On the impact of solar spectral irradiance on the yield of different PV technologies

This article presents results from investigating the impact of varying spectral irradiance on the performance of different PV technologies. Relative gains or losses were quantified for five typical PV technologies with different band gaps and, consequently, different spectral responses using spectral irradiance measured from 01.06.2010 to 31.12.2013 in Freiburg im Breisgau, Germany. With the spectrally resolved data, the effectively available annual irradiation per technology was calculated using the spectral mismatch factor, and compared to the total broadband irradiation measured by a pyranometer. The process used to calculate the spectral impact produces a result that can directly be used to estimate the effectively available irradiation for yield prediction or energy rating. The annual spectral impact was +3.4% for amorphous silicon, +2.4% for cadmium telluride, +1.4% for crystalline silicon, +1.1% for high-efficiency crystalline silicon and +0.6% for small-band-gap CIGS. Technologies with a large band gap exhibited spectral gains in summer and spectral losses in winter, and vice versa for small-band-gap technologies. The results are discussed and interpreted with consideration to uncertainties and results published so far. Furthermore, it was investigated in how far average photon energy (APE) can be used as a quantitative indicator for the spectral impact. In summary, it was found that using APE does not present actual advantages over using the spectral mismatch factor, and should rather be used for qualitative than for quantitative evaluations.