Simulation of the irradiance and yield calculation of bifacial PV systems in the USA and Germany by combining ray tracing and view factor model

Abstract

Compared to conventional photovoltaic (PV), there are more influencing factors in bifacial photovoltaics to be considered to calculate incoming irradiance and energy yield. Accurate models to investigate the influences of the elevation, the albedo of the ground, the shading conditions between the PV rows and many other rear-side related factors are required. This paper combines the ray tracing (RT) and view factor (VF) models to calculate the irradiance with a subsequent electrical yield calculation using the one-diode model. To verify the results of the developed open-source simulation program BifacialSimu, accurate data from a plant in Golden, USA (single-axis tracked) and a commercially operated plant in Germany (fixed-tilt) are used. Through comparisons to the actual data, it can be concluded that a combination of RT and VF models seems to be valid for longer simulation periods with several months since the relative errors balance out. The RT-only simulation accurately reproduces the precise hourly radiation and electrical yield pattern. Still, a continuous positive deviation was found, which does not even out over long periods and is thus less accurate than the VF/RT combination. A simulation for a single month with RT can take several hours. Thus, the best simulation mode results according to user requirements.