'Green' concept cars of 2007

The future of green motoring as shown at auto shows around the world.

Chevrolet Volt
Chevrolet Volt
The Volt, unveiled at the 2007 Detroit Auto Show, uses a "series hybrid" system. That means that the wheels are powered, at all times, by an electric motor only.

As shown at the Detroit show, a small gasoline engine could charge the car's batteries as needed. The batteries can also be charged by plugging the car into a wall outlet for a few hours. Other on-board power souces, such a diesel engine or hydrogen fuel cell, could also be used.

One major advantage of a series hybrid is that it allows that sort of flexibility. Since the powerplant isn't hooked up to the wheels in any way, it's much easier to change from one engine type to another.

For example, at the Shanghai Auto Show in April, GM showed a version of the Volt that used a hydrogen fuel cell.

Another advantage, in the event that a gasoline or diesel engine is used, is that the engine can operate at its most efficient speed at all times, never needing to run faster or slower as the car's speed changes.

The challenge with a system like this is that it takes a lot of energy to drive a vehicle at high speeds while delivering the kind of performance drivers expect. It won't be enough for the Volt to just get to 65 miles per hour. It has to get there and still be able to accelerate if the driver needs to.

That means the Volt or HySeries will need really powerful batteries. GM says it is working with battery companies to create something that's up the task.








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