Scientists Propose Turning Abandoned Mines Into Super-Efficient Gravity Batteries

(Image: Fmartin/Wikimedia, CC BY-SA 3.0) As the world comes to terms with the realities of climate change, the pressure to adopt more renewable energy is unavoidable. However, the sun isn’t always shining, and the wind isn’t always blowing. Worst of all, our ability to store that energy for the cold, still nights is still woefully inadequate. There may be a solution, and it’s not a fancy new technology—it’s a new take on something decades old. A team from the International Institute for Applied Systems Analysis (IIASA) has developed a plan to create a network of super-efficient gravity batteries that could store tens of terawatt-hours of power.

Humanity has been harnessing small amounts of energy from gravity for centuries—technically, the pendulum clock is a primitive gravity battery. In the 20th century, scientists developed pumped-storage hydroelectricity, which uses elevated water reservoirs to store gravitational potential energy. Several of these facilities exist around the world now, but most areas don’t have enough water or the right terrain to make it work. The IIASA proposal for Underground Gravity Energy Storage (UGES) would use something we already have in spades: abandoned mine shafts.

A UGES stores energy when it’s plentiful—for example, when the sun is shining on a solar power plant. A heavy container of sand or rocks would be suspended in the previously abandoned mine shaft with an electric motor raising it to the top. As long as the bucket remains at the top of the shaft, the energy isn’t going anywhere. When power generation drops, the grid can harvest power from the UGES by letting the vessel drop back down. The UGES would use regenerative brakes on the cabling, similar to the way electric cars extend their range when you apply the brakes. Unlike batteries, all of which lose power via self-discharge over long periods, sand always has the same mass, and we’re not going to run out of gravity.

According to IIASA’s Julian Hunt, mine closures often result in economic hardship for the communities that came to rely on them for jobs. However, a mine already has most of the infrastructure needed to become a gravity battery, so the IIASA plan could be a cost-effective way to ease hardship and rapidly expand energy storage.

There are millions of abandoned mines around the world that would potentially work for UGES, with most of them concentrated in China, India, Russia, and the US (where there are more than 550,000 of them). The IIASA claims investment costs would range from 1 to 10 USD/kWh, and the potential energy storage could be as high as 70 terawatt-hours. That’s enough to power the entire planet for 24 hours. That is, of course, a best-case scenario. Even a tenth of that, which is the low end of the estimated range, could be a big help as the world transitions to renewables.

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