Effects of irradiance and other factors on PV temperature coefficients

Analysis of data from several Photovoltaics for Utility Scale Applications (PVUSA) systems suggested diminishing sensitivity of array power to temperature with decreasing irradiance. At low irradiance a reversal of sign of the temperature coefficient, β, was noted indicating increasing array power with temperature. Evaluation of a simple PV system power model suggested a strong relationship between incidence angle and the model´s increasing error at low irradiance. Indoor tests confirmed that β is insensitive to irradiance and indicated a decrease in module performance beyond normal cosine losses at high incidence angles (>60°)