Abandoned mines could soon become energy storage hubs

A new IIASA-led project will transform decommissioned abandoned mines into long-term energy storage solutions.

The initiative, ‘Underground Gravity Energy Storage: A Solution for Long-Term Energy Storage,’ will utilise a groundbreaking method that stores energy by transporting sand into abandoned mines. The new technique, known as Underground Gravity Energy Storage (UGES), will help to expand the world’s sustainable energy portfolio.

Behnam Zakeri, study co-author and a researcher in the IIASA Energy, Climate, and Environment Program, explained: “To decarbonise 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.”

Innovating energy storage technologies will be crucial for the green transition

Developing extensive renewable sources will be critical to decarbonising the planet and powering the energy transition. Despite this, current renewables such as solar and wind power can be inconsistent and variable, meaning they will be insufficient to replace fossil fuels wholly.

Developing an accessible and efficient energy storage solution is critical. Although there is currently a range of daily energy storage options, such as batteries, there is still not a cost-effective long-term solution. Moreover, batteries lose energy through self-discharge over long periods.

How can abandoned mines provide sustainable energy?

The Underground Gravity Energy Storage technique can potentially provide this long-term solution, making use of the millions of abandoned mines globally. The method generates electricity when the price is high by lowering sand into an underground mine, converting the energy into electricity through regenerative braking, and then lifting the sand from the mine to an upper reservoir. Electric motors then store the energy when electricity is cheap.

UGES is comprised of the shaft, motor/generator, upper and lower storage sites, and mining equipment. The deeper and broader the mineshaft is, the more energy can be extracted, and the plant’s energy storage increases with the size of the mine.

Because the energy storage medium of UGES is sand, there is no energy lost to self-discharge, allowing for ultra-long time energy storage from weeks to even years. Additionally, the investment costs of the technique are around $1-10/ kWh, and the power capacity costs $2/kW. UGES is forecasted to have a global potential of seven to 70 TWh, predominantly concentrated in China, India, Russia, and the US.

Julian Hunt, a researcher in the IIASA Energy, Climate, and Environment Program and the lead author of the study, concluded: “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 operation.

“Abandoned 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.”