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March-April 2008
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< previous | 1 | 2 | 3 | 4 The fuel economy of American cars and light trucks averaged 12.4 miles per gallon in 1960. The oil crises of the 1970s triggered an increased demand for fuel-efficient vehicles, a pattern that continued through the 1980s, with fuel efficiency per vehicle rising from 12.2 miles per gallon in 1975 to
16.9 miles per gallon in 1991. But there has been little improvement since then, a trend reflecting the increased popularity of gas-guzzling pickup trucks and heavy-duty sport utility vehicles (SUVs). Our goal should be to raise the fuel efficiency of our cars and light trucks to an entirely new standard: 100 to 150 miles per gallon is not only feasible but could be accomplished in 20 years or less, limited by the time required for cost-effective turnover of the existing transportation fleet. Compare this with the target defined in the recently enacted United States Energy Independence and Security Act of 2007 (H.R. 6): 35 miles per gallon by 2020. The Electric OptionHybrid electric vehicles (HEVs) incorporate a conventional internal-combustion engine working in concert with an electric motor supplied with energy from a nickel-metal-hydride (NiMH) storage battery. The battery is charged “on board” the vehicle as required, using an electric generator run by the engine. The overall energy efficiency is increased by capturing a portion of the energy that would normally be dissipated as heat upon braking the car, employing it to run the generator. When the car halts in stop-and-go city driving, the engine turns off, conserving fuel. When it is time to restart, the electric motor provides the necessary power. The savings in fuel (and CO2 emissions) that could be realized if the entire U.S. automotive fleet were converted to HEVs could amount to as much as 30 percent of current gasoline consumption, with the additional benefit of improved air quality. 
©GM Corporation Chevrolet Volt plug-in hybrid, scheduled for production in 2010 Even greater savings could be realized if HEVs were replaced by so-called plug-in hybrids. With current HEVs, the energy used to propel the vehicles is provided exclusively by their on-board fuel (either gasoline or, potentially in the future, by increased use of more efficient diesel). With plug-in hybrids, a major portion of the electrical energy consumed by the vehicles could be derived from the local electricity grid. Depending on the energy source used to generate that power, the savings in terms of CO2 emissions could be even more significant. The Electric Power Research Institute (EPRI) reported in 2001 a study of the potential environmental advantages of plug-in hybrids. That study examined four cases: a conventional vehicle (CV); a standard HEV without plug-in capability (HEV 0); a plug-in vehicle with sufficient battery capacity to provide for an all-electric range of 20 miles (HEV 20); and a plug-in option with an all-electric range of 60 miles (HEV 60). Performance characteristics were taken as comparable for all four vehicles: gasoline storage on-board sufficient to provide for a range between re-fueling of 350 miles; a minimum top speed of 90 miles per hour; and a time to accelerate from 0 to 60 miles per hour of less than 9.5 seconds. For the plug-in options, the study assumed that the electricity taken from the grid was generated by combined-cycle power plants (heat that would normally be wasted in conventional plants is instead captured to generate additional electricity) consuming natural gas as feedstock with an efficiency for conversion of chemical to electrical energy of 50 percent (contemporary conventional power plants operate at efficiencies of less than 40 percent). 1 | 2 | 3 | 4 | continued >  
 
 
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