Floating photovoltaics (FPVs) are solar power plants installed on water bodies, wherein the photovoltaic (PV) panels are assembled on floats and metal frames. Recently, these systems have been deployed rapidly, owing to the growing demand for renewable energy and the advantages offered by the technology. Solar arrays placed on water surfaces do not affect other land-use types. Furthermore, the water keeps the PV systems cool, increasing the efficiency of the panels by approximately 5% compared to that of land-based PVs. Shading can affect the water quality in shallow ponds, particularly with respect to photosynthesis; however, the literature on FPVs installed in ponds is limited. To address this gap in the literature, we investigated the effects of FPVs installed in ponds on phytoplankton growth.
In Japan, nearly 90% of FPVs are installed in irrigation ponds. We selected an irrigation pond located in Japan (area =18,000 m2; average depth = 4 m) as the study region; 33% of the pond was covered by an FPV facility that we operate. Measurements were performed during summer, a period known for active phytoplankton proliferation, at two different sites: (i) underneath the FPV facility and (ii) in open water. Underneath the FPV facility, we observed 93% and 60% reduction in the irradiance on the water surface and the near-surface wind speed, respectively. The pH and dissolved oxygen levels remained relatively low, suggesting photosynthesis suppression in phytoplankton. However, the chlorophyll-a concentration in the surface water underneath the FPV facility was higher than that observed in open water. We hypothesized that the convection produced by the temperature difference between the covered and uncovered regions could be attributed to phytoplankton accumulation, resulting in the difference in the chlorophyll-a concentrations between the two sites. To test the hypothesis, we observed the movement of floating balls below the water surface. When the water temperature underneath the FPV facility was 0.4 ℃ lower than that in open water, the balls moved towards the facility. The results supported the hypothesis that the phytoplankton were transported towards the FPV facility due to convection and that the shading effect suppressed their photosynthesis and proliferation.
Overall, our study demonstrates the potential use of FPV systems in eutrophication management and ecological preservation.