Performance Degradation Analysis of Bifacial Photovoltaic Modules in Temperate Climates

Abstract

Bifacial photovoltaic modules capture reflected irradiance from both module surfaces, promising higher energy yield than conventional monofacial panels, yet long-term degradation behavior under temperate climate conditions remains less documented than performance under controlled test settings. This study analyzes multi-year field performance data from bifacial module installations across several temperate climate sites, examining how seasonal albedo variation, mounting height, and soiling patterns interact to influence measured degradation rates. Rather than relying solely on manufacturer-reported degradation coefficients, we derive site-specific degradation trends from continuous production data and compare these against standard test condition projections. Findings indicate that bifacial gain varies considerably with ground surface type and seasonal snow cover, producing degradation trajectories that diverge from monofacial baselines in ways not captured by current standardized testing protocols. Installations with elevated mounting height and reflective ground cover showed more stable bifacial gain over time, while low-mounted arrays over vegetated ground exhibited greater performance variability. These findings suggest that site selection criteria for bifacial deployment should incorporate longer-term albedo stability assessments rather than point-in-time measurements, with implications for yield forecasting accuracy in utility-scale and distributed solar projects.