Hee hee. I know where there's an already built small hydro plant for sale by a major utility. It lives at the foot of a 500' drop in a 20'x20' concrete block building with an old style soldered standing seam 250yr metal roof. As long as they don't have to maintain it, the utility will buy power all day long at their average cost of generation. The only wear part in the gizmo is the generator bearings and brushes, and it only runs at like 360rpms...

Not responsible for advice not taken...