Thermoelectric generator

Thermoelectric effect
Principles Thermoelectric effect Seebeck effect Peltier effect Thomson effect Thermopower Seebeck coefficient Ettingshausen effect Nernst effect
Applications Thermoelectric materials Thermocouple Thermopile Thermoelectric cooling Thermoelectric generator Radioisotope thermoelectric generator Automotive thermoelectric generator

Thermoelectric generators (also called Seebeck generators) are devices that convert heat (temperature differences) directly into electrical energy, using a phenomenon called the "Seebeck effect" (or "thermoelectric effect"). Their typical efficiencies are around 5–8%. Older Seebeck-based devices used bimetallic junctions and were bulky. More recent devices use semiconductor p–n junctions made from bismuth telluride (Bi₂Te₃), lead telluride (PbTe), calcium manganese oxide, or combinations thereof, depending on temperature. These are solid-state devices and unlike dynamos have no moving parts, with the occasional exception of a fan or pump.

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

Uses

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

• Many space probes, including the Mars Curiosity rover, generate electricity using a thermoelectric generator whose heat source is a radioactive element. For more details, see the article: Radioisotope thermoelectric generator.
• Cars and other automobiles produce waste heat (in the exhaust and in the cooling agents). Harvesting that heat energy, using a thermoelectric generator, can increase the fuel efficiency of the car. For more details, see the article: Automotive Thermoelectric Generators.
• In addition to in automobiles, waste heat is also generated in many other places, such as in industrial processes and in heating (wood stoves, outdoor boilers, cooking, oil and gas fields, pipelines, and remote communication towers). Again, the waste heat can be reused to generate electricity. In fact, several companies have begun projects in installing large quantities of these thermoelectric devices. Some companies include Sheetak ([1]), Thermal Electronics Corp., Custom Thermoelectric, Marlow Industries, tecteg MFR., wellentech and TEG Power. Other companies are developing consumer-level applications to capture the energy commonly wasted during cooking. A handful of USB cooking pots have emerged, such as the Hatsuden Nabe thermoelectric cookpot Stealth Power Systems, and the PowerPot. Wood stove TEG12VDC-24AIR and TEG12VDC-24LIQUID TEG Generators producing enough power to trickle charge 12VDC and 24VDC batteries. Thermal Electronics Corp.
• Microprocessors generate waste heat. Researchers have considered whether some of that energy could be recycled. (However, see below for problems that can arise.)
• 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.^{[citation needed]} The idea is to increase the efficiency of the combined solar/thermoelectric system to convert the solar radiation into useful electricity.

Efficiency

Thermoelectric generators typically have lower efficiency than mechanical generators such as Stirling engines, i.e. they generate less electric power for the same heat flow. For a discussion of the factors determining and limiting efficiency, and ongoing efforts to improve the efficiency, see the article Thermoelectric materials - Device efficiency.

Limitations

Besides low efficiency and high cost, two general problems exist in such devices: high output resistance and adverse thermal characteristics.

• High output resistance - 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 (>10Ω). 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.
• Adverse thermal characteristics - because low thermal conductivity is required for a good thermoelectric generator, this can severely dampen the heat dissipation of such a device (i.e. thermoelectric generators serve as poor heat sinks). They are only economical when a high-heat source can be used above 200°C for watts generated and if only small milliwatts are needed then any temperature difference with correct design can be achieved.^{[citation needed]}

See also

• Bismuth telluride
• Energy harvesting
• Stirling engine
• Thermoelectrics
• Thermoelectric cooling or Peltier cooler
• Thermoelectric effect
• Thermoelectric materials
• Electrical generator
• Thermionic converter

External links

• Small Thermoelectric Generators by G. Jeffrey Snyder
• Kanellos, M. (2008, November 24). Tapping America’s Secret Power Source. Retrieved from Greentech Media, October 30, 2009. Web site: http://www.greentechmedia.com/articles/read/tapping-americas-secret-power-source-5259/
• LT Journal October 2010: Ultralow Voltage Energy Harvester Uses Thermoelectric Generator for Battery-Free Wireless Sensors
• Biolite Camp Stove - Biofuel stove and Thermogenerator in one.