The Effect of a Varying Solar Spectrum on the Energy Performance of Solar Cells

The annual performance of a multi-crystalline silicon cell (mc-Si) and an amorphous silicon cell (a-Si) is calculated using modelled spectra in combination with the well-known solar cell one-diode model. Two different sets of modelled minutely spectra are utilized for modelling cell performance: 1) Simulated spectral data, using measured irradiation data from KNMI (Royal Netherlands Meteorological Institute) and the SEDES2 spectral model, 2) Scaled AM1.5 spectra using global tilt irradiance. The modelled energy performance derived from each set of spectra is compared and a mismatch factor (MMF) is determined to quantify the amount of the spectral effects. Both the modelled solar cell performance and calculated MMF are then graphed against global irradiance, air mass, and sky clearness index for every month. The results show that spectral effects are larger for a-Si than for mc-Si, as was expected. Detailed minutely data shows MMF to vary between 0.66 and 1.77 for a-Si and between 0.74 and 1.11 for mc-Si solar cells. From the annual yield based on modelled and scaled AM1.5 spectra, it is concluded that a-Si is up to 8% more effective than mc-Si per installed Wp. The annual spectral effect was found to be −3% for a-Si and −1.7% for mc-Si. This indicates that in general models, which assume the AM1.5 spectrum, overestimate the energy yield.