Waste not, want not

Converting waste heat into electricity

“Waste heat” might not be such a waste after all. The excess heat produced in everything from microelectronics to large ship engines is generally thought of as a problem for engineers to solve. But a new leap in semiconductor technology funded by the Office of Naval Research could put that troublesome heat to good use.

Dr. Mihal Gross of ONR’s physical sciences division explains, “With this class of semiconductors, when you have a temperature gradient you can generate electrical current. Or if you pass an electrical current through the material, you can get a temperature gradient for cooling.” An ONR-funded research group at Michigan State University led by Dr. Mercouri Kanatzidis has found the right combination of ultrapure lead, antimony, silver, and tellurium for a material (called LAST) that is significantly more efficient for high temperature power generation than existing thermoelectric materials. His work is described in the 6 February 2004 issue of Science.

“The Navy is looking at the material’s power generation potential,” says Gross, “We have the potential to exploit regions on a ship or land vehicle where there is waste heat, and use it to produce electricity.” Because the material can be produced in bulk, its uses could one day include replacing today’s shipboard steam plants, which run generators, with solid state modules of LAST that would produce electricity directly.

Funded through a Multi-University Research Initiative (MURI), the Michigan State group has developed a fundamental understanding of the chemical properties needed to create the ideal material with high electrical conductivity but low thermal conductivity. The secret to the new material’s efficiency seems to be in the nanostructures within it that impede the flow of heat by introducing internal boundaries.