• Thermoelectric Generator Definition: A thermoelectric generator (TEG) is a device that converts heat energy into electrical energy using the Seebeck effect, which occurs when there is a temperature difference between two different conductors.
• Working Principle: TEGs work by creating a temperature difference across a thermoelectric module, generating an electric current that can power an external load or charge a battery
Common Materials: Common thermoelectric materials include bismuth telluride for low temperatures, lead telluride for medium temperatures, and skutterudites for high temperatures.
• Applications: TEGs are used for power generation from waste heat, cooling electronic devices, and powering remote devices with radioisotopes or solar heat.
• Challenges and Future Directions: TEGs face challenges like low efficiency and high cost, but future research aims to find new materials and develop advanced systems to improve performance.
A thermoelectric generator (TEG) is a device that converts heat energy into electrical energy using the Seebeck effect. The Seebeck effect is a phenomenon that occurs when a temperature difference exists between two different conductors or a circuit of conductors, creating an electric potential difference. TEGs are solid-state devices that have no moving parts and can operate silently and reliably for long periods of time. TEGs can be used to harvest waste heat from various sources, such as industrial processes, automobiles, power plants, and even human body heat, and convert it into useful electricity. TEGs can also be used to power remote devices, such as sensors, wireless transmitters, and spacecraft, by using radioisotopes or solar heat as the heat source.
How Does a Thermoelectric Generator Work?
A thermoelectric generator consists of two main components: thermoelectric materials and thermoelectric modules.
Thermoelectric materials are materials that show the Seebeck effect, generating an electric voltage when there is a temperature difference. They are classified into two types: n-type and p-type. N-type materials have extra electrons, while p-type materials lack electrons. When connected in series with metal electrodes, these materials form a thermocouple, the basic unit of a thermoelectric generator.
A thermoelectric module is a device that contains many thermocouples connected electrically in series and thermally in parallel.
A thermoelectric module has two sides: a hot side and a cold side. When the hot side is exposed to a heat source and the cold side is exposed to a heat sink, a temperature difference is created across the module, causing a current to flow through the circuit. The current can be used to power an external load or charge a battery. The voltage and power output of a thermoelectric module depends on the number of thermocouples, the temperature difference, the Seebeck coefficient, and the electrical and thermal resistances of the materials.
The efficiency of a thermoelectric generator is defined as the ratio of electrical power output to heat input. This efficiency is limited by the Carnot efficiency, the maximum possible efficiency for any heat engine between two temperatures. The Carnot efficiency is given by:
ηCarnot=1−ThTc
Seebeck Power Generation Equation 1
where Tc is the temperature of the cold side, and Th is the temperature of the hot side.
The actual efficiency of a thermoelectric generator is much lower than the Carnot efficiency due to various losses such as Joule heating, thermal conduction, and thermal radiation. The actual efficiency of a thermoelectric generator depends on the figure of merit (ZT) of the thermoelectric materials, which is a dimensionless parameter that measures the performance of a material for thermoelectric
applications. The figure of merit is given by:
ZT=κα2σT
Seebeck Power Generation Equation 2
where α is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature.
The higher the figure of merit, the higher the efficiency of the thermoelectric generator. The figure of merit depends on both intrinsic properties (such as electron and phonon transport) and extrinsic properties (such as doping level and geometry) of the materials. The goal of thermoelectric materials research is to find or design materials that have a high Seebeck coefficient, high electrical conductivity, and low thermal conductivity, which are often conflicting requirements.
What are Some Common Thermoelectric Materials?
Thermoelectric materials can be classified into three categories: metals, semiconductors, and complex compounds.
Metals have high electrical conductivity but low Seebeck coefficient and high thermal conductivity, resulting in a low figure of merit. Metals are mainly used as electrodes or interconnects in thermoelectric modules.
Semiconductors have moderate electrical conductivity and Seebeck coefficient but high thermal conductivity, giving them a moderate figure of merit. They can be doped to create n-type or p-type materials with varying carrier concentrations and mobilities. Semiconductors are commonly used as thermoelectric materials for low-temperature applications (below 200°C).
Complex compounds have low electrical conductivity but a high Seebeck coefficient and low thermal conductivity, resulting in a high figure of merit. Complex compounds are usually composed of multiple elements with different valence states and crystal structures, which create complex electronic band structures and phonon scattering mechanisms that enhance thermoelectric performance. Complex compounds are widely used as thermoelectric materials for high-temperature applications (above 200°C).
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