Lateral distribution of the degradation of encapsulants after different damp-heat exposure times investigated by Raman spectroscopy

PV modules have to have a service lifetime of more than 20 years. It is hard to follow suitable degradation indicators during service life testing with sufficient accuracy for reliable service life estimation. Often the polymeric encapsulation material, mostly ethylene vinyl acetate, shows degradation effects. The detection of small changes of the material in a non-destructive manner helps to follow the changes over time during indoor testing. PV modules with crystalline Si-cells of seven German manufacturers were analyzed after accelerated ageing tests with Raman spectroscopy. This technology allows non-destructive measurements of the encapsulation material through the glazing so that the degradation of the samples can be followed by measuring after different exposure times. Samples had been exposed to damp-heat conditions for up to 4000 h. The results show significant differences in the materials degradation above the edges and the center of the cell. With increasing exposure times, it becomes apparent that the degradation process starts near the edges of the cells and propagates towards the center, indicating the impact of diffusion processes.