Floating solar arrays are getting a lot of attention lately, and it’s not all positive

It sounds like an environmentalist’s dream: a renewable energy source that could generate 10% of the U.S.’s electricity output — and it doesn’t require land. But dig deeper into the climatic and ecological impacts of “floating solar” technology and you’ll find that while it’s still an attractive option, it may not be quite as enticing as it sounds.

The problem, explains researcher Nicholas Ray, is that when the floating solar arrays are installed on small bodies of water, they actually increase greenhouse gas emissions from those ponds while reducing dissolved oxygen levels and water temperature, which could affect aquatic life. The University of Delaware biogeochemist reported these surprising findings in December 2024, based on experiments he and his collaborators conducted in ponds at Cornell University.

Despite his concerns, Ray doesn’t advocate stifling the enthusiasm for floating solar — he just thinks its environmental impacts need to be carefully assessed, and mitigated where possible. “We have an opportunity to do this the right way,” he says. “I think it’s a great technology, but we need to be aware of what the trade-offs are.”

While floating solar is still a relatively small contributor to global power grids, it is growing fast. Over the last ten years, China alone has built enough large floating solar farms to power about 500,000 homes — more than 2,000 megawatts worth. 

The U.S. is far behind. Its biggest facility, a recently opened array in a reservoir in Short Hills, New Jersey, has a capacity of just 8.9 megawatts. But interest is growing seemingly everywhere. “It really is taking off kind of globally,” Ray says. 

It’s easy to see why. A study from the Department of Energy’s National Renewable Energy Laboratory suggests that floating solar has the capability to produce almost 10% of American electricity.

The key advantage of floating arrays is they provide renewable power without occupying open, flat land that would otherwise be ideal for agriculture. But there are other pluses, too, including a built-in cooling system for the solar panels. If they’re in contact with water, the panels potentially  perform better and therefore produce energy more efficiently — around 6% more efficiently, as researchers from Norway’s Institute for Energy Technology found. 

Housing solar panels on bodies of water may also reduce evaporation of the water, which could be advantageous in arid places. A 2022 case study in Jordan found that floating solar could decrease evaporation from an irrigation reservoir by more than 40%.

But there are some disadvantages, too. Like all solar power technologies, floating arrays generate power only when the sun is out. They also require frequent cleaning because birds tend to gather and defecate on solar panels, explains Joey Gurrentz, director of external affairs at the New Jersey Utilities Association.

Ray’s study is one of the first to investigate the full slate of potential environmental impacts of floating solar. He and his team did so by installing solar panels on three ponds at Cornell and comparing their carbon dioxide and methane emissions to three uncovered ponds. They found that the ponds with floating solar — representing the small bodies of water that house most floating solar projects work — increased their greenhouse gas emissions by almost 27% overall. 

The amount of oxygen dissolved in the water and the water temperature both decreased significantly, Ray’s research team found. He thinks these factors could have a larger impact on the biodiversity of the ponds than the uptick in greenhouse gases because they may directly affect plant and animal life in the water. His collaborators are working on further experiments to see how solar panels affect phytoplankton, aquatic plants, insect larvae and the like.

It’s likely, he notes, that solar arrays in larger bodies of water will have less of an ecological impact, since more of the water surface will remain uncovered. “In a bigger system with maybe less panel coverage, I anticipate these effects will be smaller,” but still present, Ray says.

Solar advocates also note that the environmental impacts of floating solar should be weighed against that damage caused by other sources of electricity, including fossil fuels that pollute water bodies and contribute to climate change. “It’s worth not forgetting the impacts of fossil fuels and what those do to ecosystems as well,” says Evan Jones, an associate at the advocacy group Environment America.

Ray agrees. His research found that, while floating solar arrays in ponds increased greenhouse gas emissions, two alternatives — solar power on land and hydropower — are associated with higher emissions. “It’s not so bad compared to these other energy techniques, and still much better than fossil fuels,” Ray says.

He remains optimistic about ways to mitigate the negative effects he’s observed. “There’s a lot of possible ideas,” Ray says. To keep greenhouse gas emission low, policy makers could institute a maximum percent of allowable surface cover on these bodies of water. He also suggests changing the angle of the solar panels so that there’s more opportunity for wind to interact with the water’s surface, which would increase oxygen levels and allow greenhouse gases to vent. 

The fix he finds most promising, though, is the use of aerators to add oxygen to the system and reduce methane emissions. “There’s a ton of pumps and aerators on the market for ponds already.” This option would be the easiest, he says.