Not so impressive

August 15, 2009 

General Motors' claims for its Volt electric car (news story, Aug. 12) are grossly overcharged. The 230 mpg claim is for a distance of about 54 miles, during which the first 40 miles use up about 70 percent of the battery's charge, after which nearly 0.25 gallons is consumed. The full battery charge is 16 kiloWatt-hours (kWh), about 44 percent of the energy in one gallon of gasoline, and the battery weighs 50 times as much as one gallon. The claim for 100 miles is 100 miles per gallon, with the battery still waiting to be recharged at home.

With one gallon providing the charging for 60 miles, the remaining five gallons in the tank are supposed to provide a full range of 400 miles, or about 67 mpg. The 50 kWh of fuel burned at the power station for each 11.2 kWh expended from the battery cannot be ignored; 50 kWh is the equivalent of 1.4 gallons of gasoline.

Therefore, the 40-mile trip is equivalent to 29 mpg, the 100-mile trip is equivalent to 42 mpg, and the 400-mile trip is equivalent to 54 mpg. The longest trips place the Volt in the vicinity of the Prius mpg, but without the extra Prius features and with the burdens of overnight charging.

William T. Lynch, Ph.D.


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