![]() ![]() Spectrum: But there are benefits that don’t have a price tag attached to them-the alleviation of smog in the inner city and the avoidance of imported petroleum, for example-isn’t that true? So even though you get to operate it on electricity rather than gasoline more of the time, all the fuel savings in the future don’t add up to what you paid for a big battery up front. And even at that price, you cannot make up the cost of the batteries in fuel savings over the lifetime of the vehicle. We looked at cheaper batteries, too, but the base case might be a little bit cheap already. The base case in our study assumes batteries cost US $1000 per kilowatt-hour of capacity. JM: That is true, but just because you drive fewer miles than the electric range of the vehicle doesn’t make the vehicle better, because you have to pay for all those batteries when you buy the car. But my understanding was that an electric range of 40 miles-the projected electric range of the Chevy Volt-encompasses the daily driving of a very large fraction of the driving population. Spectrum: You found in your study that plug-in hybrids might not be good for everybody. But we wanted to see how differences in driving patterns would influence the economic and environmental implications of such cars. Most of the other studies of plug-in hybrids analyze what the vehicle does for the median driver. What turned out to matter much more is the charging pattern. So there’s definitely an effect, but it is not the most significant factor. Our study showed that moving from a battery pack sized for 7 miles of electric travel to a heavier pack sized for 60 miles of electric travel would increase the amount of electricity needed to propel the vehicle in electric-only mode by about 10 percent and increase the gasoline needed in gas-only mode by about 8 percent. So even though you get to drive in electric mode for a larger portion of your miles, you get lower efficiency. If you add it all up-especially for a large-capacity plug-in like the Chevy Volt-you really bog down the vehicle. I wanted to understand whether that added battery weight was important. ![]()
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