The stronger the sun the more energy your solar panels produce, right? Wrong. At a certain point, excessive heat can actually cause a decrease in energy output from your solar panels. Here’s why and what you can do about it.
Why Is Heat Bad For Solar Panels?
While an increase in heat doesn't affect the amount of solar energy a solar panel receives, it does affect how much energy they output.
Solar panels are tested at 25°C (77°F) under the Standard Test Condition (STC), and thus going beyond that temperature affects energy output. The amount of energy produced by a solar panel is calculated by multiplying the current and the voltage.
Based on its efficiency, a solar panel has a maximum amount of energy that it is able to produce :
Efficiency = (Max current x Max voltage) / input power from the sun
Not to get into the calculations too much, but when your solar panels are exposed to a higher temperature, the current will increase, while the voltage will decrease. Since voltage decreases faster than the current increases, you’ll have a lowered efficiency for your solar panels.
By affecting the efficiency of your solar panels, heat thereby causes your solar panels to output less energy.
How do I Calculate Energy Loss For My Solar Panels?
Look on the datasheet of your solar panels and find the “NOCT Temperature Coefficient Pmax.“ The temperature coefficient indicates by how much you can expect your solar panels to decrease in maximum energy output per each increase of 1°C.
For example, the Peimar 270W panels have a Pmax Temperature Coefficient of -0.43% / °C. If these solar panels heat up to 45°C (113°F), that means they are 20°C above the STC temperature.
Lost energy % = 20 x -0.43 = -8.6%
(100% - 8.6%) x 270W = 91.4% x 270W = 246.78W
The wattage we just calculated is actually called the PTC power, which is a better form of calculating how much energy you can expect out of your solar panels.
How Can I Prevent Heat On Solar Panels?
1. Install your panels a few inches above the roof to allow airflow that will cool down your solar panels. You can also add a ventilation fan to help further.
2. While all black panels are aesthetically pleasing, they also absorb more heat. Thus lighter colored solar panels might be a better choice if you live in an area where the temperature increases significantly.
 UCSB Science Line, scienceline.ucsb.edu/getkey.php?key=2668.