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Cars crossout-mpge

Published on December 6th, 2012 | by Zachary Shahan

7

A MPGe Smackdown

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December 6th, 2012 by Zachary Shahan 

 
The other day, we featured a story from one of our readers, a Volt Owner, on his fuel and cash savings after one year of driving the Volt. I think the discussion under the post triggered Mr. Volt Owner’s latest article, which he titled “Why MPGe really doesn’t matter much…,” but I’m reposting below and relabeling “A MPGe Smackdown” (or perhaps “An MPGe Smackdown,” depending on how you read that acronym). Let’s just get right into that:

I have long hated MPGe. Miles Per Gallon Equivalent is an often misunderstood rating, that is prominently placed and emphasized by the EPA in its window stickers, and successful in confusing consumers, dealerships, and reporters alike. I have seen many well intentioned dealerships advertise the Volt as a car with a “98 MPG” rating (dropping the ‘e’ altogether). I have seen critics wrongly try to showcase cheaper cars with a higher MPGe as better than the Volt. Competing car manufacturers are using the MPGe metric to make their inferior electric car offerings look better than the Volt. Certain electric hybrid automobile manufactures, with their offerings being short on range but high on MPGe, are playing a game of smoke and mirrors. “Ignore the short range, and put all your attention to our higher MPGe!” The devil is in the details, and I worry that too many consumers aren’t going to understand how to properly evaluate their choices.

What is MPGe?

Well, it is really an efficiency rating. The EPA determined how many BTUs of heat a gallon of gas would put off if you if burned it. Then they calculated how much electricity would be needed to generate to the same number of BTUs. This number is 34 kilowatt hours. Then the EPA determined the range of a car after consuming 34 kWhs of electricity. So, if you see a car that is rated at 95 MPGe, that means the EPA rated that car to go 95 miles on 34 kWhs of electricity. If you see a car rated at 115 MPGe, that means it could go 115 miles on 34 kWhs.

So, why is the car rated at 115 MPGe not necessarily better than the car with a 95 MPGe. There is no doubt that on a given amount of electricity, the car getting the 115 MPGe is going to do more with a given unit of energy. However, if the car getting 115 MPGe can only drive 10 miles on electricity before turning on the gas engine, and the car getting 95 MPGe can go 45 miles before turning on the gas engine, the overall efficiency of the longer ranged, yet inferior MPGe car, is going to best the shorter ranged, higher MPGe car, on all but the shortest of trips.

Looking at this from the abstract. Let’s say I need to hire a worker. I tell that worker that he/she can work up to 8 hours a day.

  • Option 1: Your first hour of work is paid at $10 an hour. All subsequent hours are paid at $2 an hour. (Compare this to Car option 1: 115 MPGe and 50 MPG on gas).
  • Option 2: Your first four hours of work are paid at $8 an hour.  All subsequent hours are paid at $1 an hour. (Compare this to Car option 2: 98 MPGe and 37 MPG on gas)

 
With option 1, the worker can make a maximum of $24 for 8 hours of work. $10 for the first hour, then $14 for the remaining 7.

With option 2, the worker can make a maximum of $36 for 8 hours of work. $32 for the first four hours, then $4 for the remaining 4.

So what can we take from this?

1) Option 1 has the highest hourly rates. The starting rate and secondary rate are BOTH higher than the second option’s rates. BUT FOR A FULL WORKDAY, OPTION TWO WILL PAY YOU MORE.

2) If the person that is going to be hired plans on working 1 hour only, option 1 is the best. The benefits of the second option don’t come into play until after the first hour, so if the worker is only going to be working one hour a day, the first option is obviously best.

3) You have to look beyond just the raw numbers, and see what fits your situation the best.

So, bringing this back to cars… A car that promises a higher MPGe than the Volt, may not be better for you at all. You need to look at the electric range of the car, estimate your daily driving habits, and come up with a combined fuel economy in your situation. This obviously extends to the MPG rating on range extended cars like the Volt and Plug in Prius. The Volt gets about 37 MPG when running on gas, with the Prius at 50 MPG. Ignoring the fact that the Prius will turn on the gas motor even during the initial electric range if the car gets to 62 MPH or if you accelerate too hard, the Prius’s superior MPG shouldn’t matter much to Volt owners. Volt owners use their gas engine so little that the added 13 MPG efficiency of the Prius won’t cut much into the fuel savings.


 
What would I like to see done about this?

Despite there being a lot of criticism on this idea, the EPA needs to consider adding other metrics to their label that reduce the bias of MPGe. Given the cheap nature of electricity compared to gasoline, one car being 10-15% more efficient with the power it consumes isnt going to amount to much difference in the wallet of the buyer, but that car only going 11 miles on a charge versus 40 is going to make a big one. It would also be nice to display the potential tax credits for the car. With the Volts much larger battery, it gets 3x the tax credit of the Plug in Prius ($7500 versus $2500). With this difference, the Volt has over 3x the electric range for about the same cost.

One final note… I know for 100% electric vehicles, MPGe is a good metric. It could also be a good ‘tie break’ metric if two cars are identical in range. Its just not a great starting point to evaluate electric cars, and the EPA can do much better.

Editor’s note: I have to admit, we here at CleanTechnica have probably overemphasized MPGe a bit while underemphasizing range, while sister site Gas2 has probably done a bit of a better job keeping a balance between the two. Will try to keep a closer eye on that in the future. Thanks for the insightful post, Volt Owner!

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About the Author

spends most of his time here on CleanTechnica as the director/chief editor. Otherwise, he's probably enthusiastically fulfilling his duties as the director/editor of Solar Love, EV Obsession, Planetsave, or Bikocity. Zach is recognized globally as a solar energy, electric car, and wind energy expert. If you would like him to speak at a related conference or event, connect with him via social media. You can connect with Zach on any popular social networking site you like. Links to all of his main social media profiles are on ZacharyShahan.com.



  • High Above Texas

    I own a Volt, had a couple of airplanes and I also own a pickup, a Malibu ECO and some other assorted vehicles…
    The easiest and most practical thing to do is to toss all the malarkey about MPGe and any other convoluted formula out the window and just work this as “MPD”..
    (Miles Per Dollar…) Nothing I have ever owned now or in the past is as inexpensive to take from point “A” to point “B” as my Volt. I am at 7,300 miles now, I have owned my Volt since June 5, 2012 and as I log this comment on 1-19-2013, I stiil have not yet put a drop of gasoline in my Volt, because it runs so inexpensively on an electric charge from my residence…

    You can follow my progress on my Flickr account. I won’t provide a link, but just Google this “Chevrolet Volt Flickr, Southwest USA” and you should easily find my photos and stories… I plan on making a video of the very first time I do put gas in my Volt, sometime later this year, so “stay tuned…”

    • Bob_Wallace

      I agree High. I’ve started making that point years ago. Forget trying to convert EV/PHEV cost of operation into miles per gallon numbers.

      Give people an app in which they can input their cost of electricity during the hours they are likely to charge. Give them a “pennies per mile” number and the equivalent numbers for a representative gasmobiles.

      In the case of PHEVs let people input some estimates of how many miles they drive beyond the battery range.

    • http://zacharyshahan.com/ Zachary Shahan

      If you’d like to write a guest post on any of this, shoot me an email at: zach@importantmedia.org

    • http://zacharyshahan.com/ Zachary Shahan

      Of course, there are other reasons to evaluate MPG/MPGe. But from the average consumer perspective, like your idea.

  • Energy Guru

    To get the best out of vehicle comparisons the cost of the vehicle needs to be dropped. The cost is a choice, some would choose a million dollar super car others public transit. A simple way without getting overly geeky is cost per mile. Then 13,000 avg miles p/year divided by 25 avg mpg X $3.50 per/gal = $1820 per/yr or 14 cents per mile.

    Volt owners frequently talk about 1,000+ MPG because the drive within their battery range. Based on $1.50 per charge with 50 mile range it comes to 13,000 miles divided by 50 miles p/charge = 260 charges X $1.50 = $390 p/y or 3 cents per mile. Close to 1/5th the cost.

    Something that is not looked at is integrating home and transportation cost into the equation. A high performance home that supplies enough energy to run a home and a vehicle like the Volt are being built today at no extra cost.

    A homeowner after Sandy ran his house from his Prius for 2 weeks on a half tank of gas. As Bucky Fuller liked to say “If you can’t find the answer to a question ask a bigger question.”

  • Pete

    We need the same thing for generator efficiency. My 2Kw gasoline pure sine wave generator is one of the more efficient small generators on the market and at a 1Kw. output will produce 4 Kwh per gallon A gasoline conversion efficiency of 4/34 or about 12%.

    It is almost impossible to compare various models on the market as they typically give run time per tank of gas with no indication how large that tank is or what power output they are using.

    The EPA standard would be very useful here.

  • Eugene

    I wish the EPA would get ride of MPG all together. But MPGe is even worse. I would rather see W/km for efficiency of electric cars and l/000km for gasoline cars and just show both for hybrids. But I agree that Range is something that should be emphasized equally.

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