A recent proposal from the International Institute for Applied Systems Analysis (IIASA) has grabbed the attention of industry experts. Their suggestion is to utilize the vast reserves of sand in abandoned mines in Africa for large-scale Underground Gravity Energy Storage (UGES).

South Africa has around 6000 abandoned mines, which pose a safety risk for local communities. As such, South Africa is uniquely positioned to benefit from UGES technology.

This concept leverages the simple principle of gravity. Two interconnected reservoirs are carved into the mine, one at a higher elevation and the other below. During charging, excess electricity powers electric motors, lifting sand from the lower chamber to the upper one. This creates potential energy as the mass of sand is raised.

Discharging is the reverse process. The sand descends back down, driving generators that convert its kinetic energy into electricity, feeding it back into the grid. The system's beauty lies in its simplicity and scalability. Deeper mines offer more power generation potential, while wider ones provide larger storage capacity. Additionally, the readily available sand eliminates the need for specialized materials, reducing costs.

The study reports that UGES technology would cost around $1-$10 (R80-R180) per kWh, but this technique becomes cheaper if the height difference between the upper and lower storage sites is larger.

Using abandoned mines for UGES technology also has an impact on regional employment, according to Julian Hunt, the lead author of the study, “When a mine closes, it lays off thousands of workers. This devastates communities that rely 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.”