About a year and a half ago, someone explained the principle underlying how a peltier tile works to me. If your unaware of these amazing little gizmos, they essentially have the power to create a heat difference; connect the tile to a power source, heat one side, and the other side will cool. Conversely, chuck an ice cube on one side, and the other side will get hot. They're often used in small mini fridges like the one you might have had in a student dorm, and rely on the warm ambient temperature on one side to chill the interior of the fridge on the other.
This ability to create a temperature difference can also be exploited in another way; if you create the temperature difference yourself, the tile can generate power. I first saw this in the following youtube video, and was baffled at how efficient it can be.
The major issue with generating power through peltier tiles is that without something to constantly apply an inverse temperature to the other side, the heat will diffuse through the device, and as a temperature difference no longer exists, no power is generated. Because of this, peltiers often feature a large heatsink on one side to cool it as quickly as possible.
I commute year round via bicycle, and in the UK this means spending a great deal of time in the dark. I've got an excellent set of lights that I use for both mountain biking and commuter duties, but remembering to keep them charged is a pain, as well as continually checking the rear of my bike as I'm riding along to ensure that my rear blinker hasn't run out of juice.
I realised that if I planted a peltier tile into my seat, I could harness the thermal energy produced from my body, and rely on the air rushing underneath the seat to cool the other side of the peltier tile. The current put out by a peltier is very small, so I ordered an ultra low voltage converter to transform it into something that could power 2 small red LED's.
I then set about hacking an old seat to pieces. I managed to find something that was wide enough to accommodate 2 peltiers side by side. These were inserted into the seat, along with an aluminium backing plate (having ceramic outer plates for good thermal conductivity, peltiers are very delicate) and an old aluminium heatsink that I bent into shape.
The end result was a very rough principle proving prototype of the system. I set my trusty commuter up on a turbo trainer, and put the saddle on the bike. I then start down and sat pedalling. After a few seconds, the LED's began to glow, and continued to do so as I stayed seated.
The addition of a small capacitor in the circuit would mean that the LED's could stay lit for a minute or so after getting of the saddle, for long efforts standing up or waiting at traffic lights.
Although perhaps not a feasible commercial product due to much more efficient dynamo's, I enjoyed playing around and am considering taking the project further. Expect a line of thermally conductive lycra soon!