yeah, good luck with that one though. it tends to be ecologically problematic, and very, very hard to find places good for this. It has happened, but you can’t just build these things as demand desires.

This is why battery based and thermal based energy storage is taking quite the aggressive focus on research and development right now. Batteries are more of a side effect, and very easily accessible, and thermal storage is probably a lot less popular than it should be.

Generally you can do a similar thing with traditional hydro anyway, plus it produces a base level of power anyway.