EV Emission Analysis

I discovered a wealth of energy and pollution info on various California state agency web sites, particularly CARB and CEC. So I computed my own figures for per-mile power plant emissions for EVs.

Gasoline/Diesel Emissions

From http://www.energy.ca.gov/fuels/gasoline/gasolinesales.html I see that the total taxable motor fuels (gasoline & diesel) sold in CA in 1996 was 15,791,759,000 gallons.

And from http://www.energy.ca.gov/reports/stats/table49.html I see that the CA average fuel economy in 1993 (latest year available) was 17.7 miles/gallon.

17.7 mpg * 15,791,759,000 gallons = 279.5e9 miles driven per year. That's 765.8 million miles/day, a figure I wasn't able to find directly. From http://www.arb.ca.gov/ceidars/emssumcat.query?F_DIV=0&F_YR=1995&F_AREA=CA" we see that the total pollutants from all that gasoline burned and on-road miles driven are (1995 figures)
 
Pollutant Tons/day grams/mile
Total organic gases 1800 2.1323
Reactive organic gases 1600 1.895
Carbon monoxide 15000 17.77
Nitrogen oxides 2100 2.488
Sulfur oxides 56 0.06634
Particulates 80 0.09477
Particulates < 10 micron 67 0.07937

 ("1 ton" = 2000 pounds, not 1000 kg)

Electric Generation Emissions

Now let's look at the situation for electricity. From http://www.energy.ca.gov/electricity/electricitygen.html I get an in-state annual electricity generation from all sources of 202,022 GW-hr, which works out to 553.44 GW-hr/day or an average of 23.06GW, which seems about right. From the emissions inventory page mentioned earlier, we can see that in 1995 in-state electric generation produced
 
Pollutant Tons/day grams/kW-hr
Total organic gases 28 0.0459
Reactive organic gases 6 0.009835
Carbon monoxide 36 0.059
Nitrogen oxides 69 0.1131
Sulfur oxides 8 0.0131
Total particulates 6 0.00983
Particulates < 10 microns 5 0.00819

 So if we use that electricity to charge EVs getting 4 miles/kW-hr, the electric generation emissions attributable to each EV mile driven would be
 
Pollutant grams/mile % of internal combustion
Total organic gases 0.011475 0.5%
Reactive organic gases 0.002459 0.13%
Carbon monoxide 0.01475 0.083%
Nitrogen oxides 0.028275 1.136%
Sulfur oxides 0.003275 4.9%
Total particulates 0.0024575 2.59%
Particulates < 10 microns 0.0020475 2.578%

Obviously it depends on the specific pollutant, but this all is pretty consistent with the 97% reduction figure I've heard for some time (power plant emissions per EV mile being 97% less than the per-mile emissions for an average gasoline or diesel vehicle). And those emissions are at the power plants, not in downtown LA or SD or wherever the cars are.

Caveats

  • I wasn't able to find all my statistics from the same year.
  • The electric generation figures are probably gross totals, so they don't include transmission losses (I think I've seen 20%).
  • I assume the current electric generation mix would apply to large numbers of EVs. This may or may not be true, depending on how much capacity is available from which kinds of plants when the EVs are charged. If  all of the miles driven in California could be electrically powered at 4 miles/kW-hr, that would work out to an average electrical load of about 8GW, which is about 35% of the average in-state electric generation of 23.06GW. About three and a half San Onofres (@2.2 GW each) would do it (just had to say it :-))
  • Most of the petroleum fuels go to cars and trucks, but the total taxed fuel sales figures might include other users (aviation, trains); depending on how polluting these users are, and how much they use, it could affect the figures either way.
  • My EV "mileage" of 4 miles/kW-hr, referenced to the AC socket, is for the EV1, and may be optimistic for larger EVs -- though given the number of cars you see on the freeway with exactly one occupant, it's clear that a lot of people could commute in the EV1. 


    • Despite these caveats, it's pretty clear that EVs have the advantage when it comes to air pollution.

    Phil Karn, January 1999