Heating Plug-in Hybrids

Heating and air-conditioning systems that use thermoelectrics could make plug-in hybrids more practical.

The potential of plug-in hybrids and electric vehicles to curb petroleum use has grabbed a lot of attention lately. But there is still a big obstacle to clear before such cars can become the dominant vehicles on the road: automakers will need to find an efficient way to supply them with heat and air conditioning. That's because conventional heating and cooling systems either don't work or are inefficient in such vehicles, significantly lowering their range in hot and cold weather.

Credit: Dani Simmonds

One of the leading candidates for an alternative system is based on thermoelectrics, semiconductor devices that can provide either heat or cooling, depending on the direction the electric current is flowing. Major automakers, such as GM and Ford, are now developing systems based on existing thermoelectric semiconductors, and experimental materials that use nanotechnology promise to make such systems even more appealing.

The first plug-in hybrids--cars that can be recharged by plugging them into an electrical socket, but have small gasoline engines to extend their range--will make use of electric heaters. When they start appearing from major automakers near the end of 2010, they'll cost thousands more than conventional cars, so automakers are looking for ways to make them less expensive to broaden their appeal. One way to do so is to find more-efficient systems of heating and cooling, which make it possible to use smaller, less expensive batteries. As a result, thermoelectric systems could start appearing in cars in 2012.

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The heating systems in today's cars rely on the fact that internal combustion engines are terribly inefficient--about two-thirds of the energy gained from burning gasoline does nothing to propel the car. But this inefficiency does generate massive amounts of heat. Some of that heat is used to warm passengers. Plug-in hybrids, which run mostly or entirely on electricity for local driving, don't generate such quantities of waste heat. So, heat has to be generated using power from the battery, draining thousands of watts that could otherwise have been used to propel the vehicles. While plug-in hybrids consume dramatically less gas thanconventional cars in mild weather, in cold weather the benefit will be much less, according to Clay Maranville, a senior researcher at Ford Motor Company.

A similar problem holds true with air conditioning--the electric range of plug-in hybrids will drop in hot weather, either because the gasoline engine needs to kick in to spin a conventional compressor, or because an electric compressor will drain the battery.