It could make a nice option for huge abandoned open cast mines - build a dam across the pit, flood it and then pump water from one side to the other using solar-generated electricity, allowing it to flow back to generate electricity as and when needed.
A big problem is those mines usually leave behind pretty toxic remains so the water you're pumping around is extremely hostile to the people and equipment you're thinking of putting it through/near. Then there's the chance of a dam collapse releasing that toxic water outside the mine.