Comparison of humidity-induced stress levels between floating and ground-mounted photovoltaics

Summary

Floating photovoltaic (FPV) modules operate above water, leading to concerns about increased humidity-induced degradation compared to ground-mounted PV (GPV) modules. However, data to assess FPV degradation are limited. This study addresses this knowledge gap by analysing multi-year meteorological datasets from seven inland water bodies and nearby locations on land and subsequently calculating module temperatures, relative humidities (RH), and moisture ingress profiles. Ambient and module temperatures over water and land were similar (absolute mean differences of under 2 °C), while RHs over water surfaces could be higher or lower than over land (absolute mean differences of up to 9 percentage points), depending on location. Over land, diurnal fluctuations in temperature and RH were higher than over water, attributed to the stabilizing influence of water bodies. Modelled internal moisture contents were almost always higher in GPV modules than in FPV ones (up to 37% higher mean concentration). Lastly, the effects of FPV system design on humidity-induced stress were studied by varying module height above water and system heat transfer efficiency. This led to changes in internal moisture contents (up to 47% and 42% differences in mean moisture concentration, respectively) that often exceeded the observed water-land differences, indicating the importance of FPV system design on humidity-induced stress. This study challenges the commonly held assumption of universally greater humidity-induced stress in FPV systems and highlights the critical role of site-specific factors and system design, thereby advancing the understanding of FPV reliability.