One of the responses I always hear from the “I don’t know what I’m talking about, but I bet I can stump the energy geek with something he hasn’t thought of!” crowd when I mention PHEVs and EVs is something along the lines of, “But what if you recharge the battery with electricity made from coal???”
The answer, as you can see below, is that you still reduce CO2 emissions a lot, even in that worst-case scenario.
The description of the graph from the source page (linked below):
Estimates from the GREET model (see Argonne National Laboratory’s information on GREET) show that passenger car PHEV10s produce about 29% fewer carbon emissions than a conventional vehicle, when plugged into an outlet connected to the typical U.S. grid. Even when PHEV10s are charged using power generated completely from coal, carbon emissions are about 25% less than those of a conventional vehicle. The use of light truck PHEV10s reduces emissions by 28% when charged on a typical grid and 23% when charged on power generated from coal. The carbon reductions are greater as the length the vehicle can travel on electricity increases.
(As you’ve probably guessed, a PHEV10 is a PHEV with a 10-mile battery range, etc. “Typical grid” electricity is defined as “50.9% coal; 20.1% nuclear; 16.7% natural gas; 11.0% renewable energy; and 1.3% petroleum”.)
See this page for the tables of data used in the graph.
There is a really good article about carbon emissions from plug-in vehicles in March IEEE Spectrum http://www.spectrum.ieee.org/energy/the-grid/how-green-is-my-plugin/0. Their conclusions were different from the graph you show here. They say it depends on the particular mix of electricity in your area.
“The moral of the story: If you’re concerned about the carbon footprint of your vehicle travel, definitely buy a plug-in— if you live in Norway, Brazil, France, or other areas with largely carbon-free electricity. Otherwise, have a look at your local grid—and think twice if you live in a place with lots of old coal-fired power plants. For you, a conventional hybrid may be kinder to the planet.”
And earlier they write:
“To figure out the amount of CO 2 that might result from running on grid power, the first thing you need to know is how much electricity a plug-in car uses. That, of course, depends on the vehicle in question. Tesla Motors has claimed that its sporty Roadster consumes just 110 watt-hours per kilometer, although some real-world measurements show its usage can be more than twice that—for reasons that may be unique to this specific high-performance car. For something like a plug-in version of a Toyota Prius, a more reasonable number to use might be 150 Wh/km, although more data are needed to know for certain.
The next key factor is how much carbon dioxide is released while the electricity is generated. For that, the U.S. electric grid provides a convenient benchmark. According to the U.S. Department of Energy, roughly 600 grams of CO 2 were emitted for each kilowatt-hour of electricity generated in the United States in 2006. The transmission and distribution of electricity is thought to incur losses of about 9 percent, and charging a car’s battery pack is about 90 percent efficient. So the actual amount of carbon dioxide emitted is probably closer to 700 grams—or 0.7 gram for each watt-hour in an electric vehicle’s battery pack.
The plug-in’s 150 Wh/km therefore translates to 105 grams of CO 2 per kilometer, assuming the car is charged on the U.S. power grid, averaged across all its many different generating sources. Remarkably enough, the standard Prius available today emits almost exactly the same amount of CO 2 : 104 g/km. And it’s possible to go even lower: a few small, ultraefficient European diesels emit less than 100 g/km.
But don’t jump to conclusions: The full analysis needs to be done on a ”well to wheels” basis. That’s because the fuel for the car must be pumped from the ground, transported, refined, and transported again to the filling station—steps that add about a third more CO 2 . And you also need to consider how much carbon dioxide would come from plugging a car into your local grid, with its particular mix of generating technologies.”