Correlation between EVA Degree of Crosslinking and Moisture Ingress into PV Laminates
The degradation of a PV module is strongly influenced by moisture ingress. Previously most of the investigations of the diffusion properties of encapsulants and backsheets were carried out on the polymer sheets alone, and thereby not accounting for diffusion properties of all involved materials. In this work, the kinetic study of the water uptake of the EVA was performed inside the laminate stack, using incorporated miniature digital humidity sensors at different EVA depths. Samples with different polymeric materials and lamination conditions were aged under a damp-heat (DH) and UV/DH (combined) conditions while applying an in-situ moisture monitoring technique for PV modules. From this data, we calculated the respective diffusion rates and determined how the different materials and lamination conditions affect the mechanism of moisture ingress/egress during the aging tests. The results demonstrate a faster diffusion in the CPC backsheet than in the TPT backsheet type. With respect to the lamination process, the effective activation energy (EAeff), calculated assuming an Arrhenius-like behavior showed slower moisture ingress for the shortly laminated sample. Furthermore, the effect of the UV irradiation on the diffusion behavior during the combined UV-DH aging test is presented.