Pumped hydro is a time-tested way to store energy. Excess power is used to pump water uphill into a storage area, usually a lake, then released as needed to power turbines.
Germany plans to use wind energy to pump water into abandoned coal mines inside a mountain for later use. The water will be continuously recycled so it can’t contaminate water supplies.
This is such an elegant solution to energy problems. If only we could get more stuff like this going I would be more hopeful about the future of our planet.
Stored energy is the Holy Grail for energy, both renewable and otherwise. Once that happens reliably on grid scale, everything changes.