What is the primary mechanism by which ethylene vinyl acetate (EVA) degradation affects the performance of a PV module, and how can this degradation be quantified?

The primary mechanism by which ethylene vinyl acetate (EVA) degradation affects the performance of a PV module is through discoloration, specifically yellowing or browning. EVA is a polymer used to encapsulate the PV cells within a module, providing electrical insulation and mechanical support. When exposed to ultraviolet (UV) radiation, heat, and humidity over time, EVA undergoes chemical changes that lead to the formation of chromophores, which are molecules that absorb light in the visible spectrum. This discoloration reduces the amount of light that reaches the PV cells, effectively shading them and reducing the module's short-circuit current (Isc) and overall power output. EVA degradation can be quantified through several methods. One is measuring the transmission loss of the EVA material using spectrophotometry, which determines how much light of different wavelengths passes through the degraded EVA compared to fresh EVA. Another is through measuring the yellowness index (YI), a single number that describes the degree of yellowness of the EVA. Furthermore, accelerated aging tests in controlled laboratory conditions can simulate long-term exposure to environmental stressors, allowing for prediction of degradation rates and expected lifetime.