A new study details how floating photovoltaics affect wind flow and irradiance in a lake, and the effect on water temperature at different depths. However, the authors say more research is needed on how to design systems to maximize the benefits of the water bodies themselves.

A team of researchers from the Fraunhofer Institute for Solar Energy Systems ISE and the University of Freiburg evaluated a floating photovoltaic (FPV) system on Lake Maywald in southwestern Germany to determine its impact on the lake's thermal properties.

In their study of a 749 kW FPV system on a lake, the researchers used extensive meteorological and hydrological measurements to study the system's effects on near-surface lateral wind flow, irradiance, water temperature and energy balance.

The team found that the uppermost water layer exhibits large variations in water temperature (ΔT w ) depending on the time of day.

"In particular, negative ΔTw values can be observed in the near-surface layer, indicating a cooling effect of the system. The depth and standard deviation of the mean water temperature difference exhibit a strong negative correlation (r = -0.87). 0 to 5 The fluctuation of water temperature difference in the m depth range was significantly higher than that in the 5 to 10 m depth range (p = 0.0007)."

According to the researchers, the findings may indicate that the impact of FPV is mainly in the upper water layer and may have different effects during the day and night, with the strongest cooling occurring in the near-surface water layer.

To determine the impact of FPV on the lake, the team used a generic lake model with global horizontal irradiance (GHI) measurements above and below the module as input. In addition, the team used data generated by small wind transmitters to analyze the differences in lateral wind speed near the surface caused by the system.

"Based on a sensitivity analysis of reduced wind, it can be observed that the effect of FPV on near-surface wind speed can have a considerable impact on the thermal properties of the lake," the study states. "Although the measured irradiance (73%) and wind (23 %) would imply an offsetting effect on climate change, but a large reduction in wind could have a stabilizing effect on stratification and significantly increase surface water temperatures in extreme years such as 2018. This in turn could further amplify climate change projections Influence."

These complexities mean that more research should be done to monitor the interaction between FPVs and water so that systems can be specifically designed "to have beneficial effects on water bodies in terms of climate change," the group said.