MPGe

MPGe:  The New Measure of Efficiency

by Steve Auger

GM's recent claim of 230 MPG for the Chevy Volt has raised eyebrows and sent engineers and analysts scrambling to figure out the truth behind the claim.  In actuality, the claim of 230 MPG is only accurate provided the Chevy Volt is driven 51.1 miles.  If the calculation had been based on 200 miles then the MPG would be substantially less.  And the gallons of gasoline are not particularly meaningful in any case since the vehicle is primarily electricity powered.

MPG is D E A D

Yes, that is correct.  And it has been the case for some time.  But the question remains as to what measure will take it's place.  The clearest alternative that I have seen is defined at the Progressive Automotive XPrize website.  After all, they are in the business of measuring/judging fuel efficiency.   The term they use is MPGe (Miles Per Gallon Energy Equivalent).   The formula is:

MPGe =  (miles driven) / [(total energy of all fuels consumed)/(energy of one gallon of gasoline)])

They provide an easy-to-use spreadsheet for converting different fuel types (including electricity) to MPGe.  (Go to  Progressive Automotive XPrize and follow link to the spreadsheet.)

Now the real question is whether or not this is a fair measure?  It seems to me that what is really important is the well-to-wheel calculation, not tank-to-wheel.  Well-to-wheel puts a whole new slant on the business of green automobile technology and will ultimately eliminate such technologies as hydrogen fuel cells.

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