The Imperium makes heavy use of thermoelectric devices and materials, an advanced form of technology based on the Seebeck effect we know now, to convert heat into electricity. The STC power-packs found lining the interior of the multi-fuel engine fireboxes, and powers the ubiquitous Imperial Guard's Lazgun, are thermoelectric devices. These power-pack are made up of a stack of layer core, much like a heat-sink, coated in a highly efficient thermoelectric material. When heated these layers convert the heat into electricity and store it in a battery.
These materials can also be incorporated into flexible materials and fashioned into a EES (extreme enviroment suits). Many environments where humans have to work in 40K are hostile, with extremes of temperature that would freeze a man solid or set their flesh ablaze in an instant, and to protect the wearer from these extremes the outer layer of the EES is often a super-insulator. While this is great for isolating the wearer from the enviroment, it also means that within the suit there is a build up of heat generated by the body. This is were the thermoelectric layer is vital as takes the build up of body heat converts it into electricity. This cools the body and keeps the internal temperature of the suit constant (as the parameters of the design only has to deal with body heat, and sub-system heat, it is easy to optimise the system), and the generated electricity is then used to power life-support subsystems via a rechargeable battery. Subsystems include the comms, air scrubber pumps, and water auto-sense gear.
Space Marines: These thermoelectric materials and devices are used in construction of the highly advanced Space Marine Power Armour. The armour incorporates a thermoelectric layer under the super-insulator ceramite armour plates. This not only cools the hyper-metabolism body of the marine, reclaiming spent power and feeding it back into the enviroment sub-system, it drastically reduces their IR (infra-red) signature make them virtually invisible to heat sensing equipment. Space Marines always appear at 'ambient temperature' when viewed through any heat sensor, auto-sense, or thermo-goggles.
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