Thermoelectric systems

To date, thermoelectric systems have been used primarily in niche markets, although large quantities are already being achieved in some areas, e.g. in applications for local cooling with Peltier elements, including vehicle seat cooling.

Currently, materials based on (Bi,Sb)2(Te,Se)3 are mainly commercially available. Sustainable use of the rare metals is essential. Bismuth and antimony in particular, but also cobalt, niobium and hafnium are also classified as critical by the EU. In the coming years, the material systems of skutterudites (CoSb3) as well as half-Heusler alloys (TiNiSn, TiCoSb) may also become available on a larger scale and find increased application in thermoelectric systems.

With growing markets and imponderable availability of the primary raw materials bismuth, tellurium, antimony and cobalt, price pressure is increasing. Furthermore, thermoelectrics is in direct raw material competition with other growth markets, for example thin film photovoltaics based on CdTe and Cu(In,Ga,)(S,Se)2 (CIS & CIGS solar cells).

Another challenge is the regionally limited availability of antimony and bismuth in particular. Suitable recycling processes for thermoelectric materials or modules are therefore becoming increasingly important. So far, there are neither coordinated approaches for the recovery of elements from pre-consumer (production waste and scrap during the manufacturing process) nor from post-consumer (end-of-life products) materials. The recovery of metals via recycling (secondary materials) is also more energy efficient than primary extraction and results in lower CO2 emissions.

Within RecycleTEAM, however, not only the metals of thermoelectric materials are to be recycled, but thermoelectric systems are to be considered holistically. The recycling of the ceramic components and the other metals they contain, such as nickel and copper, is also being investigated.


Magnetocaloric systems

The magnetocaloric effect describes that magnetic materials heat up when moved into a magnetic field and cool down when removed from it (Weiss and Piccard 1917). A magnetocaloric heat pump is a cooling apparatus based on magnetocaloric materials. It is considered an efficient alternative to conventional compressor-based cooling technology.

The main challenges for the market entry of magnetocaloric air-conditioning systems are efficient and cost-effective magnetocaloric materials on the one hand, and system development as such on the other. Recently, magnetocaloric materials have become available that consist of comparatively abundant and non-toxic raw materials.

The magnet used also represents another valuable component in the cooling system. This is typically an Nd-Fe-B permanent magnet because of the high power density required. The recycling of this material has been the subject of research at Fraunhofer IWKS and TU Darmstadt for years. First recycling scenarios have already been developed, optimal strategies require module-specific conceptions.