Floating solar panels can fully power thousands of cities

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Thousands of cities around the world could power themselves completely with solar panels floating on top of water reservoirs, according to new research. It is a relatively easy way to generate renewable energy locally and save water at the same time.

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

When it comes to problems that need to be solved quickly in a warming world, floating solar panels tick a lot of boxes

Researchers found that 6,256 cities in 124 countries could theoretically cover all of their electricity demand with solar panels on nearby water reservoirs. They should cover only 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 the potential energy generation using realistic climate data.

And since all those floating arrays would block enough sunlight to reduce evaporation, the researchers also predicted big water savings. Cumulatively, the panels would save about as much water as 300 million people could use annually (or about 106 cubic miles per year). That would be incredibly helpful as droughts, exacerbated by climate change, are draining reservoirs.

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. Drought limits hydropower generation as water levels fall. And heat waves can reduce a solar panel’s efficiency by as much as 25 percent, meaning it can’t convert as much sunlight into electricity. Fortunately, water has a cooling effect that can prevent solar cells from overheating. Crucially, floating solar farms and hydroelectric dams working together could boost power generation during hot summer days when people need more electricity for air conditioning.

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

To be sure, developers will still need to review each reservoir to narrow down any negative side effects. Covering too much of the reservoir with solar panels, for example, can reduce the amount of oxygen in the water, which can be harmful to fish. Building on artificial reservoirs rather than natural bodies of water could be a less damaging option, the study notes.

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

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