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Untapped Potential: How geothermal energy from abandoned mines offers a sustainable energy alternative

British coal mines were central to the Industrial Revolution, fueling factories and heavy machinery at a previously unimaginable pace. Coal mining in England began in the early 1500s, and production steadily increased to a peak of 287 million tons in 1913. Coal deposits are primarily extracted in two ways: from surface or open-cast mines, and from underground or deep mines. In England, a majority of coal production came from deep mining—a technique used to extract coal deposits that were typically situated between 100 and 2,000 feet below ground. Today, deep mines are a relic of the past; as of 2019, only 4 of Britain’s more than 1,000 deep mines remain in operation. Yet, abandoned mining sites could pave the way to a net-zero carbon future for England. By harnessing geothermal mine water and pumping it to the Earth’s surface, old mines could provide Britain with sustainable energy that is both locally sourced and low-cost. 

In underground coal mining, networks of roadways are driven into coal seams— deposits of coal that lie between layers of rock—so that transportation, ventilation, electrical, and water drainage systems can be installed. Although there are several distinct deep coal mining methods, each technique relies on keeping these underground systems dry through the use of water pumps. When underground mines were abandoned during the twentieth and twenty-first centuries, the pumps that previously kept water out were shut off, and the mines flooded. 

Managing the effects of abandoned mines— and controlling the billions of liters of water that currently fill them—costs English taxpayers around £2.4 billion each year. Although mineshafts have long been considered a burden, Jeremy Crooks, Head of Innovation at the United Kingdom government’s Coal Authority, highlights the potential to harness geothermal energy from abandoned mines: “When you look at the opportunities that sit around these mines, this is no longer a liability—it’s an asset of strategic importance to the UK.” 

The process of deriving geothermal energy from abandoned mine sites is relatively simple, as it leverages existing structures. First, a small hole—known as a borehole—is drilled into the workings of the mine. Water, already warmed by natural geological processes, is then pumped to the surface. A pump further heats this water before directing it into a district heating network. Then, cold mine water is reinjected into the mine through a separate borehole, and the process repeats. 

Researchers have found this system to be highly efficient. When mine water is taken closer to the surface, it usually sits between 51.8-68°F. At this temperature, heat pumps must work at a coefficient of performance (COP) of four. That is, for every one kilowatt (kW) of electricity put into the system, four kWs are produced in the form of heat. When working with deeper mines, where water can sit at 86°F, the process is even more efficient, with heat pumps working at a COP of 10

Despite the practice’s efficiency, there remain several challenges associated with harnessing energy from abandoned mines. For one, current Coal Authority projects are largely focused on new housing developments, as retrofitting older houses so that they can access district heating networks and leverage energy from geothermal mine water can be costly. Some have also raised stability concerns, as abandoned mine shafts have been left to decay for decades. However, regardless of these financial and technical challenges, geothermal energy generated from mines remains a low-carbon, sustainable heat source. And, under the right conditions, it has the potential to generate energy at a lower cost than conventional sources. 

This is especially true in the UK, where geologists estimate that one-quarter of homes— concentrated in Wales, Scotland, and northern England—sit above abandoned mine shafts, which are filled with approximately two billion cubic meters (two trillion liters) of warm water. As it stands, natural gas supplies 70 percent of Britain’s demand for heat, and heating accounts for 44 percent of energy use in the UK and 32 percent of its air pollution. Geothermal mine water could be key to the UK meeting energy demands while fulfilling its commitment to net-zero greenhouse gas emissions by 2050. Not only is geothermal mine power more sustainable than natural gas, emitting up to 75 percent fewer emissions, but it is also the more affordable power source, with experts estimating that it will cost 10 percent less than natural gas. 

Alongside environmental benefits, harnessing power from abandoned mines promises to revitalize former coal mining communities. Wracked by mine closures during the 1980s and 1990s, northeast England has some of the country’s lowest levels of economic activity and highest rates of unemployment. Investment in geothermal mine water could be key to the area’s economic resurgence. According to the Institute for Public Policy Research, investment in this energy form could create 81,000 jobs and generate up to £22 billion in private investment. 

While this strategy has yet to be implemented on a large scale, smaller geothermal heat network projects have proven successful. Adam Black, Director of Energy Projects at Lanchester Wines, recalls that he “had about 400,000 square feet of warehouse that needed heating…and it was right over four layers of mine workings, which had naturally flooded over time.” After consulting with geothermal experts, Black decided to sink a borehole and install a heat pump. He is now using geothermal mine water to heat “a couple of warehouses, a distribution depot, a local bakery, and soon a nearby car showroom, too.” The company expects its £3.5 million investment to pay for itself within 5 to 10 years. 

Geothermal mine water could be an excellent renewable energy source option beyond Britain, too. Heerlen, which was once a large coal mining area in the Netherlands, has also experimented with geothermal energy techniques. Mijnwater BV, a Dutch energy company, has connected 500 houses and commercial facilities to the town’s district heating network. By using locally generated heat to fuel the community, the area has reduced its carbon emissions from heating by nearly 66 percent. In the Asturias region of northern Spain, geothermal energy in flooded mines has been harnessed to heat a hospital, a university, a school, and hundreds of private properties—all at a lower cost than fossil fuel alternatives. It is no secret that coal is an egregious pollutant, contaminating our air, water, and land. Repurposing abandoned coal mines to leverage geothermal mine water, however, could pave the way to a greener future—not just in the UK, but across the globe.