The US is seeking ways to store renewable energy for longer periods. Many of the battery systems poop out after about four hours. Pumped hydro, which involves pumping water to an up-hill reservoir, requires a hilly topography. This Canadian company has an interesting approach: pump compressed air into a water-filled cavern in the ground.
A company called Hydrostor, based in Toronto, Canada, uses excess renewable energy on the grid to pump compressed air into subterranean caverns filled with water. That forces the water aboveground into a reservoir. When the grid needs electricity, Hydrostor lets that water flow back into the chamber, pushing the air back to the surface to drive turbines. “We’re kind of creating a piston underground of water,” said Jon Norman, president of Hydrostor. “We’re actually building a cavity out using techniques that they use in the hydrocarbon storage industry to store propane and butane.”
https://grist.org/climate/long-duration-energy-storage-batteries-store-solar-wind-power/
Being able to store excess renewable energy near where it’s used will not only save customers from paying high peak-demand prices. It should also reduce the need to build or renovate transmission lines.
Darcy Hitchcock 