GM and BMW developing way to convert car heat into electricity

GM has built a prototype, a metal-plated device that will fit around an exhaust pipe. Researchers told AP that they expect that it could improve fuel efficiency in a Chevrolet Suburban by about 5 percent, or 1 mile per gallon. The improvements would be greater in smaller, more fuel-efficient vehicles.

Auto companies are working with thermoelectrics researchers at Ohio State University to improve the efficiency of existing materials by producing an electric current from differences in temperature.

Researchers estimate that 30 percent to 40 percent of the heat generated from a car's engine is used. The rest is lost through exhaust or engine cooling.

Thermoelectric devices are already used in space exploration and in more commonplace applications, such as like cooling car seats. But research in the area, some of which was abandoned decades ago, is perking up as businesses explore new energy efficiency technologies.