Effective Spectral Albedo from Satellite Data for Bifacial Gain Calculations of PV Systems

A key requirement for increasing the accuracy of energy yield modelling is the accurate estimation of the ground albedo value of a potential site. As most natural surfaces are not white, the colour as well as irradiance of reflected light needs to be considered. In this work we use spectral ground reflectance datasets from satellite data and ground-based stations in order to extract effective spectral albedo values and their uncertainties for bifacial PV system energy yield modelling. We demonstrate satellite spectral reflectance data as a realistic case for bifacial gain calculations and validate them with the ground-based data. An effective albedo calculation methodology is introduced, where the spectral albedo dataset, spectral irradiance and spectral response of the PV module type of the potential system are considered. Comparing 20 different locations and 3 different bifacial module types, we show that it is critically important to account for diurnal and seasonal variations in spectral albedo in bifacial gain calculations. We also show that there can be significant differences between front side and rear side spectral response in silicon bifacial PV modules which can lead to differences of greater than 20 % in the effective value of ground reflected irradiance.