When Chris Bartle sees a reservoir, he doesn’t see just a body of water. He sees the future of solar power in the U.S.

Bartle, the U.S. business development manager for Ciel & Terre, one of the country’s largest floating-solar developers, said reservoirs owned by water districts and the federal government are ripe for solar farm installations. That is especially true in California and other densely populated regions where it’s sunny, and land values and renewable energy demand are both high.

“Where you’re land-constrained—where there’s other uses of the land—that’s where floating [solar] makes the most sense,” Bartle said. “Solar is maturing. This is a hot spot that’s about to take off in the U.S.”

Though the largest floating solar installations are in Asia and Europe, “floatovoltaics” represent a frontier in solar power development in the U.S., where only a handful of small floating solar farms have been built so far.

Desert Expansion

Global floating solar power production capacity could grow from about 1 gigawatt to many times that in the coming years, according to the World Bank and the National Renewable Energy Laboratory (NREL).

The World Bank estimated last year that floating solar farms built on reservoirs have the potential to generate 400 gigawatts of power globally—more than all the solar power generating capacity existing worldwide in 2017.

Floating solar technology has the potential to supply the U.S. with up to 10 percent of its electricity if all the suitable reservoirs in the country were equipped with solar panels, according to NREL research published Dec. 27.

“I think we’re going to see it really expanding in areas that are arid—areas where water evaporation is an important issue,” NREL analyst and study co-author Jordan Macknick told Bloomberg Environment.

Cutting Evaporation

Water-bound solar panels have a side benefit: In hot, dry regions, they block sunlight from reaching the surface of a lake, reducing the amount of water lost to evaporation, conserving water and saving the reservoir owner money, Macknick said.

However, more research needs to be done to determine how much money and water a reservoir owner could save by floating a solar farm on the lake surface, he said.

California, where the first floating solar installation in the U.S. was built at a winery in 2008, is ideal for the technology, especially in the Central Valley where solar and agriculture can conflict, said Rebecca Hernandez, an assistant professor studying arid land energy development at the University of California-Davis.

“Floatovoltaics to me are one way we can really see a lot of benefits both economically and environmentally at a time when we really need to shore up our renewable energy resources in a rapid manner,” Hernandez said.

California passed a law last year that all the state’s energy come from renewable sources by 2045—a measure designed to cut the state’s carbon footprint.

Reservoirs in California’s Central Valley are ideal for solar installations because water managers in the hot, dry climate need to cut their losses to evaporation, and agricultural producers want to reduce their conflicts with solar power development, Hernandez said.

Confusing to Birds

Despite the promise of the technology, environmental groups caution that the ecological impacts of floating solar need to be fully understood.

Birds rely on water bodies for food and habitat, and lake ecosystems—including aquatic plants—need sunlight reaching the lake surface, said Nathanael Greene, senior renewable energy advocate for the Natural Resources Defense Council.

“Anywhere we put [solar], whether on land or on water—the ecological impacts, we have to take those seriously and understand them,” Greene said.

Though floating solar is a promising technology, its risks to wildlife have not been quantified, Hernandez said.

Birds may easily mistake floating solar panels for the water the panels are floating on, and crash into them, she said.

The World Bank and NREL estimates for floating solar potential focus only on reservoirs, where developers say the ecological impacts of the technology are likely smaller than they are on natural water bodies.

“We’re not going after Lake Tahoe and recreational lakes and ponds,” Bartle said. “We’re sticking with man-made reservoirs.”