There are millions of disused mines around the world that are no longer of any use. A team of researchers at the International Institute of Applied Systems Analysis (IIASA) in Austria proposes turning them into gravity batteries.
Scientists have proposed a system called Underground Gravity Energy Storage (UGES). For this method of energy generation, the most important element is the mine shaft.
The technology is not very complicated. Containers full of sand are lowered into the shaft at times when demand for energy from the grid is very high. As the weight descends, a series of electric generators/motors in the well produce power through regenerative braking, a method borrowed from the automotive industry.
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For the system to be effective, lifting the weights back to the starting position at the well entrance is done, using the same electric motors, at times when there is excess power in the grid. Thus, this operation costs less then.
For even greater efficiency, one idea is to empty the sand from the containers into the mine tunnels, but this will gradually lead to them filling up. A hybrid method would be to bring only a quantity of sand back to the surface.
In this way, the old mines will in future act as emergency batteries, supplying power to the grid at times when other green sources, such as photovoltaics and wind power, cannot meet the need.
According to Julian Hunt, lead author of the IIASA study, most mines are already connected to the grid, which significantly reduces the cost of installing UGES systems in them. It can cost between $1 and $10/kWh to build such a plant. The technology may have a maximum global potential of 70 TWh.
Similar technology can also be implemented in large office buildings with many elevators.