Electric car emissions?

OK, who knows how electric car emissions compare to, say, diesel in terms of CO2/km? I mean pure battery electric, not hybrid. Obviously you have to assume some generating mix to produce the electricity, and the answer might vary for where you live: if you take France’s 70% nuclear electric then you get a different answer to our coal/oil/gas/electric mix.

But are there any decent numbers up anywhere?

[Update: the first commenter seems to have found the best ref, thanks. The answer is that EVs are a bit better but it does depend on what you’re burning to make lectric.

Note: the Times on friday had an article claiming that the UK was making a big mistake by investing in more diesel trains rather than electrification, because in trains the diff is a factor of two -W]


  1. #1 Zeke

    http://www.transportation.anl.gov/pdfs/TA/281.pdf (on page 20) seems to have the data you are looking for. For the average U.S. fuel mix, EVs seem slightly better than current hybrids in terms of GHG intensity. In a place that is virtually all coal, I imagine hybrids would be the better choice.

  2. #2 Mark Zimmerman
  3. #3 bigTom

    Because of the low efficiency of ICE, even using coal to generate the electricity the Electric vehicle will generate fewer GHG. Throw in lower carbon (Natural Gas), or nuclear/renewable and it is a big win.
    The efficiency of electric generation plus battery plus electric motor is that much higher than ICE.

  4. #4 Mark P

    Does the CO2 emission from electricity generation include transportation of fuel? I suppose for natural gas that cost would be low if it’s transported by pipe, but for coal it would not be negligible. Relating to coal, I also wonder what is the additional environmental cost of disposing of the fly ash. It’s usually buried, and any environmental effects are thus transferred to some point in the future.

    It’s also worth pointing out that the comparison should be between strictly comparable vehicles. That is, production hybrids are designed for economy, not power, while most gasoline or diesel-powered cars are (more and more often) designed for power rather than economy. My current vehicle, a 2001 VW diesel, is capable of 50 miles per US gallon, and virtually always gets at least 48 mpg, with decent performance. Later versions of this vehicle have more power and get poorer fuel economy. If internal combustion powered cars were designed for greater fuel economy the comparison might look different.

  5. #5 mxracer652

    I’m going the efficiency route, b/c all we really care about is whether or not an electric car will pollute less than a diesel.

    A 3 phase motor is on the order of 90% efficient, all the other mechanical inefficiencies & weight & “behind the scenes” cost between IC & electric cars is the same.
    Diesel cycle efficiency is around 30%.

    Estimates for gasoline production are 80% efficient, that is for each unit produced, .2 units were consumed. Use that as a diesel estimate, and the diesel process is 24%.

    Coal to electric generation & losses winds up being about 30% efficient. The only missing thing is the coal mining & transporting efficiency itself, which I can’t find. I will make the assumption that it is more efficient, otherwise it wouldn’t be cheaper than diesel. Maybe 90%. The electric process winds up being about the same 24%. Natural gas to electric will be about the same, it’s bound by the same laws of thermo & refining.

    No reasonable conclusion can be made, and realistically I wouldn’t expect fossil fueled electric to be much less polluting than burning gas/diesel outright. After all, you’re adding one more step and therefore more inefficiency to the process with electric, offsetting the gains from the near ideal processes they run. If it does pollute less, I doubt it will be reducing CO2 in the amount we need to.

    I can’t find any info on nukulur/wind/solar/hydro in terms of the energy used to produce energy, but with less burning in the process, it should result in less CO2 per joule produced.

  6. #6 Emily

    Natural gas to electric will be about the same, it’s bound by the same laws of thermo & refining.

    Actually, natural gas can be much more efficient in electricity generation, because you can run a combined cycle plant off it. Some of these plants have efficiency in the neighborhood of 60%, much, much better than coal.

  7. #7 mxracer652

    Maximum power produced has very little to do with fuel economy, because how often are you using ALL the available power?

    It only takes about 30hp for a car to maintain 60mph on a flat road, it doesn’t *really* matter if it has a 2 liter engine or a 3 liter. They will use the same amount of fuel.

    The lower mpg is the result of poor driving.

    As you increase the load on the engine (fast start, speed changes, etc) physics demands that a fuel excess condition exist, there’s no way to get around that. People will tend to get to their desired speed as fast as the vehicle will allow them, and this is why the larger engine consumes more fuel, because it can.

    For what it’s worth, I know of a Mustang with 400ish HP that gets 27mpg on the highway all day long, while my 4 cylinder with about 100HP only gets 32mpg on the highway.

  8. #8 Mark P

    mxracer652,it is true that it takes only so much power to run a given vehicle at a given speed. But you really do have to factor in the human element., “poor driving” as you call it. If I drive my 90-hp diesel on the highway all day long at a constant speed, I would expect to average at least slightly more than 50 mpg.

  9. #9 JamesG

    Of course if you use the argument that if electric cars charge up at night on base load then they use energy that is otherwise wasted, which ups your efficiency percentage more than somewhat. But the electric car will not win out until the range and charging times improve. Happily there are innovations coming up that will do that.

  10. #10 Michael Tobis

    I just got into a fair amount of trouble on Grist about exactly this. There is a plausible argument that the efficiency of a coal fired plant is much higher than that of a small gasoline engine.


  11. #11 kent beuchert

    This is pretty simple, but requires that you pick the place where the car’s electricity is generated (the state). The DOE has stats on each state’s genrating power and the amount
    of pollutants produced for each megawatt hour. Now you simply determine how many miles per kilowathour your electric car gets and then look to see what an equivalent
    gasoline (or diesel) powered vehicle produces in the way of emisions (via govt tables) and you have it.

  12. #12 mxracer652

    You’re not considering the emissions produced refining the fuel & the efficiency of that process. Even nuclear/wind/solar/hydro power produces emissions during the design, manufacturing & construction process.

    The human element is being controlled as best as possible, but there’s only so much you (plural, not singular) can do. A car needs a certain amount of available power to weight “just in case” (heavy load, steep terrain, emergency, etc). If the driver is using a lot of power frequently, that’s the driver’s own fault. You can’t save someone from themselves.

    Why do you think your car should do better than 50mpg? Friction is a given, you need to burn enough power to overcome it. It is what it is.

  13. #13 Wyatt

    One needs to consider the resistance in the electrical distribution system and losses involved in charging the batteries of the car as well.

  14. #14 Mark P

    mxracer652, I’m not sure what you’re asking me (why do I think my car should do better than 50 mpg?). I was saying that my car averages around 48 or so mpg in all of my driving, which includes some freeway, some rural highway with occasional bursts of acceleration to pass, and some city. If I were driving at a steady state at reasonable highway speeds I would expect to get better mileage than I do on average.

  15. #15 David B. Benson

    Maybe you only get to recharge your electric car battery when the wind is blowing. Then only the CO2 discharged during production, transportation and installation of the wind generators needs to be counted.

  16. #16 Adam

    “I suppose for natural gas that cost would be low if it’s transported by pipe,”

    Most is, but the UK imports an amount (insert % here) by tanker in the form of LNG from places like Qatar.

  17. #17 guthrie

    And I read recently that they have ok’d the building of a new LNG terminal in Wales, so that won’t help matters.

  18. #18 mz

    Walk up to 1 km, bike up to 5 km (these are really short conservative trips that can be done by anyone) when the weather is nice, take a train for longer trips. Use a decent sized car when you need to.

    Live near your workplace. Use the phone, instant messaging/IRC/email, teleconferences, a webcam…

    These are some more fundamental solutions to the problem of moving yourself. Often healthier, faster and cheaper too by the way.

    Btw, I do believe electric cars are in the future. The electron economy makes so much more sense than the hydrogen one.

    What I also see is lighter cars and lighter transport systems.

  19. #19 DemocracyRules

    The discussion about EV’s vs. ICE vehicles seems to hinge on this key point:

    “Global warming is a bigger threat than nuclear waste.”

    One’s answer to this will inevitably comprise some subjective threat assessment.

    — If your answer is YES, then the vote seems to favour nuclear power, and more EV’s.
    — If your answer is NO, then the vote is against nuclear power, and less emphasis on EV’s.

    (h/t to Captain Capitalism; I’m not sure what my own answer would be…)

  20. #20 Zeke

    Well, lets do some simple back of the envelope calculations on the worst case scenario for an EV (all coal-generated power) vs. a conventional vehicle.

    An average coal-fired power plant efficiency is roughly 35%

    Lets assume transmission losses of 7%

    And a conversion efficiency of electricity in to mechanical output for an EV of 90%

    This means that the ratio of energy contained in coal to energy output by your car is roughly 29.3%

    Now, a conventional gasoline engine is, on average, around 20% efficient (see http://en.wikipedia.org/wiki/Internal_combustion_engine#Engine_Efficiency)

    While 29.3% efficiency for an EV is clearly higher than 20% efficiency for an ICE vehicle, what we are really concerned about is the CO2 emissions, and the CO2 intensity of coal and oil differs significantly.

    Lets assume that oil has around 78% as much carbon emissions per joule of energy generated as coal.

    Then the final numbers become:
    EV: 22.85%
    ICE: 20%

    Now, the 20% number is a rough estimate for an average ICE. Hybrid vehicles with a mechanical efficiency of over 23% would generally be superior to EV in an area that gets all of its energy from coal (which, in general, is an unrealistic assumption, but I wanted to test an extreme case).

    EVs are generally more efficient than ICEs, but not in all cases.

    [You’ve assumed no loss of energy in putting the energy into the battery -W]

  21. #21 Eli Rabett

    Zeke, that’s a pretty good argument but you have to consider the efficiency of the refinery, transport costs for both fuels, etc, etc.

  22. #22 James Annan

    Actually you just have to consider the efficiency of a bicycle and realise that this whole debate is asking the wrong question :-)

  23. #23 mz

    There *are* nuclear options which produce little waste.
    Most of today’s nuclear waste is generated because of the chosen inefficienct methods, only a tiny fraction of it is fission products.

    Thorium molten salt reactors could run on a single container of fuel for 30 years and produce mostly short-lived waste. Prototypes were built in the sixties.
    You solve both the fuel (they run on thorium, not uranium, and need very little of it) and the waste problem.

    But the light water reactors were already “the chosen path” by then, and everybody nowadays thinks nuclear power must mean a light water reactor. (Or some think of a fast spectrum sodium cooled contraption but that’s another can of worms.)

  24. #24 Mark P

    There are other issues, like maintenance. A single, large energy plant can be maintained more efficiently and regularly than thousands of smaller plants (car engines). It is also easier to control other pollutant emissions at a fixed point than for thousands of moving, slowly degrading, infrequently serviced ICEs. Also, it’s easier to recapture energy with an electric car during deceleration and going downhill, while it’s virtually impossible to do so with regular ICEs. That can increase the efficiency in city driving (note that fuel economy ratings for hybrids, with higher city and lower highway numbers).

  25. #25 CarbonPig

    Good Question. I read this and then was wondering about electric vehicles, so I did a write-up on my blog about lifecycle impacts. You can check it out here:


    Hope this helps,


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