A thermoelectric generator (TEG) is a solid-state device that converts a temperature difference directly into electricity. It has no moving parts. The technology is proven on space missions, but it has not revolutionised the car industry or replaced conventional power generation.
The process relies on the Seebeck effect, discovered by the German physicist Thomas Johann Seebeck in 1821. When two dissimilar conductors are joined in a closed circuit and the junctions are kept at different temperatures, an electric voltage is produced. This principle allows waste heat to be turned into usable power, though efficiency remains low compared with mechanical heat engines.
How it works
A thermoelectric generator uses semiconductor solids to generate electricity when subject to a temperature difference. The basic unit is a thermocouple: two different conductive materials joined together. When one junction is hot and the other is cold, a voltage is produced.
In practice, many n-type and p-type semiconductor “legs” are connected electrically in series and thermally in parallel between a hot plate and a cold plate. Output rises with the temperature difference, so the cold side matters as much as the hot side.
The performance of a material is measured by its figure of merit, ZT. This is calculated as ZT = S²σT/κ, where S is the Seebeck coefficient, σ is electrical conductivity, κ is thermal conductivity, and T is absolute temperature. A higher ZT means higher conversion efficiency. The challenge is that good electrical conductors are usually good thermal conductors. To improve ZT, researchers must lower the lattice thermal conductivity without hurting electrical flow. This is often done by adding nanostructures that scatter heat-carrying phonons more than they scatter electrons.
Materials and the nanostructuring route
According to a 2012 review by Chen and colleagues, the best bulk materials, such as bismuth telluride (Bi₂Te₃), lead telluride (PbTe) and silicon–germanium, reach a maximum ZT of about 1, and no material had then reached the target of ZT 3 or more. Bismuth telluride works best up to about 250 °C, lead telluride suits mid temperatures and silicon–germanium high ones. Magnesium silicide is, in DLR’s words, “low-priced and non-toxic”.
Two nanostructuring results stand out. In 2008, Poudel et al. reported in Science that hot-pressing ball-milled bismuth antimony telluride nanopowder gave a peak ZT of 1.4 at 100 °C. In 2012, Biswas et al. reported in Nature that scattering phonons at atomic, nano and meso scales raised the ZT of lead telluride to above 2 at around 900 K. A 2014 Nature paper reported a record ZT of about 2.6 in tin selenide crystals at high temperature, but a 2016 response argued the samples were not fully dense, so the record is disputed. As DLR put it in 2010, such experiments are “far removed from low-cost mass production”.
Real-world examples
The proven application is in space. Radioisotope thermoelectric generators (RTGs) were first launched into orbit in 1961 and, according to NASA, have flown on 27 missions, including Apollo, Voyager, Cassini and New Horizons. The Voyager 1 and 2 spacecraft have operated on RTG power since 1977. RTGs are heated by radioactive decay rather than waste heat, but they use the same thermoelectric principle.
The modern standard is the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), used on the Curiosity rover since August 2012 and on the Perseverance rover (Mars 2020). It contains 4.8 kg of plutonium dioxide, which produces about 2,000 W of heat, yielding about 110 W of electrical power at the start of the mission. The system weighs about 45 kg and has a design life of at least 14 years.
In the car sector, TEGs have not gone beyond prototypes. A DOE programme that ended around 2011–2012 tested units in a BMW X6, a Lincoln MKT and a Chevrolet Suburban. On the bench, the TEG from Amerigon (now Gentherm) peaked at 608 W with 620 °C inlet air and a 20 °C cold side. The programme’s 5–6% fuel economy improvement was a target, not a measured result. We found no evidence of any series-production car with an exhaust TEG. A December 2025 review noted that widespread adoption in vehicles “remains limited due to low conversion efficiency, material costs, and integration challenges”.
Other uses include fuel-fired generators for remote sites. Global Power Technologies, formerly part of Gentherm, makes TEGs ranging from 5 to 550 W. They burn gas to power pipeline cathodic protection, instruments and telecoms. The company claims, in a 2018 brochure, that its units are installed at more than 35,000 locations in more than 55 countries.
What the numbers say
The efficiency of thermoelectric generators is modest. The US DOE (2008) said most systems in use achieve 2 to 5%. Chen et al. (2012) put the average TEG on the market at about 5%. The MMRTG turns about 2,000 W of heat into about 110 W of electricity, roughly 5.5%.
Laboratory results have been higher but are not commercial. In 2010 the German Aerospace Centre (DLR) reported that magnesium silicide converted 8% of the available thermal energy, and a two-stage set-up with bismuth telluride reached 12%. These are research results, not production devices.
Cost is a significant barrier. In 2008, the US DOE gave an indicative cost of $20,000–30,000 per kW for thermoelectric generation, compared with $1,500–3,500/kW for Organic Rankine Cycle (ORC) systems, and said thermoelectrics had not yet been demonstrated in industrial applications. These are 2008 figures.
Market-research firms publish TEG market forecasts, but with no series-production automotive TEG identified, automotive market figures look largely speculative.
Limitations and honest assessment
TEGs are not the most efficient way to convert heat to electricity. At low temperatures, an Organic Rankine Cycle can reach 10–20% efficiency. The DOE calls the steam Rankine cycle the most efficient option for temperatures above about 340–370 °C. The advantage of TEGs is simplicity: they have no moving parts, are silent, need little maintenance and can be small.
However, several factors limit their adoption. Bismuth telluride is, according to DLR, “often expensive or toxic”, and tellurium and lead raise toxicity and scarcity concerns. The heat exchangers and heat sinks add weight, and car exhaust temperatures vary widely. Output also falls over time: NASA says Voyager’s RTG “puts out 4 watts less each year”.
For electric and hybrid vehicles, the December 2025 review points to pairing TEGs with energy storage. Our own reading is that electrification also shrinks the exhaust heat available.
For businesses interested in industrial waste heat recovery, TEGs are rarely the main solution; larger schemes typically use steam or ORC systems. TEGs suit small, low-maintenance applications such as low-power wireless sensors, remote equipment and space probes. Like piezoelectric dance floors and human-powered energy, they are for small loads, not bulk power.
Frequently asked questions
What does TEG mean, and how does a thermoelectric generator work?
TEG stands for thermoelectric generator. It is a solid-state device that converts a temperature difference directly into electricity using the Seebeck effect. Two dissimilar conductors are joined, and when one junction is hotter than the other, an electric voltage is produced.
How efficient are thermoelectric generators?
According to the US DOE (2008), most systems in use are 2 to 5% efficient; a 2012 review put the average commercial TEG at about 5%. Laboratory set-ups have reached 12%, but these are not commercial products.
Are thermoelectric generators used in cars?
Not in series production. A US DOE programme tested prototype TEGs in a BMW X6, a Lincoln MKT and a Chevrolet Suburban, with a best bench result of 608 W. A 2025 review says widespread adoption remains limited by low conversion efficiency, material costs and integration challenges.
What are nanostructured thermoelectric materials, and why do they matter?
Nanostructured materials have features at the nanoscale that scatter heat-carrying phonons more than they scatter electrons. This raises the figure of merit (ZT): nanostructured bismuth antimony telluride reached ZT 1.4 in 2008, against about 1 for the best bulk materials, but such results remain far from low-cost mass production.
Where are thermoelectric generators actually used today?
The most significant use is in space exploration. RTGs have powered missions such as Voyager, Cassini and New Horizons, and MMRTGs power the Mars rovers Curiosity and Perseverance. Fuel-fired TEGs are also used at remote sites to power pipeline cathodic protection, instruments and telecoms.
What is the most efficient way to turn waste heat into electricity?
According to the DOE, the steam Rankine cycle is the most efficient option above about 340–370 °C. For lower temperatures, Organic Rankine Cycles (ORC) typically reach 10–20% efficiency. TEGs are less efficient but offer simplicity, small size and no moving parts.