Can Coal-Powered Cars Be Clean?

by John DeCicco

Comparing apples-to-apples based on the gasoline vs. electric Mini Cooper

In recent months, sky-high mile-per-gallon ratings have been bandied about for some upcoming electric vehicles. Skeptics point out that swapping oil-based gasoline for coal-based electricity just moves pollution around, without reducing it much if at all.

For example, General Motors recently claimed a 230 mpg rating for Chevy Volt plug-in hybrid, prompting Nissan to twitter that their Leaf EV would rate 367 mpg. The blogosphere is cluttered with off-the-cuff retorts such as the Environmental Economics experts, who asked, “What is the EPA mppc (miles per pound of coal) for the Volt when running off the electric engine?”

Indeed, half of US electricity still comes from coal. That’s an improvement from decades past, when coal’s share of power generation was near 60 percent. Some states such as California, a long-time booster of cars that can run on electricity and other alt fuels, have cleaner power than average. Nonetheless, per unit of energy delivered to a car’s tank or battery, even California electricity entails more greenhouse gas emissions than petroleum fuel. On a national average, BTU-per-BTU basis, electricity is 1.7 times as planet-polluting as gasoline.

But that’s only half the story. As any EV buff will righteously—and rightly—assert, electric drive is far more efficient than an internal combustion engine.

Doing the Math

Perhaps the best apple-to-apples comparison is provided by the Mini Cooper electric and gasoline stable mates. For the Mini E, the official EPA ratings used on the car’s window sticker are 33 kilowatt hours (kWh) per 100 miles in the city and 36 on the highway, for a combined average of 34.4 kWh per 100 miles. (Note that, unlike mileage numbers, these are consumption numbers, with a lower number corresponding to higher efficiency. So like many electric-drive products, the Mini E is more efficient in the city.)

Under average US conditions, replacing a gasoline mile with an electric mile cuts global warming pollution in half.

Now, on a straight-up, energy-equivalency basis, a gallon of gasoline in the tank is equal to 33.7 kWh of electricity. That’s the number EPA uses in a footnote on an EV’s window sticker and it can be derived by anyone from a set of basic energy conversion factors. Energy-equivalency is the most straightforward way to “do the math” scientifically speaking. Of course, that’s before getting into the economic questions, which matter for pocketbook reasons but which we’ll leave for another day.

Divide 33.7 kWh per gallon by 34.4 kWh per 100 miles and, voilá, you get 98 miles per gallon, the gasoline energy-equivalent rating of the Mini E.

How does that compare to the gasoline-powered Mini Cooper Hardtop? The base model makes for the best comparison with the Mini E, or at least as close as you can get without worrying about where the back seat went. The basic Mini Cooper Hardtop rates 28 mpg city and 37 highway, for a combined average of 32 mpg. Well, 98 is roughly 3.1 times 32, or in other words, the Mini E is 3.1 times more energy-efficient than its closest gasoline counterpart.

CO2 Per Mile

Mini E plugging in

Thus, the electric car’s efficiency gain more than makes up for the higher per-unit greenhouse gas emissions of electricity. Running the numbers for CO2-equivalent per distance driven, the Mini Cooper Hardtop using gasoline results in 357 grams of CO2 per mile. The Mini E results in 196 grams per mile, or 45 percent less. That’s pretty close to the rule-of-thumb I’ve long used, that under average US conditions, replacing a gasoline mile with an electric mile cuts global warming pollution in half.

California electricity is about 22 percent cleaner than the national average, so running that Mini E in the Golden State would result in a 57 percent cut CO2 per mile. And what if you charge your Mini E by mainlining coal-by-wire right into your battery pack? Using emissions factor for coal power from ACEEE’s Green Book methodology, the electric version is still a tiny bit cleaner than gasoline, 355 grams of CO2 per mile.

That’s probably a statistical tie, and no doubt there’s room for endless discussion about how much better or worse you can do depending on when and where you charge. One could also get into whether your gasoline comes from Canadian tar sands or Venezuelan heavy crude, instead of “average” crude oil (whatever that is). So while you might not be that much worse a climate culprit if for some strange reason you plug your car into coal, if you’re going to go through that much trouble, you should look for nuclear power—oops, did I mean to say solar panels?—instead.

Contributed by John DeCicco, senior lecturer at the University of Michigan School of Natural Resources and Environment.


  • jonak

    a well written and balanced article – thank you

  • hsr0601

    1. The EV battery is expected to act as a catalyst to accelerate development of sustainable power, specifically as a storage for wind power at nighttime and for solar panel system via recycling. In return, this situation has a chance to bring a solid win-win outcome — rendering EVs affordable.

    2. In many cases, power plants like a nuclear reactor maintain operation during night, and EVs could take full advantage of the surplus energy :

    With the concept of “V2H” (vehicle to home), the vehicle can supply 100V electricity stored in its on-board lithium-ion batteries to electric appliances in a house.

    It is possible to charge the batteries at night, when electricity is cheaper, and use it for home appliances during daytime, Mitsubishi Motors said.

    And the company claims that the batteries can provide almost all the electricity used in a normal household throughout the day.

  • Anonymous

    I can almost agree with the first comment – a well written and balanced article – except for the line that said “replacing a gasoline mile with an electric mile cuts global warming pollution in half.” I would have saluted if it had said, cuts CO2 emission in half.” This does not question the assumption but neither does undercut the well supported point of the article. Air pollution is bad, and electric cars produce less pollution.

  • Scott Z

    Very good article. The one thing I would like to add is solar power. When someone finally makes a full electric or a plug-in hybrid that I like I also plan to start adding solar cells to my home. This will certainly start tipping the scales as far as efficiency!

  • owlafaye

    This is essentially a “pump” article for Mini Coopers. Consequently you can’t take his statistics or conclusions seriously. The Mini is in no sense of the words: “leading edge technology” It ranks far behind most of the economy oriented vehicles rated in the world today. This article casts a huge shadow over the websites honesty and integrity.

  • Charles

    owlafaye, I do not understand your statement. The Mini is a fun to drive small car. Its MPG ratings fall between Toyota Corolla’s 1.8 and 2.4L offerings. Reliability is not as good as the Corolla’s, but owner satisfaction is better. As for price, there is overlap. As for performance the Mini is much better. In safety, the Mini is at least as good as the Corolla. The Mini beat the Corolla in CR’s overall score by 3 points. The Mini beats the hell out of the Honda Insight in CR’s overall score. It is behind the Prius’ and Ford Fusion Hybrid’s score by a good bit (6 and 10 points (that’s right the Fusion beat the Prius)).

    For me, if I am going to spend $22K on a car, it would be a Prius, not the Mini. The MPG performance beats the fun to drive factor by a lot.

  • Christof D-H

    This column and analysis are interesting and useful, but it reflects two dominant — and uncritical — modes of thinking.

    First, except for the quip in the last paragraph, “nuclear — oops solar” it pays little attention to the fact that with EVs, the energy forms used to generate the fuel can, and, hopefully, will change — if enough EV advocates push for green power.

    That’s not the case with oil, it always has been, always will be a dirty source of fuel for cars.

    Second, the column reflects our society’s near total obsession with carbon. Yes, global warming is a serious threat. But other pollutants — nitrous oxide, carbon monoxide, ozone, mercury, etc. — pose serious environmental and health hazards.

    Yet these are all left in the dust by Decicco’s tunnel-vision focus on carbon. Then again, his tunnel-vision only reflects our society’s tunnel vision on carbon.

  • Charles K

    Don’t forget that with a fully electric are you don’t have to process – use and dispose of 25 or so quarts of oil a year.

    Also remember that if you buy a gasoline powered car today you will always need to burn gasoline to run it. If you buy an electric car the fuel used to create the electricity to charge it will be cleaner and cleaner every year as we move towards more sustainable green energy production. Your Gasoline powered car will NEVER be green.

  • Hal Howell

    The article makes a great case for Nuclear power plants. I find it strange that we are willing to encourage NPPs everywhere but here. They can be built safe and the waste can be housed safely. In fact we have already spent the money to dig a place to store the nuclear waste then promptly abandoned the idea. We need to get our act together if using coal is so much of a problem as some think. The truth is all this concern about global warming is much ado about nothing. CO2 is used by plants and it was recently pointed out that CO2 is being soaked up by the areas of sea no longer covered by ice. Go figure.
    I have no problem doing things like wind (We have several windmills here in Texas and hopefully this will work out in the long term). As for Solar Power, it is not going to go far in the residential setting until someone can finally make it affordable. We also get a lot of sun here in Texas and I would love to have solar panels on my house but even with the tax credits, I still can’t afford to go solar. The best approach seems to be a combination of all the various forms of energy production, coal, nuclear, solar, wind and natural gas. We need to stop this limited thinking of just one or two approaches. The fact is we need to become energy independent of foreign sources if we want to be in control of our future as a nation.
    As for the environment, I have lived long enough to know that we go through cycles. You could cook an egg on the sidewalk in El Paso when I was a kid back in the ’50s and you still can. No change. However, unlike back then when you almost asphyxiated walking along where cars were, you can now actually breath. Which is to say things have gotten better, way better than they used to be. I think younger people living now have no idea of what it used to be like. So things are better and Gore needs to get a life. The oceans are not going to rise 20 ft, Florida is not going to disappear and neither is California.
    We need to stop listening to a bad politician who flunked science.

  • simon@syd

    Itsn’t it sobering to think:
    If we converted the whole worldwide fleet of cars to electricity, then we might make an improvement and be producing something like half the carbon that we do with the present gasoline fleet. Anyone care to predict the expansion of the world’s car fleet in the next 20 years?

    Unfortunately, we cant consume more efficient goods to get out of jail – we have to consume less. I dont know how we can achieve that.

  • Charles

    Hal, I did not know that U.S. Sen. James M. Inhofe had flunked science. I would have thought he never took a science course.

  • Anonymous

    I think Christof D-H and Charles K have the right idea… It is important to look at the existing scenario as well as future potentials. The word investment comes to mind. With oil, future potential is low. Let’s not keep throwing our money towards it. With EV, the existing situation may not be so rosy, but the potential is much higher for to reduce pollutions across the board.

    The tougher question is hydrogen. The upstream is significantly lower than electricity. But it is unclear how H2 would be produced. One may expect H2 would be as polluting if not more so than electricity.

    Hal Howell, I agree with your point about having various forms of energy production. However, the “cycles” you’ve been through is only tiny fraction of time and based on your localized observation. What makes climate change so challenging is the steady average global changes. It does not seem urgent enough for everyday folks to panic, yet the scale of the problem is so large that it will take everyone years to get it under control. The sad part is when polar caps completely disappear, the problem will likely be far more pronounced. Remember ozon layer? Yes the problem is still there, believe it or not, we haven’t fix that problem yet even after majority of countries co-operated.

    simon@syd, it’s true our only way out seems to be achieve higher efficiency. One root issue leaders have largely ignored is population growth. I suspect this is an issue leaders will continue to ignore.

    Good article, good discussions.

  • Mr.Bear

    “The Mini E results in 196 grams per mile, or 45 percent less. That’s pretty close to the rule-of-thumb I’ve long used, that under average US conditions, replacing a gasoline mile with an electric mile cuts global warming pollution in half.”

    I would argue that its better than half because of the way that electrical plants operate. Because on a large scale, electrical power can not be stored and has to be supplied instantly, most power plants operate producing 90% of maximum supply all day and night. Which means that during off peak hours, much of that electricity is wasted and the coal and subsequently produced greenhouse gases were needlessly produced.

    I think it is unlikely that most cars will be charged during peak hours. And since a lot of the electricity generated during off peak would be generated regardless of cars being charged, the actually greenhouse gas increase because of electrical cars is less than a straight mathematical efficiency calculation.

  • veek

    Thanks for the well-researched article. Nevertheless, carbon emissions are just one important factor out of many in a car buying decision (if you really want efficiency, you’d walk everywhere), and mathematical calculations leave important things out. For instance…

    Do your figures depend on “Southern California-like” temperatures? Many people live in areas with frequent cold, where batteries are supposedly less effective and reliable (I know our Hybrid’s batteries suffer in the cold). Also, many parts of the country have frequent power outages (which would realistically increase if electric cars become a major part of the grid), and lithium batteries for a FEV may not be as durable as current hybrid batteries. Electricity may be more efficient than gasoline, but when it’s zero degrees out and you’ve got to make it back after a long day at the office (which is too cheap to install a 220 volt adapter for the few who use electric cars), or when your utility has imposed a rolling blackout for the summer, then a gas or hybrid car may be a better choice. Economies of scale work for FEV’s may not work if they are impractical for cold weather areas or areas with inefficient electric utilities.
    Anyway, thanks for the article and for what seems like a valid comparison.

  • vgtech

    How nice that where I live, Quebec, the entire province is powered by hydro generated electricity, except for one small nuke plant and coal stations that only fire up when the temperature reaches -35 degrees Celcius (pretty rare). So, essentially, running an electric car results in a whole lot less greenhouse gas than gasoline. Also, the reduced efficiency in winter can be mitigated by an old Canadian trick-the battery warmer! Even a 100 watt light bulb or heating pad placed close to the battery does the trick. And as for the guy who complained about an employer being too cheap to install 220V for charging cars, they can be charged by 120V. I’ve already told my employees that if they puchase plug-in hybrids or Volts or whatever, they can feel free to plug into the company’s power. After all, electricity expenses are tax deductible.

  • ex-EV1 driver

    The one thing this article is missing when comparing gasoline with upstream ‘costs’ of electricity is the upstream ‘costs’ of gasoline.
    It turns out that it takes a lot of electricity to produce a gallon of gasoline.
    In fact:
    *****
    A gasoline powered car uses about the same amount of electricity as an electric powered car!
    *****
    Nissan published the figure of 7.5 kWh of electricity to produce a gallon of gasoline as part of their Leaf tour*. Taking the Mini-E figure of .344 kWh/mile (I hate kWh/100mi nomenclature), this means that a Mini-E will go 21.8 miles on the electricity used to produce a gallon of gasoline! A more efficient EV such as the Leaf or the Tesla Roadster that gets closer to .25 kWh/mile will go 30 miles on the electricity required to produce a gallon of gasoline.
    * I’ve seen other, estimates that reach similar conclusions but getting a good, justified answer from the oil companies is, of course, difficult.

  • Javier Trejo

    The Energy Problem is a difficult problem to solve and it has some answers that look obvious but they aren’t and they are several reasons why they can not be use. Is ease to say electricity do not contaminate like oil. It is ease to say the product of burning hydrogen is water. This article is trying to tell us that electricity produce les contaminants than oil. The thru is that the margin of contaminants it claim here is base on a wrong use of math. If we add the losses of sending the electricity from the source to the consumer it will be a gas engines win and if we don’t get electricity at the ideal time (night) because half of the people will not do it we are getting in a deep mud. Plus if we think about the amount of pollution we get to produce those high tech batteries that will be a complete disaster that is only with electricity. And if we see hydrogen it takes a lot more electricity than an electrical car. The new batteries they promise are not here yet. We need to find solutions to several problems before counting electricity like a solution. The ease way to solve those problems in this moment is to improve the internal combustion engines, the external combustion and other engines that can be use to gaining some time or maybe to solve this problem. It is no ease solution but we can’t lose our heads in the way because it is our survival to. Instead we need to collaborate and help each other in that way we can find a solution the fastest possible.

  • ex-EV1 driver

    Javier,
    Your thought process is good but your information is bad. Very little electricity is lost in transmission. Overall, the electrical grid is over 90% efficient (less than 10% lost). This is very good and proves that electricity is a great way to transport energy.
    Your info on ‘high tech’ batteries is also flawed. Modern NiMH and Li-ion batteries are non-toxic. It was the old Lead-acid (PbA) and NiCd batteries that were toxic (Lead and Cadmium).
    Unfortunately, better internal combustion engines (ICE) won’t solve any global problem. We are going to run out of petroleum and before we run out, it is going to get prohibitively expensive. By improving ICE, we only postpone the inevitable demise of our petroleum dependent society.

  • veek

    Thanks, es-EVI Driver, for your posts. As usual, your experience and perspective are greatly appreciated.
    Your calculations of the electricity needed to produce fuel brought to mind the 23 October 09 issue (Vol 326) of Science, regarding the issues of resource requirements for various fuels (articles by Service, and by Searchinger et al). We often calculate carbon emissions, efficiency, etc. but often leave out the resources required to bring us the energy (many of them are low cost for the time being but require considerable investment once they pass a certain level).
    Another resource we often ignore in this calculation is replaceable water (vgtec’s Quebec has this in abundance, but places like Nebraska, where much of our biofuels are grown, do not). Service’s article claculated water requirements for energy production. If you consider the liters of water to generate one megaawatt hour of energy, petroleum extraction and refining require about 150. Oil shale requires about 500 liters. A closed loop cooled nuke plant takes about 900, a geothermal plant takes around 3000, and irrigation for corn ethanol takes — are you sitting down — about 5 million liters (soy diesel biofuel? About 20 milllion). Solar was not calculated, but is probably very high. You can sometimes get around this problem by planning — for instance, you can locate nuclear plants or solar cell manufacturers near rivers — but sometimes you can’t (Nebraska has great soil for corn but lousy water reserves, unless you wrongly figure the Oglala will last forever).
    Other generally ignored costs of energy include the costs of wars for oil, social disruption, environmental cleanup, etc. You rarely see figures for these, and we assume they are either free or irrelevant.

    One point is that energy production and consumption involves many tangible and intangible factors (as you noted so well). These factors are often ignored at least as much by the bureaucrats as they are by the energy companies.

  • ex-EV1 driver

    Veek,
    Good job gathering a lot of the other upstream stuff that is often (sometimes conveniently) missed. An addition is that there is a huge amount of natural gas used in petroleum refining that I don’t think is captured in the 7.5 kWh of electricity per gallon of gasoline.
    The water issue you raise is interesting as some water users (power plants) don’t actually consume the water but rather just warm it up (not necessarily a good thing) while other users take the water out of circulation (at least for one iteration of the water cycle). Food production is of course one of these.

  • Dave in OH

    The energy footprint of EV battery production (mining and refining of the lithium ores) is also not accounted for in the article. One assumes the high price of the EV reflects this cost, which may be substantial in a lifecycle analysis.

    I, on the other hand, will continue to commute to work daily by bicycle. It is FAR more energy efficient than walking, contrary to assertions of a poster above.

    As the resident of a state with nearly 100 percent coal fired grid electricity, I am pretty sure my best bet is to select carbon-free transport, and invest in conservation of my home’s energy footprint by insulation and air sealing upgrades.

    As little as I drive, having an EV in my garage plugged in 9/10ths of the time may enable my household to only draw grid power at the very lowest-demand times of day. Now if my utility offered demand pricing to households…. and if consumers had real-time home energy dashboard information– Jeez, we are still really close to the stone age. Mountaintop removal coal mining, valley filling of thousands of miles of rivers and streams, etc. are all having more impacts than just CO2 emissions.

  • Dave in OH

    The energy footprint of EV battery production (mining and refining of the lithium ores) is also not accounted for in the article. One assumes the high price of the EV reflects this cost, which may be substantial in a lifecycle analysis.

    I, on the other hand, will continue to commute to work daily by bicycle. It is FAR more energy efficient than walking, contrary to assertions of a poster above.

    As the resident of a state with nearly 100 percent coal fired grid electricity, I am pretty sure my best bet is to select carbon-free transport, and invest in conservation of my home’s energy footprint by insulation and air sealing upgrades.

    As little as I drive, having an EV in my garage plugged in 9/10ths of the time may enable my household to only draw grid power at the very lowest-demand times of day. Now if my utility offered demand pricing to households…. and if consumers had real-time home energy dashboard information– Jeez, we are still really close to the stone age. Mountaintop removal coal mining, valley filling of thousands of miles of rivers and streams, etc. are all having more impacts than just CO2 emissions.

  • Todd

    Well, you’re forgetting that coal has much bigger environmental impact than just CO2. Coal mining produces significant stream pollution and drastically alters the landscape with practices such as mountain top removal. Coal power plants also produce significant waste products (Coal ash). Do the C02 figures for coal also include the carbon emmitted in mining, processing and transporting it?

  • Giddy up

    350-something grams of CO2 per mile? Buddy, have you even visited Europe, or gone car-shopping there? In the UK, CO2 grams per mile is a window-sticker stat, and the mini cooper stands at 127 per km… (if you haven’t heard of a km, just multiply the figure by 1.6 and you’ll get the per-mile equivalent) either Europe has the biggest CO2-per-km cover up in history, or you can’t do the math of a eighth-grader. I’m thinking the latter. (A Mercedes S55 produces something to the order of 350 grams per km…)

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  • RaphaelR

    The environmental consequences of coal-powered electric cars are a very interesting and challenging question. Are we actually building a more sustainable planet? We all want the answer to be yes, and it can be very exciting to assume electric cars will be the perfect answer. But as with most matters in energy, the devil is in the details, and the details are often complex! The environmental company, Carbon Lighthouse, actually conducted an in-depth quantitative analysis on this exact topic:
    http://www.carbonlighthouse.com/2011/08/the-coal-powered-electric-car-part-i/
    http://www.carbonlighthouse.com/2011/08/the-coal-powered-electric-car-part-i-2/

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