Proponents say gravity-based systems can help meet long-term storage needs. But there is also doubt about the future of the approach, as they require a lot of work to build and may be more difficult to maintain than expected. Energy Vault is making progress on its planned facility in China, although the company is currently deploying several lithium-ion battery installations.
The biggest squeeze
Let’s go back to high school physics for another concept: pressure. If you compress something into a smaller space, you are increasing the pressure.
Converting that pressure into useful energy is the idea behind compact-air energy storage. All you need is an underground salt cave. When you have electricity to use, you can run pumps to push air through the tunnel. Then when you need to extract power, just release a valve and let the escaping air spin a turbine to generate electricity again.
Only a pair of these facilities operate globally, one in Germany and one in Alabama. In the past, they were tied to fossil fuels because they worked with natural gas power plants. But now, companies want to re-evaluate compressed-air storage, using it for renewed goods and expanding the area where it can be used.
Earlier this year, local governments in California signed a contract with Hydroster, the world’s largest compressed air storage facility. Instead of relying on natural geological conditions, the hydroster digs three shafts into the ground to store the compressed air.
It’s a billion-dollar project, and could be up and running as soon as 2028 to help store energy and use California’s grid off the grid.
Other groups want to take a different approach to the same concept. Energy Dome, an Italian startup, wants to compress carbon dioxide instead of air to store energy. This massive underground storage never required tunnels—for more details, see my story on Energy Dome from last year.
Earth to battery
Some groups are looking to combine these new approaches with energy storage in an effort to generate electricity with new power plants that are more flexible.