Converting abandoned mines into gravity batteries thanks to sand

UGES technology harnesses the potential energy of sand to turn mines into gravity batteries

(sustainabilityenvironment.com) – Nobody knows exactly how many there are, but the most reliable estimates are around 1 million. Let’s talk about the abandoned mines scattered around the four corners of the Planet. Once they run out of useful life they become a cost and can generate significant pollution problems. But what if we could convert them into gravity batteries using simple sand?

This is what was asked of a team of researchers of the International Institute for Applied Systems Analysis in Austria. By finding a way to convert abandoned mines into precious storage sites scattered throughout the territory and able to provide renewable energy in a programmable way when it is most needed. Exploiting the difference in altitude between the entrance and bottom of mines and the potential energy of a material such as sand. The new technique developed by IIASA is called Underground Gravity Energy Storage (UGES) and is published on Energies.

How does gravity battery work in mine

What does it consist of and how does it work? Gravitational accumulation is a road that is increasingly explored with the increasing demand for storage to give stability to the network given the increase of intermittent renewable (solar, wind) in the mix. The basic principle is not new, indeed it is turning 100 years: think of pumped hydroelectric. In recent years there have been many attempts to develop innovative systems for gravitational storage. Gravitricity in Scotland uses a 25-ton weight system in a deep well. Another proposal of the IIASA, last May, proposed to transform skyscrapers into gravitational batteries.

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In the case of UGES, storage is based on abandoned mines. The technique generates electricity when the price is high by descending the sand into an underground mine and converting the potential energy of the sand into electricity through a regenerative brake (similar to that used for trams, trains and electric cars). To then lift the sand from the mine to a tank placed at a higher height using electric motors to store energy when electricity is cheaper. Obviously, the size of these gravity batteries depends on the size -depth and amplitude in volume- of the abandoned mine being converted.

As investment costs, researchers estimate $1 to $10/kWh and a cost per unit of storage capacity of about $2000/kW. Counting the amount of abandoned mines scattered around the world, especially in China, India, Russia and the United States, the global theoretical potential would fluctuate between 7 and 70 TWh.

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