Floating Solar Increases Greenhouse Gas Emissions on Small Ponds

While floating solar – the emerging practice of putting solar panels on bodies of water – is promising in its efficiency and its potential to spare agricultural and conservation lands, a new experiment finds environmental trade-offs.

In the first manipulative field study examining the environmental impacts of floating solar, published Dec. 6 in Environmental Science and Technology, researchers found that floating solar panels increased greenhouse gas emissions on small ponds by nearly 27%.

“There have been a flurry of papers about floating solar, but it’s mostly modeling and projections,” said Steven Grodsky, assistant professor of natural resources and the environment and assistant unit leader of the New York Cooperative Fish and Wildlife Research Unit in the College of Agriculture and Life Sciences, as well as a faculty fellow at the Cornell Atkinson Center for Sustainability. “This is the first manipulative study to produce empirical results. It’s saying, here’s what’s actually happening. And what we found was that there was increased greenhouse gas emissions from ponds with floating solar.”

Grodsky and collaborators covered three ponds at the Cornell Experimental Pond Facility with solar panels, at 70% coverage, and found that, almost immediately, methane and carbon dioxide emissions increased – by 26.8% compared to ponds without solar panels – and dissolved oxygen throughout the ponds substantially decreased.

“If you put floating solar on there,” Grodsky said, “you’re drastically reducing oxygen availability for organisms, you’re messing with ecological processes, how decomposition takes place, the microbes, the way wind moves across the surface of the water. It’s all connected.”

The data is particularly important because much of the floating solar development in the U.S. is currently happening on small lakes and ponds, Grodsky said. It’s also timely for New York state, where floating solar could be considered as an alternative to terrestrial solar and is the source of debate and exploration. Proponents in the state include U.S. House Representative Paul Tonko (D-20th District), who co-sponsored legislation in 2023 that called for assessments and development of U.S. reservoirs as floating solar sites, for example.   

The study offers some bright sides for floating solar: When comparing floating solar to terrestrial solar in total emissions cost, from site development to maintenance and disposal, the floating solar’s greenhouse gas emissions (per kilowatt hour of energy generated) are likely still lower than terrestrial solar and fossil fuel-based energy production. Seventy percent coverage also represents an outer limit, and the researchers made suggestions that might offset the panels’ impacts, like reducing coverage or installing a bubbler to agitate the water, although more research is needed.

“It’s all about trade-offs,” Grodsky said. “But we need to be aware of what’s happening to be able to adapt – maybe siting differently, or designing the panels differently, or changing the percentage of cover.”

The paper is part of a broader effort in Grodsky’s lab to incorporate environmental and social considerations into assessments of floating solar’s potential – and to help developers and regulators make more informed decisions.

“If you look at the history of energy transitions – from wood to fossil fuels, for example – everything was based on energy production, and the environment wasn’t taken into consideration, and now we have environmental injustice, we have climate change,” Grodsky said. “The idea here is to nip that in the bud and re-envision the way we approach this energy transition.”

Reference: Ray NE, Holgerson MA, Grodsky SM. Immediate effect of floating solar energy deployment on greenhouse gas dynamics in ponds. Environ Sci Technol. 2024;58(50):22104-22113. doi: 10.1021/acs.est.4c06363

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