Electricity from waste heat

American-based researchers say they have developed a semiconductor technology that could allow efficient electricity generation without using traditional auxiliary machinery. Associate Professor Peter Hagelstein of the Massachusetts Institute of Technology (MIT)?s department of electrical engineering and computer science and Dr Yan Kucherov of ENECO say their technology works through thermionics, whereby waste heat from propulsion plants is recovered and used to produce electricity. Their technology consists of cathode and anode conductive plates set in parallel, separated by a multi-layer semiconductor structure. The waste heat produced by an engine is used to boil electrons off the cathode. These electrons traverse through the semiconductor structure and are absorbed into the colder anode. The idea is that electricity is produced as the electrons travel ?uphill? against an electric field in the semiconductor structure region, says Hagelstein. The device is based on the basic vacuum tube, which was developed more than 100 years ago. However, whereas the vacuum tube requires operating temperatures above 1,000oC, the new semiconductor technology uses thermal diodes made of materials that operate in a temperature range of 200-450OC ? temperatures more typically associated with waste heat produced by diesel engines and gas turbines. Hagelstein and Kucherov have demonstrated two basic enabling physical mechanisms that allow the practical implementation of the technology. Their technical development is now focused on optimising the materials used in construction of the thermal diodes. The hope is that the new technology will overcome the efficiency problems that have previously plagued such developments. Early indications are that it may, with the developers claiming it is two times more efficient than its closest commercial competitor. “That such good results were obtained in the first generation of the new device technology? indicates that the general approach has great promise for improved performance in more mature implementations,” write Hagelstein and Kucherov in a paper presented at a recent meeting of the Materials Research Society.