It's obvious that the relative greenness of an electric car depends on the source of the electricity it's running on.
But perennial complaints about "coal-powered cars" forget one very important thing: turning oil into gasoline uses electricity too.
Check out the latest episode of Robert Llewellyn's Fully Charged show to learn more.
Having first offered a brief, glowing comment on the Lexis is300h hybrid, Llewellyn gets to discussing just how much electricity fossil fuel refining uses—and it is significant (skip to the 4:52 mark if you just want to check out this section). Using some back-of-the-envelope calculations (real figures are hard to come by because the industry stopped sharing them), Llewellyn claims it takes 4.5kWh to refine just one gallon of gasoline.
If that's true, and I have neither the math chops nor the knowledge of the industry to figure it out, then it seems a Nissan LEAF will go something like 15 miles just on the electricity it takes to manufacture just one gallon of gasoline.
As always, if you're arguing for bike lanes because EVs run on coal, congratulations—you have a very valid point. If you're arguing for business-as-usual then you may be out of luck—because your gas guzzler runs on coal too.