MPG AND ELECTRIC MPG

Electric cars 101: What does MPGe mean, exactly? Electric and dual-fuel cars need a new calculation: MPGe. But the EPA's new measurement doesn't tell the whole story.
Chris Gaylord, December 25, 2011 (Christian Science Monitor)

"…The 2012 Mitsubishi i stands as America's most fuel-efficient car, at 126 miles per gallon in city driving…[but] 126 m.p.g. will still be impossible…[T]he Mitsubishi i is an all-electric vehicle…[I]t's actually 126 miles per gallon equivalent (MPGe). The EPA rolled out this new term to help translate electric-car efficiency into a figure that most Americans understand…

"…MPGe works well as a shorthand, but it doesn't tell the whole story. Let's look at how the EPA calculates MPGe…Gasoline and electricity use completely different units (gallons versus kilowatt-hours)…[but] a gallon of gasoline [generates] 115,000 British thermal units of heat…[The] electricity… to generate the same amount of heat…[is] 34 kilowatt-hours (kWh)… One gallon of gasoline produces the same amount of energy as 34 kWh."

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"…[T]he Mitsubishi i will go 126 miles on 34 kWh]…126 miles per the equivalent of a gallon of gas…[the] MPGe…[But comparing] MPGe to m.p.g…compares energy consumption, not fuel costs…[K]ilowatt-hours per 100 miles…[required of] 2013 vehicles…makes actual pocketbook calculations much easier…[T]he 2012 Chevrolet Volt…offers all-electric driving with a gasoline tank as backup. Its EPA label touts both 37 m.p.g. and 93 MPGe…[but] the Volt takes 36 kWh of electricity to drive 100 miles. Or… 2.7 gallons [of gasoline] per 100 miles.

"Multiply 36 kWh by however much you pay per kWh on your home electri¬city bill…12 cents per kWh…[is] the national average…[That comes to] $4.32 to drive 100 miles using only electricity…[Multiply that] by the [gasd pump] price…2.7 gallons multiplied by the national average of $3.275 per gallon…equals $8.84 to drive 100 miles on gasoline…[D]ealers are not required to post such numbers on 2012 models…[Click here for] how far each electric car will travel on a single charge, how long it takes to fill up the battery, and how much the average driver will save…"