighttime electricity rates).

What’s in store: As the benefits of solar energy become increasingly explicit, customers will go from asking if they should go green to asking how they should go green. LACE provides a convenient way to compare the economic returns of different ways to reduce your carbon footprint.

Pantone's color of the year is "greenery" for a reason.

And there you have it! Hopefully this overview of some choice acronyms can help you stay on the forefront of this dynamic industry. If you think of some industry acronyms that are important for the solar community to know, tweet us at @AuroraSolarInc!

This is an installment of our Solar Spotlight series

With a Masters degree in Electrical Engineering and a decade of solar experience, Michelle Meier is one of those people you want in your corner and never on the other side of the ring. She is the founder of Solar Roof Services, a company that helps roofing contractors boost their income by adding solar installation services to their existing book of business. I had the opportunity to peek inside the mind of the woman who is helping drive the adoption of solar by monetizing the natural synergies between the solar and roofing industries.

### Tell me a bit about yourself and your relationship to solar over the years.

I started in solar in 2007. I have a Masters degree in Electrical Engineering and I was in the semiconductor field for 20 years before solar. When I decided to reinvent myself I got hired by a roofer in San Jose and started their solar division. I learned solar from a roofing perspective from day one, which is really unique in the industry.

I later went to work for GAF and became their national solar sales director, essentially incorporating their residential roofers into solar. When we decided to part ways, I thought "I've done this for two other companies, let me do this for myself."

### What exactly does that entail?

I teach roofers how to take their roofing business and extend it to solar. It’s logical. We do that by partnering them with their current favorite electrician! I created an office that lets that contractor have no overhead. Our office does what you guys call a proposal, I call it a financial analysis. We do all of the utility paperwork, the permit package, and I even connect them to distribution. I help roofers turn every single roof lead into a solar lead.

Michelle trains her clients to use Aurora for their remote site assessment or creates projects on their behalf.

### You’re a seasoned marketer in the solar industry. Can you describe the solar landscape from your perspective?

My best way to describe it is—when I started doing this 10 years ago, people would look at you and say “Oh my gosh, you have solar?” Another five years from now and it’s gonna be exactly the opposite: “Wow, you don’t have solar?”

In terms of the feasibility for homeowners getting solar, it varies. In California with the rates the way are, it’s almost stupid not to get solar when you can do the "no money down" options. No matter which financing option you go with, if you’re paying less for your solar payment plus whatever’s left on your utility bill than your current bill, it’s just stupid not to do it. I work with other states where it’s a little bit harder.

However, the industry is ours to win or lose. Mar our reputation or build a great reputation, it’s ours.

10 years ago, people would look at you and say “Oh my gosh, you have solar?” Another five years from now and it’s gonna be exactly the opposite: “Wow, you don’t have solar?”

### How do you help the industry win?

I come at it from the roofers. One of the things that we’ve found over the years is an average home has 14 penetrations. A bathroom vent, a kitchen hood vent, other normal penetrations on the roof of a typical home. An average solar system has 25-50 penetrations. So you took that 14 to 64! How much more of a chance did you make of having a leaky roof? Why is Joe Blow allowed to poke all those holes in a roof and not have it inspected?

The direction that I come from is what makes the difference. The more and more we can give homeowners a trustworthy installation, the better our image will become.

An average home has 14 penetrations. An average solar system has 25-50 penetrations. So you took that 14 to 64!

### What are the three most important pieces of advice that you give to your clients?

First, always lead with your value-add as a roofer. The fact that you’re licensed to do penetrations, and you’re giving them a 10-year warranty on the roof, plain. On a tile roof that’s significant, for the following reason: if you walk across even a lightweight tile roof, you’re gonna break tile.

Second, pull the local card because your locality is one of the bigger advantages against the big guys. Do you really want to depend on a company that doesn’t even have an office here?

Third, go with the facts, don’t cheat. Underpromise, overdeliver.

### What is the biggest challenge facing solar installers today?

For the roofer, the biggest challenge is that they’re new to the market and you’ve got all these established guys out there. So they have to sell their roofing reputation and hope that clients will trust them as they get into solar.

### If you couldn’t work with roofers who would you work with to help transition into solar?

Electricians. Teach them how to do the roofing properly. Those penetrations; how to find that rafter, make sure it’s in the rafter, waterproof it, etc.

### Any secret talents?

I was a competitive baton twirler. I put myself through college doing it; I was Featured Twirler for Mississippi State University for 5 years on a full tuition scholarship. That’s my secret hidden talent!

This is an installment of our Solar Spotlight series. Click here for our last interview!

The students of San Ramon Valley High School have to vie for parking spots on campus. Parking is a nightmare. According to one student, the demand for spots is so high that she rents a parking space from the Chinese restaurant across the street.

After all, who wouldn't want to park in their lot? In 2011, the San Ramon Valley Unified Schools District installed a solar PV carport structure over the lot. They probably have one of the coolest parking lots in the Bay Area - the sun-tracking solar panels shield cars from the California heat, while generating two-thirds of the school’s electricity too.

The solar carports in San Ramon Valley. Image courtesy of San Ramon Valley Unified Schools District.

Carports with solar panels were also installed in four other schools in the district. The cumulative 3.4-MW system is expected to generate two-thirds of the electricity needed to power the five schools.

The project was not cheap: the $25,000,000 construction and design costs were funded by Qualified School Construction Bonds (QSCBs), meaning that the school district did not have to pay out of pocket for the solar installation, or any interest later on. And that's not even the best part: the system will eventually pay for itself in energy savings after 16 years, and will save them millions for years to come. Along with many other California schools, the San Ramon Valley district experienced budget cuts adding up to$20 million within five years. With their savings on electricity, the district can still invest in teachers and health resources for its students. And the students never have to worry about their cars overheating. San Ramon Valley is a great place to go to school.

But the same is not true for the rest of the California. Back in 2011, the Department of Education published a report that indicated 40% of low-income schools are not receiving their fair share of funding. While the state has made efforts to restructure the school funding formula, California public schools are still lacking between $22 and$42 billion in funding, according to the California School Boards Association.

California public schools spend over $700 million on energy every year according to the California Energy Commission. So why aren’t more districts installing solar carports and saving money like San Ramon Valley? ## Barriers to installation Last week, I visited the four summer fellows of the Stanford Solar Schools Project, an initiative funded by the TomKat Center for Sustainable Energy. The undergraduate fellows spent eight weeks of their summer break addressing this exact issue. The 2016 Stanford TomKat undergraduate fellows. To begin, the team reached out to several government agencies to learn about their projects. For example, Proposition 39 is set up to help schools with energy efficiency and other energy projects through grants. While funding schemes are available for schools, getting the money isn’t easy. “There are a lot of programs out there, but it’s difficult for schools to find out about these programs and find the time and resources to fill out some of these applications, which are very expensive,” said Sneha, a junior majoring in Civil and Environmental Engineering. Schools have to submit a proposal before obtaining any sort of government loan. The upfront cost for proposals from solar procurement specialists or consultants “can be upwards of$20,000.”

“And that’s just to get the study done. You could pay the twenty grand, have the study done, and have them be like, ‘Sorry, it’s not gonna work.’” added Trevor, a sophomore studying Management Science and Engineering.

The schools that have managed to install solar on their own are typically from larger school districts that have initial funding already available, corporate sponsors, or dedicated resources. "The San Ramon Valley has a solar panel research committee set up," explained Claudia, a rising senior majoring in Mechanical Engineering. The Los Angeles Unified Schools District has a sustainability person in charge, “because they’ve had other projects before and they’re huge.”

## Solar funding for schools 101

Given these obstacles, the team began by mapping out the information gaps and making this accessible to schools.

The team compiled background materials that schools normally would had to spend weeks looking for, accompanied by a model of what a solar installation would look like on their own campus.

To guide the schools, they put together publicly available background materials. A brief three-page Action Plan, details all the steps to installing solar  from considering its impacts on a community, all the way to acquiring funding and beginning construction.

Their Policies, Regulations, and Resources document lists major sources of funding for schools, “for them to figure out how in the world they’re gonna pay for this,” described Chewy, a junior majoring in Earth Systems,.

In addition to Prop 39, loans are available. Schools could take advantage of the IRS Clean Renewable Energy bond. Trevor described it simply: “The district is the bond issuer. They find a bank to be a bondholder. The government pays the interest to the bank. So for the school, it’s basically a zero-interest way to install solar.”

Another option is the Qualified Zone Academy Bond (QZAB), another zero-interest plan. A private entity matches the bond value by 10%, either in cash or services, which helps fund the school’s academic programs, such as a renewable energy curriculum.

“So what we’re trying to do is provide resources, as well as connect them with organizations that help schools with this process,” said Sneha.

## Customized designs

"Now we’ve started looking at individual schools and designing solar plans for them along with long-term financial analyses in Aurora,” said Chewy.

Their goal is to convince each school that not only are they able to afford solar, but that the installation will prove to be an economically savvy move throughout the lifetime of the project.

“It’s possible what we’re doing with Aurora can cost schools a lot of money as well. Just providing this initial feasibility assessment with the starting point models that we’re generating helps a lot,” said Sneha.

The team hopes that the schools will bring the solar plan they generated in Aurora to the Bright Schools program, which provides free consulting up around $20,000. From there, the schools could apply to larger funding programs based on their solar designs. ## Modeling savings To create the solar designs, the team needed the school’s energy consumption data and electric rates. The information was either provided by the school or from the online database of the California Energy Commission, which contains data from 400 schools across the state. They imported the information into Aurora to closely model the load profile and potential energy savings of these schools. Then, they used the software to model the system in 3D, estimate the system’s energy production, and run a financial analysis, saving them from the hassle of having to go to the schools. A school could save anywhere from$40,000 to \$125,000 per year with a 313 kW solar PV system, according to estimates from the Environment California Research & Policy Center.

Since the designs needed to be as realistic as possible, the structural integrity of the school roofs was a key consideration. “Some of the roofs of the schools that we’re working with are really old, so probably couldn’t support the weight of solar panels,” said Claudia.

“So most of our designs are carports or some sort of shading structure on the school grounds,” she added, which also explains why carports are more popular for older schools, like in San Ramon Valley. In addition to carports, ground mounts could also be installed on unused property.

## Next steps

Over the course of the summer, the Solar Schools Project team modeled unique solar designs for 26 low-income schools across 10 school districts in California, serving a total of 20,910 students. Each proposal was complete with a shading analysis and financial estimates. While their skill with solar design can now rival that of some installers, they know that they have only scratched the surface, and that designing the models is only the first step.

While the team always waits for schools to express interest before sending the solar design proposal, they have to put faith in the superintendents and the facilities managers at the school to move forward with the project.

“We’ve shown them all the money they can save, proven that it’s worth the investment, and directed them to all the financial help they can get out there,” said Chewy.

Claudia expressed her concern that the receiving side might lack motivation: “We’re worried that they’ll think that it’s a good idea and that they’ll agree with us, but that no one is actually pushing to take action on the next things that are involved, like more work or more money going into it.”

## The power of local advocates

Even though the team has realized that there is only so much they can do from a distance, they still have hope for their proposals.

“We’ve learned the importance of the local advocate for our projects,” said Sneha. “They’re the people we’re trying to connect with, and we’re trying to give them tools to champion their project.”

All of them agreed that bureaucracy in the school system was expected, but the extent of it was still shocking. The processes can take months in the school districts, given complications with multiple stakeholders: the superintendent and the community, as well as the three-year turnovers in school boards.

“There are a lot of hoops to jump through,” Trevor reaffirmed Sneha’s statement, “That’s why again it’s so important to have a champion at the local level.”

The team has discussed using their research to make policy suggestions. They have become quite adept at navigating funding and other processes involved with solar installations for schools. “We want to give recommendations to actors at the state government level so that they can make those processes a bit simpler, based on what we’ve learned this summer.” said Chewy.

Perhaps the best local advocates are the high school students themselves. Trevor hopes that the implementation of a solar project will be a community-wide effort.

“If these superintendents get this big packet of information that we’ve provided, I can see high schoolers just jumping all over it and going to school board meetings and promoting it on a regular basis. That’s what happened in that San Ramon Valley.”