Waste Heat Recovery
What is Waste Heat Recovery?
A typical automobile converts about one-quarter of the combusted fuel energy to useful work, while the remaining energy escapes as waste heat through the radiator and engine exhaust. The American manufacturing industry as a whole does a better job of utilizing energy, but still roughly one-third of the energy consumed escapes as heat to the atmosphere or to cooling systems. Waste heat recovery recaptures this lost heat for conversion into electrical power. As researchers attempt to address this task, TE conversion continues to emerge as a prime candidate for waste heat recovery applications.
Not all waste heat streams are good candidates for thermoelectric waste heat recovery. Since thermoelectric efficiency is a function of temperature difference, most low-grade waste heat applications, at temperatures below 200°C, are not good candidates for waste heat recovery. The conversion efficiencies will be too low to provide adequate payback (e.g., three years) for the thermoelectrics, associated heat exchangers and other hardware. Higher energy waste streams, such as automobile engine exhaust, have larger temperature differences and yield higher conversion efficiencies. Higher temperatures require higher temperature thermoelectric materials with higher figures of merit (ZTs) over the temperature range of interest. Lead tellurides, skutterudites, clathrates, magnesium silicides and others are all candidate materials for these applications.