Thousands of cities around the world could power themselves entirely with solar panels floating atop water reservoirs, according to new research. It’s a relatively easy way to generate renewable energy locally while also conserving water.

Solar arrays suspended over water, or floatovoltaics, work similarly to those spread out over land. The panels sit on a raft instead of on parking lots, rooftops, or other grounded mounts. But they haven’t been deployed in many places around the world yet and only produced as much electricity as less than 1 percent of the world’s land-based solar farms in 2020. Now, a new study published in the journal Nature Sustainability shows just how much potential cities could tap into with this emerging technology.

Researchers found that 6,256 cities across 124 countries could, in theory, meet all their electricity demand from solar panels deployed on nearby water reservoirs. They would just need to cover about 30 percent of the water’s surface with floatovoltaics. The researchers analyzed 114,555 reservoirs around the world using multiple databases and then modeled potential power generation using realistic climate data.

And since all those floating arrays would block enough sunlight to reduce evaporation, the researchers also projected major water savings. Cumulatively, the panels would conserve about as much water as 300 million people might use annually (or roughly 106 cubic kilometers per year). That would be incredibly helpful as droughts made worse by climate change suck reservoirs dry.

In fact, when it comes to problems that need to be solved quickly in a warming world, floating solar panels tick a lot of boxes. Droughts curtail hydroelectricity generation as water levels drop. And heatwaves can reduce a solar panel’s efficiency by up to 25 percent, which means that it isn’t able to convert as much sunlight into electricity. Luckily, water has a cooling effect that can keep solar cells from overheating. Crucially, floating solar farms and hydroelectric dams working in tandem can boost power generation during hot summer days when people need more electricity for air conditioning.

There are other practical benefits, too. On land, large solar farms might compete for space with other priorities like agriculture or habitat conservation. Floating on water reservoirs, photovoltaic panels can avoid those disputes.

To be sure, developers will still need to assess each reservoir to limit any negative side effects. Covering too much of the reservoir with solar panels could result in less oxygen in the water, for instance, which could harm fish. Building on artificial reservoirs rather than natural bodies of water might be a less damaging option, the research notes.

The study found the most potential for floatovoltaics concentrated in places where there are already many communities living next to water reservoirs. These tended to be smaller populations of less than 50,000 people, similar to a city the size of Burlington, Vermont, or Harrisburg, Pennsylvania. Just 15 percent of the cities studied with populations bigger than 1 million people would be able to meet their entire electricity demand purely with floating solar farms. The United States is the country with the most suitable reservoirs, followed by China and Brazil.

Some floating solar projects are starting to take off. The US army deployed its first floating solar array last June at Fort Bragg in North Carolina. Floatovoltaics are already more popular in Asia. Above, you can see NASA’s satellite images of one of the world’s largest floating solar farms so far, which came online last year in Shandong province. And South Korea has more than 92,000 solar panels fashioned into the shape of plum blossoms floating atop a 12-mile reservoir in its Hapcheon County.