Other incremental improvements range from solar panels that run the air conditioning during stand-still, so fuel is not used to cool down the car, to small electric motors tucked away in the doors and powered by batteries that are charged when a car is braking.

BBC: Electric motoring: a quiet revolution

Last summer, when temperatures climbed to the low 100s, they used a small air-conditioning unit but offset much of its energy use with the solar panels soaking up the Arizona sun.

WSJ: Green Goes Mainstream for New Homes��WSJ Mansion