INFLUENCE OF MVTR OF AIR-SIDE LAYER OF BACKSHEET ON THE RELIABILITY OF BACKSHEET ITSELF AND CONSEQUENTLY ON THE RELIABILITY OF SOLAR PV MODULE

摘要

Moisture Vapour Transmission Rate (MVTR), also called Water Vapour Transmission Rate (WVTR) of air-side layer of PV Backsheets plays a significant role on the performance and durability of Backsheet and consequently on the reliability of the PV module. This study reveals that the performance and the reliability of photovoltaic modules are highly influenced by the MVTR of the air-side layer of Backsheet if the core layer of the Backsheet is Polyester based. The Backsheet manufactured using air-side Hydrolysed PET (HPET) layer having lower MVTR value shows less hydrolytic degradation of the core layer PET as compared to Backsheet made of Fluoro materials as air-side layers having higher MVTR value. Backsheets with air-side layer having lowest MVTR shows lowest degree of hydrolytic degradation irrespective of types of Backsheets. The Backsheet with structure HPET / PET / Priming layers shows better hydrolytic resistance than all remaining Fluoro based structures considered in the study. The Solar PV module having HPET / PET / Priming layer Backsheet showed lowest power loss (max 3%) up to damp heat 2500hrs. Whereas, the Modules made using Backsheet structure with Fluoro polymer as airside layer having higher MVTR value (Fluoro-2 / PET / Priming layer & Fluoro-3 / PET / Priming layer) showed more power loss ( ＞5%) after the DHT of 2500hrs. Cracking of core layer PET was observed in the modules made using Backsheets with Fluoro materials. Backsheet structure with Fluoro-1 polymer having lower MVTR value (Fluoro-1 / PET / Priming layer) showed power loss ＜ 4 % after the DHT of 2500hrs. In this study we found that when Fluoro materials are used in the Backsheet as sir-side layer, it remains stable itself for a longer time but due to its poor moisture barrier, the core layer PET of the Backsheet gets hydrolysed faster with time. This phenomenon of hydrolysis reduces the mechanical strength of the core layer PET causing mechanical cracks. Once the cracks in the Backsheet are developed, it leaves almost no protection towards moisture ingress from climate to the module, causing rapid degradation in the cells and interconnects reducing the performance and the durability of the module.