Measurement and Simulation of Moisture Ingress in PV Modules in Various Climates

Moisture plays a critical role in the degradation process of photovoltaic (PV) modules in field conditions. A commonly used approach is to evaluate the properties of PV materials by conducting tests in climatic chambers, and then apply the Fickian diffusion model in simulations to replicate field conditions, however, without experimental verification. This study describes an experimental setup for in situ measurement of moisture in fielded minimodules, using miniature temperature and humidity sensors encapsulated within the modules. Five identical setups are deployed in different climatic regions around the world, enabling a quantitative evaluation of moisture diffusion in the field and a comparison of different climates. The relative humidity measured beside the cell follow weekly weather trends due to breathable backsheet, whereas the sensors in front of the cell react much slower to outside changes and follow seasonal trends. We show that a single 2-D simulation, which is a standard practice in published studies, is insufficient to accurately depict moisture diffusion in front of the cell. Therefore, a two-stage 2-D simulation model, combining Fickian diffusion in vertical and horizontal cross section with carefully set boundary conditions, was introduced. A comparison with measurement results showed the simulation approach to be a good compromise between the simulation accuracy and speed. Finally, the results underscore the significance of understanding the local microclimate surrounding the modules, including the interface between air and backsheet, which is necessary for precise moisture diffusion simulations.