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," is the result of a study conducted by the American Council for an Energy-Efficient Economy, an independent, nonprofit organization dedicated to advancing energy efficiency. The study finds that greenhouse gas emissions reductions associated with a plug-in powered by today’s electric grid would only result in about a 15 percent decrease on average across the nation, ranging from 32 percent using California electricity to zero using Upper Midwest electricity. However, the ACEEE report estimates fuel savings relative to today’s hybrids of 30 percent for a plug-in with a 20-mile electric-only range and 50 percent for a 40-mile range. Though plug-ins’ oil savings could be quite large, battery size and cost rise steeply with the amount of fuel savings. This suggests that plug-ins with modest electric-only range will appear first. The “electric-then-gasoline” depiction of plug-in operation is not realistic, says report co-author James Kliesch, 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. Which is the better battery technology? 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-In Hybrids: An Environmental and Economic Outlook" is available for free download at A hard copy can be purchased for $16 plus $5 postage and handling from ACEEE Publications, 1001 Connecticut Avenue, N.W., Suite 801, Washington, D.C. 20036-5525, phone: 202-429-0063, fax: 202-429-0193, e-mail: