Adventure EV

Carb(on) Loading.

by on Nov.25, 2009, under Design, EV Land Rover

Let’s take a minute to look at some basic environmental ramifications of an EV conversion.  Everyone wants to know what their carbon footprint is these days.   Is an EV superior in this regard?

I’ve heard the argument by fans of oil that, “pluging in an EV just moves the emissions from the tailpipe to the powerplant.”  The phrase is absolutely correct.  All pollution generated by running an EV happens at the electricity generation plant.  But not all methods of generating electricity produce the same amount of CO2.  In the case of renewable generation sources such as solar or wind the “tailpipe” emissions from an EV are zero.

Power and communication lines in Bangkok, Thailand

Power and communication lines in Bangkok, Thailand

So if you’re charging your EV with your own PV (PhotoVoltaic solar panel) setup you aren’t contributing a whole lot of CO2 into the atmosphere.  But most people don’t have their own little power plant at home.  They rely on the electrical grid to charge up the batteries on their EVs.  How much CO2 does that electricity generation really produce?  How does it compare to burning petrol in a conventional car?

It’s hard to say without knowing the makeup of energy producing fuel sources in your area, because as we’ve seen with renewables, not every fuel produces the same amount of CO2 per kWh.  Let’s look at the CO2 emission rates of various types of fuels when generating a common amount of energy, 100,000 BTU.

Electricity Generation CO2 Emissions by Fuel Type

Fuel Type Pounds of CO2 per 100,000 BTU
Coal 21.52 (avg)
Liquified Petroleum Gas 13.90
Natural Gas 11.71
PV (Solar Electric) 0
Wind 0
Nuclear 0
Hydroelectric 0

Data from the Department of Energy

Coal is the gross polluter while hydroelectric, PV, wind, and nuclear get a clean bill of health.  Keep in mind that this is the CO2 rate for electricity generation.

The EPA estimates the amount of CO2 produced by burning a gallon of gasoline (petrol) in a car is 19.4 lbs/gallon of CO2, and a gallon contains 114,100 BTUs of energy.

To compare these figures with EV energy consumption and emissions we can convert kWH, the most common method of working with energy when talking about EVs, to BTUs; one kilowatt hour is equivalent to 3413 BTUs, so corrected that would be 33.40 kWh per 114,100 BTU or one gallon of gasoline (114100 / 3413 = 33.40).

Lots of numbers swimming around, but bear with me.  I’m going to use my conservative projections for the Land Rover’s EV performance to see how it all relates.  I’m projecting a 90 mile range @40mph if I were to deplete all the energy stored in my 32.77 kWh battery pack.  The pack contains just under a gallon’s worth of energy so that equals 91.73 mpg ( (33.40 / 32.77)*90=91.73) when corrected to a full gallon.

Now let’s pick a fuel, the dirtiest fuel… coal.  If 100% of my EV’s electrical generation were attributed to coal I’d generate 21.52 lbs of CO2 everytime I drove 91.74 miles (the distance equivalent to a gallon of petrol).  That’s 0.235 lbs/mile of CO2.

When it had an ICE the Land Rover would get about 18 mpg @ 40mph.  Remember, the EPA estimates 19.40 lbs of CO2 per gallon, so that works out to 1.078 lbs/mile of CO2 when burning petrol (19.40/18=1.078).

With the worst fuel source, coal, the EV is still 4.587 times (1.078/0.235=4.587) cleaner than its ICE counterpart when “burning” the dirtiest fuel.  Keep in mind that the relationship between the ICE and EV would remain the same, more or less, regardless of the speed traveled or the type of vehicle, providing the comparison is between the EV and ICE versions of the same vehicle.  This relationship is a reflection of the efficiency of the chassis and powertrain.  If were to drive faster my mpg would go down in both the electric and the ICE.  Compare a lighter, sleeker car and the EV version would benefit from the same attributes that the ICE version benefits from.

Cholla Coal Power Plant in Arizona

Cholla Coal Power Plant in Arizona

The reason the EV is more efficient is due to the efficiency of its drivetrain.  ICE engines waste 70-80% of the energy they consume by generating heat, and any energy used to create heat doesn’t get translated into useful motion.  Electric motors generate very little heat.  Almost all the energy they consume is translated into rotational motion.  The best brushless AC motors have efficiency ratings of around 98%.  EVs are simply more efficient, therefore they go farther on less energy, and they generate less CO2.

In the Northeast, around 50% of the power generated is from Nuclear or Natural Gas, which emits 54% of the CO2 that coal does.  Charging in the Northeast would make my EV Land Rover 849% cleaner in CO2 emissions compared to it’s ICE counterpart.

And it can only get better from there.  If you live in Vermont, 79.7 percent of your power comes from nuclear generation, so your CO2 emissions would drop to… well, a very low number indeed.

And therein lies one of the beauties of the EV, it adapts very well.  If you charge your EV from solar panels, you generate no CO2 emissions regardless of how far you drive.  No matter what you do, an ICE car will always generate 19.40 lbs of CO2 per gallon of petrol.

And there are the numbers…  One version of them, anyway.

See how your state generates its electricity in this handy Excel document:

1 Comment for this entry

  • michael

    The efficiency of the Electric Engine is so much better than the ICE!! And to think NO oil changes!!
    One of the problems of the EV is of course the range.
    Is it possible to have an onboard generator for those times you just can’t quite make it home? Hopefully it would be a backup only. Besides the weight of the generator, what are the limitations of a system like this? Is it possible to generate enough electricity to charge onboard batteries when they reach a certain discharged level?

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