Gravity Energy Storage Systems: Transforming Defunct Mines Into Efficient Energy Producers

January 07, 2024 by John Nieman

As the shift to renewable energy reduces fossil fuel mining, mine shafts will undergo costly decommissioning. But one company’s solution may turn these mines into energy producers and obviate decommissioning expenses altogether.

The global pivot to renewable energy drives innovation and conversations about the next technology frontier that can aid this shift. While new technologies and systems are being built, the old ones must be decommissioned, recycled, or otherwise discarded, which can create significant complications. Former mines are one example of obsolete energy infrastructure quickly becoming relics as renewable energy sources replace fossil fuels. Mines no longer used must be decommissioned, resulting in an expensive and time-consuming process that uses even more resources. Gravitricity, a gravity energy storage firm based in the United Kingdom, is pioneering a process to turn these mines into energy production and storage sites by hoisting and lowering heavy loads to generate electricity. 


A side view of an underground mine shaft repurposed by Gravitricity.

A side view of an underground mine shaft repurposed by Gravitricity. Image used courtesy of ABB


Gravitricity will partner with ABB Electrification, which will provide engineering and product development services, including the design of hoists and controls for the mine shafts. ABB will also assist in identifying unused mines and shafts where GraviStore might be installed.


The Hazard of Abandoned Mines 

The downward trends are apparent and indisputable when it comes to mining as a means of coal extraction. Experts estimate that in 2024, approximately 466 million tons of coal will be mined. Without context, such a figure might seem impressive, but it is, in fact, a new record low. This quantity would be the least amount of coal mined since 1962. 

A longitudinal overview reinforces that, in recent years, there has been a steady decline in coal-producing mines and a drop in the reactivation of old mines. It is noteworthy, however, that the number of idle mines that have not been repurposed remains more steady. 


Data on U.S. coal mines spanning 12 years.

Data on U.S. coal mines spanning 12 years. Image used courtesy of the U.S. EIA


Even the terms “abandoned mine” or “idle mine” obscure the problems associated with mines no longer operating. They are not innocuous or simply inactive sites – they continue to decay and deteriorate if they are not properly decommissioned. According to U.S. Department of the Interior estimates, millions of Americans live within a single mile of an abandoned coal mine.

Limiting the abandoned mine problem to coal mines alone is not accurate, although these are indeed problematic. Experts estimate up to 159,735 abandoned metal mines also create various pollution issues. 

These other abandoned mines can present significant hazards to local water supplies. Mines associated with precious metals can release mercury into the environment, contaminate local sediment, and cause lead to leach into the ground. The presence of sulfide mines can result in acidic mine drainage. Hundreds of deaths and injuries from falling accidents are also on record. 

While the fiscal cost of properly decommissioning a mine varies by country, the range is expensive regardless of location. The average cost to decommission a mine in India is $58 million, and in the United States, the average is approximately $117 million.  


Turning Mines Into Gravity Energy Storage Systems 

Gravitricity is pioneering a system of hoisting and lowering weight inside these abandoned mines to generate power. The technology is similar to pumped hydro storage, which uses water flow and differences in elevation to generate electricity. The energy can then be stored and deployed when needed. 

The Gravistore system exploits gravity's power to raise and lower weight inside the mine shaft to create energy that can subsequently be stored and deployed on short notice to a strained network or utility grid

The advantages of Gravistore include low cost and longevity, which make the system an attractive option for repurposing inoperative mines. Initial costs are minimal because the basic infrastructure (i.e., the mine itself) is already built. Gravitricity also asserts the Gravistore system can function for decades without significant maintenance challenges and store more than 20 MWh.

The converted mines can function as energy producers and storage facilities for decades after they would have otherwise become a costly and dangerous nuisance to the environment. The stored energy could be quickly deployed in cases of emergency. 

Yesterday's mines can become a renewable energy source today, showing how creative engineering solutions can turn a problem into a solution.