Energy from waste heat

New thermoelectric materials could help to harvest heat lost by trucks, aircraft and factories. A material's initial composition, the processing techniques, the structures formed and final properties of the material are important.

Energy

Since fuels are costly both financially and in terms of their effects on the environment, they are an obvious choice for improvement of efficienciesMuch of the energy used in trucking, aviation and factories is wasted by heat loss. The figure can be as high as 70 % of the chemical energy of petroleum fuel. High-performance lightweight modules used for exhaust pipes can convert some of this heat loss into electricity. The 'Nanostructured energy-harvesting thermoelectrics based on Mg2Si' (THERMOMAG) project is mainly aimed at trucks, power plants and factories because they have potential for major scaling-up. The principal scientific objective is to understand the behaviour of thermoelectric (TE) materials based on Mg2Si, from the initial composition through to final properties. Processing techniques and the structures formed, at both micro- and nano- levels, are of special interest. Among the many project achievements so far are a supply chain analysis for magnesium and silicon, a life-cycle analysis and a cost-benefit analysis for trucks and passenger cars. The researchers studied n-type and p-type doping, and selected higher manganese silicides as alternative p-type materials. THERMOMAG tests also involved inter-lab collaboration. Manufacturing Mg2Si from silicon nanopowder proved difficult at all stages. It was impossible to make pellets with the desired properties, but an alternative method, mixing powders of different grain sizes, was successful. The final nanostructured products did not have the desired thermoelectric properties, and there may be significant limitations on using nanostructuring to improve the TE properties of Mg2Si. Research is continuing on this aspect. Since so much energy is lost as heat in many industries and processes, even a small percentage of energy harvesting could provide valuable financial savings. It would also lessen environmental impacts. Along with road transport and aviation, the space sector and industry generally could all benefit.