In a recent study, researchers from the European Environmental Bureau (EEB), the Stockholm School of Economics (SSE), and the Potsdam Institute for Climate Impact Research (PIK) questioned the planned development of new nuclear capacities in the energy strategies of the United States and certain European countries.
…the up is at the surface and the down is at the bottom of the mine shaft? I’m not talking about horizontal ones, of course. You let water in, generating power, and then, to regenerate empty space and with that the capacity to again generate power, you spend energy to pump it up.
As to volume, there’s some gigantic mineshafts, but even small ones might warrant small installations it’s not like some pipes and a pump and generator are much of an investment. Of course, don’t try that in a salt mine geology will play an important part.
And lastly: Mineshafts aren’t the only option. There’s a lot of mountains, and they have many sides, and also plateaus and valleys. Build two concrete basins, connect them via pipe, ship in water from somewhere, voila, pumped hydro storage.