The widespread use of plug-in hybrid vehicles -- which could be driven up to 40 miles on electric power alone -- would significantly reduce greenhouse gas emissions in the United States without overloading the nation's power grid, according to a new study.
The upbeat news for plug-ins, seen by many as the next big step in environmentally friendly automotive technology, came with two caveats. Achieving the maximum air quality improvements would require a significant cut in the pollution produced by electric utilities. It's also dependent on large-scale adoption of plug-in hybrids, which may not be in new-car showrooms for several years.
Even so, backers of plug-in technology were heartened by the latest findings, which could help defuse the claim that the vehicles simply would transfer the source of air pollution from vehicle tailpipes to power station smokestacks.
The study "finally gives an environmental stamp of approval" to plug-in hybrids, said Felix Kramer, founder of CalCars.org, an advocacy group in Palo Alto. "It shows that even with today's power grid, plug-in hybrids are a great idea."
The current generation of hybrid cars and SUVs reduce fuel consumption by switching between a gasoline engine and a battery-powered system that is recharged during braking.
Several major automakers, including General Motors Corp., Toyota Motor Corp., Ford Motor Co. and Nissan Motor Co., are working on plug-ins. Barring a breakthrough in battery technology, however, most say it will be several years before the vehicles are available at dealers.
Ford Chief Executive Alan Mulally, in Southern California last week to announce a plug-in hybrid pilot project with Southern California Edison, said a production model was five to 10 years away. GM has said it hopes to have the Volt, a plug-in electric car, in showrooms by 2010, but that date is contingent on "a technological breakthrough" on more powerful lithium-ion batteries, a spokesman said.
Cost is also an issue. Some experts estimate plug-in technology could add $10,000 to the sticker price. Even with gas selling for more than $3 a gallon and electricity costs for plug-ins pegged at the equivalent of less than $1 a gallon, that's a significant markup.
Converting a hybrid into a plug-in can cost even more. It also voids the car's warranty, a Toyota spokesman said.
A raft of proposals has been introduced in Congress that would provide incentives to manufacturers and buyers of plug-ins, as well as provide additional funding for battery development and mandate the use of plug-ins in government vehicle fleets.
"It's frustrating for a consumer," said Quyen Ton of Tustin, an electrical engineer who said he would buy a plug-in if one were available. "Even though you know it's valuable technology, you can't go out and actually buy one."
Hybrid versions of traditional cars can improve fuel economy by 40% or more. The Toyota Prius, the bestselling hybrid, gets 46 miles per gallon in combined city-highway driving, according to the latest government estimates. The average for all 2006 model cars sold in the U.S. was 24.6 mpg.
Plug-in hybrids use a more powerful array of lithium-ion batteries and are recharged using a standard home electric outlet. That enables the car to travel up to 40 miles, by some estimates, on electricity alone before the battery is depleted and the hybrid powertrain takes over.
That could allow the typical Southern California commuter to make it to work and back only on electrons, based on government estimates that the average commute in the region in 2005 was around 19 miles each way.
Priuses modified to run as plug-ins have achieved more than 100 mpg.
The study released Thursday was conducted by two nonprofit groups, the Electric Power Research Institute and the Natural Resources Defense Council. It measured how the nation's air quality would be affected under varying levels of plug-in hybrid use and pollution control at power plants.
According to the study, a marginal improvement in power plant emissions, coupled with ownership of plug-ins by 20% of U.S. drivers by 2050 -- the report's worst-case scenario -- would cut annual greenhouse gas emissions by 163 million tons.
Under a "middle case" scenario, which assumes plug-ins make up 62% of U.S. passenger vehicles by 2050 and utilities adopt more stringent pollution-control measures, emissions would be cut by 468 million tons a year.
That would be equal to removing 82.5 million vehicles, about a third of the light vehicles on the road today.
"The study clearly shows that the benefits from pluggable hybrids are greater if the power sector is cleaner," said Dan Lashof, science director of the Natural Resources Defense Council's Climate Center.
Reducing greenhouse gas emissions would help combat global warming, and increasing the fuel efficiency of passenger vehicles would reduce the nation's dependence on petroleum, the nonprofit groups said.
The study estimated that a 60% market share for plug-in hybrids would tap only 7% to 8% of the electricity available nationwide in 2050. That finding jibes with a study released late last year by the Department of Energy that concluded that "the existing electric power system could generate most of the electricity consumed" by plug-ins. However, the DOE study noted that the power supply situation is tighter in California, a popular market for hybrids.
Although the study estimates that plug-ins would become available in 2010, the outlook for the vehicles is murky. That's mainly because of questions about lithium ion batteries, which have caused fires in laptop computers.
"We have no indication that lithium ion batteries are a practical application for automobiles yet," said Robert Faraday, publisher of the Truth About Cars website.