Here is an Idea for free hot water.
Simply make a grid of black plastic (or whatever) tubes on the roof of the house.
Connected to the water-tank.
Remember Hot water goes up... Cold water goes down... So connect on both sides of the water box, but one higher then the other... Thus, the water will flow on it's own, and heat up.
Here is an idea for free light... only day time... sorry
Get a 2 Liter coke bottle. Fill it up with clean water. 1 Lid of bleach. 1 of those black camera "film containers", placed over the lid (to protect the lid from the weather)
Place the bottle on the roof, with only the upper part (the conical part that ends at the lid / or 1/3rd of the bottle) on the outside. The rest of the bottle inside.
Due to the light refraction, a room will light up the very well. Output would be something like a 60w incandescent.
4 or 5 will be equivalent to a couple of florescent tubes lights.
Don't wary about cloudy days, there isn't much change to the illumination.
CHECK:
http://www.rts.org.br/noticias/destaque-2/litros-de-luz
AND CHECK:
http://www.youtube.com/watch?v=KeM8PhtUXGk