Does the Chevy Volt produce more CO2 from its battery than from its gasoline engine?

The hybrid Chevy Volt is touted by General Motors as producing less carbon dioxide than purely gasoline-powered cars.  But that may not be true according to an analysis by Junkscience.com:

According to the EPA the 4-seat Volt is capable of driving 35 miles on its 16 kilowatt hours (kWh) of stored electric charge. The Volt’s gas-only fuel economy rating is 37 mpg.

Since two oxygen atoms from the atmosphere combine with each carbon atom when gasoline is burned, a gallon of gas produces about 19.6 lbs. of carbon dioxide (CO2) when burned. So when operating on gasoline, the Volt produces 0.53 lbs. of CO2 per mile (19.6 lbs. of CO2 per gallon divided by 37 miles per gallon).

Since we can’t quantify accurately just how much transmission loss there is between electricity generation and charging points, we’ll assume an impossible 100 percent efficiency at the charger to work out the CO2 emissions for the Volt’s 16 kWh stored charge.

In 2007, national “average” CO2 emissions were 2.16 lbs per kWh from coal-fired generation and 1.01 lbs per kW for gas-fired generation. according to Power Systems Analysis. Given that 44.46 percent of electricity in the U.S. is coal-fired and 23.31 percent is gas-fired, on a national basis, then, the mean emission of CO2 per kWh is 1.2 lbs/kWh. (2.16 lbs/kWh x 0.4446 = 0.96 lbs/kWh from coal, plus 1.01 lbs/kWh x 0.2331 = 0.24 lbs/kWh from gas).

The Volt’s “emissions mileage” from its stored charge is then 16 kWh x 1.2 lbs/kWh divided by 35 MPG = 0.55 lb CO2/mile.

So on an “average” basis, the Volt emits more CO2 from battery use than from gasoline use (0.55 lbs/mile vs. 0.53 lbs/mile).

Maybe you don’t think that’s a big difference, but the difference becomes more pronounced when the Volt is charged in states that rely more on coal-fired electricity.

When I first read this analysis I wondered how one gallon of gasoline, which weighs about 6 pounds could produce almost 20 pounds of carbon dioxide.  Well according to a Department of Energy website, it works like this:

It seems impossible that a gallon of gasoline, which weighs about 6.3 pounds, could produce 20 pounds of carbon dioxide (CO2) when burned. However, most of the weight of the CO2 doesn’t come from the gasoline itself, but the oxygen in the air.

When gasoline burns, the carbon and hydrogen separate. The hydrogen combines with oxygen to form water (H2O), and carbon combines with oxygen to form carbon dioxide (CO2).

A carbon atom has a weight of 12, and each oxygen atom has a weight of 16, giving each single molecule of CO2 an atomic weight of 44 (12 from carbon and 32 from oxygen).

Therefore, to calculate the amount of CO2 produced from a gallon of gasoline, the weight of the carbon in the gasoline is multiplied by 44/12 or 3.7.

Since gasoline is about 87% carbon and 13% hydrogen by weight, the carbon in a gallon of gasoline weighs 5.5 pounds (6.3 lbs. x .87).

We can then multiply the weight of the carbon (5.5 pounds) by 3.7, which equals 20 pounds of CO2!

 

 

 

 

 

 

15 comments

    1. Then the comparison would not apply, but only 20% of our electricity is produced from nuclear generation.

      1. Well that may be however your math is seriosuly flawed due to incorrect data interpretation. While the EPA did rate the Volt at 35 miles, it does so using only 10.4 kwh of it’s 16kwh total energy capacity. Additonally 35 miles of electric range represents an average for climates that will include winter temperatures below freezing. Someone in Florida will generally get 40+ miles of EV range.

  1. What this report fails to show is that one of the primary markets for the Volt, California doesn’t use Coal but rather Hydro and Nuclear for power, so the numbers aren’t as relevant.
    The other element that no one seems to get is that if we tip past a point where ‘volt’s are common cars, then we can: 1. Get away from Foreign Oil, 2: Improve our power capacity and generation away from Coal.
    The other idea, is why don’t we focus on making Coal plants more efficient and cleaner versus putting down the Volt in any vein possible.
    I’m tired of people nit picking the Volt.
    My old grip is the price, 41K, really GM, Really?
     

    1. I pick on the Chevy Volt because it is politically correct. It is expensive and doesn’t really solve the perceived problem with oil imports. Better would be to develop our domestic resources, but the feds are imposing many impediments to that.
      Also, I think these electric vehicles and hybrids are just playthings for the wealthy and they don’t work much better than they did 100 years ago. See my post:
      http://tucsoncitizen.com/wryheat/2010/08/09/the-chevy-volt-just-the-latest-expensive-toy/

  2. The Volt only uses about 60% of its total battery charge to go the 35 mile range you listed.  So your CO2 calculations should be revised.   Check out Wikipedia for the facts.   By the way, I own a Volt and have been getting 44 miles electric range per charge.

  3. The better solutions have consistently been blocked by special interests. I’m astounded that the volt even exists to be honest.
     
    New sources of petroleum isnt a better solution.

  4. I own a Volt. The battery uses is about 10 kwh which due to some loss takes about 13 kwh of electricity to charge.

    Junk science.

  5. Dear Mr. DuHamel,
    Your analysis is unfortunately flawed by the fact that you incorrectly assume that it requires 16 kwh for the Volt to go 35 miles.  In fact, the Volt only uses about 70% of its battery pack by design–about 11 kwh–to go 35 miles.  In fact, using all your other numbers, but making this one correction completely changes the whole point of your story.  The Volt issues about 30% LESS CO2 emissions on electricity than on gasoline.   If you have integrity, you will retract your incorrect story.  Your headline gives your readers the completely wrong impression of the truth. 

  6. The Chevy Volt’s little dirty secrets:In fact this car is the best Hybrid example on the market but it fails to deliver the best gas mpg and cost way too much for a sedans with this type technology. The cat is out the bag and now as consumers we need to support this technology and demand better gas mileage from our new cars. Even though Toyota has the dominate Hybrid market share it doesn’t have the best hybrid technology.It appears Chevy’s Volt is the first stop gap to a growing and changing hybrid market. First it satisfies low government EPA standards which needs to changes. Second the market is seeking a long term growth and stainable profits for our current market structure. That’s why Chevy’s Volt technology meets those requirements. The obvious reason for Volts delay for so many years was due the fact this technology can produce a car that can drive 100 miles to 200 miles on a gallon of gas. The industry knows it will be a matter of time when gas prices will rise to $20 dollars a gallon and our cars will need to drive 200 to 300 miles per gallon to offset the high prices and kept inflation to minimum.Will this technology be a market changer as was the iPod to the music industry? What lessons have we learned about new efficient conveniences? It can give people limitless music options at the tip of our fingers as well as damaging a whole industry. The iPod was such a game changer that music industry was decimated because the eased of stealing music and digital file sharing through napster and Limewire wasn’t regulated or shut down in time. Stealing music file are not as easy as yester years and the music industry has to adapt to different revue streams through more ticket sales and merchandising upon other various streams.Why the Volt’s technology will be a game changer? Well it runs on an electric motor to propel the car and is powered by lithium batteries for the first 35 miles and a 1.4 liter 87whp gasoline generator which produces 36kwh per 100 miles. This generator output enough power to drive the car and recharge the battery. The problem is the current batteries technology cannot store enough energy to drive our cars long term or battery systems refuel fast enough to run beyond 250 miles such as the Tesla car super sport car without hooking up to an outlet for an 8 hour charge. The most obvious convoluted flaw is the 1.4 liter gas generator producing 36kwh per 100 miles. You can find on the internet electric generator for motorhomes running on gas or diesel 600cc engine producing the same electric power or more. It’s about managing the electric power through storage and consumption. The compact and gas saving generator wasn’t utilized because the industry needed a long term growth and profits. Volt’s current set up isn’t optimized for the best gas mileage. It’s a shame because the American invention and industry has been stolen by foreign business. Can we afford to lose this idea too??

  7. Your math is certainly interesting but you have left out a few variables.  For each gallon of gas your non-electric car consumes how about figuring how much energy (and CO2) is used to:

    Find the oil. 
    Drill the oil well.
    Extract the oil.
    Transport the oil to a cargo ship.
    Move the cargo ship to America.
    Unload the oil.
    Refine the oil.
    Transport the oil to distribution centers.
    Fill a gasoline tanker.
    Move the gasoline tanker to a gas station.
    Unload the tanker.
    Pump the gasoline into your car.

    And if you have any time left over after scanning Wikipedia (or JunkScience.com) for those answers, then look for how much energy it takes for:

    Training our military troops.
    Sending our troops overseas to places with the oil for your car.
    Building the caskets to hold the bodies of our fallen soldiers.
    Transporting the caskets overseas.
    Transporting the caskets back home.
    And finally
    Making the fabric for the flag that will be draped over the casket.

    1. Much of the same goes for the resources needed to make the battery and copper wires in an electric vehicle.

  8. Know what I like about the Volt? “Volt owners drove an average of 800 miles between fill-ups since the Volt launched in December, and in March they averaged 1,000 miles,” said Cristi Landy, Volt marketing director. “When the majority of miles driven are electrically, gas usage decreases significantly.”

  9. William has some good points that people usually forget to account for.
    Other strangely often “forgotten” are the benefits of getting polution out of our cities and roads that we breath each time we drive our car.  How much does that cost us in health and life quality? There’s less impact and it’s more cost-effective to handle and reduce the polution in power plants outside the city.

  10. Let’s not forget also that these are new technologies, it’s normal that they’re expensive and not the most efficient in the beginning. Even if they fail, it’s no reason to stop trying. Let’s at least give them a chance and not trash them even before they mature.

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