Researchers at Oak Ridge National Laboratory have developed new modeling tools to evaluate whether thousands of abandoned U.S. coal mines could serve as underground reservoirs for pumped storage hydropower, effectively turning old mine shafts into giant water batteries. The concept would pump water into elevated mine chambers when electricity demand is low, then release it downhill through turbines to generate power during peak hours. With the U.S. Department of Energy backing the effort through hundreds of millions of dollars in funding, the initiative represents one of the most ambitious attempts to repurpose the country’s coal legacy for clean energy storage.
How Water Batteries Work Underground
Pumped storage hydropower is not a new idea. It already accounts for the overwhelming majority of utility-scale energy storage in the United States, according to Oak Ridge National Laboratory’s overview of pumped storage research. Traditional systems use two surface reservoirs at different elevations: water flows downhill to spin turbines when electricity is needed and gets pumped back up when surplus power is available. The underground mine version replaces one or both reservoirs with the voids left behind by decades of coal extraction, taking advantage of existing vertical shafts and horizontal tunnels that already reach deep below the surface.
A detailed assessment from Carbon Solutions LLC, hosted by the Department of Energy, provides a technical foundation for this approach. That engineering evaluation covers site screening and ranking, multiphase reservoir modeling, techno-economic analysis, preliminary system designs, and a commercialization pathway. The work confirmed that abandoned underground mines could, in theory, provide the elevation differences and water containment needed for pumped storage, while also flagging major questions about long-term reservoir behavior, sealing old workings, and whether such projects can compete economically with conventional surface facilities or emerging battery technologies.
Mine Chemistry Threatens Equipment and Stability
The biggest technical obstacle is not moving water through old tunnels. It is what happens when that water interacts with decades of exposed coal seams, mineral deposits, and residual mine dust. Oak Ridge researchers have documented how mine-related chemistry can damage hydraulic equipment and undermine structural integrity in former coal workings. Acidic drainage, iron-rich sediment, and calcium sulfate scaling could corrode turbines, clog pumps, and weaken tunnel walls over time. These are not hypothetical risks. They are well-known problems in abandoned mines that have never been subjected to the repeated pressure cycles and flow rates of a working hydropower plant.
To address these hazards, the Oak Ridge team is building hydrodynamics and chemical interaction models that simulate water movement through complex mine geometries and predict how rock–water reactions will evolve over years of operation. Those models draw on laboratory tests, field data, and advanced characterization tools, including neutron scattering facilities at Oak Ridge’s neutron science campus, which can probe how minerals and corrosion products form at the microscopic level. The goal is to identify which mines pose acceptable chemical risks, which would require extensive water treatment or lining, and how maintenance schedules and component choices should be adapted for such harsh underground environments.
Federal Dollars Flow to Mine Land Projects
The Department of Energy has moved beyond basic research to pilot-scale deployment. Through its Clean Energy Demonstration Program on Current and Former Mine Land, or CEML, DOE is offering substantial support for projects that turn coal country into clean energy hubs. The program’s formal funding announcement, cataloged in DOE’s database of mine land demonstrations, underscores that federal officials see mine-to-energy conversion as a repeatable model rather than a one-off experiment. The Associated Press has reported that DOE earmarked $475 million for clean energy projects on mine land, including up to $81 million for a flagship pumped storage hydropower facility at a former coal mine site in Kentucky.
That Kentucky project illustrates how federal investment is being steered toward regions hit hardest by the coal industry’s decline. Appalachian communities offer a combination of deep underground infrastructure, a workforce experienced in subsurface operations, and an urgent need for new economic anchors. DOE’s technical documentation for these efforts, summarized in a recent project report, emphasizes job creation, tax base recovery, and local ownership structures alongside grid benefits. By pairing storage projects with workforce training and community engagement plans, federal agencies hope to avoid a repeat of boom-and-bust cycles that left many mining towns with few alternatives when coal demand fell.
Beyond Water: Gravity Storage and Geotourism
Pumped storage hydropower is not the only second life envisioned for abandoned mines. Researchers and developers are also exploring gravity-based storage, in which heavy masses are raised and lowered in mine shafts to store and release energy without relying on large volumes of water. DOE-backed analyses of alternative mine uses describe how hoist systems, counterweights, and advanced control software could transform existing shafts into mechanical batteries. In principle, such systems could avoid some of the chemical and leakage issues that challenge water-based storage, while still capitalizing on the depth and vertical drop that mines provide.
Other proposals focus less on grid services and more on economic diversification. Some communities are considering underground data centers or secure archives that take advantage of the stable temperatures and isolation of deep mines. Others are turning to geotourism, repurposing accessible sections of mines as museums, adventure parks, or educational sites that interpret industrial history and geology. DOE’s broader catalog of mine redevelopment concepts notes that pairing energy projects with tourism, conservation, or light manufacturing can spread risk and create more resilient local economies. In this view, pumped storage is one anchor in a portfolio of uses that collectively replace the economic role coal once played.
Balancing Promise, Risk, and Community Priorities
Even with strong federal backing and sophisticated modeling, turning abandoned coal mines into water batteries is far from straightforward. Many candidate sites suffer from flooding, subsidence, or unresolved environmental liabilities that complicate construction and permitting. Detailed techno-economic studies, such as the Carbon Solutions assessment and subsequent DOE analyses, highlight how site-specific factors (shaft depth, rock quality, existing access, and proximity to transmission lines) can swing a project from viable to uneconomic. A recent synthesis of storage cost drivers stresses that underground projects must be carefully matched to grid needs, especially as batteries and other storage options become cheaper.
Community consent and long-term stewardship are equally critical. Many mining regions have lived through broken promises about reclamation and job replacement, making residents wary of new megaprojects. DOE’s program guidance, reflected in its mine land planning documents, calls for early engagement with local governments, tribal nations, and labor groups, as well as guarantees on monitoring and environmental safeguards. For Oak Ridge and its partners, success will depend not just on solving complex engineering and chemistry problems underground, but also on proving that these water batteries can deliver durable economic and environmental benefits on the surface. If they can, the same shafts that once funneled coal to power plants could help stabilize a cleaner, more flexible grid for decades to come.
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*This article was researched with the help of AI, with human editors creating the final content.
