How millions of abandoned mineshafts could hold a renewables treasure

Researchers say the holes in ground could be a power-storage solution.

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It’s crossed many renewables geeks’ minds: technologies that could power the whole planet without the unpredictability of solar and wind. And energy storage that doesn’t require resource-gobbling batteries.

As we have noted several times, there’s tidal energy, where the world’s waters keep on churning, unlike its breezes and sunshine, while also meaning less need for updated transmission grids. And geothermal, which, as we reported in the fall, is increasingly being exploited. Both technologies also have the advantage of being entirely concealed underwater or underground, meaning no unsightly turbines and fields of ugly voltaic panels.

But now another hidden-away source is being examined — and in an unexpected place: the world’s millions of abandoned mineshafts.

It works in a similar way to hydroelectric plants with a pump system, in which water, during periods of low demand, is returned to the reservoir to be sent back through the turbines when power is needed. It combines both energy creation and storage.

In the case of mineshafts, research by the Austria-based International Institute for Applied Systems Analysis (IIASA) points to the elevator shafts of discarded mines to move sand around in a similar way to the pump systems of some hydroelectric projects.

“The proposed technology, called Underground Gravity Energy Storage (UGES), can discharge electricity by lowering large volumes of sand into an underground mine through the mineshaft,” the study says. And then, “When there is excess electrical energy in the grid, UGES can store electricity by elevating sand from the mine and depositing it in upper storage sites on top of the mine.”

And, report the researchers, another issue is removed: “Unlike battery energy storage,” they say, “the energy storage medium of UGES is sand, which means the self-discharge rate of the system is zero, enabling ultra-long energy storage times,” adding that “the use of sand as storage media alleviates any risk for contaminating underground water resources as opposed to an underground pumped hydro storage alternative.”

The potential is so great, the scientists say, that mines — particularly those in the U.S., Europe, China, India and Russia — could harbor a total of seven to 70 terawatt-hours. To put that in perspective, in 2021 alone, the total usage of global energy was 25 terawatt-hours.

How about combining tidal energy and sand storage? Something, it appears, that should be given deep thought.

(A native of England, veteran journalist Matthew Diebel has worked at NBC News, Time, USA Today and News Corp., among other organizations. Having spent much of his childhood next to one of the world's fastest bodies of water, he is particularly interested in tidal energy.)