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Is Solar a Good Fit for This Bavarian Castle?

Posted by Andrew Gong on Nov 26, 2019 5:16:07 PM

In our Solar Landmarks series, we explore solar designs for landmarks around the world—from Buckingham Palace to Independence Hall—all from the comfort of the Aurora office. In our latest installment, we took a look at one of the most fanciful sites yet: Neuschwanstein Castle.

Neuschwanstein Castle was built in the late 1880s and sits on rugged terrain near the German-Austrian border overlooking the town of Hohenschwangau. The famous castle attracts hundreds of thousands of visitors annually—and even served as inspiration for Walt Disney’s castle designs.

Although we wouldn't expect to see solar added to this site anytime soon, given its historical significance, analyzing the solar potential of Neuschwanstein Castle presented a good challenge for Aurora’s design tools and irradiance engine.

Not only does this location provide a chance to utilize Aurora’s expanded international LIDAR data, but its mountainous location also provides a perfect venue to put Aurora’s new horizon shading functionality—which accounts for the shading impacts of surrounding terrain—to the test.

Let’s take a look at what we found in our remote site assessment for Neuschwanstein Castle. Could onsite solar be a good choice for meeting the castle’s energy needs?

Modeling the Castle

To understand whether a solar installation was feasible for this site, we began by creating an accurate 3D model of the castle. A 3D model makes it possible to precisely determine shading at the project site, determine where it is possible to place solar panels (and ultimately how much energy could be produced if solar were installed).

Understanding the Site: Global Google HD and LIDAR

Precisely modeling this complex site was made easier by the presence of robust LIDAR— a form of 3D data—at this location. LIDAR makes it easy to determine the heights and slopes of roofs, towers, and trees so that we can ensure our remote analysis is accurate.

Thanks to our partnership with Google, users can access LIDAR and crisp images worldwide. Learn more about this partnership and the coverage area here.

LIDAR data of Neuschwanstein Castle, which allowed accurate site assessment in Aurora solar softwareLIDAR data, available through a partnership with Google, provides a detailed view of the building, terrain, and trees at Neuschwanstein Castle. This allowed us to be confident in the accuracy of our site model and shading analysis, without physically visiting the site.
 
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Creating an Accurate 3D Model with SmartRoof

Modeling a complicated structure like Neuschwanstein Castle can be managed by combining several smaller roof sections, similar to how we modeled San Francisco City Hall.

We began by outlining the main rectangular sections of the roof using Aurora’s SmartRoof tool and then applied a steep pitch to the two sides. To ensure the pitch was correct, we used Aurora’s “Fit to LIDAR” option, to match the pitch of the roof faces to the actual conditions at the site.

The spires were modeled by creating a tall circular obstruction (again Fit to LIDAR helped to accurately model the height). From there, to create their conical roofs, we traced the perimeter to create the outline of the roof. If all the edge lengths are similar, the resulting structure will closely resemble a cone.

Adding dormers to the top of the castle was a breeze. We placed one using Aurora’s dormer tool, edited the edges, and then cloned it across the roof.

And there you have it—the completed castle:

A 3D model of Neuschwanstein Castle, created in Aurora solar software. 
A 3D model of Neuschwanstein Castle, created in Aurora solar software. 

Assessing Irradiance

The next step of our remote site assessment to determine the feasibility of a solar for Neuschwanstein Castle was to calculate the irradiance at the site. With the design completed, we pressed the irradiance button to run an irradiance analysis of the site.

Aurora then calculated the irradiance on each roof face at the site, by simulating the position of the sun for every daylight hour of the year at this location, in addition to accounting for other factors like diffuse irradiance.

A color-coded irradiance map of Neuschwanstein Castle, generated by Aurora solar software
A color-coded irradiance map showing the irradiance on the roof faces of Neuschwanstein Castle, generated by Aurora. The values in the bottom right corner show the irradiance where the user's cursor is on the roof; the values shown are for a less sunny area on the north face of the roof but Aurora users can mouse over their designs to see irradiance in different areas. 

As you can see in the resulting, color-coded irradiance map, the solar access at this site is not optimal. Many of the lower roof surfaces are shaded by towers and parapets.

Additionally, the spires and many of the roof faces have such steep slopes that their available sunlight is quite low on the year because of poor tilt and orientation factor (TOF) values. (As we explain in this blog post, the tilt and orientation of a roof have a big impact on how much sunlight reaches the surface).

A 3D view of our model of Neuschwanstein Castle, showing the irradiance on the roof. The dark colors indicate lower irradiance that is not optimal for solar. 

On the north face of the main roof, the solar access is as low as 45% in some areas; even on the more optimal south face, solar access varies widely due to shading from dormers and towers. In the sunniest locations on this roof face, the Total Solar Resource Fraction never exceeds 87%.

How Does Horizon Shading Impact This Roof?

In addition to poor TOF and shading from the castle’s many ornate architectural features, there’s another big factor at play in the poor irradiance levels we find at this site: horizon shading.

As we mentioned earlier, Neuschwanstein Castle is in the southern area of Germany, right up against the Bavarian Alps. The photo below shows some of the large peaks to the east and south of the castle. As you might guess, these have a noticeable impact on the sunlight this site receives at certain times of the day and year. With Aurora’s new horizon shading feature, we can determine exactly how that impacts irradiance.

A photo of Neuschwanstein Castle, showing the tall mountains surrounding this site that contribute to horizon shading.
A photo of Neuschwanstein Castle, showing some of the tall mountains that surround this site and contribute to horizon shading. 

Aurora’s horizon shading feature takes the surrounding terrain data and scans it to create an elevation profile, like the one shown below. This reflects how much of the sky is blocked by surrounding land features. (This is influenced both by the height of a given terrain feature and how close it is.) Here you can see the closer eastern and southern peaks show up as high elevation points, while the more distant mountains shown in the cover image at the top of this article show up as only around 5 degrees of elevation.

A horizon profiles, like this one for Neuschwanstein Castle, underpin Aurora's horizon shading analyses. 
Horizon profiles, like this one for Neuschwanstein Castle, underpin Aurora's horizon shading analyses. 

Using the horizon profile, Aurora calculates the times when the direct rays of the sun are blocked, as well as how the overall diffuse irradiance at the site is reduced by the mountains.

If you look at the monthly Solar Access charts Aurora provides, you can see that the winter months are more heavily affected by the horizon shading; a larger percentage of those hours have the sun blocked by the mountains. Overall, solar access at this site is reduced by 10% as a result of the surrounding mountains!

Failure to account for this source of shading, which would be easy to do without automated horizon shading analysis, would result in a significant overestimate of the solar access of this location—as we can see in the comparison below of the monthly solar access with (right) and without (left) horizon shading.

Monthly solar access without accounting for horizon shading (left) and with horizon shading calculated (right)Monthly solar access without accounting for horizon shading (left) compared to solar access when the impacts of horizon shading are calculated (right)—a 10% decrease.

Site Assessment Conclusions

Given the poor irradiance at this site—not to mention the strikingly steep pitch of the roof faces on this seventeen-story castle—we conclude that installing solar onsite at Neuschwanstein is not a great fit. (We imagine the Bavarian Palace Administration, which maintains this historic site, would agree!) Perhaps a community solar array in the surrounding lowlands could be a better fit for reducing the presumably hefty electricity bills of this building.

While not an ideal site for solar, Neuschwanstein Castle provides an excellent illustration of how horizon shading can have a significant impact on the amount of solar energy available at certain sites with steep surrounding terrain. Aurora is the only solar design software that automatically pulls in terrain data and accounts for its impacts on shading by default.

This, combined with robust international LIDAR data, allowed us to get a precise understanding of the actual irradiance levels at this site in Germany, without ever leaving our California office. Incorporating this kind of remote site assessment for solar prospects can help your solar company save on site visits and close more solar sales.

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Topics: horizon shading

What Is Horizon Shading and Why Is It Important for Solar?

Posted by Brett Harvey on Nov 11, 2019 12:50:54 PM

When forecasting how much energy your solar PV system will generate for a customer, accuracy is paramount. If your modeling software overlooks something important, like the stringing configuration of your system or shading from a nearby tree or other obstruction, it could result in errors and an unhappy customer.

Advances in solar software have given solar contractors the tools to confidently design PV systems and accurately model their economics and energy production without physically taking measurements at the project site.

Horizon shading, the latest addition to Aurora’s suite of modeling tools (released last week), adds an additional degree of accuracy for solar production estimates. It is also the first time that this functionality has been automated by a solar software (no need to import terrain data!), ensuring time savings for solar companies who want accuracy they can stand behind.

Want to learn more about horizon shading?  Tune in to a recording of an educational webinar on this topic!

What’s Changing?

Aurora’s irradiance maps and performance simulations have been a huge part of its success as a tool for remote site analysis. However, their benefit hinges on the ability to accurately model the physical characteristics of the site. For select sites where hills or mountains could cause shading, the need to model the terrain around a project could present a challenge.

Prior to the release of this feature, Aurora assumed that a flat landscape surrounded a project site. Objects and obstructions such as trees and surrounding buildings were manually added by designers, which worked well when modeling “near-shading” at the site, but the modeling of “far-shading” from surrounding hills and distant mountains was more difficult. A workaround employed by some users was to create polygon obstructions to model terrain. However, this proved time-consuming and error-prone. To make modeling this type of far-shading much easier for users, we decided to develop a feature called horizon shading.

Before Aurora released horizon shading, elaborate models like this were a workaround for more accurate solar production.An example of terrain that would have been labor-intensive to model for shading purposes, prior to the release of Aurora’s new horizon shading feature.

What Is Horizon Shading?

Horizon shading enables the automatic modeling of shade due to the terrain surrounding a site, to support more accurate assessment of shading and improved solar production estimates.

When an irradiance map is generated or a performance simulation is run, Aurora collects over 1 million elevation measurements from the nearby area and uses them to create a profile of the surrounding terrain. The resulting 360-degree elevation map is known as a horizon profile.

A diagram of how the horizon profile can block the rays of the sun in areas with horizon shading.A diagram showing the sun path (yellow) throughout the year and the horizon profile (green) of the terrain for a building with a large hill to the southwest. The sun follows the top of the sun path from east to west in the summer and the bottom in the winter.

When calculating irradiance, Aurora checks to see if the sun is below the horizon profile. If that’s the case, the beam component of irradiance is blocked. Additionally, at all hours, the amount of diffuse light is reduced because some of it is blocked by the horizon.

Horizon shading is enabled by default for all new irradiance maps and performance simulations in Aurora. Learn more here.

Where Does Horizon Shading Matter Most?

In many cases the horizon blocks less than 1% of available light, but the effect can be much more drastic in hilly regions. Houses in valleys, canyons, or even those situated on the side of a hill can all experience varying degrees of shading from the land.

The effect of horizon shading on utility bill savings can also be amplified by time of use (TOU) rates. In the example profile above, a large hill sits to the west of the site, which would reduce production during peak-pricing hours in the afternoon according to California’s current TOU schedules.

The distance between a site and prominent terrain also influences the impact of horizon shading. The example below illustrates horizon profiles for four sites situated at various distances from Japan’s Mount Fuji. The mountain obscures more of the sky at the site that is only 10 km from the peak, compared to the site that’s 16 km away.

Copy of Copy of FujiHorizon profiles for four sites situated north of Mt. Fuji at different distances. Note that the sites that are further away also have other, closer hills to the north.

The automatic calculation of horizon shading represents a major step forward in the accuracy of remote shade assessment and solar production modeling with solar software. The automation of this functionality—a first in solar design software—is another way that Aurora is working to help solar contractors save time and money by getting the most accurate assessments with fewer site visits.

For an example of an extreme case of horizon shading, check out our related Solar Landmark article!

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Topics: irradiance, horizon shading

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