Zero Pollution Motors is a 15-year-old company based in France that is planning on releasing a car next year in the U.S. that runs on compressed air. Their cars use air tanks filled with compressed air to drive the engine. At less than 35 mph the engine uses the air exclusively, at higher speeds a heater warms and speeds up the air, recharging the air tank along the way. At the lower speeds a tank of air would take you 20 miles, traveling at faster speeds (engaging the heater and air compressor) would get you 100+ miles.
Air powered cars have disadvantages -- they can take a long time to recharge. Zero Pollution Motors expects a four-hour recharge time for their tanks, and some experts question the true efficiency of the model -- air compressors take a lot of energy to run and appear to be less efficient than hybrid cars in terms of miles/unit of energy.
But I think air powered technology comes out on top for one simple reason -- it doesn't require batteries. Batteries are heavy, expensive and made from exotic and limited materials like lithium. Air-powered cars just need an air tank and a compressor. It might not turn out to be the best choice for every transportation need but will find a few niches that it's perfect for. I'd love to have an air-powered riding lawn mower and would enjoy tooling around town in a small car exhausting nothing more than air.
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