Report: Plug-In Hybrids Are Most Efficient, Sometimes

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.

Plug-ins carry larger batteries so they can travel farther than standard hybrids in electric mode.

But maximizing efficiency depends on availability of charging facilities and the ability to match typical trip length to the plug-in's electric-only range, according to a team of researchers from Lamar University, Iowa State University and Oak Ridge National Laboratory.

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 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.

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