Perhaps you know something about this sort of energy I read about involving waterways as a source of renewable energy. The difference between it and solar or wind was that when the supply exceeds the demand there was no need for batteries because the system would automatically move the massive amount of water back up to the top of whatever collector they were using should there be no demand for the energy at the time.

Is this ringing any bells for you? You seem a great deal better-informed than I do on this topic so I am hoping you can help me out here.