Thermal electric conversion. Also known as thermocouples generates electrical energy via a temperature differential.
Make thermocouples into a thin pliable foil shaped cells. and use this to make the outside layer of the coat.
On cold days the escaped heat energy could be used to place resistive heating elements in your gloves, armpits, hat or other areas that would improve "comfort" If you made the heating elements out of peltiers. In the summer you could use the excess body heat to cool you or power a fan. Using TEC's could increase the insulation efficiency of your coat by a significant factor or cooling rate on a hot day!
This could also be used to charge your cell phone or ipod via convenient usb cable.
A body averages 100w of energy release, but more like 200+ during times of heavy activity. TEC's have an efficiency of about ~10% so theoretically we could generate 10-20 W from our coat alone! Definitely enough to charge a cell phone and more discrete than solar cells on your jacket.-- metarinka, Dec 07 2010 But, um, wouldn't this lead to a net loss of heat from your body in the winter?-- DIYMatt, Dec 08 2010 // net loss of heat //
No, a net would be even colder. Try a string vest.-- 8th of 7, Dec 08 2010 no this would be a gain. If we think of a person standing out in the cold it is assumed that eventually ALL the heat from the body will be lost to the surrounding air. putting a thermal electric layer on the outside simply "catches" the heat on the outside of the coat before it is lost anyways and turns it into electricity. A coat that is even 5 percent warmer is still warmer.-- metarinka, Dec 10 2010 But the peliter effect works by transfering heat - to generate electricity it has to move heat from the inside of the coat to the outside, which will in turn cool you faster than just having a thick coat. Not to mention that to get any measurable voltage from this you would have to have a very thin coat in the first place for enough heat to get through.-- DIYMatt, Dec 10 2010 random, halfbakery