This is part one of a two-part series on ways that coal infrastructure is being repurposed to meet the needs of renewable energy.
From Europe to North America, an energy revolution is breathing new life into empty, long-forgotten coal mine shafts — by repurposing them into places to store renewable energy.
Using “gravity batteries,” these underground facilities aim to tackle one of renewable energy’s greatest challenges: storage. The method is simple: Excess renewable energy is used to power winches that lift heavy weights — such as containers filled with sand or rock — up the mine shaft. When additional energy is needed, these weights are released, generating power as they descend.
This approach not only gives these disused mines a second life but also offers economic and environmental benefits to communities once reliant on coal.
Hundreds of thousands of abandoned mines — about 550,000 in the U.S. alone — pose economic, environmental and safety risks. In some areas, these old shafts have caused collapses or polluted groundwater, while in others, the loss of mining jobs has hit local economies hard. Meanwhile, as renewable energy scales up, storage limitations become a pressing issue, especially with solar and wind, which are naturally intermittent. This year, solar is expected to surpass coal as a leading global power source, according to the International Energy Agency, highlighting the need for reliable storage to balance supply and demand. During the U.K.’s 2020 lockdown, for example, National Grid warned of potential blackouts when energy demand dropped by 20 percent, leading to excess renewable power that went unused.
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Their potential is already being realized. In Rudong, near Shanghai, the first commercial grid-scale gravity battery was connected to the grid in December 2023. Capable of storing up to 100 megawatt hours of energy, it can power nine homes for an entire year using only stored electricity. Across China, nine additional projects are in development, while in Switzerland, a commercial demonstration unit has been connected to the national grid for testing since 2019, showcasing the technology’s promise on a global scale. And now, other countries, from Finland to Australia, are getting on board.
Bridging past infrastructure with modern technology
Repurposing old mine shafts into gravity batteries is more than just a clever use of existing infrastructure — it’s a promising new model for energy storage that combines modern technology with remnants of our industrial past. In a 2024 report, The Nature Conservancy describes brownfields and former mine sites as a “critical, underutilized resource” for renewable energy. In fact, the National Renewable Energy Laboratory (NREL) suggests that contaminated and disturbed lands across the U.S. could support enough solar power to meet the Department of Energy’s SunShot goal of 715 gigawatts by 2050, which would supply over 120 million homes. The EPA goes even further, identifying about 20 million acres of brownfields and former mine lands in the U.S. that could generate around 1,300 gigawatts of solar power annually — enough to power over 200 million homes each year.
This shift toward renewable storage in abandoned mines is supported by research from the International Institute for Applied Systems Analysis (IIASA). Their findings suggest that using Underground Gravity Energy Storage (UGES) in abandoned mines has the potential to provide substantial, long-term energy storage at a low cost.
A key advantage of repurposing mine shafts for gravity batteries is their depth. Many are already a kilometer or more deep, eliminating the need to construct towering new structures. As Chris Yendell, project development manager at renewable energy storage company Gravitricity, explains, “Fundamentally, to make a storage project economically effective, having a significant vertical distance is key.” These vertical distances, once used to transport coal, now serve as ideal channels for energy storage with minimal additional construction. Repurposing the infrastructure means engineers can focus resources on refining the lifting equipment rather than building from scratch, which significantly lowers costs.
Researchers from IIASA estimate that UGES in abandoned mines could store up to 70 terawatt-hours of energy globally. That’s enough to power the U.K. for nearly three months or meet the entire world’s electricity needs for a day. Mines with shafts over 200 meters are particularly suited for UGES, which has the added benefit of zero self-discharge — meaning the energy stored in these systems remains ready and available without loss, even over extended periods. This makes UGES not only a reliable storage solution but a highly efficient one.
Ripple effects
Revitalizing old coal mines for energy storage can offer coal-dependent communities a stake in the clean energy revolution. The U.S. Inflation Reduction Act of 2022 (IRA) is a key piece of this transition, offering clean energy incentives specifically for areas historically dependent on fossil fuels. “The IRA is designed not just to lower energy costs and combat climate change but to promote broad-based economic opportunity and create jobs in communities that have been at the forefront of energy production, especially coal communities,” Deputy Treasury Secretary Wally Adeyemo said in a statement.
With projected global growth of energy storage investments — expected to reach $50 billion annually by 2040 — communities impacted by coal’s decline are poised to become leaders in the green transition. According to The Nature Conservancy, the government could provide targeted tax credits and other financial incentives to help companies invest in turning brownfields and mine lands into renewable energy hubs. Such support can bridge economic gaps, transforming communities that once depended on coal into clean energy strongholds. “These legacy mine workings are more than just structures; they hold a long history and social legacy,” says Christopher McDermott, a professor at Edinburgh University’s School of Geosciences. “For communities, reusing these spaces, developed by past generations, is very positive. Many mines shut down in the ’80s and ’90s, and while environmental issues remain, using these sites to create new energy brings a sense of continuity.”
But the shift isn’t without challenges. Converting old mines into energy storage sites can be costly, especially when accounting for repairs and liability risks. “The challenge isn’t just the engineering; it’s the risk,” says Katherine Vaz Gomes of the Kleinman Center for Energy Policy at the University of Pennsylvania. “Developers are wary of hidden costs, from structural repairs to environmental liabilities.” For sites that come with complex histories — like coal fly ash impoundments or legacy asbestos mines — this risk is even higher. Gomes suggests the U.S. Superfund program could be an effective tool if expanded to cover these types of projects, providing liability protections and cost-sharing mechanisms to support developers while ensuring environmental justice.
In the U.S., incentives like the IRA and Illinois’ Coal-to-Solar Energy Storage initiative encourage clean energy investment in “energy communities” by providing extra tax credits to projects in fossil fuel-reliant areas. Globally, policies that support affordable permitting, tax breaks and partnerships with local communities are turning former mine sites into new energy centers. “The infrastructure’s there, the community is willing — often all that’s missing is the support to get these projects moving,” says Gomes.
The road ahead
Underground Gravity Energy Storage (UGES) offers a powerful approach to seasonal storage. These systems could store energy generated during high-sunlight summer months for use in winter, with an efficiency rate of 80 percent and the capacity to store up to 10,000 hours of energy. Such a setup would strengthen the grid during peak demand and low renewable output, providing a sustainable alternative to lithium-ion batteries, which degrade over time and need frequent replacement.
Countries around the world are recognizing this potential. In Germany, energy giant LEAG is transforming its lignite mines in Lusatia into a “green energy hub” with integrated solar, wind, hydrogen and battery storage. Australia’s AGL Energy is repurposing the Liddell Power Station into a battery storage site, aiming for 500 megawatts of capacity by 2025. Finland’s Pyhäsalmi Mine, one of Europe’s deepest, is set to become a UGES site under Gravitricity’s guidance, with a projected two-megawatt storage capacity. “These legacy mine workings are a physical change to the geology, creating an underground network of open spaces,” McDermott explains. “Their underground spaces can now be used to transport fluids or hoist heavy weights for gravity storage.”
By some estimates, renewable energy may account for 41 percent of global electricity by 2028, but reliable storage is essential to ensure grid stability. Repurposing mines as storage systems provides infrastructure that links communities to the future while honoring their industrial past. As McDermott puts it, “It’s a way to give these sites new life while respecting the local history and legacy.”
