Thermoelectric refers to the direct conversion between heat and electricity in certain materials. When one side of a thermoelectric material is hotter than the other, it generates a small voltage. Flip the process by running electricity through the same material, and one side gets hot while the other gets cold. This two-way relationship between temperature differences and electric current is the foundation of thermoelectric technology, used in everything from portable coolers to spacecraft power systems.
How the Thermoelectric Effect Works
Three related physical effects make thermoelectric technology possible, and they all happen simultaneously in a working device. The Seebeck effect is the most intuitive: when two different conducting materials are joined and their junctions are held at different temperatures, a voltage appears. This is how thermoelectric generators produce electricity from heat. The size of that voltage depends on the materials involved, described by a value called the Seebeck coefficient.
The Peltier effect is essentially the reverse. When electric current flows through a junction of two different materials, heat is absorbed on one side and released on the other. This is how thermoelectric coolers work, pumping heat from a cold surface to a warm one without any refrigerant or compressor. A third phenomenon, the Thomson effect, describes heating or cooling that occurs within a single material when current flows through it while a temperature gradient is present. In practice, all three effects operate together in any thermoelectric device.
What Makes a Good Thermoelectric Material
The ideal thermoelectric material does three things well: it generates a large voltage from a temperature difference, conducts electricity easily, and resists conducting heat. That combination is captured in a single number called the figure of merit, abbreviated ZT. A higher ZT means better performance. The formula multiplies the square of the Seebeck coefficient by electrical conductivity and temperature, then divides by thermal conductivity. In plain terms, you want electrons to move freely while heat stays put.
For decades, bismuth telluride has been the workhorse material for near-room-temperature applications. It performs best between roughly 25°C and 225°C, with top ZT values around 1.2 for the best-prepared samples. Lead telluride picks up where bismuth telluride leaves off, operating effectively in the 325°C to 625°C range. More recently, tin selenide has shattered performance records. Polycrystalline tin selenide samples have reached a ZT of roughly 3.1 at about 510°C, the highest figure of merit ever recorded in a bulk thermoelectric material. That result, published in Nature, suggests practical, cost-effective devices could eventually reach much higher efficiencies than what’s available today.
Thermoelectric Generators: Turning Heat Into Power
Thermoelectric generators (TEGs) convert waste heat directly into electricity with no turbines, no steam, and no moving parts. Historically, their conversion efficiency has been modest, around 6 to 8%. That’s been the main barrier to widespread adoption. However, the U.S. Department of Energy has identified a path to 20% efficiency using advanced materials, a threshold that would make waste heat recovery economically competitive in industries like manufacturing, steelmaking, and glass production, where enormous amounts of heat simply escape into the environment.
The technology already powers some of the most remote and demanding applications on Earth and beyond. NASA’s deep-space probes, including the Voyager missions, rely on thermoelectric generators fueled by radioactive decay heat because solar panels are useless far from the sun. On a smaller scale, researchers are developing flexible thermoelectric generators that harvest body heat to power wearable electronics. A recent device published in Nature Communications achieved a power density of 18.4 microwatts per square centimeter when worn comfortably on skin at 33°C. That’s enough to run low-power sensors, health monitors, and small displays without batteries.
Thermoelectric Coolers: Solid-State Refrigeration
Thermoelectric coolers (TECs), often called Peltier coolers, use electricity to move heat from one surface to another. You’ll find them in portable car fridges, wine coolers, CPU cooling systems, and precision temperature-controlled equipment in laboratories. Their big advantage is simplicity: no compressor, no refrigerant gas, no noise, and very few parts that can fail.
The trade-off is efficiency. In a head-to-head comparison of portable cooling technologies, a thermoelectric cooler achieved a coefficient of performance (COP) of 0.69, meaning it moved less cooling energy than the electrical energy it consumed. A traditional vapor compression system, the same technology in your kitchen refrigerator, scored a COP of 2.59, making it roughly four times more energy efficient. Thermoelectric coolers consumed about 330 watt-hours per day compared to 110 for vapor compression. That efficiency gap is why thermoelectric cooling thrives in niche applications where small size, silence, precise temperature control, or the absence of moving parts matters more than energy cost.
Advantages and Limitations
The defining strength of thermoelectric devices is their solid-state nature. With no moving parts, they produce no vibration and no noise. They’re compact, lightweight, and can be scaled down to tiny sizes or shaped into flexible films. Maintenance is minimal compared to mechanical systems with pumps, compressors, or turbines.
Reliability is generally high, though not unlimited. Under repeated heating and cooling cycles, the interfaces where thermoelectric legs connect to metal electrodes can develop microscopic cracks. These defects grow over time due to thermal stress from the mismatch between different materials expanding at different rates. For applications with stable, steady-state temperatures, thermoelectric modules can last for many years. In environments with frequent temperature swings, interface degradation is the primary failure mode.
The main limitation remains efficiency. At current ZT values for commercial materials, thermoelectric devices convert only a small fraction of available energy. They also struggle with large temperature differences, where traditional heat engines or vapor compression systems dominate. Cost is another factor: high-performance thermoelectric materials like bismuth telluride and tin selenide involve elements that aren’t cheap to refine at scale.
Where the Market Is Heading
The global thermoelectric modules market is valued at roughly $820 million in 2025 and is projected to reach $1.48 billion by 2032, growing at about 8.8% annually. The main drivers are demand for energy-efficient cooling solutions, waste heat recovery in automotive and manufacturing, and the expanding market for consumer electronics that benefit from compact, silent thermal management. As material science continues pushing ZT values higher, the efficiency gap between thermoelectric devices and conventional systems will narrow, opening applications that aren’t economically viable today.