Researchers Look To Turn Decommissioned Mines Into Batteries

By Brian Westenhaus - Feb 09, 2023

• Researchers are studying a new energy storage technique using decommissioned mines. 
• The technique called Underground Gravity Energy Storage aims to turn abandoned mines into long-term energy storage solutions.
• The deeper and broader the mineshaft, the more power can be extracted from the plant, and the larger the mine, the higher the plant’s energy storage capacity.

The International Institute for Applied Systems Analysis (IIASA) has offered a new technique called Underground Gravity Energy Storage that turns decommissioned mines into long-term energy storage solutions.

Renewable energy sources are central to the energy transition toward a more sustainable future. However, as sources like sunshine and wind are inherently variable and inconsistent, finding ways to store energy in an accessible and efficient way is crucial. While there are many effective solutions for daily energy storage, the most common being batteries, a cost-effective long-term solution is still lacking.

In a new IIASA-led study, an international team of researchers developed a novel way to store energy by transporting sand into abandoned underground mines. The new technique called Underground Gravity Energy Storage (UGES) proposes an effective long-term energy storage solution while also making use of now-defunct mining sites, which likely number in the millions globally. The study paper ‘Underground Gravity Energy Storage: A Solution for Long-Term Energy Storage.’ has been published in the journal Energies.

Underground Gravity Energy Storage system: A schematic of different system sections. Image Credit: © Hunt et al. International Institute for Applied Systems Analysis. More information and images at the study paper link.

UGES generates electricity when the price is high by lowering sand into an underground mine and converting the potential energy of the sand into electricity via regenerative braking and then lifting the sand from the mine to an upper reservoir using electric motors to store energy when electricity is cheap. The main components of UGES are the shaft, motor/generator, upper and lower storage sites, and mining equipment. The deeper and broader the mineshaft, the more power can be extracted from the plant, and the larger the mine, the higher the plant’s energy storage capacity.

Julian Hunt, a researcher in the IIASA Energy, Climate, and Environment Program and the lead author of the study explained, “When a mine closes, it lays off thousands of workers. This devastates communities that rely only on the mine for their economic output. UGES would create a few vacancies as the mine would provide energy storage services after it stops operations. 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.”

Other energy storage methods, like batteries, lose energy via self-discharge over long periods. The energy storage medium of UGES is sand, meaning that there is no energy lost to self-discharge, enabling ultra-long time energy storage ranging from weeks to several years.

The investment costs of UGES are about 1 to 10 USD/kWh and power capacity costs of 2,000 USD/kW. The technology is estimated to have a global potential of 7 to 70 TWh, with most of this potential concentrated in China, India, Russia, and the USA.

Behnam Zakeri, study coauthor and a researcher in the IIASA Energy, Climate, and Environment Program offered the conclusion, “To decarbonize the economy, we need to rethink the energy system based on innovative solutions using existing resources. Turning abandoned mines into energy storage is one example of many solutions that exist around us, and we only need to change the way we deploy them.”

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This might be the furthest reach for the gravity method of storing electricity. Pumping water back above the generators has some merit as well. One might note that the mechanical losses are mentioned in the study paper for this idea, but hard to locate for the water method.

So far engineering hasn’t really started in on innovations to gain efficiency. That is a area in this field in dire need of attention.

The production costs are not covered in the press release. For those curious the study paper (Not behind a paywall at posting date.) offers much more information.

Both this type of idea and the hydro idea have yet to see a concerted effort in application. The tech isn’t at a high level and the “interesting” perspective isn’t terribly interesting.

This is simple, doable and fairly practical. One wonders why it isn’t being done. Oh, its not really needed, except where politics have cut the power supply. Good luck getting those places motivated to store some power at low cost. This is way cheaper than buying batteries even though the operation losses are noteworthy. Then getting personnel might be quite a problem as well.

It good to know it can be done. Maybe it will when politics pay more attention to practical needs than special interests’ hysterics and cash contributions.

By Brian Westenhaus via New Energy and Fuel