The module temperature is critical for determining the losses due to the temperature coefficent. If I remember correct the module temperature is calculated by a pre set factor (typically 0,035) times the irradiation which is added to the ambient temperature. I ask since after some evaluation of data from a few sites it seems this factor varies (significantly?) depending on system type and weather. For example a free field system I follow closely in Sweden; the very few all sunny days the factor is approximately 0,025 but the most common value for all these days with a mix of clouds and sunshine is between 0,015 and 0,020. For a completely integrated system the values are 0,45-0,47 for the few all sunny days, but typically around 0,3 the average Swedish summer day. An average error in operating temperature of 10 degrees would result in a four percent performance difference. Any thoughts on this?
