Mismatch Loss in Bifacial Modules Due to Nonuniform Illumination in 1-D Tracking Systems

Abstract

We apply ray tracing to compute the light-generated current IL within each solar cell of a bifacial tracking module, and circuit modeling to quantify how the spatial variability in $I_{L}$ (i.e., current mismatch) reduces the module's output power P MP. We find that 10 million rays are required to accurately map $I_{L}$ for a central module in a photovoltaic (PV) system at a given insolation condition. The relative reduction in P MP is found to be 1) greatest in the middle of the day for sunny conditions, 2) independent of time for very cloudy conditions, 3) higher for edge modules than central modules, 4) higher for one-high portrait configurations than for two-high, and 5) higher when the ground albedo is higher. We trace 2 billion rays on 2000 parallel cores to solve a module's annual energy yield for a system located at Golden CO with a sandy soil. The yield reduction in a one-high configuration due to nonuniform illumination is 0.23% for a central module and 0.35% for an edge module. Thus, in this example, mismatch loss due to nonuniform illumination within an individual tracking module is relatively low, despite the rear of the module being shaded by a torque tube.