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Lisa Cohn
Author

Lisa Cohn

Lisa Cohn been writing about energy for more than 20 years. Her stories have appeared in Renewable Energy World, Windpower Monthly. She began her career covering energy and environment for The Cape Cod Times and first became interested in energy as a student at Wesleyan University, where she helped design and build a solar house.

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How to Read a Solar Panel Specification Sheet

Lisa CohnLisa Cohn

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.

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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.

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Lisa Cohn
Author

Lisa Cohn

Lisa Cohn been writing about energy for more than 20 years. Her stories have appeared in Renewable Energy World, Windpower Monthly. She began her career covering energy and environment for The Cape Cod Times and first became interested in energy as a student at Wesleyan University, where she helped design and build a solar house.

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