gravity (notably pumped hydro) is cheap for even more capacity but has limited opportunities, and it’s not nearly as fast to trigger as the other, so it’s better used to store capacity over one week. Evaporation is a problem, but cheaply fixable.
I wonder whatever happened to the earth piston idea I saw floated a bunch of years ago. It involved cutting a cylindrical piston in the earth and drilling beneath it at an angle. You then pump water down into the space beneath the piston, causing it to lift. To extract the stored energy you simply let the pressure provided by the piston force the water back out through a turbine.
The main trick to getting it all to work is with the surfaces. You want the piston to be able to slide up and down smoothly without water infiltrating the earth or going around the side of the bore, so the whole thing needs to be sealed and smooth like an engine cylinder. The other trick is for your pumps, valves, and turbines to be able to operate reliably with huge water pressures.
I haven’t heard about the idea in years so I have no idea how it went, though I would guess it didn’t pan out for some reason.
I wonder whatever happened to the earth piston idea I saw floated a bunch of years ago. It involved cutting a cylindrical piston in the earth and drilling beneath it at an angle. You then pump water down into the space beneath the piston, causing it to lift. To extract the stored energy you simply let the pressure provided by the piston force the water back out through a turbine.
The main trick to getting it all to work is with the surfaces. You want the piston to be able to slide up and down smoothly without water infiltrating the earth or going around the side of the bore, so the whole thing needs to be sealed and smooth like an engine cylinder. The other trick is for your pumps, valves, and turbines to be able to operate reliably with huge water pressures.
I haven’t heard about the idea in years so I have no idea how it went, though I would guess it didn’t pan out for some reason.