Site-specific relationships between algal biomass and floating photovoltaic solar energy in human-made bodies of water

Cagle, Alexander E. and Narwold, Benjamin P. and Armstrong, Alona and Sadro, Steven and Pasquale, Giulia and Di Blasi, Miriam Lucia Vincenza and Hernandez, Rebecca R. (2025) Site-specific relationships between algal biomass and floating photovoltaic solar energy in human-made bodies of water. Frontiers in Water, 7: 1614008. ISSN 2624-9375

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Abstract

Eutrophication and climate-driven warming are degrading aquatic ecosystems by promoting harmful algal and cyanobacterial growth, while global decarbonization efforts are intensifying land-use conflicts for renewable energy. Floating solar photovoltaic (FPV) systems—solar panels installed on human-made waterbodies—offer a potential solution, yet their effects on algae and water quality remain poorly understood. We assessed algal biomass and water quality beneath FPVs and in open water at four FPV-hosting ponds across the United States, spanning a range of FPV coverage levels, trophic states, climates, and bathymetry. Sampling occurred twice daily across all seasons from 2021 to 2022. Results showed minimal overall differences in phycocyanin, chlorophyll-a, dissolved oxygen, pH, conductivity, and temperature between FPV-covered and open-water areas, though some site-specific trends emerged. At one mesotrophic site (4.8% coverage), chlorophyll-a and phycocyanin were significantly lower beneath FPVs in multiple seasons, with up to 80% reductions in chlorophyll-a observed in spring. In contrast, at a eutrophic site (22% coverage), chlorophyll-a was occasionally higher beneath FPVs, while two mesotrophic sites with high coverage (60–71%) showed no consistent differences. Dissolved oxygen and temperature exhibited limited site-specific variations but no consistent trends across FPVs. Overall, within-pond differences in algal biomass and water quality between FPV-covered and open-water areas were largely minimal, underscoring the need for further research with more FPV sites, before–after control–impact designs, and high-frequency monitoring to better understand FPV–algae interactions and potential water quality benefits.