Generating and Storing Clean Energy through Former Coal Mines
A proposal by the International Institute for Applied Systems Analysis (Iiasa) near Vienna renders a novel idea to harness the energy needed to combat climate change through the use disused coal mines. Dubbed as Underground Gravity Energy Storage (UGES) in English and “Almacenamiento de energía en gravedad bajo tierra” in Spanish, the proposal consists of electricity generators activated by sand, instead of water.
In this process, the sand is dropped into containers at the bottom of wells or mineshafts which uses gravitational forces to slow down and creating electricity in the process. As sand is an abundant and long-lasting raw material, the UGES system can contribute electricity to the grid when pricing is high and recalled for storage when the price is cheaper.
While the initial investment for such a system is high, with an estimate of 160 million dollars for a 1000-meter mine with 30 MW capacity, the cost of storage with sand is also twenty times cheaper than batteries. Moreover, mine shafts as a form of a dam provide effective long-term storage of up to ten years, with no energy loss over time as opposed to water which is prone to evaporation.
With this proposal, both climate change and job loss due to the closure of mine could be somewhat mitigated. The study further claims that more than 3000 coal mines around the world possess the potential to store 7-70 TWh of energy.