Martin Reynolds

Nissan’s LEAF electric vehicle is a remarkable achievement, but our interest lies in the simple carbon arithmetic that surrounds the vehicle. Before we go there, we note that electric drivetrain, battery and controller components will reshape the auto industry over the next decade.

The vehicle has a reported range of 100 miles, of a 24kWh battery. If we assume the average U.S. emissions factor for electricity generation of 1.34 pounds per kilowatt hour, charging the battery has an implicit emission of 32 pounds, or 0.32 pounds per mile. In practice, a complete 24kWh charge will require about 20 percent more input energy because of battery cycle efficiency, voltage drops, and converter efficiency. Therefore, a reasonable emissions estimate is 0.38 pounds of carbon dioxide per mile.

Now, an 18 mile per gallon vehicle emits about a pound of carbon dioxide per mile – so we can see that the LEAF is equivalent to a gas-powered fossil fuel vehicle that gets about 47 mpg. The Toyota Prius hybrid already achieves 48MPG. And the Honda Insight, a conventional lightly hybrid vehicle, achieves 40MPG.

Using data from the DoE,  we can demonstrate how emissions efficiency vary by region. Note that these numbers are aggregates, and there will be significant regional variations.

State Equivalent Emissions rate

Average             45 mpg

California          98 mpg

Texas                41 mpg

Idaho           2,000 mpg (Idaho has minimal fossil fuel)

So we observe:

1) The vehicle has no tailpipe, but is capable of creating plenty of emissions elsewhere.

2) To impact emissions, the vehicle is most effective in low-carbon areas.

3) On average, hybrid vehicles are better – but this isn’t about averages. It is about cutting peaks.

4) Further deployment of renewable and nuclear energy will make electric cars much more attractive – in a few decades.

As noted, green isn’t easy.