Water as a Battery: Pumped storage hydropower gets rejuvenated

By Oct 14, 2022

When you hear the term “energy storage,” you might picture large lithium batteries housed in shipping containers.




When you hear the term “energy storage,” you might picture large lithium batteries housed in shipping containers. While a burgeoning market, it is not the biggest by far. That honor goes to pumped storage hydropower (PSH). The U.S. Department of Energy (DOE) estimates PSH represents 93% of all U.S. utility-scale energy-storage capacity. It has been helping provide clean grid power for over a century. PSH seems to be an energy-storage option hidden under a bushel. The hydropower industry would like to turn that bushel right side up as the energy-storage marketplace grows.

The forgotten giant

“When we talk about hydropower, it really is the forgotten giant of renewables,” said Alex Campbell, head of research and policy for the International Hydropower Association (IHA), London. “Today it represents more than wind and solar combined.”

Globally, the top three countries invested in pumped hydro are China (35 gigawatts and aggressively growing), Japan (25 GW) and the United States (22 GW), Campbell said. European Alpine nations are fourth. Of the 1,360 GW of total hydro-produced power in the world, about 10% (163 GW) represents PSH.

In terms of hydroelectric power, the Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tenn., estimated that in 2021 there were 130 new U.S. hydropower projects in the development pipeline, offering a combined capacity of 1,501 megawatts (MW).

“That’s less projects than one year earlier, but the ones that have entered the pipeline were bigger on average than the ones that left,” said Rocio Uria-Martinez, ORNL researcher and one of the main authors of the DOE’s “U.S. Hydropower Market Report, January 2021.”

During this same period, 96 new PSH projects were proposed, three of them already licensed by the Federal Energy Regulatory Commission (FERC).

“If the three newly licensed PSH projects move to construction, they would increase installed U.S. PSH capacity by [about] 10% (2.1 GW),” she said. “The combined capacity of all proposed PSH projects as of end of 2021 would more than triple the capacity of the existing fleet.”

Though “triple” would surpass a previous estimate of 72.7 GW delivered through hydro storage, Uria-­Martinez did emphasize only a small fraction of projects in early development make it to licensing. Currently, 43 PSH plants are in operation in the United States, with a total installed capacity of 21.9 GW and 553 GWh of energy storage.

One important question

So, this question arises: how can it be that pumped hydro represents more than 90% of grid electricity storage in the world, yet it seems like a new idea to so many?

“One hypothesis is that not having had new investments in this technology in decades has made it progressively less known among the public,” Uria-Martinez said. “In the United States, the last large-scale pumped storage facility in this country started operation in 1995.”

Campbell added that better marketing can help raise the profile of PSH. His organization launched its “We Can, With Hydropower” campaign, with a focus on pumped storage in concert with wind and solar. In 2019, the DOE’s Water Power Technologies Office introduced HydroWIRES, an initiative to reintroduce the merits of hydropower and PSH and promote it as a cost-effective and flexible addition to renewable resources energy storage within the U.S. electricity system.

For the record, the United States has the fourth-largest conventional hydropower fleet in the world and is the third largest in the world for pumped storage operations.

Hello, it’s me again

A rediscovery of PSH seems to be underway as it provides longer power duration.

“Batteries are excellent at four hours of storage, but beyond that they become very costly,” Campbell said. “Pumped hydro offers a 4- to 10-hour period. Larger facilities can generate 2 GW [or more], extending storage power 10 to 12 days. Additionally, you need deep storage like pumped hydro offers when the weather is not playing ball with other forms of renewable energy [e.g., solar and wind]. If you want to provide grid services with quick response for a couple of hours, battery storage is great. But for deep reliance over half a day or longer, pumped hydro is a solution.”

Campbell added that while natural gas disrupts the PSH market, with more solar and wind coming online as a clean energy source, pumped storage is getting a renewed look. Federally, the Infrastructure Investment and Jobs Act allocated $1 billion for hydropower development.

How it works and what’s new

Pumped hydroelectric stations use water storage as a battery. During grid peak periods, water from an upper reservoir is released through tunnels to a lower reservoir that is either manufactured or natural, such as a river. 

The released water spins turbines to produce electricity. When energy demand is low, the water can be pumped back to the upper reservoir for storage until additional power generation is needed. This is called open loop.

A closed loop can deliver energy further from the source. It does not involve a connection to an outside body of water. Both methods require power from a generator/motor or powerhouse and a submerged turbine/pump.

“The closed-loop concept allows more siting flexibility,” Uria-Martinez said.

Closed-loop siting can be closer to residential, commercial and industrial customers. In addition, PSH energy could cross county borders and possibly state lines, if allowed.

HydroWIRES’ “A Review of Technology Innovations for Pumped Storage Hydropower, April 2022,” produced by Argonne National Laboratory in Lemont, Ill., reviewed 12 new or developing PSH technologies. Argonne found three had the best potential for U.S. deployment. 

These include submersible motor-generators avoiding the construction of an aboveground power house; geomechanical PSH (releasing water pumped and held between specific rock layers) that can lower cost and open siting to locations not previously amenable to PSH; and repurposed, decommissioned open-pit mines as PSH reservoirs.

The study also found that closed-loop PSH projects could add significant energy storage with minimal environmental impacts, avoiding new dams on rivers and waterways. The report’s authors are confident PSH can “serve as the backbone” in decarbonizing the grid.

While drought in the West impacted hydropower (U.S. electricity generation decreased 3% in 2020 relative to 2019), installed capacity increased by more than 100 MW that year thanks to six new hydro projects coming online (e.g., RC Thomas Hydroelectric Project/Lake Livingston, in Texas), and refurbishments/capacity additions for 10 hydroelectric plants.

“Even though hydropower generation in the Southwest was near the bottom of the 2010–2020 range, the rest of the fleet produced at average values (Northwest) or near the top of the 2010-2020 range (Midwest, Northeast, Southeast),” Uria-Martinez said. “Therefore, the average or better-than-­average generation levels in the rest of the country offset the decline in the Southwest.”

New PSH projects

New pumped storage projects are on the rise domestically and aboard. The U.S. Hydropower Market Report, January 2021 shared that by year-end 2019, FERC licenses were issued for Eagle Mountain in California, Gordon Butte in Montana and Swan Lake in Oregon. Eagle Mountain (proposed 1,300 MW) is a closed-loop project that will repurpose abandoned mine pits as upper and lower reservoirs. Swan Lake (proposed 393 MW) is also closed-loop. Developers of the Gordon Butte (400 MW) closed-loop project have set a construction start deadline of December 2022.

The report’s authors reported that except for 2015, more developers in the past five years submitted preliminary permit applications each year than surrendered their permit or license. So, the number of projects in development has steadily increased.

Industry proponents of PSH point out its other advantages, which include its ability to store substantial amounts of energy for long periods of time; flexible, dispatchable generating capacity; and an economic lifetime of 50 years or more without significant performance degradation. 

Some PSH infrastructure is designed for 80 or more years of operation, if properly maintained. While replaceable, power units (pump-turbines and motor-generators) can last 30–40 years.

The largest pumped storage station in the world resides in the United States. The grid-scale Bath County Pumped Storage Station in Virginia powers an estimated 750,000 homes. Its net generating capacity is 3,003 MW. This pumped storage station is jointly owned by Dominion Energy (60%), Bath County Energy LLC (24%) and Allegheny Power System (16%). The upper reservoir is 265 acres, and the lower reservoir is 555 acres. Distributed energy resources have driven interest in smaller PSH plants of less than 10 MW.

Because of favorable geography, which typically involves a significant elevation difference between the lower and upper reservoirs, most existing U.S. PSH plants have been constructed in mountainous areas near the East and West coasts. PSH projects have also been constructed in the Midwest, including the Ludington project in Michigan (1,876 MW), which uses Lake Michigan as its lower reservoir.

The National Renewable Energy Laboratory recently completed a large-scale study of potential closed-loop PSH sites. “Closed Loop Pumped Storage Hydropower Resource Assessment of the United States,” released in May 2022, reported that spatial mapping identified nearly 15,000 suitable locations for closed-loop PSH in the continental United States, Alaska, Hawaii and Puerto Rico.

What does this mean for ECs?

While electrical contractors may have already been called to help with PSH power houses and other site power needs, a rediscovery of PSH could propel what is old to seem new again. Industry table setting will be in order, and that includes communicating the business case and value of PSH, and how it works. Its upfront capital costs are high.

“For the existing pump storage, we don’t need demos,” Campbell said. “Rather, you need to figure out what a 10- to 15-year contract might look like. Investors in forms of long-duration storage, such as pumped storage hydropower, need long-term revenue visibility. Are there incentives available to defray or reduce cost? Other innovative market models we are seeing include a mix of revenues for energy, for ancillary system services and availability payments. Collaborating with all stakeholders needs to happen to really reintroduce pumped storage as another clean energy option.”





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