In many everyday and industrial processes, waste heat is generated that is not hot enough to be used sensibly. Typically, it is discharged unused into the environment, for example in the case of IT servers or at the outlet of power plant cooling towers. So far, there are hardly any application-ready technologies for converting this low-temperature waste heat into electricity. Hopes are pinned on thermoelectric materials in which an electrical voltage can be generated directly from the heat difference of the material. Another possibility is the use of thermomagnetic generators - and scientists at the Leibniz Institute for Solid State and Materials Research Dresden (IFW) have now taken this principle one important step closer to commercial use.
Thermomagnetic generators take advantage of the fact that the magnetic properties of certain alloys depend very strongly on temperature. One such material, for example, is the alloy of the elements lanthanum, iron, cobalt and silicon, which was previously used for magnetic cooling applications. Below about 27 degrees Celsius, the material is magnetic, while at higher temperatures it is non-magnetic. If the alloy is alternately brought into contact with hot and cold water, the magnetization of the material changes continuously. This in turn induces a voltage in the applied coil that can be used for a consumer.
This principle of thermomagnetic generators was developed more than a hundred years ago. However, the yield has so far been significantly lower than that of thermoelectric generators, although theoretical calculations show that much better ratios should be achievable.
By cleverly arranging the individual components, the IFW scientists in cooperation with the Dresden Technical University and the German Federal Institute for Materials Research (BAM) in Berlin have succeeded in improving the performance of thermomagnetic generators by orders of magnitude. They used a magnetic circuit consisting of two magnetic sources and two elements of the thermomagnetic alloy. The individual components are connected with magnetically conductive material, which is wound