The canonical example of harvesting the heat differential is the biolite stove[1] it uses a thermoelectric generator[2] to provide up to 4 watts (peak) of power.
I'm on beer fuel atm and have only read it briefly, but isn't that pure, free energy? With a solid state device. Why do we not have some of these things around our fridge etc.
Because if it generates energy from your fridge it means you deeply failed at insulating your fridge, and you have to spend several times as much energy putting the cold back inside.
In most places you can use significantly more efficient devices to turn heat differences into electricity.
I think he is more talking about the heat that the fridge outputs to cool the inside, which is likely warmer than the ambient temperature in the room. Just a guess.
I was; the fridge outputs quite a bit of heat, good for raising seedlings on top of. But I would imagine the expenses involved in this stuff wouldn't make it sensible for a fridge (I don't think they draw that much power anyway).
I just had never heard you could harness this, it's cool.
Edit: Bit late to the party, 1821. Bit of catching up to do.
Okay, then that means you're ventilating the output heat poorly. If there is a significant difference in temperature between the coils and the room, you're spending more power than you need to when you pump heat out of the fridge. Adding fins or fans would save you more power than you could ever recover.