Well, an UNLIMITED power source spawning powerful demons.
Bit of a heads up: This may have to be postponed for a few years whilst I complete school. However I should have proper internet on by about April.
I’m thinking watermills would be harder to implement unless you just ignore fluid mechanics and consider any shallow puddle as having a positive flow, or restrict them to shallow river tiles-- or city swimming pools. Infinite energy! 
As to windmills… I’ve never really understood why people are so against windfarms IRL. I mean people give reasons like they make too much noise or ruin the skyline. Really? It’s so short-sighted. Even ignorant. Sure, some people might be worried about the value of their homes depreciating, but still-- You’d rather have some fugly oil or coal powerplant nearby chucking out smog? or brown-outs? When there is a clean renewable source of power all around us? Christ almighty.
Oh, also for those that like to live by the ocean riverside-- how about those funky tide buoys?
Not quite sure how to build one out of scrap though. 
A few 30ft ropes, a few plastic jerrycans or gallon jugs, scrap metal for ratchets and pinions, floatation vests for added bouyancy vs weight of all the machines inside…plenty of wires, more scrap metal and wire for transformers…
Also opening rifts in reality to draw in power from a higher dimension is a really bad idea. Not a bad idea, as potentially it’s free energy forever, or at least until the energy states of the two dimensions equalize, but… Yeah. Gordon freeman and the Mi-Go say hi.
Then again the world is already a disaster zone. You’re a survivor. Who cares if creatures from clown hell want to invade if you can knock them senseless-- and power your doom-mobile’s seatwarmer at the same time.