- Also called:
- Peltier-Seebeck effect
- Key People:
- Johann Wilhelm Ritter
thermoelectricity
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What is thermoelectricity?
Thermoelectricity is the direct conversion of heat into electricity or electricity into heat via the Seebeck effect and the Peltier effect. The Seebeck effect generates a thermal electromotive force at a junction, and the electromotive force is approximately linear with the temperature difference between two junctions of dissimilar metals, called a thermocouple. The Peltier effect describes the cooling or heating of a junction when an electric current is maintained in a circuit made of two different conductors. Thermoelectric power generators have the same basic configuration: a heat source, a heat sink, and a thermoelectric converter.
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How can heat be used to create electricity?
Thermoelectricity directly converts heat into electricity using the Seebeck effect. This phenomenon occurs when a temperature difference is applied across two dissimilar electrical conductors or semiconductors, producing a voltage.
In a thermoelectric power generator, heat flows from a heat source through a thermoelectric converter to a heat sink, creating a temperature differential that generates direct current (DC). The amount of electricity produced depends on the Seebeck coefficient, the current, and the temperature difference.
Thermoelectric generators are employed in devices that require a reliable power source in isolated or remote locations, such as in spacecraft or weather monitoring stations.
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What is the thermoelectric effect?
Thermoelectricity is the direct conversion of heat into electricity or electricity into heat via the Seebeck effect and the Peltier effect.
The Seebeck effect describes the generation of a thermal electromotive force at a junction of different metals. The Peltier effect refers to the absorption or release of heat at a junction where an electric current exists. These effects also occur at the junction between a metal and a semiconductor and at the junction between two semiconductors. Thermoelectric devices can convert thermal input power directly to electrical power or transform electrical energy into thermal power for heating or cooling.
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What kinds of materials are used in thermoelectric devices?
Thermoelectric devices rely on materials that facilitate the Seebeck effect and Peltier effect, which convert heat into electricity and vice versa.
While the Seebeck effect exists in junctions of different metals, it is relatively small. A larger Seebeck effect can be achieved using p-n junctions between p-type and n-type semiconductor materials like silicon or germanium. Practical thermoelectric devices can be made of multiple p-type and n-type semiconductor legs, connected electrically in series and thermally in parallel between a heat source and a heat sink. The performance of these materials is evaluated using the Seebeck coefficient, electrical resistivity, and thermal conductivity.
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What are some uses of thermoelectricity in real life?
Thermoelectricity involves converting heat directly into electricity or vice versa, utilizing the Seebeck and Peltier effects.
Real-world applications of thermoelectricity include:
- Radioisotope thermoelectric generators These generators are reliable power sources for remote locations, such as isolated weather monitoring stations and spacecraft, using the decay of radioactive isotopes to generate heat.
- Temperature measurement Thermoelectricity is used in thermocouples to measure temperature, with the choice of metals depending on the medium's chemical properties and required sensitivity.
- Refrigeration Semiconductor thermocouples are used in Peltier refrigerators to cool small objects, maintaining precise and stable temperatures in applications like microscope stages.
- Solar thermoelectric generators These have been used to power small irrigation pumps in remote areas.
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How do thermoelectric generators work and what are their advantages and disadvantages?
Thermoelectric generators directly convert heat into electricity using a temperature difference across a thermoelectric converter. The heat flows from a heat source, through the converter, to a heat sink, producing direct current (DC).
The Seebeck effect describes the thermoelectric property of a device. A larger Seebeck effect can be achieved using p-n junctions between p-type and n-type semiconductor materials.
Thermoelectric generators have been used to power portable communication transmitters, small irrigation pumps, and in spacecraft. They are versatile and reliable power sources for isolated or remote sites.
Advantages:
* Direct conversion with no intermediate steps
* Reversible energy flow for heating or coolingDisadvantages:
* Low efficiency compared to other power generation methods
* Require better materials to improve performance1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
thermoelectricity, direct conversion of heat into electricity or electricity into heat through two related mechanisms, the Seebeck effect and the Peltier effect.
When two metals are placed in electric contact, electrons flow out of the one in which the electrons are less bound and into the other. The binding is measured by the location of the so-called Fermi level of electrons in the metal; the higher the level, the lower is the binding. The Fermi level represents the demarcation in energy within the conduction band of a metal between the energy levels occupied by electrons and those that are unoccupied. The energy of an electron at the Fermi level is −W relative to a free electron outside the metal. The flow of electrons between the two conductors in contact continues until the change in electrostatic potential brings the Fermi levels of the two metals (W1 and W2) to the same value. This electrostatic potential is called the contact potential ϕ12 and is given by eϕ12 = W1 − W2, where e is 1.6 × 10−19 coulomb.
If a closed circuit is made of two different metals, there will be no net electromotive force in the circuit because the two contact potentials oppose each other and no current will flow. There will be a current if the temperature of one of the junctions is raised with respect to that of the second. There is a net electromotive force generated in the circuit, as it is unlikely that the two metals will have Fermi levels with identical temperature dependence. To maintain the temperature difference, heat must enter the hot junction and leave the cold junction; this is consistent with the fact that the current can be used to do mechanical work. The generation of a thermal electromotive force at a junction is called the Seebeck effect (after the Estonian-born German physicist Thomas Johann Seebeck). The electromotive force is approximately linear with the temperature difference between two junctions of dissimilar metals, which are called a thermocouple. For a thermocouple made of iron and constantan (an alloy of 60 percent copper and 40 percent nickel), the electromotive force is about five millivolts when the cold junction is at 0 °C and the hot junction at 100 °C. One of the principal applications of the Seebeck effect is the measurement of temperature. The chemical properties of the medium, the temperature of which is measured, and the sensitivity required dictate the choice of components of a thermocouple.
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The absorption or release of heat at a junction in which there is an electric current is called the Peltier effect (after the French physicist Jean-Charles Peltier). Both the Seebeck and Peltier effects also occur at the junction between a metal and a semiconductor and at the junction between two semiconductors. The development of semiconductor thermocouples (e.g., those consisting of n-type and p-type bismuth telluride) has made the use of the Peltier effect practical for refrigeration. Sets of such thermocouples are connected electrically in series and thermally in parallel. When an electric current is made to flow, a temperature difference, which depends on the current, develops between the two junctions. If the temperature of the hotter junction is kept low by removing heat, the second junction can be tens of degrees colder and act as a refrigerator. Peltier refrigerators are used to cool small bodies; they are compact, have no moving mechanical parts, and can be regulated to maintain precise and stable temperatures. They are employed in numerous applications, as, for example, to keep the temperature of a sample constant while it is on a microscope stage.