How Does The Temperature Coefficient Work?
All solar cells have a temperature coefficient. This is a measurement of how much the solar cells output power decreases for every degree Celsius above the reference temperature (usually 25°C).
Generally, mono-crystalline solar cells have a temperature coefficient of between -0.3%/°C and -0.5%/°C. This means a mono solar panel will lose between a third and half of one percent of its power for every degree above 25°C that the solar panel reaches.
Solar panels are all tested for their efficiency at 25°C as the Standard Test Condition (STC), however, when solar panels are installed on a roof, they often reach much higher temperatures, particularly on warm sunny days. This means that the efficiency of your solar system can be reduced on hot days when the temperature coefficient causes a decrease in the system’s output power.
How Does The Temperature Coefficient Affect My Solar System?
Let’s say the temperature of a 250W mono-crystalline solar panel installed on a roof is 65°C, and the temperature coefficient of my panel is -0.5%/°C.
The solar panel’s power loss can be calculated as follows:
65°C – 25° = 40°C
40°C x -0.5% = -20%
Therefore panel power loss = -20% x 250W = -50W
Therefore panel power = 250W – 50W = 200W