A GM I would actually buy...

Details were finally revealed today on GM's highly anticipated (at least by me) plug-in hybrid concept: the Chevy Volt. We knew that it would be a plug-in serial hybrid (as opposed to a parallel version), but not a whole lot more than that. What we found out today is really exciting! Here are the crucial bullet points:

• Serial hybrid - The electric motor alone drives the wheels. The onboard gas engine kicks in only to generate electricity to charge the battery and/or power the motor. In the Prius, the electric motor and/or the gas engine can drive the wheels.


• Plug-in - Li-ion batteries store enough juice to power the car for 40 miles without burning any gasoline. This means if you drive less than 40 miles per day, you'll never have to buy gas.


• Range - 640 miles using 12.8 gallons of gas: 50 MPG over the trip


• Performance - 0-60 in 8.5 seconds, top speed is 120 mph (more than reasonable)


• Realizability - not possible yet, but with batteries improving as they are, it shouldn't be too long (two or three years) until we see this thing on the road.

The main technical issue with this concept is the number of deep discharge cycles required of the battery. Lithium-ions have a limited number of charge cycles, so they must be engineered to last the car's 10+ year lifetime. Either that or have a mid-life battery replacement as part of the maintenance program.

The Prius does not suffer from this problem because it doesn't go through deep discharges: the charge level is maintained within a narrow band of the total capacity to ensure long life. You can't do this with a plug-in without compromising the original reason for having a plug-in.

The next step would be to replace the gasoline component with something renewable. The concept is already flex-fuel (accepting ethanol up to E85), and there are plans to try other fuels such as biodiesel, hydrogen, cow-dung, etc. Also needed is to clean up the American power grid (coal, coal, coal), but that's another story.

More info:
NYTimes article
Edmunds.com article
SciAm article
Why electricity is better than oil