JSE-listed precious metals miner Sibanye-Stillwater has been named as the client for which Thyssenkrupp Uhde Africa is undertaking an underground pumped energy storage prefeasibility study (PFS).

Thyssenkrupp earlier this month reported that it had been appointed to undertake the study in collaboration with German State-owned mine closure company Wismut.

The project involves repurposing unused shafts and associated mine tunnels for renewable underground pumped hydroelectric energy storage (Ruphes), at the Driefontein mine.

The PFS aims to test and develop the technical and commercial concept to enable Sibanye to assess the viability and benefits of the project as an option for mine closure and facilitation of the post-mining economic development of communities through the provision of sustainable energy and water.

South Africa has a national electricity generation supply deficit, world-class solar and wind resources and a commitment to achieve net zero emissions by 2050. 

However, a challenge to material renewable energy penetration and the national response to climate change is cost-effective energy storage. 

Sibanye believes a Ruphes system may support its commitment to carbon neutrality by 2040.

Underground pumped energy storage uses development mining tunnels, previously used to access the gold reefs, as upper and lower reservoirs which will enable energy storage and generation. 

When excess electricity from renewable or other sources is available, water is pumped to the upper reservoir.  As soon as the electricity is required, the water discharges from the upper reservoir to the lower reservoir under gravitational force, generating electricity through a generator coupled to a turbine in the shaft system.

Traditional hydroelectric energy storage projects require several years to build water storage dams to be used as reservoirs. 

The development of reservoir dams for traditional storage are typically half the cost of the total project.

Repurposing mining development tunnels to store water, therefore, could enable cost-effective energy storage as well as reduce the time it takes to build storage projects.