The utilization of waste heat makes a significant contribution to a sustainable energy supply. Scientists at the Karlsruhe Institute of Technology (KIT) and the University of Tōhoku in Japan have now come much closer to the goal of converting waste heat into electricity at low temperature differences. As they reported in the journal Joule, they have increased the electrical output of thermomagnetic generators based on thin films of a Heusler alloy by a factor of 3.4 in relation to the base area.
Many technical processes only use part of the energy used for them; the rest leaves the system as waste heat. This heat often escapes unused into the environment. However, it can also be used to provide heat or generate electricity. The higher the temperature of the waste heat, the easier and cheaper it is to utilize. Thermoelectric generators, which convert the heat directly into electricity, offer one way of using low-temperature waste heat. However, the thermoelectric materials used to date are expensive and sometimes toxic. Thermoelectric generators also require large temperature differences for efficiencies of only a few percent.
Thermomagnetic generators represent a promising alternative. They are based on alloys whose magnetic properties are strongly temperature-dependent. The changing magnetization induces an electrical voltage in an applied coil. Researchers presented the first concepts for thermomagnetic generators back in the 19th century. Since then, researchers have experimented with various materials. However, the electrical performance has so far left much to be desired.
