Storing renewable energy in old mines
By transforming underground mines into gravity batteries Metal Tech News - January 16, 2023
Last updated 4/16/2023 at 6:56am
Can old mines be repurposed as giant batteries for cost-effective and long-term storage of renewable energy? A peer-reviewed paper by a team of researchers led by the International Institute for Applied Systems Analysis (IIASA) makes a compelling case for underground gravity energy storage systems that do just that.
Matching electrical generation capacity with consumer demand is key to transitioning to a sustainable low-carbon energy future. This has been a longtime problem with traditional power sources such as coal or natural gas that could not cycle generating capacity in-step with consumer demand, which was overcome by generating extra electricity. The mismatch between supply and demand, however, becomes much more profound with the transition to renewable energy sources dependent on sunshine or wind for their electrical generating capacity.
Currently, the primary solutions for storing renewable energy for delivery to the grid when there is not enough sunshine or wind to meet consumer demand are lithium-ion or similar batteries.
While these are sufficient to meet daily fluctuations, they typically are not very good for storage times measured in days, weeks, or longer. With grids increasingly reliant on intermittent energy sources, longer-term solutions are required.
The IIASA-led research team has found that abandoned underground mines provide much of the infrastructure needed to create batteries that utilize sand and gravity for long-term energy storage.
"To decarbonize the economy, we need to rethink the energy system based on innovative solutions using existing resources," said Behnam Zakeri, a coauthor of the study and researcher in the energy, climate, and environment program at IIASA. "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 it works
The basic idea behind the underground gravity energy storage system proposed by the international research team is to store sand both on the surface and underground at a mine.
When there is excess electricity that needs to be stored, that energy is used to run motors that lift the sand to the surface or an upper reservoir. When power needs to be fed into the grid, the system converts the potential energy of the upper sand reservoirs into electricity via regenerative braking as the sand is lowered into the mine.
The deeper and broader the mineshaft, the more power can be generated, and the larger the mine, the higher the plant's energy storage capacity.
Since the storage mediums are sand and gravity, such a system can store energy for weeks or even years without any loss.
The IIASA team estimates that investment costs of transforming an underground mine into a gravity battery is around US$1 to $10 per kilowatt-hour.
While there are already enough abandoned mines around the world for 7 to 70 terawatt-hours of storage capacity – mostly in China, India, Russia, and the United States – newly closed mines would be ideal from both a societal and cost standpoint.
"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," says Julian Hunt, lead author of the study and researcher in the energy, climate, and environment program at IIASA. "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."
The peer-reviewed paper Underground Gravity Energy Storage: A Solution for Long-Term Energy Storage was published on Jan. 11, 2023 in the journal Energies.
The International Institute for Applied Systems Analysis conducts research into the critical issues of global environmental, economic, technological, and social change faced in the 21st century.