Harry Bloomfield wrote:
Water?

I would not think the water capacity of a disused mine would be enough
to make it worth while.

The argument goes that, since PE=mgh, you can get away with less m by having
a bigger h. If the mine is 2km down, you can use 10x less water than pumped
storage where you might only get 200m.

Unfortunately, the problem is that mines contain corrosive things and all
those nice support structures that are keeping the mine open may not stay up
for long with all this corrosive water sloshing about.

THeo