UV-induced degradation: comparative analysis of PV module testing and stabilization procedures against outdoor behavior

UV-induced degradation (UVID) represents a critical reliability concern for TOPCon-based photovoltaic modules, yet the correlation between laboratory testing and real-world performance remains poorly understood. This study validates indoor UVID testing protocols against outdoor degradation through comprehensive analysis of four module types across five outdoor sites with up to 28 months of field exposure. We demonstrate that post-UV stabilization via brief light soaking is essential for accurate laboratory assessment, effectively reversing dark storage effects that otherwise confound UVID measurements. Comparative analysis reveals a strong relation between indoor testing (following IEC 61215-2:2021 MQT10) and outdoor degradation when proper stabilization is applied, with indoor slightly but consistently overestimating field degradation for TOPCon modules. Notably, while dark storage effects cause significant power loss under laboratory conditions, they do not significantly impact outdoor performance, most likely due to rapid morning stabilization upon light exposure. These findings provide experimental validation for stabilization procedures in testing standards and demonstrate that properly conducted indoor UVID tests can reliably predict long-term outdoor performance, enabling more accurate module reliability assessments for the photovoltaic industry.