Turning waste heat into eletricity
Thermoelectric generators (TEGs) convert heat into electrical energy and thus enable the utilization of waste heat, for example from industrial processes. To leverage the major potential of this technology for thermal energy recovery, Creavis has developed an innovative manufacturing process for these generators. The concept won the German Sustainability Research Award in 2016. Evonik’s first TEG modules from small-batch production are now about to enter the sampling and system integration phase with selected development partners.
The energy potential of waste heat generated each year in Germany alone – particularly in heat-intensive industrial processes – is estimated to reach some 300 TWh. So far, this potential has remained largely unexploited, although thermoelectric generators represent a smart method for direct conversion of waste heat into electrical energy. These modules are able to generate power from temperature differences, without emissions nor noise, relying on a solid-state effect that has long been known as the Seebeck effect. Although only five percent of the thermal energy can be directly converted in this manner, it makes sense to utilize waste heat as a regenerative source of energy and to boost process efficiency with promising sustainability impact.
Until now, TEGs have only been used in niche applications due to the complexity of the conventional laborious manufacturing process which includes numerous cost intensive manual fabrication steps. The available materials are another obstacle: they are quite expensive, but can only be used at temperatures below 200°C. As a consequence, many hotter waste heat sources inindustry can therefore not be exploited.
After work spanning several years, a team at Creavis has now come up with a high-performance approach that allows the production of TEG modules in a fully automated industrially scalable process and therefore at reduced cost. The durable, powerful TEG modules which come in a completely new design are to be marketed under the brand name ESPRYX™. Thanks to their choice of materials and a special black protective coating ESPRYX™ performs well at temperatures up to remarkable 280°C.
Energy-intensive industries such as the production and processing of cement, glass, ceramics and metal offer particularly high potential for energy recovery from waste heat. Such facilities frequently reach temperatures far above 200°C. Further, TEGs offer a compact solution to recover waste heat from the exhaust tract of truck or ship diesel engines.
Other potential applications include autonomous energy systems such as gas-operated fan heaters for large tents Such tents are frequently set up in places without a power source, for example as emergency shelters. High-efficiency TEGs could directly generate power from the waste heat to operate lights, phones or similar applications. The application range can further be extended to self-sufficient heating systems and remote sensor powering as required by the Internet of Things (IoT).
A TEG module consists of many paired thermoelectric (TE) legs, which are only a few cubic millimeters in size and are made of a semiconductor material. In operation, one side of the module faces the heat source (hot side), while the other side is averted from it (cold side). The temperature difference between the two sides generates a proportional voltage in the thermoelectrically active material. So-called n-type doped and p-type doped materials are employed to utilize the thermoelectric properties. In each case, an n-type leg and a p-type leg together form a pair of legs. A large number of such legs are electrically connected in series to generate a suitable voltage.
The state-of-the-art manufacturing of TEGs relies on manual assembly of a multitude of individual TE legs. The process developed by Creavis enables the simultaneous production of all legs of a TEG within a mechanically robust, thermally and electrically insulating carrier material. The well-established semiconductor bismuth telluride (Bi2Te3) with its high Seebeck coefficient and good temperature stability serves as the active material. The process also permits the use of new innovative materials with superior properties that are under development.
As the 288th out of 1,000 positive examples for climate protection in and from North Rhine-Westphalia, the KlimaExpo.NRW initiative selected Creavis' HighTEG project.
Stefan Schumann, Dirk Lehmann, Patrick Stenner, Sascha Hoch: Abwärmenutzung mit thermoelektrischen Generatoren. GIESSEREI 104 (10/2017), p. 64 ff.