In very limited cases, based obviously on local geography, pumped storage works.
That said, there is a risk most are willing to ignore — what if the pipes break? Water has (& will) go somewhere and it ain’t gonna wait for you to pull your head out.
Case in point. I used to work for PacificGas&Electric. A project associated with mine was pump storage. Built and ready to go. Would have made us bushels of dosh, and on the year’s bonus for getting it done on time (i.e., personally it was worth $16k to me).
Well, the damned pipe broke and flooded a town. Ensuing lawsuit not only doomed the project but killed the bonus. Bugger.
Any project that does not seriously address the “What if?” issues is run by idiots.
Damn, good story! Hopefully just property damage downstream.