A Thermoelectric power generator is any solid-state device that can convert heat directly into electricity. Such devices are based on thermoelectric effects involving interactions between the flow of heat and of electricity through solid bodies.
All thermoelectric power generators have the same basic configuration. A heat source provides the high temperature, and the heat flows through a thermoelectric converter to a heat sink, which is maintained at a temperature below that of the source. The temperature differential across the converter produces direct current (DC) to a load (RL) having a terminal voltage (V) and a terminal current (I). There is no intermediate energy conversion process. For this reason, thermoelectric power generation is classified as direct power conversion. The amount of electrical power generated is given by I2RL, or VLI.
With thermoelectric modules the direction of energy flow is reversible. For example,if the load resistor is removed and a DC power supply is substituted, the thermoelectric device can be used to move heat from the “heat source” element and lower its temperature. In this configuration, the reversed energy-conversion process of thermoelectric devices is invoked, using electrical power to pump heat and produce refrigeration. Any thermoelectric device can be applied in either mode of operation, though the design of a particular device is usually optimized for its specific purpose.
A systematic study began on thermoelectricity between about 1885 and 1910 by 1910 by a German scientist named Edmund Altenkirch. Altenkirch satisfactorily calculated the potential efficiency of thermoelectric generators. Unfortunately, the only materials available at the time were metallic conductors, leaving the thermoelectric generators with an efficiency of mo more than 0.5 percent. By 1940 a semiconductor-based generator with an efficiency of 4 percent had been developed. After 1950, thermoelectric power-generating efficiency gains were small, and efficiencies had reached not much more than 10 percent by the late 1980s. Regardless, low-power varieties of thermoelectric generators have proven to be of considerable practical importance. For example, those fueled by radioactive isotopes, which are generally used to power data transmissions from space.
Thermoelectric power generators vary in size and shape, depending on the type of heat source/sink, the and the power requirement. During World War II, some thermoelectric generators were used to power portable communications transmitters. Improvements made in semiconductors between 1955 and 1965 expanded the practical range of applications. In practice, many units require a TEG power regulator to convert the generator output to a usable voltage.
Thermoelectric generators have been constructed to use natural gas, propane, butane, kerosene, jet fuels, and wood, as heat sources. Commercial units usually range from 10- to 100-watts of output power. They are used in remote area applications such as navigational aids, data collection and communications systems, and cathodic protection.
Solar thermoelectric generators have been designed to supply orbiting spacecraft power, though they have not been able to compete with efficient silicon solar cells. Thermoelectric devices can generate electrical power for use by other thermoelectric devices in dark areas of the spacecraft and to dissipate heat from the vehicle, utilizing solar heat from the Sun exposed side of the spaceshuttle.
Radioactive isotopes can be used to provide a high-temp heat source for thermoelectric generators. As the thermoelectric modules are resistant to nuclear radiation the generators provide a useful source of power for many unattended and remote applications. For example, radioisotope thermoelectric generators can provide electric power for deep-ocean data collection and various isolated communication systems. The power range of radioisotope thermoelectric generators can exceed over 100 watts. An example of this application is the Mars Curiosity Rover.
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