3/12/2014 | 1 MINUTE READ

Plug-in Hybrids More Energy Efficient...Sometimes

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Plug-in hybrid electric vehicles can be as much as 60% more energy efficient than conventional gasoline-fueled cars and 40% more efficient than standard hybrid-electric vehicles.

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Plug-in hybrid electric vehicles can be as much as 60% more energy efficient than conventional gasoline-fueled cars and 40% more efficient than standard hybrid-electric vehicles.

But not always, according to research by a team of scientists from Lamar University, Iowa State University and Oak Ridge National Laboratory.

Plug-ins carry larger batteries so they can travel farther in electric-only mode than can standard hybrids. The researchers say the key to maximizing a plug-in's efficiency is a combination of publicly available charging stations and the ability to match typical trip length to the vehicle's electric-only range.

The team analyzed the operating costs of 415 conventional, hybrid and plug-in vehicles over 3-18 months in metropolitan Seattle. It estimated operating costs over three, five and 10 years for plug-ins with electric-only ranges of 10, 20, 30 and 40 miles.

The group says a regular hybrid may be the better choice than a plug-in for drivers with relatively long commutes, particularly in areas without public charging facilities. One reason: The weight of the plug-in's larger battery results in less fuel efficiency when the car is being powered by its piston engine compared with a standard hybrid that totes a lighter battery.

Not surprisingly, the analysis confirms that larger-battery plug-ins become more economical as the price of gasoline rises. At $3 per gallon, for example, a plug-in with an electric range of only 10 miles is the most cost effective, according to the analysis. As fuel prices rise to $4 or $5 per gallon, longer-range plug-ins become more attractive.

Even so, the researchers say, the incrementally higher price for a large-battery plug-in is difficult to justify based on incrementally lower operating costs unless the vehicle's purchase price is partly offset by a subsidy. And though quick-charge facilities may be convenient for plug-in owners, the team says they contribute little to energy cost savings.

The researchers report their findings HERE in the online publication ScienceDirect, a publication of Elsevier Ltd.