John Voelcker’s article ”How Green Is My Plug-In?” delves into the carbon impact of plug-in hybrid electric vehicles (PHEVs), and it generated quite a bit of discussion. After that article appeared in March 2009,IEEE Spectrum’s David Schneider spoke with Jeremy Michalek, an assistant professor of mechanical engineering and of engineering and public policy at Carnegie Mellon University (CMU). Michalek’s upcoming study in Energy Policy looks at the sizing of batteries for such cars; in it, he calculates that plug-in hybrids with large battery packs—like the 2011 Chevrolet Volt—may never save consumers any money.
The Electric Power Research Institute (EPRI) has a different view of the future than Michalek does. Here, in an interview with Voelcker, Mark Duvall, director of electric transportation at EPRI, explains the results of his organization’s detailed analyses of the environmental and energy impacts of PHEVs—which were conducted with the Natural Resources Defense Council (NRDC)—and relates some of the experiences developing models of the impact of plug-in hybrid technology.
IEEE Spectrum: What was your goal in doing the EPRI-NRDC study?
Mark Duvall: We wanted to conduct the first comprehensive study of the environmental impacts of plug-in hybrid vehicles—both for greenhouse-gas emissions and air quality. To really analyze these issues, you need sophisticated and detailed models of the electricity sector to understand which power plants would be used to generate the electricity to charge PHEVs.
Spectrum: Did that study assess the costs of cutting carbon using plug-in hybrids?
MD: That’s very difficult to do for vehicle technologies. While transportation as a whole is a large emitter of greenhouse gases, each vehicle saves a very small amount of carbon [one liter of gasoline produces about 3 kilograms of CO 2 ; 1 gallon, about 11 kg]. If you don’t get all of the costs exactly right—especially the purchase cost of the vehicle—you get really large variations in cost-effectiveness, all the way from saving money by cutting carbon to costs of US$ 1000 or more per ton of carbon. Our work indicates that PHEVs, once the technology matures and they attain volume production, can be manufactured and sold for a reasonable price and that owners can expect to save money over the useful life of the vehicle.
Spectrum: One area where you differed with the Carnegie Mellon study was the cost of batteries, which it pegged at $1000 per kilowatt-hour. How do you view that estimate?
MD: We agree that until battery costs reach some more reasonable level (for example, $500/kWh), no plug-in hybrid can save enough fuel to cover its higher production cost. However, we’ve done quite a lot of cost modeling. Once batteries drop to the $500/kWh range, our studies indicate that plug-in hybrids with 10, 20, and 40 miles of range will all save money over their useful life—and this was with gasoline at about $3 per gallon. If gasoline costs more, as many analysts seem to expect, then the savings increase.
Spectrum: When do you see batteries dropping to that level?
MD: We are seeing some indications that battery costs for high-volume orders may be below $1000/kWh already. With the large number of production PHEVs now planned, and the current focus on developing cell-manufacturing capacity, I expect that we will see these price levels by the time the second generation of PHEVs arrives, in 2015 or so.