Comment by bananabreakfast

You're wildly underestimating how complicated pumped hydro is.

For one thing, existing dams absolutely cannot be converted to pumped hydro. Dams do not store water below them. Water flows downstream because a dam is in a river. There is no water to pump uphill. Unless, of course, you also build a second dam very close downstream to create another lower reservoir. This is usually a bad idea, and better to just find better geography that will support a new pumped hydro dam.