The invention of a “gravity” technology to turn mines into giant energy batteries

In recent years, energy storage has gained interest among actors in the energy sector. It effectively makes it possible to ensure the frequency of the electrical network by balancing consumption and production. It is also a means of compensating for the variation of solar power and windmill. For these reasons, many storage solutions are being studied. Recently, international researchers published their research regarding the invention ofa new storage method to utilize abandoned mine shafts. In fact, numbering in the millions worldwide according to the researchers, these sites have an interesting storage potential that deserves to be explored. They also estimate that the world potential corresponds to 7 to 70 TWh. Their system is called “Underground Gravity Storage” or WEEKS meaning “Gravity Underground Storage”.

A regenerative braking system

WEEKS is a type gravity storage. Basically, this system consists of releasing a heavy load. By gravity it falls and generates electricity during its fall. UGES is based on this technique. The idea is to move sand down the mine shafts via elevators. The researchers apply a regenerative braking system to it to create power. Take effect, kinetic energy lost during braking can be converted into electricity, which is implemented during peak load on the network. Some of the electricity produced is then used to drive the elevators up to the top of the shaft.

An optimized system

To optimize energy production, the cabins are filled with sand when they go. When they have reached the bottom of the well, they are unloaded so that they can be brought up as light as possible. Deflated, the elevators require less energy to regain altitude. Thus, at the bottom of the wells there are cavities storage dedicated to sand.

Gravity energy storage is a technology that uses gravity to store electrical energy. This is done by using masses that can be raised and lowered to store mechanical energy, which can then be converted into electricity when needed. Photo credit: Hunt et al.

Obviously, storage areas are likely to fill up over time. To avoid this, the elevators still transport sand upwards, but only at certain times, and thanks to the power of the network. This scenario is carried out during times of overproduction of electricity, where the prices are lowest. Underground trucks drive to the bottom of the shafts to load and unload the elevators.

Gravity energy storage is an efficient way to store electrical energy on a large scale, but it requires expensive facilities and large storage areas.
Gravity energy storage is an efficient way to store electrical energy on a large scale, but it requires expensive facilities and large storage areas. Illustrative photo not contractual. Credit: Shutterstock

A more efficient alternative to the lithium-ion battery

That huge batteries is one of the most popular storage solutions today. But over long periods of time they lose energy through self-discharge. This is an almost non-existent drawback of UGES. Since the sand is at the heart of the system, no energy is lost through self-discharge. Thanks to this, the storage can thus take place over a very long period, up to several years. Added to this are the investment costs for underground storage is only estimated at between 1 to 10 USD/kWh the infrastructure is already “ready”. Next, giant batteries like Tesla’s Megapacks cost up to several hundred dollars per kilowatt-hour. More information : dx.doi.org

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