Probing Dynamic Influence of Moisture Ingress on Cell Deflection in Photovoltaic Modules

Investigations into photovoltaic (PV) modules are driven by the desire to increase their reliability and lifetime, thereby decreasing the levelized cost of electricity (LCOE) and improving the bankability of PV installation projects. Critical to both the reliability and lifetime of a module is the mechanical stability of the cell since cell cracking accounts for up to 8% annual degradation in power output. This study uses Water Reflectometric Detection (WaRD) and X-Ray Topography (XRT) to investigate the effects of water incorporation on the encapsulated cell deflection in-situ. Repeated XRT imaging of the cell as it dries from pre-conditioning at
$85^{\circ}\mathrm{C}$
and 85% relative humidity show changes in the obtained diffraction signal over time, corresponding to changes in cell deflection. Measurements of local water concentration over time show that water diffuses out of the rear of module after saturation through the backsheet, while moisture remains in the encapsulant on the front side of the module. We show that drying out from a humid condition can increase the curvature of the cell near its edges, which we hypothesize is due to changes in encapsulant strain or modulus as water diffuses out of the rear EVA. We have shown that the cell responds mechanically to changes in environmental humidity, raising the question of the role of humidity in fatigue, mechanical cycling, and cell cracking as the module ages.