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Austrian scientists have developed a long-term energy storage system that uses regenerative braking to adjust the rate of descent of sand into mine shafts and generate electricity.
Researchers led by Austrias International Institute for Applied Systems Analysis (IIASA) have suggested the use of regenerative braking to store renewable energy in decommissioned mining operations.
Regenerative braking is an energy recovery mechanism that takes advantage of the energy wasted in the process of decelerating a vehicle.
The proposed concept of Underground Gravity Energy Storage (UGES) involves lowering sand into an underground mine and raising this sand to an upper reservoir using electric motors to store energy at times of low demand.
“UGES uses regenerative braking to adjust the rate of descent of the sand into the mine shaft and generate electricity,” explains researcher Zakeri Benham. “It has the advantage of leveraging existing infrastructure and providing clean, cheap, long-duration energy storage without material intensity, as well as being already close to the power grid and roads.”
The system consists of a variable depth and diameter well, a motor/generator, upper and lower stores, and extraction equipment.
"To maximize energy capacity, the wells sand containers occupy approximately 50% of its volume," the scientists explain. "The other 50% of the space is needed to fill and empty the containers with sand."
The loading mode consists of collecting the sand from the lower deposit, at the bottom of the mine, with excavators and transporting it to the pit with electric trucks or conveyor belts. The energy is stored using cheap or surplus electricity from the grid or from a large nearby solar PV park to drive the sand up the shaft with the motors/generators. Once the sand reaches the top of the mine, it is stored in sand piles.
The unloading mode is to collect the sand from the upper storage place at the top of the mine with bucket wheel conveyors and transport it to the mine shaft using a small amount of electricity. Electricity is generated by lowering the heavy volumes of sand into the well. Several motor/generators generate electricity with regenerative braking throughout the well. When the sand reaches the bottom of the shaft, it is transported by conveyor belts or electric trucks to fill all the caverns of the mine with sand.
“The investment costs of the UGES are from 1 to 10 USD/kWh and the costs of energy capacity of 2,000 USD/kW”, explain the scientists. “The technology is estimated to have a global potential of 7 to 70 TWh, with most of this potential concentrated in China, India, Russia and the United States.”
They presented the system in the article “ Underground Gravity Energy Storage: A Solution for Long-Term Energy Storage ”, recently published in Energies. Other IIASA research groups have recently developed an energy storage technique based on the use of electric trucks for high-altitude hydroelectric power generation and a gravity energy storage technology for weekly cycles in high-rise buildings in urban environments. . |
