Pumped hydro use cheap electricity at night made by evil coal fired power stations to pump water uphill to a high reservoir, when demand and prices are high during the day and evening water is run through turbines and out to the lower reservoir, late at night cycle starts again. The hydro station makes a profit on the arbitrage opportunity it makes no additional electricity in fact loses about 30% due to inefficiency, all it can do for the electricity market is in theory is to take a little off the spike highs but raise the prices at low demand times, for politicians to claim extra electricity is a fraud, a huge white elephant for the benefit of civilian engineering and construction firms, all about getting the idiot green and 'think big' vote.
