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Transforming a former coal mine into a gigantic, 287-megawatt energy storage facility is not an easy stunt to pull off, especially when the technology involves pumped storage hydropower. Only a few dozen similar facilities exist in the US, and none have been built within the past 30 years or so. Nevertheless, a new pumped storage project is beginning to take shape, and it will put Kentucky on the map as the showcase for many more to follow.
More Energy Storage For Wind & Solar Power
Called the Lewis Ridge Long-Duration Energy Storage Project, the new pumped storage facility will be located in Bell County in the southeast corner of Kentucky. The project comes under the wing of Lewis Ridge Pumped Storage LLC as a branch of Rye Development Acquisition, a newly formed venture of the investment firm Climate Adaptive Infrastructure and EDF Inc., which is part of the global energy company EDF Group.
New strategies for long duration energy storage have crossed the CleanTechnica radar over the years, but pumped storage still beats everything else in the field by a wide margin. Even without any new projects coming online since the 20th century, pumped storage accounts for 96% share of utility scale energy storage capacity in the US (see more long duration background here).
The idea behind pumped storage is simple enough: Let the natural force of gravity do some of the work. When electricity demand is low, excess generating capacity is deployed to pump water to a reservoir at a higher elevation. When demand rises, the water is released to flow downhill, to a generating station below.
About 40 or so pumped storage facilities were built in the US before the turn of the century. Now that wind and solar are surging, pumped storage can play an important role in grid decarbonization. The challenge, though, is to find sites with suitable topography and water resources, without running into environmental conflicts and community opposition. Opportunities to overcome both hurdles can arise when the site has already been disturbed, as is the case with Lewis Ridge.
$81 Million For Long Duration Energy Storage
By “long duration,” Rye means that the Lewis Ridge project will provide for about eight hours of energy storage. That’s a much longer period of time than conventional lithium-ion battery arrays. Li-ion energy storage typically lasts for about 4–6 hours, which is sufficient to handle daily grid-related tasks involving demand spikes and variable access to wind or solar power. With long duration storage, the extra hours provide additional flexibility, helping to accommodate more wind and solar assets on the grid.
The US Department of Energy has been supporting innovations in the long duration energy field, with priority placed on technology that can store wind or solar power for at least 10 hours, ranging up to days, weeks, and months. The Lewis Ridge project doesn’t quite meet the minimum, but it came close enough to win preliminary approval for an Energy Department cost-sharing award of $81 million last spring.
On October 22, Rye announced that the award has been confirmed, beginning with an initial tranche of $12 million towards the total of up to $81 million.
“This type of long-duration energy storage is required to successfully integrate additional intermittent power, such as solar and wind, onto the grid,” Rye emphasized.
“Pumped storage hydropower facilities typically operate for decades and are the most climate-friendly energy storage technology, according to a National Renewable Energy Laboratory study released in 2023,” the company added for good measure.
Plenty More Long Duration Energy Storage Where That Came From
The Lewis Ridge project is not a one-off. The Energy Department funding came through the Office of Clean Energy Demonstrations, with the expectation that the energy storage technology can be replicated elsewhere around the country.
Rye does not intend to disappoint. “We have identified additional coal mine sites in the U.S. that are suitable for pumped storage hydropower, where insights gained from the Lewis Ridge facility can support future projects,” explains Rye CEO Paul Jacob.
The NREL study cited by Rye helps to explain why the Energy Department is zeroing in on pumped storage. Published last year, the study assesses the lifetime greenhouse gas emissions of pumped storage compared to other large scale energy storage systems. Emissions are an important consideration for pumped storage because it is an infrastructure-heavy technology that involves diesel-powered construction equipment and carbon-loaded materials like concrete and steel. In addition, the pumps run on electricity that could be sourced from fossil fuels, depending on the grid mix.
Still, the NREL research team found that pumped storage is the “smallest emitter of greenhouse gases” among the five utility-scale energy storage systems included in the study. The other four were compressed-air systems, lithium-ion batteries, lead-acid batteries, and vanadium redox flow batteries.
“The finding suggests that PSH [pumped storage hydropower] could offer substantial climate benefits by playing a key role in accommodating wind and solar generation,” the team concluded.
The study was published last year and it forms the basis of a free interactive tool for energy storage developers — and anyone else who is interested — to calculate lifetime greenhouse gas emissions for a pumped storage projects. The tool is available online under the title, Pumped Storage Hydropower Life Cycle Assessment.
“Lifetime emissions vary depending on numerous site-specific factors, such as construction materials, components, and especially the grid electricity mix used to operate the facility,” NREL emphasizes.
Run-Of-The-River Pumped Storage Is Also Coming
The Lewis Ridge energy storage project is a closed-loop system that recycles water back and forth between two human-made reservoirs. Rye has other closed-loop systems in the works, and the company has also spotted an opportunity to construct open systems that draw water from a river, pump it to a reservoir, and let it flow back to the river.
Rye aims to recruit the nation’s fleet of existing dams into the effort. Though some dams are slated for removal, many others have a long life ahead of them.
“By powering existing structures that are not at-risk for removal, Rye’s projects add a net-benefit to the environment, [by] repurposing an existing structure, investing in the regions infrastructure, and using that non-powered dam to drive local economic investment while bringing new renewable energy online,” the company explains.
Rye notes that there are about 90,000 dams existing in the US and only 3% of them are being deployed to generate electricity, making the other 97% ripe with possibilities.
Keep an eye on southwestern Pennsylvania and other parts of the Northeast and mid-Atlantic, where Rye has already scouted some favorable conditions for run-of-the-river systems.
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Image (cropped): Pumped hydropower is the basis for 96% of utility-scale energy storage capacity in the US, and it is ripe with potential for expansion (courtesy of Lewis Ridge Pumped Storage LLC).
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