A Benchmark and Validation of Bifacial PV Irradiance Models

In this paper, we compare the accuracy of four bifacial irradiance models used in the photovoltaic industry, by benchmarking them against field measurements. Using the bifacial irradiance modeling tools bifacial_radiance (ray tracing), bifacialvf, pvfactors and PVSyst, we modeled the front- and backside irradiance at two test sites: a fixed-tilt PV system installed in Albuquerque, NM and a single-axis tracker PV system installed in Davis, CA. We found that all four models predicted annual energy impact of bifacial gain within ±1% of one another, and the fast view-factors-based models matched the accuracy of the more computationally intensive ray tracing model. We also investigated the impact of albedo and found bifacial gain values of about 4% for the 0.16 albedo condition and about 9% for the 0.56 albedo condition for the single-axis tracking system. Our model validation work shows that pvfactors is an accurate and highly customizable solution for evaluating the front and backside irradiance in bifacial PV systems.