I ran into this article and of course was pretty ticked off about it, pointing out as others have that the right headline should be "Coal plants are poisoning us and should be shut down". My next thought was: what percent of the electricity from coal-fired plants is consumed by electric cars? I figured it was probably 0.1%. I did some math and came up with a rough answer: 0.0775%. So yeah. The solution for coal plants being dirty is not to stop making electric cars because it wouldn't make much difference (yet).
Assumptions:
People who own electric cars drive the same average number of miles/year as gas car owners. It may be lower due to lower range of some electric cars?
I got the average electric car efficiency by just summing Leaf + Volt + Model S 85 and dividing by 3. Probably within 10% of the real number.
I ignored the real possibility that electric cars are more prevalent in states that have less coal-fired power plants.
Now the math:
# of electric cars in US:
260,000 (
source)
Average miles a car travels in a year:
13,476 (
source)
Electric miles driven (multiply above two numbers together):
3,503,760,000
Average electric car efficiency (wh/mi):
335 (
source)
or, 0.335 kwh/mi
kwh used by all electric cars (miles driven * kwh/mi):
1,173,759,600
or, 1,173,759.6 mwh
dividing by 8766 hours per year (365.25*24),
133.8991 mw of generation capacity needed
Energy in US coming from coal plants (in 2012):
1,514,043 gwh (
source)
divided by hours/year,
172.717 gw
or,
172,717 mw of generation capacity in coal plants
So finally, percent of coal plant electricity used by electric cars:
133.8991 / 172717 = 0.0775%