Can Pumped Storage Hydroelectric Systems Give Britain’s Disused Mines a New Lease on Life?

In late September, the United Kingdom’s last coal-fired power station—the Ratcliffe-on-Soar facility in Nottinghamshire—ceased operations. The event marked the end of the United Kingdom’s relationship with coal for power generation, and closely followed the blocking of the first planned coal extraction development since the United Kingdom ceased deep mining operations in 2015—the Whitehaven underground coal project in Cumbria—the previous week.

The demolition of the Ratcliff-on-Soar plant, planned to take place more than 2 years, is fallow ground for a British energy industry that is seeking to reinvent itself. But the question of how to repurpose old plants has recalled another legacy problem of Britain’s coal industry: what to do with the decommissioned mines that riddle over 14% of the United Kingdom’s total land area?

With the phasing out of British coal, how could disused shafts be repurposed for clean, on-site energy systems? With gravity storage systems gaining traction globally, hydroelectric storage seems an obvious opportunity. Pumped underground storage systems operate by sequentially storing water at different elevations, then draining this to lower levels—and past generator turbines—to generate electricity. This method, called Pumped Hydro Energy Storage (PHES), can effectively convert old shafts into on-demand energy sources.

Until recently an academic concept, an ecosystem for repurposing old coal mines has emerged. Companies like Sustainable Energy Solutions have developed dedicated, renewably powered Underground Pumped Hydro Storage (UPHS) technology for controlling this process. Other vendors are tackling the ecological challenges of repurposing mines. For example, to prevent the release of contaminated water, Clearwell, a Swedish company, offers a specialized water purification system that containerizes and cleans any run-off before it is released into the local environment.

Commercialization of gravity storage systems is underway. In December 2023, Scottish-based Gravitricity and ABB, a leading engineering vendor, signed a collaborative agreement to prepare the former’s flagship GraviStore product for commercial adoption. Elsewhere, PHES projects are gaining pace. In October, Rye Development Acquisition, which is undertaking the first U.S.-based pumped hydro project in a disused Kentucky coal mine, announced the 287 Megawatt (MW) development will receive up to US$$81 million of funding from the Department of Energy. Some pumped storage mines are already operational. In China, the Shenhua Daliuta coal mine was repurposed as a demonstration project in the 2010s and has total capacity of 31 million cubic meters.

With the United Kingdom’s recent shift from coal power, now is an ideal time to open the debate on how legacy coal infrastructure is used.

Repurposing coal mines could become an integral part of the national energy strategy, providing resilience and capacity for a grid that must urgently modernize. On a micro level, PHES facilities, built on land adjacent to enterprises, can provide storage for local demand or support commercial microgrids, reducing reliance on battery alternatives for mitigating the intermittency of solar and wind sources. By fulfilling this requirement, pumped hydro systems can become a valuable part of these companies’ energy portfolios and, if the U.S.-based Rye mine project is indicative, provide significant capacity for their operations.

However, there are significant obstacles to installing PHES systems in existing mines:

• Scoping Projects: British mines were often abandoned long before detailed surveying could be undertaken. Mapping prospective shafts, establishing their viability, and understanding what was mined within them will be important steps to determine the feasibility of projects.
• Costs: Dependent on viability, size, and the complexity of a given mining system, installation of the PHES system may be prohibitively expensive.
• Ecological Considerations: Abandoned coal mines are already a topic of debate among U.K. wildlife and ecological agencies, with run-off causing significant damage to rivers and other habitats. PHES installations will need to be integrated with water purification technologies to ensure they are supported by these groups.
• Safety: Old mines may be structurally unsound, in which case PHES installation may cause collapses or landslides in local areas. Careful vetting—which will increase costs—will be needed before construction.
• Regulations: Although abandoned, many of Britain’s mines are still covered by regulations that limit their repurposing. Planning permission—often a long process involving multiple agencies—would also be required before work can begin.

While feasibility must be determined on a case-by-case basis, the United Kingdom is well-situated to benefit from PHES systems in repurposed shafts. Britain receives large quantities of rainfall, which can feed these systems, and is home to approximately 250,000 abandoned mines. As pilot projects gain traction elsewhere, it would be a wasted opportunity—both for the wider grid, and for the enterprises that would benefit from high-capacity, on-site storage—not to investigate this potential.