Experimental determination of the structure shading factor and mismatch losses for bifacial photovoltaic modules on variable-geometry, single-axis trackers

Abstract

Rear irradiance on bifacial modules exhibits greater spatial non-uniformity compared to frontal irradiance, impacting performance metrics like the Structure Shading Factor (SSF) and Mismatch Loss (MML). SSF quantifies the fraction of rear irradiance obstructed by the mounting structure, while MML measures the resulting power losses due to non-uniformity.

We propose a new experimental methodology to determine SSF and MML for one-in-portrait (1P), and 2P trackers, considering full-cell and half-cell modules. For 1P trackers, SSF is 10.0 % and MML is 0.46 %(0.40 %) for full-cell(half-cell) modules. For 2P trackers, SSF is 2.7% and MML is 0.35 %(0.21 %) for full-cell(half-cell) modules. The influence of tracker geometry is examined by varying the torque tube distance (1P) and East-West panel gaps (2P), providing mathematical relationships for SSF and MML.

Measurement uncertainties are estimated at 4 % (1P) and 2 % (2P) for SSF, and 4 % for MML in both trackers. When used for annual energy yield modelling, uncertainties rise to 10 % in SSF for both trackers and 20 %(30 %) in MML for 1P(2P) trackers, yet their impact on energy yield uncertainty is below 1 %.