Comparison of Spectral Correction Methods: Spectral Irradiance Measurements and Parameterized Spectral Models

A standard solar spectrum is assumed for photovoltaic (PV) module performance calculations, but spectral solar irradiance is continuously changing, impacting PV efficiency and energy yield. We calculate the spectral mismatch modifier (SMM) for one year of measured spectral irradiance data in Roskilde, Denmark. Irradiance wavelength measurement range affects the calculated SMM: neglecting long-wavelength irradiance above 1700 nm underestimates module current increase due to clouds and overestimates module current increase due to air mass. We also compare five parameterized spectral correction methods. Tilt of the spectral irradiance measurement (or of input training data for parameterized models) is non-negligible when calculating SMM. Parameterized methods relying on clearness index predict large positive spectral effects due to clouds, an effect that is neglected in other models. Further work is required to ascertain the most effective spectral correction approaches.