You can water pump uphill, or, as they're experimenting with here, you can pump air underwater: https://www.torontohydro.com/sites/electricsystem/GridInvestment

You can water pump uphill, or, as they're experimenting with here, you can pump air underwater: https://www.torontohydro.com/sites/electricsystem/GridInvestment/powerup/Pages/CompressedAirEnergyStorageProject.aspx https://www.torontohydro.com/sites/electricsystem/GridInvest... I'm sure compressed air in other forms would be a good store. You could also raise and lower weights into a mine, it doesn't matter so long as you can convert between electric energy and kinetic potential of some kind.