I was looking at an interesting approach to micro-hydro power, which involves using solar-powered pumps to move water UP to a retention pond some distance up a hill, and then when you need electric power and it's cloudy or night, you run water from the up-pond to the down-pond. No, it's not terribly efficient, however, if you have the right terrain and the ability to cut a below-frost-line channel for the necessary piping, it's an interesting approach for micro-hydro.

It's also done on a HUGE scale for some hydro-electric generating stations, they take some of the excess grid energy capacity they have during low-need times to pump water back up into the reservoir and then during high-demand times, they just use the hydro power to supply the grid. It augments the natural fill rates for the systems.