UC San Diego

Water accelerates various modes of degradation in silicon photovoltaic (PV) modules including encapsulant yellowing, delamination, and contact corrosion. Moisture primarily enters silicon PV modules through the polymeric module components (encapsulant and backsheet). To mitigate moisture-induced degradation, we must understand the dynamics of moisture in state-of-the-art encapsulants and module architectures. In this work, we present a robust optical method to quantify water content on the front and rear side encapsulants in bifacial silicon PV modules and use such measurements to validate a model for simulating water concentration in these modules. First, we quantify the solubility and diffusivity of water in four modern encapsulants: ethylene vinyl acetate (EVA) and polyolefin (POE) both with and without UV-blocking additives. Second, we measure water concentration within glass-glass and glass-backsheet using water reflectometry detection (WaRD), tracking the diffusion of moisture throughout the modules as a function of time and environmental condition. Crucially we separate the water content from the front encapsulant and rear encapsulant and backsheet within the glass-backsheet modules. Third, we present a model of moisture dynamics in bifacial silicon PV modules and show it to be consistent with our measurements. Finally, we apply this model to simulate the concentration profile of water typical fielded climates as a function of time, environmental conditions, cell size, and module architecture. Overall, our work presents: 1) a quantitative picture of water dynamics in industrially relevant module architectures and field conditions, and 2) a framework to extend this approach other encapsulants and module designs.