Energy

Scientists propose turning abandoned mines into gravity batteries

Scientists propose turning abandoned mines into gravity batteries
The scientists behind a new study estimate that, worldwide, there are likely millions of disused mines suitable for energy storage
The scientists behind a new study estimate that, worldwide, there are likely millions of disused mines suitable for energy storage
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The scientists behind a new study estimate that, worldwide, there are likely millions of disused mines suitable for energy storage
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The scientists behind a new study estimate that, worldwide, there are likely millions of disused mines suitable for energy storage
A diagram of the proposed Underground Gravity Energy Storage system
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A diagram of the proposed Underground Gravity Energy Storage system

Once a mine has been exhausted of its ore, there's really no use for it anymore – it just becomes an abandoned hole in the ground. According to a new study, however, the shafts of such mines could serve in energy-storing gravity batteries.

First of all, just what is a gravity battery?

Well, in a nutshell, it's a system in which electricity is generated by releasing a heavy load, allowing it to drop. That electricity can then be used at times when demands on the municipal grid are high. At other times, when there's excess energy in the grid, the gravity battery system uses some of that energy to pull the load back up, effectively storing the energy for later use.

One of the most common types of the technology is what's known as a pumped-storage hydroelectric system. In this setup, water is released from a high elevation, generating electricity by spinning up turbines as it flows downhill. When excess energy is available, that water is pumped back up to the starting point.

Last year, scientists from Austria's International Institute of Applied Systems Analysis (IIASA) proposed a different type of gravity battery. The basic idea was that the elevators in high-rise buildings would use regenerative braking systems to generate electricity while lowering weighted payloads from higher to lower floors. Autonomous trailer robots would pull the loads in and out of the elevators, as needed.

That brings us to the mine-based Underground Gravity Energy Storage (UGES) system, recently proposed by the same researchers. It would likewise utilize elevators, but these ones would be in existing disused mine shafts, and they'd be raising and lowering containers full of sand.

A diagram of the proposed Underground Gravity Energy Storage system
A diagram of the proposed Underground Gravity Energy Storage system

A series of electric motor/generator units on both sides of the shaft would move each elevator up and down, generating electricity via regenerative braking on the way down, then using some of that electricity on the way back up.

For maximum efficiency, the elevators could take on a sand load at the surface, have that load removed at the bottom of the shaft, then return to the surface empty. Needless to say, the storage area at the bottom of the shaft would eventually fill up with sand in this scenario. For this reason, when there was an excess of energy in the grid, the elevators would have to bring some of the sand back topside. A combination of electric conveyor belts and dump trucks would be used for the on- and offloading.

The scientists estimate that UGES could have a global energy storage potential of 7 to 70 TWh (terawatt hours), with most of the plants being located in countries where there are already a lot of abandoned mines, such as China, India, Russia and the US.

"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 IIASA's Julian Hunt, lead author of a paper on the study. "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."

The paper was recently published in the journal Energies.

Source: IIASA

30 comments
30 comments
Whodis
Pure conjecture ...that hasnt considered some basic facts. Not all underground mines have shafts - most modern UG mines in Australia tend to use declines ( a spiralling vehical ramp). Those that do have a shaft.. is the shaft in good enough condition or does it need changing. If it needs changing the engineering costs are significant. For example a gold mining company I worked for spent $80m on engineering before they started sinking the shaft.
Finally most Underground mines have significant ongoing costs in pumping out water, if they stop, the mine floods. This bill runs at a couple of million per year to maintain pumps, pipes and power infrastructure. What about ventilation to operate machinery / conveyors and the people underground to maintain that gear.
The costs alone will kill the viability of this approach before its even off the drawing board.... again pure conjecture
globaleducator

You are way behind the curve. Look at https://gravitricity.com/, already testing.
Whodis
@Globaleducator - just because a technology is being tested doesnt mean its viable. Add in factors that reduce that technologies effectiveness and its going to struggle. In this case your inferring that they need mines close to power infrastructure ( not a lot in Aus), with a suitable ~300m or greater shaft (not a lot in Aus), without water table issues costing $$$ and not needing ventilation costing $$$. The ROI is going to be marginal at best against competing technology like batteries.

So while I might be behind the times for startups like gravitricity, I am at least realistic about the costs that will kill this in almost all circumstances except a few.
windykites
Passengers and goods could be used directly in lifts for energy storage and regeneration
Hasler
Mine shafts have a fatal flaw. Ground water. Pumping water out is expensive and water can be contaminated, requiring costly treatment. Also hazardous gases seeping out of disused mine levels, requiring ventilation and alternative escape routes. Working underground is very specialised, highly regulated and risky, especially for a decades old shaft.
Captain Danger
@whodis You bring up valuable points. I think a lot of these proposals by "Scientists" are not rooted in reality but in the need to publish papers and get funding.
vince
the best gravity battery locations are above the deep 6 mile trenches in the oceans. Consider barging huge amounts of rocks to a conveyor site above a 30,000 foot Aluetian trench like near Alaska or some near Puerto Rico are 5 miles deep. Then simply allow the weight to fall 5 to 6 miles down and generate a lot of potential energy as the conveyor turns a turbine to make electricity. The barges themselves can be totally solar driven and clean or use hydrogen generated from solar to push the barges to the dump sites. One unfortunate thing about this is eventually you will begin raising sea levels as you fill up the trenches but that would take millions of years to raise sea levels even an inch or two.
gtiern
abandon mines could have been used for years to filter water, but guess that would never happen.
michael_dowling
To store the power you would get from pumped storage hydro power,you would need weights equivalent to the billions of tons of water you would get from pumped hydro power storage,which ain't gonna happen..
notarichman
most shafts are not very big in diameter, so you might be able to raise/lower one or two cables with a heavy weight on them. the sides of the shaft may not be perfectly
plumb and definitely are not smooth, so the weight would be rubbing against the shaft sides and possibly destroying the shaft.
you can use the mine for growing mushrooms. you MIGHT be able to pressurize the mine and use the air to run a turbine generator. but that might cause earthquakes
if the pressure is too high?
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