The study also found that the next generation of plug-in hybrids could require hundreds of billions of dollars in government subsidies to take off.
Even then, plug-in hybrids would not have a significant impact on the nations oil consumption or carbon emissions before 2030, the report estimated. Savings in oil imports would also be modest, according to the report, which was financed by the Energy Department.
Several carmakers, including Toyota and General Motors, are developing plug-in hybrid models, which will appear in showrooms next year. Toyota just announced that it planned to begin selling tens of thousands of plug-in hybrid Priuses in two years.
Plug-in hybrids are cars that would be built to run primarily on an electric battery, but if extra power were needed for a long drive, a gasoline engine would kick in.
Users would recharge the cars by hooking them to electric power outlets at home or work, meaning they could cover most or all of a daily commute on battery power, not gasoline.
The report found that plug-in electric vehicles could number 40 million by 2030 provided that rapid progress was made in battery technology, and that the government provided large subsidies and incentives. However, the study suggested that a more realistic number would be closer to 13 million vehicles. That would represent 4 percent of the 300 million vehicles projected to be on the road by then.
The main reason for the slow rollout is the potential cost of batteries. Manufacturers are betting on lithium-ion battery technology similar to that in laptops and cellphones. While the technology has evolved rapidly, the report noted that declines in cost would not be steep enough over the next few decades to crowd out other types of cars.
Under the reports most optimistic assumptions, 6.5 million plug-in hybrids could be sold annually in the United States by 2030, out of total sales of 19.4 million vehicles. Under the more realistic assumptions, 1.8 million plug-in hybrids would be sold that year.
Michael P. Ramage, who headed the study, said that its assumptions and results were more conservative than other studies. Over the next 20 years, we felt that a 50 percent reduction in battery costs would take place, he said in a telephone interview. Other people have assumed a lot greater battery cost reductions.
Building a plug-in hybrid electric vehicle that could run for 40 miles on electricity would cost $18,000 more than for a similar conventional car, including a $14,000 battery pack, according to the report. While each mile driven on electricity costs less than a mile powered by gasoline, it is likely to be several decades before lifetime fuel savings start to balance the higher first cost of the vehicles, the report stated.
More recharging outlets, as well as other infrastructure improvements, must also be in place for plug-in hybrids to reach large numbers of American households, the report said.
The National Research Council, in Washington, provides scientific and technical advice to the federal government under a Congressional charter.