Vast, Untapped Pumped Storage Potential in US

January 24, 2022

Above, Patti Poppe, now CEO of PG&E, was formerly Chair at Consumer’s Energy, the nation’s 10th largest utility, based in Michigan.
In a lecture I recorded a couple years ago, she describes how a massive pumped storage power plant on the shore of Lake Michigan will help integrate variable clean energy into the electric grid.

Only 43 such units exist in the US, but recent survey’s show potential for much more.

While battery innovations get a lot of attention, there’s a simple, proven long-term storage technique that’s been used in the U.S. since the 1920s.

It’s called pumped hydro energy storage. It involves pumping water uphill from one reservoir to another at a higher elevation for storage, then, when power is needed, releasing the water to flow downhill through turbines, generating electricity on its way to the lower reservoir.

Pumped hydro storage is often overlooked in the U.S. because of concern about hydropower’s impact on rivers. But what many people don’t realize is that most of the best hydro storage sites aren’t on rivers at all.

We created a world atlas of potential sites for closed-looped pumped hydro – systems that don’t include a river – and found 35,000 paired sites in the U.S. with good potential. While many of these sites, which we located by satellite, are in rugged terrain and may be unsuitable for geological, hydrological, economic, environmental or social reasons, we estimate that only a few hundred sites are needed to support a 100 percent renewable U.S. electricity system.

Why Wind and Solar Need Long-Term Storage

To function properly, power grids must be able to match the incoming electricity supply to electricity demand in real time or they risk shortages or overloads.

There are several techniques that grid managers can use to keep that balance with variable sources like wind and solar. These include sharing power across large regions via interstate high-voltage transmission lines, managing demand – and using energy storage.

Batteries deployed in homes, power stations and electric vehicles are preferred for energy storage times up to a few hours. They’re adept at managing the rise of solar power midday when the sun is overhead and releasing it when power demand peaks in the evenings.

Pumped hydro, on the other hand, allows for larger and longer storage than batteries, and that is essential in a wind- and solar-dominated electricity system. It is also cheaper for overnight and longer-term storage.

Off-River Pumped Hydro Energy Storage

In 2021, the U.S. had 43 operating pumped hydro plants with a total generating capacity of about 22 gigawatts and an energy storage capacity of 553 gigawatt-hours. They make up 93 percent of utility-scale storage in the country. Globally, pumped hydro’s share of energy storage is even higher – about 99 percent of energy storage volume.

Pump hydro projects can be controversialparticularly when they involve dams on rivers that flood land to create new reservoirs and can affect ecosystems.

Creating closed-loop systems that use pairs of existing lakes or reservoirs instead of rivers would avoid the need for new dams. A project planned in Bell County, Kentucky, for example, uses an old coal strip mine. Little additional land is needed except for transmission lines.

An off-river pumped hydro system comprises a pair of reservoirs spaced several miles apart with an altitude difference of 200-800 meters (about 650-2,600 feet) and connected with pipes or tunnels. The reservoirs can be new or use old mining sites or existing lakes or reservoirs.

On sunny or windy days, water is pumped to the upper reservoir. At night, the water flows back down through the turbines to recover the stored energy.

A pair of 250-acre reservoirs with an altitude difference of 600 meters (1,969 feet) and 20-meter depth (65 feet) can store 24 gigawatt-hours of energy, meaning the system could supply 1 gigawatt of power for 24 hours, enough for a city of a million people.

Little pumped storage has been built in the U.S. in recent years because there hasn’t been much need, but that’s changing. 

In 2020, about three-quarters of all new power capacity built was either solar photovoltaics or wind power. Their costs have been falling, making them cheaper to build in many areas than fossil fuels.


Michigan Technological University, with funding by the Alfred P. Sloan Foundation, is studying whether communities could transform abandoned mines into valuable energy storage. University researchers are partnering with the Marquette County city of Negaunee, population 4,500, on a pilot project that could help mining communities turn liabilities into assets.

Public concerns with the ecological impacts of water diversions and impoundments, combined with resistance to infrastructure development by neighboring property owners, has often meant that permitting utility-scale systems is difficult. “If we move the entire system below ground and make it self-contained, there would be no effect on surface water flow, ecological systems, or landscapes and scenic views. An underground pumped hydro storage system might be essentially invisible,” Sidortsov said.

The American West is rife with abandoned mines, a legacy of policies like the 1862 Homestead Act and 1872 Mining Law that enabled the settling of the region and triggered a seemingly lawless development of resources. Numerous companies and individuals abandoned many mines after extracting their precious minerals.

The most concerning situation created by abandoned mines is their threat to water resources, namely acid mine drainage, which is highly acidic wastewater that is toxic to fish and other aquatic species. It can also pose major threats to human health. The EPA estimates that 40% of the West’s headwater watersheds have been polluted by mining.

2 Responses to “Vast, Untapped Pumped Storage Potential in US”

  1. J4Zonian Says:

    A pair of 250-acre reservoirs?

    If partly covered by solar panels (let’s say half) they would produce 166 GWh/yr of solar energy; it could provide a good part of the energy stored in the reservoir and incidental on-site power, and reduce evaporation. The reservoirs would also provide rain catchment over their watershed, and if stocked with fish and educators, a food and recreation supplement and school outing site for the million people in the city.

    Especially if it were a particularly sunny spot, it might be worth using double axis tracking panels, extending production into mornings, evenings, and winters.
    If there were a fair amount of rain in the area, it might be worthwhile to equip the panels with triboelectric capability, so they could generate power from falling rain, which would of course also clean them. Since some of that would happen when the dam was producing power, an onsite battery could temporarily store that power, or it could just be fed into the grid, and/or could be used at peak production times to power and fill a small holding/settling tank for an on-site water treatment plant and pumping station to provide potable water for those onsite and nearby. While the storage may “only” be 75-80% efficient, all the other possible projects could more than make up for it.

    1 acre of solar panels produces 1820 Kwh/day average, or 664,300 KWh/yr

    • rhymeswithgoalie Says:

      Pumped-storage reservoirs are a weird type of battery where the measured “efficiency” depends in part on the rainfall patterns in the area.

      Watch out for developers/realtors who only like reservoirs for their lakeside mansion possibilities, and who would object to covering them up with solar. At least with a new reservoir, you can set the rules from the get-go, but heaven help anyone who tries to cover any existing artificial lake with the goal of reducing evaporation and producing clean energy.

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