As I understand it, the main challenge with pumped storage is that you can't do it everywhere. You need fairly specific geography for it, and it's a big civil engineering project.
Here's a good video on by Practical Engineering:
> You need fairly specific geography for it, and it's a big civil engineering project.
You need elevation difference and fairly stable soil. Everything else is technologically solveable. It's a big civil engineering project but its a profitable one and not particularly challenging.
seawater is saline, you have to be careful what you do with it because you dont want to literally salt the earth where you are (soil remediation friggin sucks).
seawater is also not valuable. You don't care about the water quality in the reservoir, you just let it fall back into the sea. If it evaporates you're losing energy but you aren't losing potable water that you sell, and it doesn't require a connection to a water distribution main.
https://youtu.be/66YRCjkxIcg