Hey Mr. Green,

Approximately how much energy (measured in equivalent of gallons of gas) does it take to manufacture a new car? My old car meets my driving needs and averages 32 miles per gallon, and I use less than 100 gallons per year. If I get a more efficient car, would it benefit the planet, or would the resources used to build the car be more than the savings in energy usage?

—Judy, in Oakland, California

It takes roughly the equivalent of 260 gallons of gasoline to make the typical car of around 3,000 pounds, according to an exhaustive study by the Argonne National Laboratory. (And I do mean exhaustive. These guys have factored in darn near everything but the calories consumed by the assembly-line workers.) A hybrid car takes about 25% more energy than a regular car, or around the equivalent of 325 gallons because it requires more juice to make the batteries.

Whether to replace depends on how much you drive. If your car gets 32 miles per gallon, then you’re putting on only 3,200 miles a year, as opposed to the ghastly national average of more than 13,000. So if you buy, say, a plug-in Prius, which gets about 50 miles per gallon and drive it the same distance, you'd be using 36 fewer gallons of gas a year than with your old car. So it would take 9 years before your Prius will have “caught up” with your old car and saved enough fuel to offset the energy needed to make it. After that, your 18 miles extra per gallon will be pure savings in energy and emissions. But if you were driving your old car that customary 13,000 miles a year, burning 406 gallons a year, it would only take about 10 months before you’d have burned up the amount of energy needed to create a road-worthy Prius. 

Of course energy is not the only consideration, because the Prius (or any more-efficient car) will be responsible for less pollution than your old car. And remember, not all energy is created equal. If, for example, your plug-in Prius was charged up by solar or wind power, its environmental impact would be further diminished. Which reminds me that during the month of October, Sierra Club members who are residents of Arizona, Colorado, California, Connecticut, Delaware, Massachusetts,  Maryland, New Jersey, and New York are eligible for a $1,000 rebate on home solar installations by the Sungevity solar company. Promise me you'll look into this deal!  —Bob Schildgen

Got a question? Ask Mr. Green!

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 --illustration by Little Friends of Printmaking