Precision Cooling with Peltier Elements
Traditionally, thermoelectrics are primarily used for cooling, in addition to temperature measurement using thermocouples.
Peltier elements operate in mobile coolers and silent hotel refrigerators; in cars, they air-condition seats and cool beverage containers. In electric vehicles, battery temperature control can ensure optimal operation and charging.
Peltier coolers enable highly effective cooling in very small spaces in laser, computer, and medical technology. They respond very quickly and achieve a very high power density. This enables precise thermal management of precision devices such as semiconductor lasers and processes, for example, for applications in biomedicine.
Thermoelectrics: Converting Waste Heat into Electricity
Waste heat is generated in all areas of daily life: in industry, households, and transport. In Germany alone, this amounts to a waste heat potential of 300 TWh per year. This amount of energy corresponds to almost half of the total energy consumption of German industry. So-called thermoelectric generators (TEGs) can tap into this vast energy reservoir and convert the “waste energy” into a higher-value form of energy without moving parts. They utilize waste heat and generate electricity from even small temperature differences.
Thermoelectrics can be used for energy recovery from waste heat as well as for cooling and temperature regulation. Direct energy conversion requires no moving parts and works in both directions: Thermoelectrics can convert thermal energy into electrical energy or use electrical energy for cooling.
Thermocouples are primarily used as temperature sensors, as so-called Peltier elements for temperature control, and as thermogenerators for waste heat recovery. With the goal of enabling broader application of thermoelectrics, researchers are working to improve the system efficiency of energy conversion from thermal to electrical energy; this currently amounts to up to 7%, depending on the temperature range. This can be achieved partly through improved quality of commercially used materials and partly through minimizing losses in the module and the system. Many technical processes utilize only 30 to 40% of the input energy. The vast majority is usually lost as waste heat. At high waste heat temperatures, it is economically and ecologically worthwhile to utilize this energy. To date, mechanical systems such as turbines or Stirling engines have been used for this purpose. The disadvantages of these technologies are the moving components and the associated limited service life, as well as the associated maintenance costs. Thermoelectric converters, on the other hand, operate vibration-free and silently without moving parts. They convert heat directly into electrical energy and can be integrated into existing heat exchangers. Despite their many advantages, energy recovery with thermogenerators is still largely unknown. This is because, due to their relatively low efficiency, such generators have so far been used mainly in niche applications.
Durable and maintenance-free
Thermoelectric generators are durable and require no maintenance. Space technology has been using them to power space probes for more than five decades. The Voyager probes have operated flawlessly since their launch in 1977. Such long periods of uninterrupted and maintenance-free operation are extremely rare for technical applications in general, making them a unique feature of thermoelectrics. Another advantage is that residual heat recovery allows for the use of low temperature differences that are unsuitable for other types of heat conversion into usable energy. Because they are very small and compact, thermoelectric modules can be easily integrated into existing systems. Until now, high manufacturing costs and low overall efficiency have slowed the further spread of the technology.
Maintenance-free power supply for sensors
Thermoelectrics are particularly important for powering self-powered sensor and transmitter 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 powering the sensors. This eliminates the need for cables or batteries to power the sensors or transmit data – the required energy can be generated directly from the ambient heat. Temperature differences of just a few degrees Celsius are sufficient for this. Such self-powered wireless sensors make it possible to reliably monitor inaccessible locations, especially in automobiles and aircraft, as well as in process and plant engineering.