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Chevy Volt Beats Nissan LEAF and Tesla Roadster Using MPGe

 
3,532 views Aug 28, 2009
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2013 Chevrolet Volt SS with aerodynamic wheel covers, conception by artist Rick Feibusch

2013 Chevrolet Volt SS with aerodynamic wheel covers, conception by artist Rick Feibusch

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There has been a lot of press lately stemming from GM's announcement that the Chevy Volt would get 230 mpg on city driving and Nissan's follow-up announcement that its LEAF EV would get 367 mpg.

These calculations were made though using very different measurements and technically aren't comparable.  Indeed, this highlights the fact that the rising tide of pure and partial EVs have the potential to render the current MPG determination standards obsolete.  So where do we go from here?

Progressive X Prize is a marketing-neutral organization that is sponsoring a contest that will award $10 million to a company whose vehicle gets more than 100 MPGs.  They are promoting a new measurement system called miles per gallon equivalents (MPGe) which is given by the following formula:

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

This system levels the playing field by converting all energy sources going into powering a car into a common value (energy) and then determines how many gallon-equivalent of gas it takes to propel the car a mile.

It works well for pure EVs like the LEAF or Tesla Roadster but still is hard to apply to the Volt, because it switches energy sources after 40 miles.

According to X Prize senior adviser John Shore to account for that, "you might want to estimate the Volt’s MPGe at the various trip lengths listed in the table on page 36 of the Competition Guidelines – current version available here.   You could then estimate a combined MPGe by taking a weighted average with the distribution weights shown in the table."

The table he refers to is the NHTS statistical distribution of trip lengths driven by US drivers in 2001.

If we do the calculation he recommends and assume the Volt gets 50 MPG in generator mode (GM's initial claim) we get the following results:

Chevrolet Volt:  166 MPGe
Tesla Roadster:  158 MPGe
Nissan LEAF:  142 MPGe

Source (GM-Volt.com)





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Comments (13)

  1. By Jason M. Hendler Posted: 8/28/2009 7:14am PDT

    I wonder if that is the result of gasoline having better energy / weight ration than batteries.
     
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  2. By Verde Posted: 8/28/2009 9:00am PDT

    Why not convert EV efficiency measures into units of "energy of one liter of peanut butter"? Makes about as much sense as "energy of one gallon of gasoline". Then we could compare the efficiency of driving cars with that of riding a bicycle to work.
     
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  3. By Doug Posted: 8/28/2009 10:35am PDT

    Lyle, I don't understand how you got to your conclusion. At the GM 230 MPG media event, GM said, "EPA methodology results show 25 kilowatt hours/100 miles electrical efficiency in city cycle." One gallon of gas has 37 kWh of energy. So in all electric mode, that works out to 148 MPGe. What assumptions did you use to get 166?
    As a scientist, I would prefer we go purely metric and use some 10^x multiple of Joules per meter (J/m). But kWh/mile is likely most practical in this unit challenged country. Certainly we should measure in units of something universal like energy as opposed the volume of some liquid. So MPGe is a small step in the right direction.
     
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  4. By Chris O Posted: 8/28/2009 10:56am PDT

    Why would the Volt get 50 MPG in generator mode? If using a generator/electric motor drive train were that efficient wouldn't every car have it's ICE hooked up to an electric motor rather than a mechanical transmission? And how is it possible that a PHEV that uses it's inefficient ICE part of the testcycle gets better MPGe than an all-electric car?
     
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  5. By  Electricnick Posted: 8/28/2009 2:39pm PDT

    What worries us more is that the unbeatable GM marketing behemoth is going to take this and run away with it...
    The Electricnick.com team.
     
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  6. lyle avatar Lyle Dennis Posted: 8/28/2009 4:22pm PDT

    #3 Doug
    Here is the link to their methodology and spreadsheet calculator:
    http://autoblog.xprize.org/axp/2009/08/calculating-mpge.html
     
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  7. By Jason Posted: 8/28/2009 4:55pm PDT

    I find it funny no matter what numbers come out, many of you will always cry foul. That is not to say every number posted by companies is legit but please dont try to hide your bias for GM with "factual" commentary.
    What is wrong with using a MPGe? I think that is a very relevant type of system to use and just because you don't like what the number spits out doesn't mean it isn't a good system. Comparing it to peanut butter is just plan ridiculous.
     
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  8. By Jason Posted: 8/28/2009 4:59pm PDT

    In response to Chris,
    The reason the volt gas engine gets great MPG is because it is not directly linked to the wheels. The motor is not straining to provide power to the wheel, only the battery. Unless you are on a step climb, the motors RPM will be very low. I don't understand how that is hard to grasp.
    Give credit where credit is due, and the Volt surely deserves some.
     
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  9. By EVNow Posted: 8/28/2009 11:15pm PDT

    Lyle, the calculation is wrong.
    You use only 8kwh for Volt (and assumes 40 miles) - not 16kwh. But for Nissan Leaf uses all 24kwh. Obviously Nissan volt use full 100% battery for their 100 miles …
    Pls correct the calculations.
     
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  10. By newbie Posted: 8/28/2009 11:30pm PDT

    i don't know about you guys!...mpg..mpge...whatever!...i just want an EV with generator built with it...that's all i want. and the VOLT is the answer...
     
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  11. By  r embrey Posted: 8/29/2009 9:03am PDT

    What would happen if a car went 250 miles on one charge and could recharge in 5 min. What would be the MPG of that?
    I can't believe noone is talking about the company eestor.
     
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  12. By Noel Park Posted: 8/29/2009 11:24am PDT

    newbie:
    Amend. Second the motion.
     
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  13. By luisgoru Posted: 9/18/2009 9:39pm PDT


    Actually Chris O, thats correct. Its more efficient using the gas to power an electric motor/engine than using it to power a mechanical motor/engine.
    The last century practical every train that is powered by gas in the world, use gas to produce electricity to power an electricity motor/engine.
    Why then we dont get this in every peoples cars? You are pissed, every smart person is pissed, cause we consumers overpay for moving cars the last couple of decades.
    Automakers are the ones to blame, and now they talk about pushing green solutions, give me a break? They only are going "green" cause they get bigger profits and great subsides.
    Its sad that natural balance had showed many times that the car industry is horrible wrong since it was created... from the design, manufacter, financing, sustainability, etc all are so wrong, and even in the last years weak up call, nothing had changed for good.
    Too sad the world, including us, is paying a high price to make a few greedy stupid people rich.
     
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