Electric Car MPG

There is an interesting article in Business Week about the difficulty of measuring MPG of electric cars and other green cars like the plug-in hybrid Chevy Volt and all electric Nissan Leaf

Posted by Royce at 8/18/2009 09:32:00 AM
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6 comments:

  1. RoyceAugust 18, 2009 at 9:51 AM

    Raises a good question - what is the best way to rate mileage or fuel consumption for cars with new technologies?

    I kind of like the price per mile, cause it's easy to understand, but you'd need a calculator or specific website to help you do it for your local area's energy/fuel costs.

    The other easy option would be to conver to a standard energy metric - joules or something? Anyone know what it would it be? And then you'd figure out how many joules (or whatever) are in a gallon of gas, and that's your baseline for miles per joule (or whatever).

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  2. AaronAugust 18, 2009 at 4:53 PM

    I think the government is more likely start using joules/mile and having a quick online calculator, of cost per joule in different zip codes, than than the government successfully cutting out waste and inefficiency from Medicare.

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  3. RoyceAugust 18, 2009 at 5:42 PM

    I can't tell if that's your way of saying that it's pretty likely we move to joules/mile, or your way of saying that we'll get efficient health care when hell freezes over?

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  4. AaronAugust 19, 2009 at 11:36 AM

    Both.

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  5. RoyceAugust 20, 2009 at 12:42 PM

    Ok, I found a link describing how much energy is in a gallon of gas:

    "When you burn gasoline under ideal conditions, with plenty of oxygen, you get carbon dioxide (from the carbon atoms in gasoline), water (from the hydrogen atoms) and lots of heat. A gallon of gasoline contains about 132x106 joules of energy, which is equivalent to 125,000 BTU or 36,650 watt-hours:

    If you took a 1,500-watt space heater and left it on full blast for a full 24-hour day, that's about how much heat is in a gallon of gas.


    If it were possible for human beings to digest gasoline, a gallon would contain about 31,000 food calories -- the energy in a gallon of gasoline is equivalent to the energy in about 110 McDonalds hamburgers!"

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  6. RoyceAugust 20, 2009 at 1:00 PM

    Now obviously that is a lot of energy... we are going to have get used to thinking of 1 gallon gas = 14 kilojoules (kJ?) or 36.6 kilowatt-hours (kWh)

    Another thing to consider, however, is engine efficiency. The math by the "True Cost Blog" (linked) claims that gas engines are apparently only 30% efficient at best, versus an efficiency of 90% for electric engines. This jives with other estimates I've read.

    Considering the whole life cycle of energy creation for the car, this is what the True Cost Blog estimates for total energy efficiency for each vehicle: 14% total efficiency for a gas engine, and 34% total efficiency for an electric engine.

    Does this mean we should consider the final "energy produced" figures for new vehicles, factoring in total efficiency?

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