Spatially Resolved Degradation of Solar Modules in Dependence of the Prevailing Microclimate

In this work, a holistic approach to analyze solar module degradation is undertaken. The degradation kinetics of UV additives in the ethylene-vinyl acetate copolymer (EVA) encapsulant are derived using a quantification method. In addition, minimodules are analyzed after combined accelerated aging (UV irradiation at 85$^\circ$C and 60% relative humidity) at different positions. In this way, the local degradation reactions of the encapsulant are determined as a function of the prevailing stressors and additive consumption. These findings are correlated with the electrical characterization ($I-V$ and electroluminescence measurements) to expand the understanding of module degradation. Performance losses are mainly due to a combination of hydrolysis and Norrish type II reactions of the encapsulant, as acetic acid is produced in both cases corroding the electrical contacts. Independent of the local stressor, the UV stabilizer shows first-order degradation kinetics, which is directly linked to the degradation of the encapsulant and, thus, indirectly to cell degradation. It is shown that the UV stabilizer consumption is an early precursor of module degradation and could be utilized to evaluate the remaining lifetime of a PV module.