Impact of Gel Content on Water Vapour Transmission Rate and Damp Heat Reliability of EPE Encapsulants in High-Power Photovoltaic Modules

Abstract— Encapsulants play a critical role in the long-term reliability of photovoltaic (PV) modules as per IEC, particularly under hot and humid climatic & other environmental conditions. EVA -POE -EVA (EPE) encapsulants are increasingly used in high-power solar modules due to their lower water vapour transmission rate (WVTR) and improved PID resistance. However, wide variability in encapsulant formulation and crosslink density leads to significant reliability differences. In this study investigates the influence of gel content on WVTR and damp heat test (DHT) as per IEC 61215 degradation behavior of 625 Wp PV modules using EPE encapsulants from multiple suppliers. Modules were subjected to extended DHT up to 3000 hours. Measured power degradation trends are correlated with gel content and inferred moisture ingress behaviour. Results clearly show that optimally crosslinked EPE encapsulants (75–90 % gel content) exhibit the best long-term reliability, while both under- and over-crosslinked materials suffer accelerated degradation. Index Terms—Photovoltaic module reliability, EPE encapsulant, gel content, WVTR, damp heat test, moisture ingress.