General Motors at its centennial celebration in Detroit on Tuesday is expected to showcase the Chevy Volt, a plug-in hybrid electric car that carries the heavy expectations of reversing GM's slide and slashing consumers' fuel use.
Buzz around the Volt picked up last week when photos of the production car were captured, showing a less sporty look than the original concept car. But what are the environmental and cost benefits of the Volt?
The Volt will be able to run 40 miles on lithium-ion batteries and get a range of 400 miles from an internal combustion engine that charges the battery. The four-door sedan with a hatchback is set for release at the end of 2010.
GM has not offered many details on the Volt's fuel economy and didn't respond on Monday to a request for more specifics. But early estimates indicate that the Volt will deliver a significant boost in mileage and be cheaper to operate than a gasoline car.
Plug-in electric cars also stand to reduce, although not eliminate, air pollution.
"The Volt story has gotten much more interest than other (GM) product introductions because it represents such a dramatic departure. Historically, things were more incremental," said David Cole, the chairman of the Center for Automotive Research in Ann Arbor, Mich.
GM says the Volt will get the equivalent of 50 miles per gallon on longer trips where an expected four-cylinder engine will be engaged.
But mileage will improve substantially if a person stays within the batteries' 40-mile range. GM designers targeted a 40-mile battery range because most people drive less than that in a day.
In all-electric mode, drivers can expect the equivalent of about 100 miles per gallon, said David Goldstein, the president of the Electric Vehicle Association of Washington D.C.
In a mixed mode, where the gasoline engine kicks in, Golstein thinks that overall mileage for a 100-mile trip would be about 50 miles per gallon, but would go down to 35 miles per gallon for a 200-mile trip because the gasoline motor is working more.
Compared with a gasoline car, plug-in hybrids like the Volt stand to be cheaper to operate. Goldstein estimates that people will pay between 2 and 6 cents per mile with the Volt, depending on electricity rates.
That price per mile estimate for the Volt is less than the 15 cents per mile that a typical gasoline car costs, calculated Scott Sklar, an alternative energy consultant at the Stella Group.
Comparing the cost per mile of a gasoline car with a battery-powered vehicle is complicated by the fact that many regions in the U.S. have different electricity tariffs that depend on usage and time of day.
Martin Eberhard, the founder and former CEO of Tesla Motors, is one of the first customers of the all-electric Tesla Roadster. After a few months of driving, he reported in his blog that the cost per mile of the Roadster is between 2 and 6 cents per mile.
From an environmental perspective, plug-in hybrids have the lowest greenhouse gas emissions over their product lifecycle compared with other transportation technologies except all-electric vehicles, according to a recent analysis done on the future of transportation published in August by the Massachusetts Institute of Technology.
That's because electric motors are more efficient than gasoline engines, said Goldstein. Also, electricity generation is several times more efficient than the energy conversion that happens in a car, said Cole.
Similarly, the the Electric Power Research Institute and the National Resources Defense Council (NRDC) last year concluded that adoption of plug-in hybrid electric vehicles would lower global warming emissions, improve air quality, and reduce petroleum consumption by 3 million to 4 million barrels per day in 2050.
But for all the promise of the Volt, there are some real engineering and business challenges.
The biggest technical issue is the reliability of lithium-ion batteries, in which nearly all auto makers are investing.
The useful life of these batteries is still not totally clear, as they haven't already been tested in vehicles for decades.
One business model that automakers are looking at is a leasing option, where consumers would lease a plug-in hybrid electric car's batteries for 10 years, said Cole. After that, the battery would be replaced and potentially used in less-demanding applications such as power grid storage.
A drop in the price of petroleum, which has fallen dramatically since earlier this year, could also put the brakes on the investment in engineering to make plug-in hybrid vehicles less expensive.
Recent reports said that GM is planning to charge about $40,000 for the Volt, more than what was originally anticipated. For the price to go down, there needs to be a multi-year ramp-up in battery production.
"Anyway you look at it, out of the box, this is going to be expensive. These are going to be expensive batteries," Cole said.
In its report, MIT estimated that plug-in hybrids will be commercially competitive with gasoline cars in eight to ten years.
The battery will weigh 400 pounds, be 5 feet long, and be placed under the car, Bob Boniface, GM's Chevy Volt design director said in an interview. Boniface said GM had to make a break from the initial concept car design to improve the aerodynamics and fuel efficiency.
The Volt is a series hybrid, which means that the car's internal combustion engine only charges the battery, rather than drives the car directly. That means an automaker can design engines that run on different fuels.
Cole said that the biggest environmental pay-off from this design will come once ethanol from nonfood sources, called cellulosic ethanol, becomes commercially viable.
A car that uses E85 fuel, a mix of ethanol and gas, could get 400 miles per gallon of gasoline, he said. There are a handful of pilot cellulosic ethanol plants in the U.S., but none are producing at large scale.
For GM, the Volt is meant to help change its image as a vendor or SUVs and other trucks, while giving it important technical know-how in fuel-efficient cars.
"All GM brands are candidates to receive this technology," said Cole.