Scientists Are Turning Abandoned Mines Into Gravity Batteries – Popular Mechanics

This might be the coolest energy storage solution yet.
Supplying the world with renewable energy is a two-fold problem. The first is making technologies like wind and solar as robust and affordable as coal and natural gas. With recent estimates suggesting solar will outpace coal in 2025, that first problem is quickly being solved. The second one, figuring out how to store that energy, is a bit trickier.

Unlike fossil fuels, solar and wind can’t provide an uninterrupted stream of energy. After all, the sun sets and winds die, but scientists and engineers have developed myriad ways to store that renewable energy for when the grid needs it. One idea is to supplement lithium-ion batteries with iron-air batteries that could charge our homes via rust (yes, rust), or transform existing coal-fired power plants into nuclear ones. But another much talked about technology is what’s known as “gravity batteries,” which use regenerative braking and, well, gravity to send energy to the grid.
The big problem is exactly that—they’re big—making them unfeasible (and unattractive) for certain areas. However, earlier this month, scientists revealed a gravity battery that takes advantage of vestiges of dirty energy’s past by using millions of abandoned mines worldwide (with an estimated 550,000 of them being in the U.S. alone) to store energy.
The research into these new batteries, led by the International Institute for Applied Systems Analysis (IIASA), examined a technology known as Underground Gravity Energy Storage (UGES). At its most basic, this battery lowers large containers of sand into a mineshaft when energy is expensive (aka peak hours). Using regenerative braking, these mines would transform the sand’s potential energy into actual energy, and the bigger the mine, the bigger the battery.

To recharge, the mine then brings sand back to the surface when energy is cheap. Unlike conventional batteries such as lithium-ion, gravity batteries experience zero self-discharge, which is the slow loss of energy over time while being stored. That means these mines can be on standby to provide much needed energy for months or even years. Using abandoned mines also provides tons of benefits as it preserves jobs, hides unsightly infrastructure underground, and leverages connections to the grid that already exist.
“Mines already have the basic infrastructure and are connected to the power grid, which significantly reduces the cost and facilitates the implementation of UGES plants,” IIASA researcher Julian Hunt said in a statement. The researchers published their results in the Multidisciplinary Digital Publishing Institute journal on Thursday.
According to the BBC, some companies are already investigating ways to transform abandoned coal mines into next-gen batteries. However, others find the geographic limitations of mine-based gravity batteries could limit the adoption of the technology worldwide. The IIASA even admits that the world’s greatest benefactors of this technology would be countries like Russia, India, and the U.S., where a lot of mines already exist. That’s why outfits like Energy Vault, a Swiss-based gravity battery company, are trying to build aesthetically pleasing gravity batteries that can be dropped anywhere and even feel at home in urban and suburban settings.
Just like how humanity’s green energy future will likely be a mix of solar, wind, and next-gen nuclear power stations, energy storage will also be an eclectic mix of chemical and gravity batteries — both above and below ground.

Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough. 

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