Thermoelectrics: Converting Waste Heat into Electricity
Waste heat is generated across all sectors of daily life—industry, households, and transportation. In Germany alone, the untapped potential of waste heat amounts to approximately 300 TWh per year. This is equivalent to nearly half the total energy consumption of the entire German industrial sector. Thermoelectric generators (TEGs) can harness this vast reservoir of energy by converting waste heat into valuable electrical power—efficiently, silently, and without any moving parts. Even small temperature differences can be used to generate electricity.
Thermoelectric systems offer dual functionality: they can recover energy from waste heat and also serve for precise cooling and thermal regulation. The process of direct energy conversion is solid-state and reversible: thermoelectric materials can either convert heat into electricity or use electricity to create a temperature difference for cooling.
Thermocouples are commonly used as temperature sensors, while Peltier elements are used for active temperature control, and thermogenerators serve to recover energy from waste heat. To promote broader adoption of thermoelectrics, researchers are working to improve the conversion efficiency from heat to electricity. Current system efficiencies can reach up to 7%, depending on the temperature gradient. Enhancements in material quality and system design are key to reducing thermal and electrical losses.
Most conventional industrial processes use only 30–40% of their input energy, with the majority lost as heat. At higher waste heat temperatures, reclaiming this energy becomes both economically and ecologically viable. Historically, this has been attempted with mechanical systems such as turbines or Stirling engines. However, these systems come with drawbacks—moving parts that reduce service life and increase maintenance needs.
In contrast, thermoelectric converters operate without moving parts. They are silent, vibration-free, and offer a direct path to electricity generation from heat. Additionally, they can be integrated into existing heat exchanger systems.
Despite these advantages, thermoelectric generators remain relatively unknown. Their relatively low efficiency has so far limited their use to niche applications. However, as materials and system designs continue to improve, thermoelectrics represent a promising avenue for sustainable energy recovery from waste heat.
Durable and Maintenance-Free
Thermoelectric generators (TEGs) are exceptionally durable and require no maintenance. For over five decades, they have been used in space exploration to power deep-space missions. The Voyager probes, launched in 1977, continue to operate reliably to this day. Such extended, maintenance-free operation is rare in technical systems and highlights a unique strength of thermoelectric technology.
Another major advantage of TEGs is their ability to utilize low temperature gradients—those typically unsuitable for conventional energy conversion methods. Due to their compact size and modular nature, thermoelectric modules can be seamlessly integrated into existing systems. However, high manufacturing costs and relatively low conversion efficiency have thus far limited their widespread adoption.
From Niche Technology to Mass Market
Thermoelectrics is still a niche technology; estimates and market analyses indicate high growth potential, but the figures vary widely. While a 2003 market analysis assumed a global market volume of €160 million with a rapidly rising trend, an estimate in 2008 reached €500 million. A more conservative estimate predicts that the market volume will reach nearly $100 million by 2016. Experts believe that the market volume could increase tenfold if the thermoelectric figure of merit of commercial modules could be doubled. Researchers and developers are working to make thermoelectric materials and generators more efficient and cost-effective. They expect significantly higher efficiencies in the near future; substantial increases have already been achieved in the laboratory.
Important starting points for this are improvements in thermoelectric material properties, packaging and connection technology, and thermal and electrical integration into the overall system. Future markets in the field of thermoelectrics will include: decentralized energy supply for sensor systems, decentralized energy recovery from waste heat in automotive and industrial applications, energy recovery in energy-intensive technological processes, and temperature regulation and air conditioning, for example, in e-mobility. Thermoelectricity is now considered a potential key technology for energy recovery from waste heat.
Maintenance-Free Power Supply for Sensors
Thermoelectrics are particularly important for supplying energy-autonomous sensor and transmission systems with power in the milliwatt range. As their power consumption continues to decrease, thermogenerators—with their low weight and fast switching times—are becoming increasingly suitable for this purpose. This eliminates the need for cables or batteries to power the sensors or transmit data—the required energy can be obtained directly from the ambient heat. Temperature differences of just a few degrees Celsius are sufficient for this. Such energy-autonomous wireless sensors make it possible to reliably monitor inaccessible locations, especially in automobiles and aircraft, as well as in process and plant engineering.