The truth about “zero emissions”

The truth about "zero emissions" vehicles

Everyone wants to go “green”, in theory anyhow. And it has been asked many times why the electric car is not more commonly used, as it is said to give off “zero emissions”. And recently with Tesla motor company joining forces with Toyota to create the Model S electric sedan, it seems it’s time to really evaluate just what “zero emissions” means in the USA.

First, we should examine where our electricity comes from. It is estimated that in the USA about 50% of electricity is derived from coal.  After coal, the second most common energy source is natural gas, which produces about 20% of the USA’s electricity.

The final 30% of the USA’s electricity comes from non-combustible resources (gives off no CO2), what one could consider “green”; Nuclear, Hydro, and finally about 2% of electricity is derived from “renewable resources” Solar and / or wind.

The 2010 Tesla Roadster boasts a 0 – 60 mph time of under 4 seconds, a fine time for any automobile; but even more impressive when one considers that the Roadster is an electric car. Acceleration like that must need a lot of power. According to the Tesla website the Roadster’s motor puts out about 288 hp, or 215 kilowatt’s. So we can assume that if we were driving the Roadster for one hour, at full throttle, we would use at least 215 kilowatt/hours of electricity.  Or closer to 86 kilowatt/hours at 40% throttle.

As was stated earlier coal power is the most common form of electricity in the USA (and Canada). So just how much coal would need to be burned to power a Tesla Roadster at full throttle for one hour?

One Kilogram of coal can produce 6.67 KWh. Unfortunately a coal power plant is not 100% efficient, in fact it is only about 30% efficient, the rest of the energy being lost to heat and friction. A kilogram of coal actually only produces about 2 kilowatt hours of electricity. Meaning, to drive a Tesla Roadster for one hour (215 KWh) at full throttle we would need to burn over 100 kg’s of coal, or 30-40% of that in actual daily driving conditions.

What about gasoline?

Gasoline at full efficiency produces 13 kilowatts per kg. Of course a car’s engine isn’t 100% efficient, though it is much more efficient than a coal power plant. It can be estimated that the average car engine is about 40% efficient, of course power is also lost through the transmission, so in the end we can estimate that about 20% of the energy given off by the gasoline is actually reaching the wheels. So to produce 215 KWh’s of power a car’s engine would have to create 288 HP (1HP is 746Watts) which is unrealistic.  But 86 HP is more attainable and is 30% of the power; more in line with daily driving conditions.  That would require approximately 5.1 L, or 6.6kg of gasoline.

What does this mean for “zero emissions”?

With over half of the USA’s energy coming from coal, driving any electric vehicle more often than not would be creating more CO2 than if one drove a standard gasoline based vehicle:

1 Kg of Coal produces 1.83 Kg’s of CO2, 1 Kg of gasoline produces 3.2 Kg’s of CO2. If we drove our Tesla Roadster at 30% throttle for one hour, using 65 KWh’s of electricity, the electric car using coal power would create about 55 Kg’s of CO2, the gasoline based car would clearly need much less.

Now of course these numbers are rough, as no one drives a car the same or necessarily at 30% throttle all the time. But as you can see per kilowatt hour coal actually produces far more CO2 than gasoline.

So why do we call it “zero emissions”?

The truth is an electric car does give off zero emissions, at the tail pipe. But to create that electricity pollution is given off a few hundred miles away at the nearest power plant.

Does “zero emissions” exist?

“Zero emissions” only exists in cases where energy is not derived from combustible sources. As was stated earlier, 30% of the USA’s energy comes from non-combustible sources, such as Nuclear and Hydro. Technically, both these forms of electricity give off zero emissions, but both still create other forms of pollution. So in a short answer for all practical purposes right now “zero emissions” is a myth.


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10 Comments

  1. Dan F says:

    having driven a model of the tesla and banking energy by letting the momentum of the vehicle recharge the battery while decelarating (not using the brakes) I was able to drive from San Francisco to Woodside, north on skyline, out to half moon bay on 92 and back to the city on hwy 1 using about $1.90 of electricity. Distance covered was just over 90 miles.
    The author of this misinformation does not take into account that when a person takes their foot off the pedal it works as a very efficient brake and the energy goes back to the batteries.
    On the drive mentioned above i only put my foot on the brake pedal 5 times for sudden stops in heavy traffic and stop lights.
    It is a fantastic technology to be studied with attention to all of the facts.

  2. Anthony says:

    Uhh… guys… you forgot about the rest of the holes in the calculations that you could drive an oil rig through…

    Quote: “If we drove our Tesla Roadster at 30% throttle for one hour, using 65 KWh’s of electricity”…. YOU WOULD EXHAUST THE BATTERY!!

    hmmmm… interesting isn’t it. The Tesla Roadster has over 200 miles of range. Yet only has a 53 KWh battery. ( of which it only uses 45KWh or so. ) The overall mistake here is comparing some fractional power output of the engine to energy consumption and saying that represents “daily usage”. Just compare energy per mile to energy per mile and call it day. You don’t even have to deal with engine efficiency numbers then… take a look..

    The Tesla Roadster uses between 0.25 and 0.30 kW hours per mile. (53kWh / 200 mile range) That accounts for the losses in the motor, but not the charging side. So I’ll use the higher number for the Tesla. A gas vehicle getting 30mpg is going to use 1/30th of a gallon of gas per mile. That also nicely accounts for efficiency losses in the engine and transmission. So, how much carbon does burning coal for .3kWh produce? We’ll use your estimates of 30% efficiency and say we get 2kWh for 1kg of coal. That means we need to burn .15kg of coal to create .3kWh of electricity. That in turn creates (.15kg X 1.81kgCO2=)

    Electric Car: .27 kg of CO2 per mile.

    For the gas car 1 gallon of gas at 2.835 kg divided by 30 is about .1 kg. Burn to make CO2 and we get..

    Gas Car: .32 kg of CO2 per mile.

    Using fairly low efficiency numbers and “Coal Only” electricity we still get a reduction in CO2 output. When also factoring in extra carbon output for idling gas engines current and future cleaner electric generation options then coal,e lectric cars are an absolute net benefit to us all.

  3. My TWIKE is truly zero-emission :

    I have a contract with my power provider that guarantees renewable generation of all electricy my family consumes. Not only for mobility, but also for lighting, cooking, washing, etc…

    Moreover, my TWIKE is frugal : its human/ballast ratio is much better than that of cars.

    And yes : a bicycle is an even better solution :-)

  4. Dylan Darroch says:

    I agree with the last poster in that IF most electricity came from clean sources THEN electric cars SHOULD be called ‘zero emissions’.
    As it stands right now ‘zero emissions’ is more a slogan than reality.

    That’s the whole point. Nothing against electric cars, but then again nothing against gasoline powered vehicles either.

  5. The author is completely missing the point with electric vehicles. The point is that unlike gasoline vehicles, EVs CAN use any source of electricity. Electricity CAN be from green sources, and new green energy sources are coming on line all the time. Electric vehicles will mostly charge up at night when the demand for electricity is low and power plants are idling. Also many people are taking advantage of incentives for solar systems to not only charge their EV and offset their entire house’s energy consumption, but also provide excess power to the grid, thus offsetting even more emissions. Even though some EVs will charge up with dirty power, the power CAN be clean, even if it takes some time for to become main stream.

    Check out this link for more information.

    http://www.mnn.com/your-home/green-building-remodeling/blogs/which-should-come-first-a-solar-roof-or-a-green-garage

  6. Dylan Darroch says:

    As author I will admit that I made a mistake in the calculation of weight to volume of gasoline.
    Though the calculations for carbon emissions is accurate.

    I also didn’t factor in energy lost as power is sent from the plant down the power lines to people’s homes.

    The point of the article is that zero emissions does not exist.

    The fact is per KJ of energy transferred to the wheels of a car, in an average American/ Canadian city, there will be more CO2 given off via electric car than via gasoline.
    PERIOD.

    We can argue about the efficiency of car engines, transmissions etc…
    What is not arguable is the inefficiency of coal power plants (max 30%).

  7. Lucky 13 says:

    Zero Emissions means zero emissions FROM THE VEHICLE – end of story.
    If you want to include the generation of the electricity into the equation you need to do the same for gas vehicles and guess what, gasoline comes from oil. The drilling and refining of oil into gasoline isn’t emission free.
    Plus, as others pointed out, the calculations presented are so full of holes you could drive a coal truck through them. For instance, even though the author states that 50% of electricity to derived from coal in the US he calculates the efficiency of the Tesla using 100% coal. Gasoline comes from the gods but electricity comes from coal. Right.
    Hardly the truth as the title claims…

    For the real story, you should look at the Wells to Wheels study published by the California Air Resources Board in 2003: http://www.transportation.anl.gov/pdfs/TA/273.pdf

    Thank you for spreading more half truths and misinformation on the subject.

  8. ThaDude says:

    22kg’s of gasoline is actualy about 30 litres. But the carbon ouutput is based on weight not volume. The carbon output is correct. The calculation should be 1kg of gasoline to 1.3 litres, not 1.3 litres to 1 kg.

    The efficiency of an internal combustion engine is arguable, but it is higer than 20%…it depends on the engine and the transmission. Obviously newer cars are more efficient.

    But the author is correct in stating that it is less efficient to burn coal, create electricity and then power a battery to power a car rather than using gas.

  9. Wetdog says:

    Your full throttle (accelerator) example would work against the gasoline engine as that would the least efficient use of a gasoline engine. There is no possibility of a 288 hp gasoline engine using only 17 litres of gasoline on full throttle for an hour.

  10. Wetdog says:

    Your analysis seems a bit off. The efficiency of a internal combustion engine is closer to 30% at constant rotation and optimal rpm, whereas in variable load (real road accelerating/decelerating) it is closer to 15%-20% efficient. The electric motor remains a relatively constant 70 – 80% efficiency under variable load.

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