Electric cars have arrived and new hybrids are proliferating. As a result, the fuel economy of the average affordable car is finally starting to climb. In fact, there are so many choices for efficient cars that it can be hard to know which technology is best for the environment and your wallet.
Weighing your green options gets more complicated because of regional differences in gasoline prices, electricity rates, and how the electricity (to power your EV) is produced. “Greenhouse gas emissions associated with plug-in vehicles depend strongly on which power plant is generating the electrons that charge the vehicle,” said Jeremy J. Michalek, associate professor of mechanical engineering and public policy at Carnegie Mellon University.
To start my region-by-region comparison, I assumed 15,000 miles of driving per year. To determine CO2 emissions for gasoline, I used Argonne National Laboratory’s well-to-wheels factor of 23.7 pounds of CO2 for each gallon burned in your car. The CO2 numbers for electricity come from the Environmental Protection Agency’s eGrid data. Rather than making a small adjustment for primary energy source extraction, transportation, and processing, I used the eGrid numbers at face value. That’s because those numbers—the best ones anybody has these days—were produced in 2005, and the grid is getting greener every day. (I told you it was complicated.)
For electric car efficiency, I used the EPA’s value of 3.6 miles per kWh, which accounts for losses during EV charging. I assumed 30 mpg for a fuel-efficient gas car, and used 50 mpg for a hybrid-electric vehicle. For all the vehicles—and everything else you see in the table below—your mileage may vary. Drive less and drive slower to get the most bang for the buck and for planet Earth. Gasoline and electricity prices are average U.S. retail from July 2010. The electricity rates are averages tracked by the Department of Energy—not special time-of-use rates that EV drivers may be able to take advantage of. The cities used are representative of larger regions. Remember: Electrons on the grid don’t obey city or state borders.
Change the assumptions and you might get different numbers, but the regional pattern seems clear. As Professor Michalek said, “If you have a city where gasoline is expensive, and electricity is cheap and clean, it’s a better fit for a plug-in vehicle than a city where gasoline is cheap and electricity is expensive and dirty.” In a couple of those cities where electricity is especially dirty, the 50-mpg hybrid actually beats the electric car for low CO2 emissions. At first, that surprised me, but I quickly came to see it as the exception that proves the bigger and more important rule: For a myriad of reasons—from less local air pollution to greater reduction of our dependence on oil—the pure electric car is as green and cheap as it gets.
To see details of the methodology and math used, visit www.plugincars.com/EVmath
[Witten with help from Constantine Samaras of the Rand Corp.]