How does the temperature coefficient affect the efficiency of a solar panel?
What is the impact of the temperature coefficient on efficiency? The datasheet of every solar panel includes the temperature coefficient. But what exactly does this value mean—and what does it tell us about efficiency?
Efficiency losses in solar panels
The efficiency of solar panels is not constant. It depends on the amount of sunlight and on the temperature of the solar cells. Manufacturers determine efficiency under Standard Test Conditions (STC): 1000 Watts per m² of irradiance and a cell temperature of 25 degrees Celsius. As soon as the cell temperature exceeds 25 °C, efficiency starts to decline. The ambient temperature is less relevant; what really matters is the cell temperature, which can reach 60–70 °C on sunny days—especially on dark rooftops or in low-wind conditions.Efficiency loss occurs because higher temperatures increase the electrical conductivity of the cells. This makes it harder to separate electric charges, leading to voltage loss and ultimately lower energy yield.
What is the temperature coefficient?
The temperature coefficient tells you how sensitive a solar panel is to temperature increases in the cells. This value is found on the datasheet and is expressed as:
- TC of Voc
- TC of Isc
- TC of Pmp
The associated units vary and include %/°C, %/K, or mA/°C. The most commonly used value is the percentage of Wp loss per degree above 25 °C: Pmax (%/°C). For today’s panels, this is usually between -0.2% and -0.4% per degree.The temperature coefficient is also important when calculating the maximum string length. At low temperatures, voltage increases—impacting how you design your system. For more on that, check out our FAQ.