Plug-Ins Promising—But Better Batteries Cleaner Power Plants Essential

September 21, 2006

Media Contact(s):

Wendy Koch, 202-507-4753, Senior Director, Marketing & Communications

Washington, D.C. — Plug-in hybrid vehicles could contribute greatly to reducing automobile oil consumption and emissions, but reaching those goals requires major progress in key areas. According to a report released today by the American Council for an Energy-Efficient Economy, the environmental and economic appeal of plug-in hybrid vehicles will depend heavily upon cleaner power sources and further battery advances. The report, Plug-In Hybrids: An Environmental and Economic Outlook, examines the benefits of plug-ins relative to today’s hybrids.  It finds that greenhouse gas emissions reductions associated with a plug-in powered by today’s electric grid would be about 15% on average across the nation, ranging from 32% using California electricity to zero using Upper Midwest electricity.

Plug-ins’ oil savings could be quite large. Battery size and cost rise steeply with the amount of fuel savings, however, suggesting that plug-ins with modest electric-only range will appear first.  According to report co-author James Kliesch, the “electric-then-gasoline” depiction of plug-in operation is not realistic and has contributed to overstatements of the fuel savings potential of plug-ins in the popular media. “Achieving adequate battery lifetimes and minimizing battery costs will require a vehicle control logic that turns on the internal combustion engine when extra power is needed, even within the ‘electric-only’ range of the vehicle,” said Kliesch.  The ACEEE report estimates fuel savings relative to today’s hybrids of 30% for a plug-in with a 20-mile electric-only range and 50% for a 40-mile range.

With high volumes and a drop in nickel prices, the cost of the nickel-metal hydride batteries used in hybrids at present could fall quite dramatically.  To reach an appropriate balance of size, weight, and power for a long-range plug-in, however, researchers’ bets are on lithium-ion batteries, which still need technological breakthroughs to reach commercial production for plug-in applications.  Projections of long-term costs for plug-in batteries imply that the incremental cost of a plug-in could match that of a hybrid today.

“Plug-ins represent a major step toward the electrification of the transportation sector, a transition that has tremendous potential to help solve some big problems,” said report co-author Therese Langer. “But realizing this potential means maintaining an all-out effort on advanced batteries, cleaning up electric power generators, and adopting policies that drive efficiency technologies by requiring a sustained ramp-up of average fuel economy.”

Plug-In Hybrids: An Environmental and Economic Outlook is available for free download at or a hard copy can be purchased for $16 plus $5 postage and handling from ACEEE Publications, 529 14th Street, N.W., Suite 600, Washington, D.C. 20045, phone: 202-507-4000, fax: 202-429-2248, e-mail: