Vehicle of the Future

EV enthusiast and activist

MPGe

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There’s all this talk about MPGe (Miles per Gallon equivalent), what it really means, and how it’s calculated. The truth is, there’s no good way to compare EVs to internal combustion through MPGe. If you really want to compare in any meaningful manor check out the miles per $ metric.

That said, there’s really three ways to calculate MPGe. I call it the three E’s, Efficiency, Emissions, and Economy. It’s really about comparing some measurable characteristic of an EV and cross multiply to get rid of the unwanted units.

The following calculations are based on June 15th data from an earlier blog post.

MPGe Efficiency

This is how the EPA, auto companies, and Big Oil want you to calculate MPGe. Basically, a gallon of gasoline can be burned and rendered useful as kWhs of electricity, thus comparable to an EV that uses kWh of electricity. The conversion is: 33.7 kWh electricity per gallon of gasoline.

So, my Leaf which gets:

(3.36 mi/kWh) X (33.7 kWh/gallon) = 113 MPGe

MPGe Emissions

Using the calculator at AfterOil EV, one may compare MPGe by total CO2 emissions from generation to wheels by emissions ratio. I used 50.3 miles @ 35MPG, comparable vehicle to my Leaf, and a very liberal estimation at that.

(31.8 lbs CO2 Ave Car) / (14.09 lbs CO2 Leaf) = 2.25 ratio (times fewer emissions)

(2.25) X (35 MPG) = 79 MPGe

MPGe Economy

This is how I’d like to measure MPGe. After all, why compare vehicles using a metric of economy (MPG) unless one does so using units of economy.

(3.36 mi/kWh) / ($0.12/kWh) = 28 mi/$

(28 mi/$) X ($3.999/gallon) = 112 MPGe

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Written by devinserpa

June 28, 2011 at 1:18 pm

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