With regards to thermoelectric heat pumps and power generation: In a previous job I used to use Peltier Effect heat pump modules. These were approximately 40mm x 40mm x 4mm thick and could be fed with anything up to 35V at 2A. The modules were use for heating an cooling scientific lab samples prior to viscosity measurements being made.
If you put a load across the terminals and a temperature difference across the device then it would supply current to the load i.e. thermoelectric generation. A friend and I devised an idea for an aluminium pyramid (square base) bonded to the hot side of the peltier module and water cooling behind. The apex of the pyramis could safely be put into a candle flame and the aluminium pyramid would evenly spread the heat flux across the whole surface area of the peltier.
I have retraced the supplier as Marlow Industries and they make a 71W device which will handle a delta-T of 68 Centigrade – cost is about US$50. A new sort became available which would handle 135 Centigrade across the device. I am still trying to locate the supplier
A small quantity of these panels could power a laptop PC from a source of near-boiling water – such as a wood stove. The cooling effect is also quite impressive if you reverse the current and I remember seeing frost form on the surface of the cold side after a few seconds of current being reversed. I think we used to be able to do 90 centigrade to -10 and back in under a minute! Using platinum resistance thermometers we used to be able to control the temperature to better than 0.1 Centigrade.