MPGe Is Inaccurate

This is a followup to an earlier blog posting; intended to more concisely highlight how MPGe claims are provably misleading, by nearly a factor of three.

An all-electric vehicle doesn't consume gasoline, but Americans are accustomed to measuring vehicle efficiency in gasoline's Miles Per Gallon (MPG).

As a result, the US-EPA came up with Miles Per Gallon equivalent (MPGe), as a means of measuring an alternative-energy vehicle's average distance traveled per unit of energy consumed. This number is presented to the American public as a representation of vehicle energy efficiency.

The problem, is that MPGe is based upon a very outdated 1981 paper, which completely ignores the EPA's own measurements, and grossly overstates real world efficiency of alternative-energy vehicles by nearly a factor of three.

Simple Comparisons

According to the US EPA & DOE:

  • 1 gallon (G) of gasoline produces 115,000 BTU of energy
  • 33.7 kilowatt-hour (kWh) of electricity produces 115,000 BTU of energy

Therefore, the EPA claims:

  • 1 MPG equals 1 gallon of gasoline consumed to travel one mile
  • 1 MPGe equals 33.7 kWh of electricity consumed to travel one mile

Conflicting Numbers

The EPA's MPG/MPGe assertion completely ignores their own emissions measurements:

  • 1 kWh of electricity results in the production of 689.551 grams/CO2
  • 1 gallon of gasoline produces 8,887 grams/CO2

Therefore the EPA's own measurements show that 33.7 kWh of electricity produces 23,237.8687 grams/CO2.

Let's review those numbers again:

  1. The EPA's measurements show that 1 MPGe produces 23,237.8687 grams/CO2
  2. The EPA's measurements show that 1 MPG produces 8,887 grams/CO2

Which one is it? If MPG and MPGe were equal comparisons, then their emissions should also be very similar, but measured MPG/MPGe emissions are not even close.

The Real MPGe

If we adjust our 1 MPGe numbers, to account for an emissions of 8,887 grams/CO2, then we need to downrate the EPA's MPGe measurement by a factor of 2.615. Which means that, to calculate a true MPG/MPGe comparison, you need to divide existing MPGe numbers by 2.615.

This means, that a car claiming 93 MPGe fuel efficiency, has instead a real-world energy efficiency of approximately 35MPG.

Conclusion & Followups

The facts are abundant here: MPGe is a grossly overinflated number that wildly misrepresents electric vehicle energy efficiency.

I propose we stop fooling ourselves; that we drop this silly MPGe nonsense, and instead promote energy efficiency numbers that focus on what our final goal is: reducing CO2 emissions from tailpipes and chimneys. We would do this by using an easy-to-understand, global CO2 emissions standard, measured simply in grams per mile (or, grams per kilometer).

While the focus was on CO2 emissions, we shouldn't also ignore other energy production emissions. Such as a recent study showing that all-electric vehicles cause nearly 100% more air pollution related deaths than diesel.