Greater environmental protection measures have led to a push
for more fuel efficient vehicles. Along with the development of catalytic
converters, air fuel ratio sensors,
and O2 sensors
for standard gasoline engines, automakers have looked for alternative ways to fuel our transportation needs. Most popular today are gasoline-electric hybrids, but
more recently, fully electric vehicles have been in the spotlight as the most
green and efficient option available today.
One challenge for the EPA was how to relate the fuel efficiency
of 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 powered
vehicles, so the solution has been to provide a MPGe, or miles ger gallon
equivalent, rating for all electric and hybrid vehicles.
The MPGe metric was introduced in November 2010 by the EPA
to label the fuel efficiency of the new Nissan Leaf and Chevrolet Volt electric
cars. The ratings are based on the EPA’s formula, in which 33.7 kilowatt hours
of electricity is equivalent to one gallon of gasoline. This is based on the
energy 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 necessary
charge the battery; and the other is the transmission efficiency of that electricity from its
source into the battery. This makes the calculations much more difficult, but
it is essential for getting an accurate depiction of the fuel efficiency of
electric vehicles.
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| 2012 Ford Focus Electric |
Even with all those factors taken into consideration, new
all electric vehicles have impressive fuel efficiency. The 2012 Ford Focus
Electric gets 105 MPGe and has a range of 76 miles. Certainly not capable of
road trips, but it will get most people to work and back, and perhaps a trip to
the grocery store, with some charge to spare. This satisfies what most people
do with their cars on a daily basis, and can save a good amount of money in the
long run on gas.
Does MPGe make sense to you?
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