Recycling Waste Heat Into Energy

University of Houston researchers have created a new thermoelectric material with greater efficiency and higher output power than currently available materials. The material, germanium-doped magnesium stannide, is intended to generate electric power from waste heat, such as from a vehicle tailpipe or an industrial smokestack.

Zhifeng Ren, M.D. Anderson Chair professor of physics and a principal investigator at the Texas Center for Superconductivity at UH, says the new material has a peak power factor of 55, with a figure of merit of 1.4. This figure of merit is a key factor in determining efficiency. Ren says it is important to look for materials with a high power factor, or output power density, in addition to the traditional focus on a high figure of merit, or efficiency, commonly referred to as ZT.

“Pursuing high ZT has been the focus of the entire thermoelectric community,” he said. “However, for practical applications, efficiency is not the only concern. High output power density is as important as efficiency when the capacity of the heat source is huge, such as with solar heat, or when the cost of the heat source is not a big factor, such as in waste heat from automobiles or the steel industry, for example.”

He says one typical application would be to use it in a car exhaust system to convert heat into electricity to power the car’s electric system that, in turn, would boost mileage. Another would be to use it in a cement plant, capturing waste heat from a smokestack to power the plant’s systems.

Ren has formed a company, called APower, to commercialize the material, along with a frequent collaborator from the Massachusetts Institute of Technology and two former students.