[wmjinman]

It's the "water cycle". Sun AND gravity causing water to constantly rise and fall. The weight of the water at higher elevation (like above the dam) is "potential energy". When if falls, it becomes "kinetic engergy", transferred to the turbine becoming mechanical energy, and then electrical energy. - if I remember my grade school science class correctly -

I'm not sure gravity is actually "energy"? It's a "force", right? When interacting with objects of mass, "potential energy" is created out of that interaction....

As I recall, even Einstein was struggling to figure out what gravity actually is ......