Moisture Ingress and Distribution in Bifacial Silicon Photovoltaics

Water participates in multiple modes of degradation in photovoltaic (PV) modules including encapsulant yellowing, delamination, and contact corrosion. To mitigate moisture-induced degradation, we must understand the kinetics of moisture in state-of-the-art encapsulants and module architectures. In this article, we present a robust optical method to quantify water content in the front and rear side encapsulants of bifacial silicon PV modules, then use such measurements to validate a model for simulating water concentration in these modules. First, we quantify the solubility of water in four modern encapsulants: ethylene vinyl acetate and polyolefin, each with and without UV-blocking additives. Second, we use water reflectometry detection to measure the diffusion of moisture within glass-backsheet modules as a function of time and environmental condition. Third, we present a model of moisture transport in bifacial silicon PV modules and show it to be consistent with our measurements. Crucially, our methodology enables the separate evaluation of water content in the front encapsulant and the rear polymers within glass-backsheet modules. Overall, our work presents a quantitative picture of moisture in emerging module architectures and a framework to extend this approach other encapsulants and module designs.