Quantifying Edge Brightening and Current Mismatch Loss in Fixed-Tilt and Single-Axis Tracked Bifacial PV Systems

Common photovoltaic (PV) performance modelling software approximate energy yield using a central irradiance sampling line within an infinite row of modules. In such an approach, user-defined corrective factors must represent the irradiance non-uniformity across a row of bifacial PV modules. To contribute to a growing understanding of the upper bound for corrective factors in utility scale systems, this study quantifies the net effect of edge brightening gains and current mismatch losses for central rows in a 2-in-portrait fixed-tilt and single-axis tracked (SAT) PV test-bed at 55°N. Using the DUET PV energy yield software, this study demonstrates optical and electrical calculations for 200,000+ sample points across the row, including two-dimensional non-uniformity profiles for the front and rear of each row in each system. Rear edge brightening ranging from 18.3-32.7 W/m2 contributes to a 0.3-0.5% annual edge brightening gain in energy yield counteracted by 0.1-0.2% current mismatch losses, depending on the system. A method combining the per-timestamp current-voltage curves of all 88 modules in the row demonstrates +0.3% and +0.25% net energy yield gain for fixed-tilt and single-axis tracked systems, respectively, as compared to a central module approximation. Any model that does not inherently capture irradiance non-uniformity along a row of modules should thus allow a net positive corrective factor.