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A reality check on plug-in hybrids

Vehicles that draw power from the electricity grid offer uneven benefits, a new study finds.

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There are hybrid vehicles, whose gasoline/electric engines get great mileage. And then there are "plug-in" hybrids, only about a dozen of them in the US, which have been modified to store more electricity in beefier batteries by plugging in at night to the electricity grid.

Felix Kramer's "plug-in" Toyota Prius gets about double the mileage of a conventional Prius – about 100 miles per gallon. To him, it is the holy grail of cars, zapping pollution, oil imports, and high pump prices all at once.

So, should the whole country jump on the band wagon?

A groundbreaking study released last week sounds a cautionary note to the consumer. Plug-ins do burn less gasoline than regular hybrids – and gobs less than gasoline-only vehicles – but the high cost of their bigger battery packs will probably neutralize even significant savings at the pump, according to a report by the American Council for an Energy-Efficient America (ACEEE).

The study is the first to compare the performance – and the costs – of two hybrid technologies: the conventional versus the plug-in. It comes even as President Bush, energy-security hawks, and many environmentalists are talking up plug-in hybrid-electric vehicles (PHEVs). Dozens of cities, too, have signed on to promote a new Plug-in Partners program, and Toyota and other automakers say they're working on the technology.

"We want government policy based on reality, not overstating what [plug-in technology] can achieve and when," says report coauthor Therese Langer, ACEEE's transportation program director. "We don't want what happened with the hydrogen hype to happen with plug-in hybrids, too," she adds, referring to optimistic assessments of a timetable for shifting to a hydrogen-powered vehicle fleet.

Cleaner skies, in some places

Environmental impacts of PHEV technology, for instance, would vary dramatically by region – benefiting some areas but not others, the report found.

For a plug-in owner in California, where most electricity on the grid is generated by low-pollution facilities, driving a PHEV might cut emissions of carbon dioxide by one-third compared with driving a regular hybrid.

But if the same PHEV were charged in the Midwest, where coal-fired power plants supply the electricity, reduction of CO2 emissions would be nil. Nitrous-oxide emissions (which form smog) would fall slightly, but sulfur-dioxide emissions (which contribute to acid rain) would quadruple.

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