Thermoelectric generators are devices that convert temperature differences into electrical energy, using a phenomenon called the "Seebeck effect" . Their typical efficiencies are around 5–8% however there are several units available boasting efficiencies as high as 12 - 14%. These are solid-state devices and can work with no moving parts using passive cooling however many high temperature applications necessitate fans or pumps.
Thermoelectric generators have a wide array of uses. Typically, thermoelectric generators are used for small applications where heat engines such as Stirling engines would not be possible. Thermoelectric generators are more reliable and have a smaller chance of breaking over time and use. Spacecraft are a typical example of an application where maintenance is next to impossible after launch.
Many space probes generate electricity using a thermoelectric generator using a radioactive element as the heat source. Cars and other automobiles produce waste heat. Harvesting it, using a thermoelectric generator, can increase the fuel efficiency of the car.
Waste heat is generated in many places, for example industrial processes like oil refineries, generate low and high temperature heat. Also heating systems ( i.e.wood stoves, pellet stoves, gas & propane boilers) can produce a lot of electricty having a minimal impact on the operation of the heating system.. Again, the heat can be reused to generate electricity. In fact, several companies have begun projects in installing large quantities of these TEGs to capture industrial waste heat from exhaust stacks.
Thermoelectric generators currently have a lower efficiency than mechanical generators such as Stirling engines, though it is widely believed that TEGs will surpass the mechanical generators in the near future just as LED bulbs surpassed the incandescent bulb. Currently there are several models of Thermoelectric Generator Modules that are available with up to 14% efficiency. One company claims to have developed a module with 30% efficiency.
Tegpro Thermoelectric Generator Modules available at Tegmart
With the current technology, two general problems exist besides the low efficiency and high cost: high output impedance and unfavorable thermal characteristics.
High output resistance - in order to get a significant output voltage a very high Seebeck coefficient is needed. A common approach is to place many thermo-elements in series, causing the effective output resistance of a generator to be very high. Thus power is only efficiently transferred to loads with high resistance; power is otherwise lost across the output resistance. A generator with very high output impedance is effectively a temperature sensor, not a generator. This problem is solved in some commercial devices by putting more elements in parallel and fewer in series or by using state of the art energy harvesters & regulators such as the Tegulator products.
Unfavorable thermal characteristics - because low thermal conductivity is required for a good thermoelectric generator, this can severely discourage the heat dissipation of such a device . TEGs must be used with heat sources above 200°C when many watts are needed, but if only small power (milliwatts) is needed, then almost any temperature difference can be achieved with correct design.
More information about Thermoelectric Generators (Wikipedia)
Videos of Thermoelectric Generators (YouTube)
Thermoelectric Generator Forums (TEGPower.com)
More information Web Sites about Thermoelectric Generators below:
Basics of Thermoelectric Generators
Thermoelectric Generator Definitions
Basic information on the Thermoelectric Generator
More information on the Thermoelectric Generator
Electricity from Heat Educational Page
Stove Lite (World's First Wood Stove Powered Thermoelectric Lantern)
Devil Watt (Wood Burning Stove Thermoelectric Generators)
TEGPRO (Experts of TEG systems)
Tegulator (Complete line TEG power regulators Made in the USA)
Tegmart (Online Store: Wood Burning Stove Thermoelectric Generators, Energy Harverting Regualtors (Tegulator), and other Accessories)