Floating solar has massive potential in the US

When we think of solar, we tend to picture shimmering expanses of panels spread across farmland or mounted on rooftops. But how about attached to a raft, floating atop a reservoir?

Floating solar photovoltaics, also called ​“floatovoltaics,” is an emerging technology that’s taken off in countries across Asia and Europe, especially near urban areas with limited space available for land-based solar.

It’s also an untapped resource for the U.S. clean energy transition, according to a new study by researchers at the Department of Energy’s National Renewable Energy Laboratory. They found that federally owned or managed reservoirs could hold enough floating solar to produce up to 1,476 terawatt-hours of clean electricity — enough to power about 100 million homes each year.

“We know we’re not going to be able to develop all of this. But even if you could develop 10% of what we identified, that would go a long way,” said Evan Rosenlieb, geospatial scientist and study co-author.

Even under the most conservative scenario the researchers considered, the potential of floating solar equals more than half of the solar capacity required for a fully carbon-free grid in the U.S. in 2050.

Besides minimizing land use, floating solar shades water bodies, which reduces evaporation and conserves limited water supply at reservoirs. Water also cools down the panels, making them up to 15% more efficient than land-based solar.

But so far, floating solar only makes up a tiny fraction of the U.S. solar market and is mostly limited to small-scale projects, including at a wastewater treatment plant in Healdsburg, California; a reservoir in Cohoes, New York; and a lake at the Fort Liberty military base in North Carolina. The country’s largest floating solar project is an 8.9-megawatt installation at a water treatment plant in Millburn, New Jersey.

Compare that with projects like Thailand’s 45-MW floating solar farm in the Sirindhorn Dam reservoir, or China’s massive 550-MW system that sits atop a body of water used for fish farming in the city of Wenzhou. ​“In the United States, we don’t have a single project over 10 MW,” said study co-author Aaron Levine.

Floatovoltaics are often installed on reservoirs, water treatment ponds, and other human-made bodies of water, as currents, tides, and salt water can damage solar panels.

The NREL study specifically focused on the siting potential at federal reservoirs, including ones at hydropower projects, which could enable hybrid energy systems that produce both solar and hydropower. Floating solar at hydropower sites could take advantage of existing transmission infrastructure and provide backup power in case water levels drop during a drought, for example.

Researchers narrowed down which sites could feasibly host floating solar based on a range of technical criteria. For example, overly shallow reservoirs and those with strong currents were excluded. So were bodies of water located anywhere with extremely low temperatures, since projects typically cannot withstand high amounts of ice and snow.

The remaining federal reservoirs that could support floating solar are scattered across the country, with Texas, California, and Oklahoma taking the lead in potential capacity. More than half of the potential projects could generate between 10 MW and 1 gigawatt of power each, with a median capacity of 123 MW.

The study didn’t consider social, economic, or legal limits to developing floating solar, such as environmental regulations, the availability of transmission lines, and project costs. Those factors are ​“likely to be substantial,” NREL scientists noted. Meanwhile, research on the environmental impacts of floating solar is still nascent, limiting scientists’ understanding of how projects affect water quality and aquatic life.

But this study adds to the growing evidence that floating solar could supercharge clean energy production.

A 2018 study that looked at a broader range of reservoirs, including ones not federally owned or managed, estimated 2,116 GW of U.S. floating solar capacity. NREL researchers called that finding ​“broadly compatible” with their own study. Another study last year estimated that covering 10% of the world’s lakes and reservoirs with floating solar could generate four times the annual power consumed in the United Kingdom.

NREL researchers hope that their latest study will further illuminate not only the potential of floating solar, ​“but also where this capacity may be more likely to be built.”