Renewable energy is fundamental to the transition to green energy for a more sustainable future. And even though its sources, such as wind and sunlight, seem unlimited, storing the energy they generate in a more efficient and accessible way is also crucial to the transition.

There are quite a few energy storage options — batteries being the most common. However, they are not yet a long-term cost-effective solution.

An international researchers' team has come up with a method of storing energy by transporting sand into underground mines that have been abandoned. The study is led by the International Institute for Applied Systems Analysis (IIASA).

Underground Gravity Energy Storage (UGES), is what the new energy technique is called. It proposes an effective way to store energy, that is also a long-term solution, while also utilising now-defunct underground mines, which are likely in millions across the globe.

The method

When the price is high, UGES generates electricity by lowering sand into a defunct underground mining site and converts the sand's potential energy into electricity by regenerative braking, following which the sand is lifted from the mine to a reservoir which is at a height, using electric motors that store energy when power is cheap.

Potential energy is basically the energy that an object holds or stores.

The fundamental components of UGES are the motor/generator, shaft, mining equipment and upper and lower storage sites. The more broad and deep the mineshaft is, the more power is likely to be extracted from the plant. The larger the mine is, the more is the energy storage capacity of the plant.

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One of the researchers said that the UGES would also create some vacancies at the mine as it would provide the service of energy storage after the mines become defunct.

The researcher added that mines already have the most basic infrastructure which is connected to the power grid. This reduces the cost significantly and also facilitates the UGES plants in their implementation.

Pros over batteries

Other storage methods/devices such as batteries lose energy over time via self-discharge over long periods.

In UGES, the energy storage medium is sand, which means no energy can be lost to self-discharge, and enables an ultra-long time energy storage that can range from weeks to many years.

As per the IIASA blog post, UGES' investment cost is around $1 to $10/kwh and the cost of the power capacity comes up to $2000/kilowatt hour (kwh). It is estimated that the technology has a global potential of 7 to 70 terrawatt hour (twh). It has the most potential in India, China, US and Russia.

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(Edited by : C H Unnikrishnan)