It is true that wind and sun are widely used renewable energy nowadays. However, they’re not the most consistent source that we need for a sustainable switch. For a greener future, we need to find ways to store energy in an accessible and efficient way.
When we speak of energy storage, maybe the first thing that comes to mind is battery. It is common, but we still need cost-effective, long-term solutions.
An international team of researchers led by IIASA (International Institute for Applied Systems Analysis) has found a more refined way to store energy using abandoned underground mines.
They call the method Underground Gravity Energy Storage (UGES), which may provide effective, long-term energy storage solution while utilizing unused mining sites at the same time.
Co-author Behnam Zakeri said, “To decarbonize the economy, we need to rethink the energy system based on innovative solutions using existing resources. Turning abandoned mines into energy storage is one example of many solutions that exist around us, and we only need to change the way we deploy them.”
How UGES works
When there’s a need for electricity (say, when price is high), sand is lowered into an underground mine. Energy from the sand is then converted into electricity, and when the sand is lifted from the mine to an upper reservoir, it stores energy when electricity is cheap.
Within a mine, UGES needs the shaft, motor/generator, upper and lower storage sites, and mining equipment. More power can be available if the mineshaft is deeper and broader. At the same time, there will be more storage capacity if the mine is larger.
Lead author Julian Hunt said, “When a mine closes, it lays off thousands of workers. This devastates communities that rely only on the mine for their economic output. UGES would create a few vacancies as the mine would provide energy storage services after it stops operations.
“Mines already have the basic infrastructure and are connected to the power grid, which significantly reduces the cost and facilitates the implementation of UGES plants.”
Unlike batteries, which lose energy as they self-discharge over long periods, UGES uses sand as an energy storage medium. Meaning, there’s no loss of energy caused by self-discharge—a long, long time energy storage that ranges from weeks to several years.
As for price, the investment costs of this technology are about 1 to 10 USD/kWh and power capacity costs of 2,000 USD/kW. According to the research estimate, UGES has a a global potential of 7 to 70 TWh, with most of this potential concentrated in China, India, Russia, and the USA.
Similar technology, Gravitricity
UGES isn’t the first technology that uses old mines and gravitational forces. In 2021, Scottish energy storage start-up Gravitricity successfully constructed, commissioned, and operated a 250kW, grid-connected demonstration project.
After testing their technology, which patent was filed in 2011, for three months, the start-up got the data they needed for full-scale projects.
Gravitricity is based on raising and lowering a heavy weight (which takes form of many things, like water) to store and release energy. The system suspends weights in a deep shaft using cables. From there, it generates or absorbs electricity by dropping or raising the weight.
Since the system needs big vertical holes to work, abandoned mines are perfect for it. The start-up had aimed at South Africa, which has numerous high-quality, empty mine shafts; some could be as deep as 3 km. But they were also discussing with mine owners in other countries to take over mines for the technology.
In South Africa, the company has worked together with several mining houses, and the Innovate UK’s Energy Catalyst program has supported them. This could potentially help South Africa’s energy crisis.
As long as the weights needed for the system can be dropped over and over, many times a day, for years, and any time there’s available gravity, the system can generate energy at a lower price. And additionally, without relying on fossil fuels.
Hydropower operation in mines
Genex Power has used an abandoned gold mine in Queensland, Australia as the site of the company’s renewable energy system. They used two existing mining pits that will form an upper and a lower reservoir for a 250MW hydropower operation.
The mine is called Kidston Township, which was first discovered in 1907 and it operated until 2001.
During peak periods, water will be released from the upper to lower reservoir to generate electricity, before being pumped back to the upper reservoir. This process will be repeated each day, with a storage capacity of 2,000MWh.
Currently, Genex has four different projects in Kidston, and they’re not going to stop any time soon. Per the company’s website, “With over 470MW of renewable energy & storage projects in development, Genex is well placed as Australia’s leading renewable energy and storage company.”
Other examples of reusing old mines
Let’s say that you know one or two abandoned mines around you, and they just look miserable, but you don’t know what to do with it and circumstances don’t allow you to make them into renewable energy source.
Worry not, as there are some other uses for abandoned mines. Mind you, they’re not exactly eco-friendly because the “easiest” ways to transform them revolve around tourism or leisure. However, it may help the economy.
For example, there’s an old quarry in Shanghai in China which has become the magnificent InterContinental Shanghai Wonderland hotel. As opposed to a skyscraper, this hotel is a ‘groundscraper’ which descends vertically 16 stories from ground level into the depths of the quarry.
The bottom of the quarry was flooded to create an artificial lake and submerge the bottom 2 floors of the hotel. Therefore, hotel guests can dine in the underwater restaurant while watching fish swimming by. Other than a waterfall down the quarry wall opposite the hotel, there are also a range of water sports for guests.
There’s also The Comfort Inn in Coober Pedy, Australia, which used to be a mine famous for its opals and had been mined for about 50 years during the 1900s.
Let’s not forget about UK’s The Eden Project, the gorgeous botanical garden in Cornwall which used to be a clay pit and Slate Caverns Adventures owned by Zip world which offers thrilling ziplining experience through 200-year-old slate mines in Wales.
Sometimes, it’s not always tourism or leisure, though. For example, an abandoned iron ore mine in Japan was turned into an underground running track because it’s a great high altitude training venue due to its low oxygen levels.
Many possibilities with abandoned mines
You can always discuss what to do with the abandoned mines with your community or local officials. Regardless of the choice of reusing unused, old mines, I personally believe that it’s better to repurpose them than just letting them be.
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