[sir_bearington]

Pumped hydroelectric has good capacity, but doesn't scale well. The right geography is the main limiting factor, accessibility is a second. The places with good hydroelectric potential tend to be very remote, in the mountains. It's extremely hard to do large earthmoving and concrete construction in remote places. The places that have simultaneously the right topology and relatively easy accessibility are limited.

[AstralStorm]

The alternative is essentially big water towers, and that has serious construction challenges not solved yet.