|CO2 emissions associated with all electric use of a PHEV varies significantly with the regional power-generation mix—and, in some regions, also over time. Total US is the dashed red line. Click to enlarge.|
Plug-in hybrid vehicles could contribute greatly to reducing automobile oil consumption and emissions, but reaching those goals requires major progress in key areas such as improving battery technology and cleaner power generation, according to a new report by the American Council for an Energy-Efficient Economy (ACEEE).
The consumption- and emissions-related benefits of plug-ins will vary substantially based on the method of power generation for the local grid, the vehicle’s electric-only range, operational strategy, and drive cycle characteristics, the authors argue.
The report 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.
Although reduction of fuel consumption with plug-ins could be quite large, according to the report, the authors suggest that plug-ins with modest electric-only range will appear first because of the steep increase in battery size and cost linked to increased fuel savings.
Furthermore, the authors are not optimistic about the full-electric scenario for PHEVs in the short term (that the hybrid operates as a full-electric vehicle up to the state of charge determined by its operating strategy, then switching to a conventional hybrid mode).
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—James Kliesch, co-author
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.
The report concludes that plug-ins are likely to emerge through gradual increases in the electric-only range of hybrids and can therefore be regarded as one of several elements in the evolution of the hybrid, albeit one with enormous potential to lessen the vehicles’ environmental impact.
The authors caution that work on plug-in development should not divert attention from readily available measures to lessen the oil dependence and greenhouse gas emissions of the transportation sector.
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. 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.—Therese Langer, co-author