. "6. Implications of a Transitionto Hydrogen in Vehicles for the U.S. Energy System." The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs. Washington, DC: The National Academies Press, 2004.
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The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs
sent an optimistically fast rate of penetration of hydrogen vehicles into the marketplace.
In order to examine the impacts of the hydrogen introduction, the committee examined a case in which no hydrogen vehicles are introduced, but hybrids capture the entire market share that would have been captured by hydrogen vehicles. In this case, the time path of conventional vehicles remains the same as in the committee’s plausible but optimistic vision. For every additional hydrogen vehicle in this analysis, there is one fewer hybrid electric vehicle.
The market shares of new vehicle sales of the three classes of vehicles in the vision are shown in Figure 6-1.
Once new automobiles are sold, they are driven for many years.3 Thus, the fraction of miles driven by each class of vehicles lags well behind the market share of new vehicle sales. Figure 6-1 shows the fractions of all miles assumed to driven by each class in the committee’s vision, in addition to the fractions of new vehicles sold by each class. The fractions of all miles are calculated as the fractions of all vehicles on the road, adjusted by the assumption that new vehicles are driven more than old vehicles are.
During the years in which it is driven, each type of vehicle must use the fuel for which it is was designed. And, in the committee’s analysis, it also assumed that the fuel economy of each vehicle is determined at the year the vehicle is sold, and that the fuel economy remains constant during the lifetime of the vehicle.
Figure 6-2 shows the fuel economy assumed for the three classes of vehicles over time. New and existing conventional vehicles are assumed to achieve, on average, 21 miles per gallon (mpg) of gasoline in 2002. However, this average fuel efficiency is assumed to increase by 1 percentage point per year during the entire time horizon. No assumptions are made about whether this increase is determined by regulations such as changing corporate average fuel economy standards, improved technologies, market forces, or some combination of factors. The committee notes that historic trends in light-duty-vehicle fuel economy, on a fleetwide basis, reached a plateau in the mid-1980s (EPA, 2003).
New GHEVs are estimated to have a 45 percent higher fuel economy than that of conventional vehicles in any year (see Chapter 3 for a discussion of efficiency differences); new hydrogen vehicles are estimated to have 2.4 times the fuel economy of conventional vehicles (or a 66 percent higher fuel economy than that of GHEVs). (For both types of vehicles, the average fuel efficiency is assumed to increase by 1 percentage point per year during the entire time horizon.4) Thus, the ratio of miles per kilogram for new hybrid vehicles to miles per gallon for gasoline-fueled vehicles remains constant over time, with all fuel economies growing steadily. This assumption about the relative efficiencies is designed to provide an optimistic view of the fuel efficiency of hydrogen vehicles.
In the committee’s analysis, both the number of new cars sold and the total vehicle miles traveled increase at 2.3 percent per year, consistent with the Energy Information Administration’s (EIA’s) Reference Case forecast of growth in vehicle miles traveled for light-duty vehicles.5 (This forecast rate of increase is consistent with recent historical trends, but the committee recognizes that it could be subject to alteration by many factors.) The total vehicle miles traveled for each type of car is proportional to the number of each type on the road, adjusted so that new cars are assumed to be driven more than older cars are.
Taken together, the assumptions about new-car sales, new-car fuel economy, proportions of the different types of vehicles, and vehicle miles traveled allow the committee to estimate the amount of hydrogen and of gasoline that would be used for light-duty vehicles if those assumptions in the optimistic vision came to pass. Figure 6-3 shows the consumption of hydrogen by light-duty vehicles estimated for this vision. By the year 2050, light-duty vehicles would be consuming 101 billion kilograms, or 111 million tons, of hydrogen per year. The consumption can be compared with the current U.S. industrial production of hydrogen of about 8 billion kilograms annually (see Chapter 2). In the committee’s vision of the possible penetration of hydrogen vehicles into the marketplace, light-duty vehicles could be consuming 8 billion kilograms of hydrogen annually by the year 2027.
In contrast, gasoline consumption would continue to rise only until the year 2015, after which it would begin declining until it reached zero in 2050. This trajectory of gasoline consumption is shown in Figure 6-4. Note that this figure includes two scales, measuring gasoline use in millions of barrels per day (right scale) and in quadrillion British thermal units (Btu) per year (left scale).6
Figure 6-4 also displays two other trajectories of gasoline consumption. The first shows an estimate of gasoline consumption in the absence of either hybrid electric vehicles or hydrogen vehicles. It shows that gasoline consumption would continue increasing at rates consistent with historical
In the committee’s analysis, automobiles are driven for 14 years, with annual vehicle miles (per car from the given vintage) declining as the vehicles get older. New vehicles are assumed to be driven 15,000 miles annually; 5-year-old vehicles, 14,490 miles; 10-year-old vehicles, 7,758 miles; 14-year-old vehicles, 603 miles. This decline reflects both the scrapping of vehicles over time and the reduced mileage of older vehicles.
Note that the increase in vehicle fuel efficiency (for all three types of vehicles) is assumed in all of the analyses and is independent of the choice of supply technology, that is, “current” or “possible future.”
New car sales have grown less rapidly. But the committee’s estimates are most sensitive to vehicle miles. Therefore, the model was calibrated to vehicle miles data from the EIA. Estimates were made for year 2000 vehicle miles traveled to be 2523 billion miles for light-duty vehicles, using the estimate from Annual Energy Outlook 2003 (EIA, 2003).