It's been a while, hasn't it? Job hunting kinda drained away my ideas, so I'm going to describe a basic principle today.
Brownian motion is the hardest means of harnessing energy, but also in a way the most useful. Brownian motion is the random molecular motion from heat, and it can technically be harnessed to do useful work.
I once read a piece (I forget where, like most things I know), asking the reader to imaging having a car with no engine, perfect brakes, and in the middle of a massive hailstorm. The car is in front of a hill. When the brakes are deployed, the car doesn't move, when not deployed, the car is pushed by the momentum imparted by the hail. Using the brakes cleverly, depressing them when hail lands in front and releasing when hail lands in the back, the car can go up the hill. Even go up the hill reasonably quickly. This is how brownian motion can work for you.
Technically, this means that you could recycle heat directly into useful work, but you'd have to be very clever to do so. Probably more clever than current engineering allows. (Although biologists tell me that our own cells have some Brownian motion utilization systems, which is interesting.) But for now, the closest we have to this technology is Stiller's engine.
The reverend Stiller lived in a highly industrial town, and many of his parishioners were maimed in boiler explosions. Boilers didn't explode very often, but there were so many in town that somebody inevitably was around one. So he studied mechanical engineering to try and find a better way to transfer power. One that could not explode. He eventually produced a heat-differential type engine that had no moving parts. The user put one end into a fire, and the other hung in the room, and the temperature difference made power. This was useful, completely silent (except for the fire, but fires are reasonably quiet), and most importantly, didn't explode under pressure. Stiller's parishioners were safe. Since then, the technology is often used in submarines, to produce completely silent operation. I recommend them for any power system that needs to be quiet, and has a readily available heat difference. (Or where you can build a fire, which is the beauty of it -- any heat source at all works.)