The role for natural gas is sure to be an issue in the fall debate over energy policy, as discussed in a recent  New York Times article.  We thought it would be worth a few minutes to figure out how efficient it is to use natural gas in a car versus a power plant.  

A high efficiency, natural gas-fired combined-cycle power plant might consume about 7000 Btus of gas to produce one kilowatt-hour of electricity. That would be about 7 cubic feet of natural gas. It would therefore take about 35 cubic feet of gas to generate 5 kilowatt-hours of power.  Assume a transmission loss of 20 percent (which is two to three times the actual average transmission loss), and 35 cubic feet of gas generate enough electricity to move an average electric vehicle about 16 miles.

When used to fuel cars, natural gas is measured in gallons of gasoline equivalent (GGEs), which is the volume of gas that contains about the same amount of energy as a gallon of gasoline.  A GGE is 127 cubic feet of natural gas.  Assume that the average car travels 24 miles per gallon of gasoline. The 35 cubic feet of natural gas that generates enough power in an efficient natural gas power plan to move a car 16 miles is about 27.5 percent of a GGE.  Yet, 35 cubic feet of natural gas burned in a car would fuel the car for about 27.5 percent of 24 miles, which is about 6.6 miles.  

Stated simply, 35 cubic feet of natural gas burned in an efficient power plant will move an electric car about 16 miles.  The same volume of natural gas burned in a natural gas vehicle would power the car for less than 7 miles.

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