A Benchmark and Validation of Bifacial PV Irradiance Models
Amir Asgharzadeh1,3, Marc Abou Anoma1, Chetan Chaudhari1, Gregory M. Kimball1, Adam Hoffman1, Sushrut Bapat1, Richard Perkins1, Dan Cohen1, Daniel Riley2, Fatima Toor3, Ben Bourne1
1SunPower Corporation, San Jose, CA, United States
/2Sandia National Laboratories, Albuquerque, NM, United States
/3Electrical and Computer Engineering Department, The University of Iowa, Iowa City, IA, United States

In this paper, we compare the accuracy of four bifacial irradiance models with field measurements.  Using the bifacial irradiance modeling tools bifacial_radiance (ray tracing), bifacialvf, pvfactors and PVSyst, we modeled the front- and back-side 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. 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.

Index terms – bifacial PV, open source PV modeling, view factor models, ray tracing