Solar Edge Pros
6 minutes
Temperature Coefficient of Solar Panels: Power Lost per Degree
The temperature coefficient of a solar panel tells you how much power it loses for each degree of heat. Data sheets list it in percent per degree C, counted from 25 C, the standard test temperature. For most silicon panels it is about -0.3 to -0.4 percent per degree. Heterojunction and thin-film panels often do a bit better. The cause is mostly voltage. Heat makes the junction leak more current, so Voc falls. You can estimate the loss: power change in percent = coefficient x (cell temperature - 25). On a hot roof, cells often run 20 to 30 C above the air. With air at 35 C and cells at 60 C, a panel at -0.35 loses about 0.35 x 35 = 12 percent. The coefficient comes from cell design and chemistry. Better passivation and a higher Voc give a smaller loss. Mounting with an air gap keeps cells cooler. This matters for the footprint too. For the same sunshine, hotter cells make fewer kilowatt-hours. So the factory's energy and carbon are spread over less output. Heat also speeds aging chemistry, such as acid release from EVA. After this Concept you can read the coefficient on a data sheet, estimate summer power loss on your roof, and compare panels for a hot site.