Mismatch loss in bifacial modules due to non-uniform illumination in 1D tracking systems
Keith R McIntosh1, Malcolm D Abbott1, Ben A Sudbury1, Jenya Meydbray2
1PV Lighthouse, Coledale, Australia
/2PV Evolution Labs, Berkeley, CA, United States

We apply ray tracing to compute the light-generated current IL within each solar cell of a bifacial tracking module, and SPICE modelling to quantify how the spatial variability in IL (i.e., current mismatch) reduces the module’s output power PMP. We find that 10 million rays are required to accurately map IL for a central module in a PV system at a given insolation condition. The relative reduction in PMP is found to be (i) greatest in the middle of the day for sunny conditions, (ii) independent of time for very cloudy conditions, (iii) higher for edge modules than central modules, (iv) higher for one-high portrait configurations than for two-high, and (v) 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. The yield reduction in a one-high configuration due to non-uniform illumination is 0.23% for a central module and 0.35% for an edge module. Thus, mismatch loss due to non-uniform illumination within an individual tracking module is relatively low, even when the rear of the module is shaded by a torque tube.