Thermoelectric generator (TEG): definition and meaning

A thermoelectric generator (TEG) is a solid-state device that produces electricity when one side is kept hotter than the other. It has no moving parts, makes no noise and needs little maintenance, but it converts only a small share of the heat that passes through it into power.

How it works

TEGs rely on the Seebeck effect, described by the physicist Thomas Johann Seebeck in 1821: when the two junctions of a circuit made from different conductors sit at different temperatures, a voltage appears. A practical module packs many small legs of n-type and p-type semiconductor between a hot plate and a cold plate. They are wired electrically in series, to add up the voltage, and thermally in parallel, so heat flows through all of them at once.

Output rises with the temperature difference, so the cold side has to be cooled as carefully as the hot side is heated. Material performance is summed up by a figure of merit called ZT. Common materials include bismuth telluride for lower temperatures and lead telluride for medium ones.

How efficient are they?

Example	Conversion efficiency
Typical systems in use (US DOE, 2008)	2 to 5%
NASA MMRTG at start of mission	About 6%

For large industrial waste heat streams, turbines driven by steam or organic fluids normally recover more electricity per unit of heat, which is why TEGs remain a niche choice.

Where they are used

The best-known use is in space. A radioisotope thermoelectric generator (RTG) is heated by the decay of plutonium-238. NASA’s Multi-Mission RTG, which powers the Curiosity and Perseverance rovers, starts with about 2,000 W of heat and delivers about 110 W of electricity, falling year by year as the fuel decays.

On Earth, TEGs power small loads where reliability matters more than efficiency: remote pipeline and telecoms equipment heated by a gas burner, and low-power wireless sensors fed by waste heat. Car makers have tested exhaust TEGs, but they have not reached series production.