How Clean are Electric Cars?

Note:  this post has been updated as of 3/5/2012.  Please see: "How Clean Are Electric Cars--Revised"

One criticism of electric cars that I often hear is that they still require fossil fuels to generate the electricity.  Of course that is true, and that is why I support solar panels and renewable energy as a way to zero out the carbon footprint of our cars.  Unfortunately, there is a lot of misinformation on this point, so I'd like to clear things up.

My contention here is that we don’t have to wait for our electric grid to be completely renewable, or for our homes all to have solar panels, for electric cars to be far superior to internal combustion engine (ICE) cars with respect to greenhouse gases (and in other ways as well).

For an average utility with a mix of coal, natural gas, nuclear power, hydroelectric, and some renewables, switching to an electric car would reduce CO2 emissions by 69% for an average car.  Here in Oakland, where we use almost no coal to generate electricity, the savings would be 85%.  Even if your utility burns only coal to generate electricity, the reduction would be 52%.  (Stay tuned for further discussion on this about dirty oil--tar sands.)

Even compared to a car that gets 40 mpg, electric vehicles reduce CO2, and even if the electricity is generated by coal—although we should be working to stop using coal as much as possible.  The numbers here are:

Average power plant—electric car reduces CO2 by 42%

PG&E, non coal utility—electric car reduces CO2 by 73%

Utility using only coal—electric car reduces CO2 by  11%

Here are the calculations I am using (please correct me if I’m wrong!):

Carbon dioxide emissions from burning a gallon of gas include:

Extraction—1.5 pounds of CO2  (from Oil Sands Watch Pembina Institute)

Refining--      6     “  (see discussion below)

Burning--    19.4     “  (see for example:   http://www.ehow.com/facts_7311765_much-dioxide-per-gallon-gas_.html)

Total--         27  pounds of CO2 per gallon.

This doesn’t include deforestation, oil spills, or other sources of CO2, but I don’t know how to quantify those in terms of CO2. 

Refining a gallon of oil requires about 4 – 7 kilowatt hours (kwh).  See for example, http://gatewayev.org/how-much-electricity-is-used-refine-a-gallon-of-gasoline.  I used a low estimate of 4.5 kwh per gallon in the numbers above.  Given a mix of coal, natural gas, nuclear, hydroelectric, and renewables, the International Energy Agency (page 109) estimates 508 grams of CO2 is produced per kilowatt hour of electricity in the U.S.  I believe this does not include some additional CO2 produced in mining and shipping fuels.  I will check into this, but for now, will use 1.3 pounds CO2 per kwh.     4.5 kwh/gallon x 1.3 lbs CO2/kwh = 5.95 pounds of CO2 per gallon.

What’s interesting here is that electric cars can drive just about as far on the energy it takes to extract and refine a gallon of gas, as an ICE car can drive on that gallon.  I've heard this referred to as Big Oil's Dirty Little Secret.  Our Chevy Volt and other electric cars go about 3.3 miles or more per kwh.  Divide that by the national average of 1.3 lbs CO2/kwh and you get 2.5 miles per pound of CO2, or 0.4 pounds per mile.  So an electric car will go 2.5 miles per pound of CO2 x 6 pounds CO2 to refine 1 gallon of gas = 15 miles on the energy required just to refine one gallon of oil.  If you add the extraction, an electric car will go 7.5 x 2.5 = 18.8 miles on the energy to produce one gallon.  But the average U.S. car only gets 21.4 miles per gallon.  See:  http://www.project.org/info.php?recordID=384  --  article published January 27th, 2009 by Lacy Loftin; see graph below:
                                

In other words, an electric car creates only as much CO2 as an ICE car does just on the energy to produce gasoline, not even counting burning the gasoline. 

The exact comparison between ICEs and EVs is:

ICE car:  27 pounds of CO2/÷ 21.4 miles/gallon = 1.26 pounds of CO2 per mile

Electric car:  0.4 pounds per mile

Reduction:  (1.26 – 0.4) ÷ 1.26 = 68%

If CO2 generation by the utility company is lower than the average 1.3 pounds (587 g) per kwh, the reduction is even better.  For example, our utility company here in Northern California, PG&E, estimates 0.524 pounds per kwh (238 g/kwh) (http://www.pge.com/about/environment/calculator/assumptions.shtml).  This means the total CO2 per gallon for an ICE drops to about 24 pounds.  At 21.4 mpg, an ICE car produces 24 pounds CO2/gallon÷21.4 miles/gallon = 1.1 pounds of CO2 per mile.   Now an electric car uses:  0.524 pounds of CO2/kwh÷3.3 miles/kwh = 0.16  pound of CO2 per mile.  This is only 15% (.16/1.1) of what an ICE car produces for a reduction of 85%. 

If the CO2 is all based on coal, electric cars are still cleaner than ICE cars.  Coal may generate as much as 2.3 pounds of CO2 per kwh.  See:   http://cdiac.ornl.gov/pns/faq.html

In that case the total CO2 generated by one gallon of gas goes up to 31.5 pounds.  At 21.4 miles per gallon that is 1.47 pounds per mile (31.5/21.4).  To drive an electric car takes 2.3 pounds of CO2/kwh÷3.3 miles/kwh = .70 pounds of CO2/mile.  So an electric car still reduces CO2 by 52%.

But what if you drive a car that gets 40 mpg?  Is an electric car still cleaner? Here are the numbers:

Average utility (587 g/kwh)

ICE car:  27.5 pounds of CO2/÷ 40 miles/gallon = .69 pounds of CO2 per mile

Electric car:  0.4 pounds per mile

Reduction:  (.69 – 0.4) ÷ 0.69 = 42% reduction

The reduction would be greater for PG&E (238 g/kwh):

ICE car:  24 pounds of CO2/÷ 40 miles/gallon = .60 pounds of CO2 per mile

Electric car:  0.16 pounds per mile

Reduction:  (.60 – 0.16) ÷ 0.60 = 73% reduction

And there would still be a benefit, albeit smaller, for an all coal utility:

ICE car:  31.5 pounds of CO2/÷ 40 miles/gallon = .79 pounds of CO2 per mile

Electric car:  0.70 pounds per mile

Reduction:  (.79 - .70) ÷ 0.79 = 11% reduction

Of course, the greatest reduction is for having solar panels on your roof.  In our case we generate about 64% of our electricity with solar, which produces no CO2.   So that leaves 36% x PG&E’s 0.524 pounds/kwh = .19 pounds CO2 per kwh.  At 3.3 miles per kwh that gives  0.06 pounds of CO2 per mile.  Compared to a car that gets 40 mpg or 0.69 pounds of CO2 per mile, that is a 91% reduction. 

But it’s too soon to celebrate.  At 10,000 miles per year, we still produce 600 pounds of CO2, out of a goal of 2200 pounds (one tonne per person per year—see:  http://www.westernite.org/annualmeetings/sanfran10/Papers/Session%206_Papers/ITE%20Paper_6B-Fleck.pdf  page 2)  And we still drive another 2,000 miles a year on vacations at 37 mpg with the Volt, so that adds another 1300 pounds of CO2.  One possible solution for that is that I understand that the new Tesla sedan is designed to go 300 miles on the batteries.  If that is true, most of those road miles could be on electricity, not gas.