While exhausted mines are often seen as obsolete, new research suggests they may hold untapped potential as energy-storing gravity batteries. A 2023 study introduced the concept of utilizing abandoned mine shafts for sustainable energy storage, a concept that will continue to gain traction in 2025.
A gravity battery is a system where electricity is generated by releasing a heavy load, allowing it to descend and produce energy. When there is surplus energy in the grid, the system uses some of that electricity to lift the load back up, storing energy for future use.
One of the most established forms of this technology is the pumped-storage hydroelectric system. This method generates electricity by allowing water to flow downhill, spinning turbines, and then pumping the water back uphill when excess energy is available.
In 2022, researchers at Austria’s International Institute of Applied Systems Analysis (IIASA) proposed a new type of gravity battery. They suggested equipping high-rise building elevators with regenerative braking systems to generate electricity by lowering weighted payloads between floors.
Expanding on this concept, IIASA researchers proposed the Underground Gravity Energy Storage (UGES) system for disused mine shafts. Instead of water, the UGES system would use containers of sand, raised and lowered by elevators within the mine.
A network of electric motor/generator units on both sides of the shaft would facilitate energy generation. When lowering sand-filled containers, the system would generate electricity via regenerative braking. Conversely, when grid energy was in surplus, the system would use that power to lift the containers back up.
For maximum efficiency, the elevators would transport sand from the surface to the mine’s base and return empty. To prevent the mine from filling up, a portion of the sand would need to be periodically transported back to the surface using conveyor belts and dump trucks.
Scientists estimate that UGES could offer a global energy storage capacity of 7 to 70 terawatt hours (TWh). Countries with a high number of abandoned mines, such as China, India, Russia, and the United States, could particularly benefit from this technology.
“When a mine closes, it lays off thousands of workers […] UGES would create a few vacancies as the mine would provide energy storage services after it stops operations,” said Julian Hunt, lead author of the study. He also noted that existing mining infrastructure and power grid connections would lower implementation costs.
Since the original study was published, Hunt has received significant interest from multiple stakeholders, including mine owners, investors, and project developers. He also hints at further advancements in gravity-based energy storage, expected to be published later in 2025.
