Characterizing the Impact of Solar Spectral Irradiance on PV Module Output

Abstract

The energy delivery of PV devices for a specific location is determined by the interaction of the electrical performance of the PV device and the site specific environmental and meteorological conditions. The spectral response curve of a PV device is a determining factor for its energy yield performance with regard to spectral effects. For a given spectral irradiance distribution the generated photocurrent results out of the product of both curves. Deviations to AM 1.5 of measured real sun spectra can be either subject to a blue shift when the composition of the spectrum shows a higher intensity in the low wavelength range or a red shift when a higher intensity for high wavelength range is observed. Accordingly, PV devices with a narrow band of spectral response will benefit from a blue shift of spectral irradiance. Global solar irradiance is commonly measured with spectrally neutral pyranometers. Therefore, the effective irradiance for photocurrent generation of a PV device can be higher or lower depending on the spectral composition of solar irradiance. This relation is described by the spectral mismatch correction factor (MMF), which is a direct measure for spectral gains (MMF > 1) or losses (MMF <1). We analyzed spectral shifts in the solar spectral irradiance using the average photon energy (APE) and quantify the impact on the performance of eight PV technologies in Arizona and Italy using the spectral mismatch factor.