More eye opening facts about the Chevy Volt

August 18, 2009

OK, so maybe the Chevy Volt doesn’t really get 230 miles per gallon.  Are such exaggerations justified because they serve a greater cause?  The Chevy Volt will help save the world, after all, by reducing  Co2 emissions, right?


In fact, in some cases the amount of CO2 generated per mile for the Chevy Volt is the same as a conventional automobile getting only 21 miles to the gallon.  Read on…

When running on gasoline (known as “charge sustaining operation”) the Volt will get 50 miles per gallon.   According to the EPA burning one gallon of gasoline yields 19.4 pounds of CO2.  That means the CO2 emitted per mile driven while running on gasoline will be 0.39 pounds.

 ( 19.4 lbs of CO2 / Gallon) / (50 miles / gallon) = 0.39 lbs of CO2 per mile

How much CO2 will be emitted per mile when the Volt is powered by energy from the electrical grid that has been stored in its battery?  That depends on how the energy on the grid is generated.  If you live in an area where the power on the grid is generated primarily with coal, then the amount of CO2 per kilowatt-hour generated is fairly high.  If you live in an area where the power on the grid is generated primarily from nuclear, then the amount is fairly low.  On the average, though, there are 1.34 pounds of CO2 pumped into the atmosphere for every kilowatt-hour of energy generated for the electric power grid in the United States, according to the Department of Energy (2000).

The fully charged lithium-ion batteries hold 16 kilowatt-hours of energy and will propel the Volt 40 miles.  That works out to 0.4 kilowatt-hours per mile.  So that means on the average, 0.54 pounds of CO2 will be put in the atomosphere for every mile that the Volt drives on energy drawn from the electrical grid, assuming perfect charging efficiency.

(1.34 lbs of CO2 per grid kWh) x (0.4 kWh per mile) = 0.54 lbs of CO2 per mile

But charging a lithium-ion battery off the grid is not 100% efficient.  There are grid transmission losses and grid to battery conversion losses which add up to about 10%.  So running your Volt  off of electric grid power will yield closer to 0.59 pounds of CO2 for every mile your drive.  That is 151% of the CO2 put in the atmosphere by the running the Volt off of gasoline.

How many miles per gallon must a conventional automobile get in order to put the same amount of CO2 into the atomsphere per mile as a Chevy Volt does when running off of grid power?  That’s easy- about 33 miles per gallon.  Here are some cars that will do better.

( 19.4 lbs of CO2 per Gallon) / (0.59 lbs of CO2 per mile) = 33 miles per gallon

If you drive in an area where the electric grid is primarily powered by coal, then the numbers are even worse.  Burning coal to power the electric grid yields about 2.1 pounds of CO2 for every kilowatt-hour generated.  Driving your Volt with grid generated power will yield about 0.92 pounds of CO2 for every mile driven (when 10% conversion inefficiencies are added in).

(2.1 lbs of CO2 per grid kWh) x (0.4 kWh per mile)  x 1.1 = 0.92 lbs of CO2 per mile

That is the same amount of CO2 per mile as a conventional automobile that gets only 21 miles per gallon!

( 19.4 lbs of CO2 per Gallon) / (0.92 lbs of CO2 per mile) = 21 miles per gallon

So don’t be fooled by astronomical claims of miles per gallon for the Chevy Volt.  And if you are worried about CO2 (I’m not), then don’t count of the Chevy Volt to save you – it won’t.

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  1. This is Rob Peterson from GM.

    Although the Volt has a 16 kWh battery, only 8 kWh is used. This will significantly impact the rest of your calculations and your synopsis. Please post a correction based on this fact.

    As for the Volt’s city fuel efficiency rating of 230mpg – this is based on the EPA’s draft methodology. The same methodology which will be used for all other vehicles of this type.


  2. Rob,

    Thank you for your comment. If you are correct, then I am way off the mark.

    I have searched for confirmation of your 8 kWh per 40 mile statement and have not been able to find one. I have found various blogs that make more or less the same claim without references to any official specs.

    If you can provide references then I will certainly consider them.

    Best Regards,

  3. More on Rob Peterson comment, above:

    First, readers should know that Rob Peterson is the spokesman for GM.

    Since I have Rob’s ear at the moment, I will suggest that GM include the miles per kilowatt-hour in their in their specs for the Volt. It would be the least ambiguous spec.

    My guess is that the industry (i.e. GM) had much to say int the EPA’s “draft methodology” that Rob refers to. Rob, you can correct me if I am wrong about that. Either way, it is bogus and misleading to claim that the Volt will get 230 miles per gallon. It simply is not true – period.

    Perhaps GM protested this “draft methodology” in favor of something more meaningful? If so, I would be interested in hearing the facts regarding that protest.

    I sincerely hope that Rob is correct in his claim that the Volt will actually get to its 40 mile per charge range with only 8 kilowatt-hours input from the electric grid. Despite the projected $40,000 price tag for the Volt at this time, it might lead to plug-in hybrid vehicles in several years that are actually affordable.

    I am looking forward to an official spec from GM that claims the Volt will get 5 miles per grid kilowatt-hour (or alternatively, 0.2 kilowatt-hours per mile).

    This is a case when I want to be proven wrong.

    Best Regards,

    • Tom,

      You definitely have my ear and I assure you the Volt uses only 8kWh to accomplish it’s 40 mile EV mission. As you note, this will definitely change your calculations and hopefully your opinion of the Volt’s potential.

      Although you may not agree with the EPA’s MPG methodology or the mpg rating for vehicles like the Volt, it is what consumers understand and use for fuel economy comparison. It is also the clearest current measurement by which the general public can come to understand the tremendous fuel economy potential for these vehicles. As consumer understanding of PHEVs and EREVs becomes mainstream a move toward kWh/mile rating (or someother) by the EPA is possible. But remember, we are the same society that couldn’t manage the switch to the metric system.

      We are on the cusp of a revolution in transportation – the move from vehicles powered primarily by gas to those powered by electricity (EREV, PHEV or fuel cell). We can quibble over the EPA’s methodology – we don’t have to agree – but consumers must understand the benefits in terms they understand otherwise the technology will never be commercialized nor its potential realized.


      • Dear Mr. Peterson,

        I recently sent GM the following E-mail:


        In the past, I’ve owned and been pleased with GM automobiles. However, when the government acquired a prominent role in GM, I became disinclined to buy a GM automobile. With GM’s misleading claim that the Chevrolet Volt gets 230 miles per gallon of gasoline, I became adamant. Although your [GM's] mileage claim may be (a) technically accurate in that for every gallon of gasoline “pumped into the Volt gas tank”, the Volt may travel 230 miles (depending on how many “home recharges” are performed per gallon of gas “pumped into the gas tank”), and (b) consistent with EPA rules for computing operating efficiency, your claim is misleading–and I believe deliberately so. The energy needed to charge the battery from a home electrical outlet must come from somewhere and should be included in your computation of gas mileage. Electric energy comes from a variety of sources (coal, hydro, nuclear, oil, geothermal, etc.). If, as would be consistent with ethical behavior, when computing the gas mileage of the Volt you assume gasoline is the source of the electrical energy used to charge the battery, I believe the fuel efficiency of the Volt would be considerably reduced. Your blatant attempt to misrepresent reality and thus mislead the public is deplorable. The next automobile I buy will definitely NOT be a GM product.

        Reed Coray”””

        In my opinion, your [Mr. Peterson's] justifying such claims based on the “current level of public understanding” is self-serving. At a minimum, I believe GM should provide a disclaimer indicating its method for computing Volt gas mileage does NOT take into account the “fuel” required to provide electrical energy needed to charge the battery. You further claim: “…but consumers must understand the benefits in terms they understand otherwise the technology will never be commercialized nor its potential realized” is also self-serving. My question is “what benefits?” There may actually be benefits, but 230 miles per gallon of gasolline isn’t one of them.

        Reed Coray

        Mr. Moriarty

  4. Good job. I’m glad someone is digging into the numbers. However, I checked the doe table and can not figure out how pounds co2/kWh of 2.095 (coal), 1.969(petro), 1.321(gas), and 1.378(other) average out to 1.341. Also since it is clearly not weighted for the proportion of kWh produced in the US (coal , it can hardly be considered an average for calculating the CO2/kWh used in electric mode. Intuition tells me that the true mpg needed for a conventional vehicle will be much high, but it would be worth running the numbers.

  5. A minor point, but if you include the distribution (in)efficiencies of electricity, you should really include the same for fuel; ie the difference between getting bulk fuels to the power stations compared to getting them to petrol stations.

    I don’t think it makes any significant difference; that’s a well put article. Like hydrogen fuel, the ‘electricity is clean’ ignores the source of the energy.

  6. [...] Sanity « More eye opening facts about the Chevy Volt I was (partially) wrong August 20, 2009 I recieved  comment form the GM spokesman, Rob [...]

  7. See more discussion on this issue, especially Rob Peterson’s comments in this new post.


  8. Lapping The Web: Auto News Roundup…

    This last week around the web seems to have brought new focus to alternative fuel vehicles, specifically electric and hybrid. Let’s have a closer look.

    Has the “mythical” Prius “come back to mother earth?” Independent tests by the Sydney Morning Hera…

  9. I agree with you. A lot are getting concerned on how they could contribute in strengthening the fight against global warming and other conditions that go with it.

  10. Couldn’t agree more that there needs to a closer look at alternatives. But also a closer look needs to had at the existing alternatives.

    The Prius is mentioned above. But how does the enviromental cost of disposing of the battery pack compare to the eco savings of the hybrid?

  11. [...] Government General Motors weighs in the comments on a post questioning the veracity of claims about the Volt’s mpg. [...]

  12. face it….the volt is a loser

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