Renewable energy sources are central to the energy transition toward a more sustainable future. However, because 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 study led by the International Institute for Applied Systems Analysis (IIASA), 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.

An open-access paper on the work is published in the journal Energies.

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.

Underground Gravity Energy Storage system: a schematic of different system sections.

Other energy storage methods, such as batteries, lose energy via self-discharge over long periods. The energy storage medium of UGES is sand; 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 US$/kWh and power capacity costs of 2.000 US$/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 US.

Resources

• Hunt, J.D., Zakeri, B., Jurasz, J., Tong, W., Dabek, P.B., Brandão, R., Patro, E.R., Ðurin, B., Leal Filho, W., Wada, Y., van Ruijven, B., Riahi, K. (2023). “Underground Gravity Energy Storage: A Solution for Long-Term Energy Storage.” Energies. 16, 825. doi: 10.3390/en16020825