Field degradation of bifacial photovoltaic modules in northern Europe

Despite the rapid deployment of bifacial photovoltaic modules, few studies report their degradation outside accelerated stress testing. In this study, we analyze the degradation of 189 PERC modules from four types after 2.1 to 4.5 years of outdoor exposure in the Danish climate. From flash testing, we find a weighted mean Rd of 0.63%/a on the front side compared to datasheet specification, exceeding the 0.5%/a benchmark for monofacial modules. Electroluminescence imaging showed a dark imprint around three sides on the perimeter of half-cut solar cells in one module type. Though rarely described in literature, the fault matches a report about UV-induced degradation. Its impact on P m p degradation is limited to 0.75%/a in the first 2.5 years. On modules from non-serial production, we observed potential-induced degradation, which caused high current and power loss more prominently on the rear side. On frameless modules, backside glass breakage occurred during operation, primarily caused by rock chipping from mowing activities. Handling also induced breakage when modules were removed from substructures and stacked. In contrast, framed glass-glass modules proved more robust. Additionally, we observed dark cell edges, line cracks, busbar issues, finger contact issues, dark spots, and a hotspot. • 189 bifacial PV modules of four types tested after 2.1 to 4.5 years of outdoor aging. • Weighted mean degradation rate of 0.63%/a compared to data sheet specifications. • PID in one module type with high current and power losses especially on the rear side. • New fault showed a dark imprint around the cell edges in EL identified as UVID. • Frameless modules disproportionally affected by glass breakage.