Performance measurement reference conditions for terrestrial photovoltaics

One important aspect of measuring terrestrial photovoltaic array electrical performance is the choice of a reference solar spectrum. Sensitivity to this choice is caused by the narrow spectral response of photovoltaic materials and the associated dependency of certain annual energy output calculational procedures. The accuracy of energy output calculations based on commonly used reference spectra is examined for a variety of array types and site locations in the US using tapes of hourly solar irradiance and temperature measurements in conjunction with solar spectrum models. Conclusions are drawn relative to the accuracy associated with the commonly used air mass 1.5 reference spectrum, and alternative reference spectra with improved accuracy are illustrated.