Hydropower

with flow ,head height vs outlet height calculate how much available power can be extracted.

beavers are some of the best dam builders there are so live trapping can be worthwhile if you need to for smaller creeks.

peltier wheels can be 3d printed in pla or abs and are cost effective for power production.

squirrel cages from old furnaces work well for keeping batteries charged.

http://www.zotloeterer.com/welcome/gravitation-water-vortex-power-plants/

very neat technology, on a mass global scale it could influence earths rotational energy ?