Companies to watch in green tech: Transportation

With Earth Day upon us, CNET News.com's green reporters sat down and selected five leading companies in five different clean-technology categories. Here are the transportation companies selected:

1. A123 Systems: Like a number of other companies, A123 wants to sell lithium-ion battery packs for electric cars and plug-in hybrids. The difference is that A123, which spun out of MIT, has influential friends. General Motors invested in the company and is testing A123 batteries for its hybrids, including the Chevy Volt expected in 2010. So is Norway's Think, which makes an electric town car. In all, the company has raised more than $100 million, including funds from potential users like Procter & Gamble.

The company's batteries employ a nanophosphate electrode, and other tweaks that make them less likely than conventional lithium-ion batteries to experience a "runaway thermal reaction"--or explode to you laymen. Others in this category: Altair Nanotechnologies, which has a lithium-titanate battery, and EnerDel.

2. Tesla Motors: No need to explain much here. The San Carlos, Calif.-based company played a huge role in bringing the electric car back from the dead. Chalk it up to good engineering and clever marketing: aiming electrics at the high end of the market up-ended the harsh economics of trying to build a battery-based car. Celebrities have lined up to buy the Tesla Roadster.

Tesla's next big challenge is Whitestar, a luxury sedan coming in 2009. Two versions will exist: a full-electric version and a gas-electric hybrid. Other ones to watch: Fisker Automotive (a luxury hybrid from the renowned designer), Lightning, and Nissan.

3. ZeaChem and Coskata: This one's a tie. What's the best way to convert plant mass and other cellulosic materials into fuel? Some companies, like Range Fuels, are betting on thermochemical processes. Others, such as Mascoma and Gevo, are scouring the landscape for microbes that can convert biomass biologically.

ZeaChem and Coskata combine both chemical and biological processes. ZeaChem claims they can get 160 gallons of fuel per ton of matter, higher than most if can hit that mark. Coskata, meanwhile, says it can accommodate a variety of feedstocks--like garbage, old tires, and weeds--in its processes. Turning cellulosic ethanol from a lab experiment to a multibillion dollar industry will take years, several strategic alliances, and lots of work. But progress is being made. Along with those mentioned here, keep your eye on Amyris Biotechnologies (synthetic biology), Catchlight Energy (a joint venture between Chevron and Weyerhauser), and Blue Fire Ethanol (garbage).

4. Transonic Combustion: 100 miles a gallon--it's the modern day Holy Grail for mechanical engineers. Transonic has an injection system that lets a diesel engine run on gas, which is easier to find, and hit 100 miles a gallon.

Also stay on the lookout for EcoMotors and Achates Power, which are developing opposed piston/opposed cylinder diesel engines that can get 100 miles a gallon. The engine design dates back to the '30s when Junker used this kind of motor in some airplanes.

5. Venture Vehicles: Outside of movies and street fairs, you don't see a lot of three-wheeled cars like the VentureOne, coming in 2009. But with more people moving into cities, a market is developing for small, energy-efficient vehicles that you can park almost anywhere. Plus, it's a lot easier to hit a manageable price point ($20,000-$24,000) with an electric car when the car only has to go 120 miles between charges and might never see a freeway.

And the novelty factor doesn't stop with three wheels: the car tilts like a motorcycle when you drive it, which is sort of fun. Others in the urban transpo market include cycle makers Zero Motorcycles and Vectrix.