Updated math for Grand Coulee Dam, one of the biggest hydropower plants in the United States, puts the comparison in plain terms: to match the dam’s usual 21 billion kilowatt-hours a year, you’d need at least 23 million 500-watt solar panels, and possibly many more, because each panel typically produces only about 500 to 900 kilowatt-hours a year, depending on sunlight and where it’s installed.
That scale is the real point. For one massive dam, solar can add up on paper, but only with an enormous amount of hardware. A 2019 study in Nature Sustainability did find that all U.S. hydropower could, in theory, be replaced by solar photovoltaics covering 529,885 hectares, or 1.31 million acres, roughly the size of Delaware. Even so, that’s only about 13% of the land now covered by hydropower reservoirs.
For a broader comparison, the United States still gets about 6% of its electricity from more than 1,400 hydropower plants. Solar supplied about 4% in 2023, according to the U.S. Energy Information Administration. The EIA also projected that solar would generate 14% more electricity than hydropower in 2024, and the technology keeps getting better as panel prices have fallen about 90% since 2010, with improvements in cells, manufacturing scale, and batteries.
Dams, of course, do more than make electricity. They also handle drinking water, irrigation, navigation, flood control, and firm dispatchable power. At the same time, they can damage fish migration, sediment flow, water temperatures, floodplains, and Indigenous communities, while also raising aging, cost, and safety concerns. That’s why you’re more likely to see hybrid setups like Thailand’s 45MW floating solar plus 36MW hydro Sirindhorn project, or Germany’s solar panels installed on dam walls.
You can find the study in Nature Sustainability and the U.S. generation figures from the EIA.
Author: Manuel Bosque
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