Thermo-electric generators can provide us free energy from heat that would otherwise be wasted.
Thermo-electric generators have been around for a while now, but never as efficient or small as they are today. Simply put, they generate electricity when they get hot. The amount of energy these little guys produce is directly proportional to how hot it is. Here's a little diagram of how it works. Essentially an sandwich of different types of semiconductors. The heat provides the energy to transfer electrons between them, thus creating electricity. The best part about this technology is we can use any excess heat source to create free energy. Car mufflers, hot pipes in buildings, or any industrial process can have energy siphoned off from it. These generators help us take energy that would other wise be completely wasted. One of the best uses of this technology is around the campfire, or a nice wood burning stove. These create the ideal amount of heat for the generator. Here's a great video on how to make your own.