Waste heat is a valuable resource of energy that, if harvested, could make cars go more for less, phones and laptops could run for longer, etc. As we all know, heat is produced every time electrons move through a conductor – so, at normal operating temperatures, not in superconductors, it’s unavoidable – it’s basically friction.
Recovering wasted heat is one of the fields some specialized scientists are working in, but until now, using class thermoelectric technologies, they could only get 10% of what’s theoretically possible. The Carnot Limit, calculated in the 19th century, demonstrates and sets the maximum efficiency that any device can achieve in converting heat into work. Theoretically and practically, you can’t go over that limit. So, the devices constructed up to now only get a tenth of Carnot’s limit.
Peter Hagelstein, an associate professor of electrical engineering from MIT, has discovered a novel approach towards making thermoelectric devices very efficient. Their experiments dealt with thermal diodes. Hagelstein, along with Yan Kucherov, consultant for the Naval Research Laboratory, and other coworkers demonstrated that their newly-born thermoelectric device can output as much as 40 percent of the Carnot limit, and calculated that they could theoretically push that efficiency to 90 percent.
The scientists started from scratch rather than trying to improve the performance of existing devices. They carried out their analysis using a very simple system in which power was generated by a single quantum-dot device – a type of semiconductor in which the electrons and holes, which carry the electrical charges in the device, are very tightly confined in all three dimensions. By controlling all aspects of the device, they hoped to better understand how to design the ideal thermal-to-electric converter.
Quantum dot devices are implemented in a specialized kind of chip where charged particles are very narrowly confined to a very small region. It is still only a developmental technology, but when it will become commercial, in a few years, the new thermoelectric technology these MIT scientists developed will boost the efficiency of every working device, thus lowering energy consumption.