Greater environmental protection measures have led to a pushfor more fuel efficient vehicles. Along with the development of catalyticconverters, air fuel ratio sensors,and O2 sensorsfor standard gasoline engines, automakers have looked for alternative ways to fuel our transportation needs. Most popular today are gasoline-electric hybrids, butmore recently, fully electric vehicles have been in the spotlight as the mostgreen and efficient option available today.
One challenge for the EPA was how to relate the fuel efficiencyof fully electric vehicles to consumers. We are all used to the standard MPG –or miles per gallon – rating to compare the fuel efficiency of gasoline poweredvehicles, so the solution has been to provide a MPGe, or miles ger gallonequivalent, rating for all electric and hybrid vehicles.
The MPGe metric was introduced in November 2010 by the EPAto label the fuel efficiency of the new Nissan Leaf and Chevrolet Volt electriccars. The ratings are based on the EPA’s formula, in which 33.7 kilowatt hoursof electricity is equivalent to one gallon of gasoline. This is based on theenergy content of gasoline: burning one US gallon of gasoline is 115,000 BTU.The formula for calculating MPGe is shown below.
Two things must be taken into consideration for MPGe of electric vehicles: one is the energy consumed to generate the electricity necessarycharge the battery; and the other is the transmission efficiency of that electricity from itssource into the battery. This makes the calculations much more difficult, butit is essential for getting an accurate depiction of the fuel efficiency ofelectric vehicles.
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| 2012 Ford Focus Electric |
Even with all those factors taken into consideration, newall electric vehicles have impressive fuel efficiency. The 2012 Ford FocusElectric gets 105 MPGe and has a range of 76 miles. Certainly not capable ofroad trips, but it will get most people to work and back, and perhaps a trip tothe grocery store, with some charge to spare. This satisfies what most peopledo with their cars on a daily basis, and can save a good amount of money in thelong run on gas.
Does MPGe make sense to you?
