Nondestructive Detection of Water Ingress in Solar Modules Using Near‐Infrared Absorbance Spectroscopy

Moisture ingress is a key factor in the degradation of photovoltaic module components. This study employs near‐infrared absorption spectroscopy to nondestructively quantify water uptake in backsheets and encapsulants, using a water index derived from the 1910‐1920 nm absorption band. Measurements covered short‐term dynamics during rainfall, long‐term outdoor monitoring, and spatial mapping. Short‐term monitoring showed a 14% increase in the water index within 20 min of observations. Five months of rooftop measurements revealed strong sensitivity to humidity and temperature: the index rose by 75% as relative humidity increased from 20% to 50%, and fell by 50% as temperature rose from 0°C to 40°C. Comparative field campaigns in 2021 and 2023 showed material‐specific trends: under identical conditions, polyamide and fluoropolymer‐coated backsheets exhibited average water index increases of 32%, while polyvinylidene fluoride showed only a 17% increase. Changes in distribution shape indicated differing moisture resistance among materials. Gravimetric analysis confirmed material‐dependent water retention. Spatial mapping and immersion tests revealed localized moisture accumulation and saturation‐type sorption, with uptake rates—derived via kinetic fitting—ca. 27% higher in field‐aged modules than in stored ones. These results establish near‐infrared spectroscopy as a scalable and noninvasive tool for detecting moisture‐related degradation in photovoltaic modules.