Deciphering the thermal behavior of floating photovoltaic installations

Floating photovoltaic systems are an attractive, emerging concept to extend the area available for solar energy production to the water. Among the advantages of floating PV, frequently a cooling effect is mentioned. Yet little to no quantitative information about this cooling is provided in available literature. In this study, we present observations that challenge the role of water for photovoltaic module cooling. When comparing temperatures of two photovoltaic installation in Cambodia, we found that photovoltaic modules from a commercial floating installation at noon were significantly (9.1 ± 2.8 K) hotter than those from a nearby, small-scale installation on a metal rooftop. This large difference was all the more unexpected because the rooftop installation was on top of a room with electronic equipment that generated additional heat. When reproducing the temperatures of either system by modeling, we found that the most likely cause for this temperature difference is different exposure to wind of the two installations due to different PV module heights. Comparing temperatures at night, we find that the floating installation is 1.2 ± 0.5 K cooler than the rooftop installation. This difference can likely be attributed in parts to evaporation cooling. We conclude that the presence of water is a minor- or an indirect factor in the thermal balance of floating photovoltaic installations. Exposure to wind and module height are the differentiating elements for photovoltaic system cooling, at least in areas with small overall wind speeds.