A couple of weekends ago, I was on a remote Gulf Island with some friends. They had a lovely cabin on a bluff, but it didn’t have any electricity. I was, I’m a little embarrassed to admit, delighted by this device, called the Ecofan (click to enlarge):
This little fan sits on top of the wood stove, and whirs like magic, pushing the stove’s heat around the room. Here’s an ad that shows how they work.
There were six arts majors at the cabin, so nobody could explain with any kind of authority how it worked. I had the notion that it had to do with a thermoelectric process, but, well, lacked the words.
The fan has something called a Peltier element in it, which works as a heat sink. Electricity is generated by the difference in temperature between the side facing the stove, and the other side. This electricity powers the fan. I gather that’s why the top parts of these fans have all of the metal bits, to increase the surface area and the temperature difference.
In any case, I thought it was pretty cool. Here’s a video showing somebody’s hacked together homemade version:
Coincidentally, I read about some rubber boots on Springwise today that aspire to exploit a thermoelectric effect to recharge your mobile phone. It apparently takes you 12 hours of charge time to get one hour of phone power, so it’s really more gimmick than useful tool.