Re: green lunacy
pumping - generating - pumping - generating. Each time, what, 30% efficiency?
Pumped storage hovers in the 70-80% efficiency range between storing electricity (pumping with some efficiency loss through the 90%+ efficient electric motors) and generating (releasing water through the 90%+ efficient electric generators.) There are additional losses, like turbulence, heating, friction in pipes, etc. that bring you a bit below 80%.
It's much better than, say, batteries. The only competitor on a similar scale is underground compressed air storage, though I might be forgetting another GW-scale power storage system.