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{{Thermoelectric effect|cTopic=Applications (Power generation)}}
'''Thermoelectric generators''' (also called '''thermogenerators''') are devices which convert heat (temperature differences) directly into electrical energy, using a phenomenon called the "[[Seebeck effect]]" (or "thermoelectric effect"). Their typical efficiencies are around 5-10%. Older Seebeck-based devices used bimetallic junctions and were bulky while more recent devices use [[bismuth telluride]] (Bi<sub>2</sub>Te<sub>3</sub>) semiconductor [[p-n junction]]s and can have thicknesses in the millimeter range. These are solid state devices and unlike [[dynamo]]s have no [[moving parts]], with the occasional exception of a fan. 

[[Radioisotope thermoelectric generator]] can provide electric power for spacecraft. [[Automotive thermoelectric generator]]s are proposed to recover usable energy from automobile waste heat. 


==Uses==
Thermoelectric generators can be applied in a variety of situations. Usually, thermoelectric generators are used for small applications where [[heat engine]]s (which are bulkier but more efficient) such as [[Stirling engine]]s would not be possible.

The use of [[waste heat]] in combustion engines promises to be a high volume application field. Not only the exhaust but also cooling agents are targeted. <ref>Recodrive News [http://www.recodrive.eu/window.phtml?id=1089#293 source]</ref>

Two general problems exist in such devices: high output resistance and adverse thermal characteristics. In order to get a significant output voltage a very high Seebeck coefficient is needed (high V/°C). A common approach is to place many thermo-elements in series, causing the effective output resistance of a generator to be very high (>10kOhm). Thus power is only efficiently transferred to loads with high resistance; power is lost across the output resistance otherwise. A generator with very high output impedance is effectively a temperature sensor, not a generator. Secondly, because low thermal conductivity is required for a good TEG, this can severely dampen the heat dissipation of such a device (i.e. TEG's serve as poor heat sinks). For example it is not generally considered wise to place a TEG on an essential IC chip that requires cooling. Because of the low thermal conductivity of a TEG device, that IC is cooled at a slower rate.

Cars produce waste heat, and harvesting it can increase the fuel efficiency of the car. See the article [[Automotive Thermoelectric Generators]] for the attempt to take advantage of this.

[[Space probe]]s to the outer [[solar system]] make use of the effect in [[radioisotope thermoelectric generator]]s for electrical power.

Solar cells use only the high frequency part of the radiation, while the low frequency heat energy is wasted. Several patents about the use of thermoelectric devices in tandem with solar cells have been filed. The idea is to increase the efficiency of the combined solar/thermoelectric system to convert the solar radiation into useful electricity.

==See also==
*[[Bismuth telluride]] 
*[[Energy harvesting]]
*[[Stirling engine]]
*[[Energy harvesting devices#Thermoelectrics|Thermoelectrics]]
*[[Thermoelectric cooling]] or Peltier cooler
*[[Thermoelectric effect]]
*[[Thermoelectric materials]]
*[[Electrical generator]]

==References==
{{Refs}}

==External links==
*[http://www.electrochem.org/dl/interface/fal/fal08/fal08_p54-56.pdf Small Thermoelectric Generators by G. Jeffrey Snyder]

[[Category:Electrical generators]]
[[Category:Energy harvesting]]

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