committee in Chapter 3, which is 45 billion gge/year and assumes 703 million dry tons per year of cellulosic feedstock. The two runs of the model both assume this additional biofuel, largely in the form of drop-in gasoline components that displace petroleum, and the difference in the two runs is just the assumption on the fuel efficiency of vehicles. As in the case above, the first run assumes all vehicles are at the midrange efficiency. In this run, the share of petroleum-based gasoline as a liquid fuel falls to about 25 percent by 2050. The second run assumes optimistic fuel efficiency for ICEVs and HEVs. In this case, bio-based ethanol, bio-based gasoline, and a small amount of CTL and GTL, make up all liquid fuel, with almost no petroleum-based gasoline.
• Emphasis on fuel cell vehicles. This case also has four different runs of VISION to capture variation in both vehicle efficiency and fuel carbon content. In all of these runs, the share of fuel cell vehicles (FCVs) increases to about 25 percent of new car sales by 2030 and then to 80 percent by 2050, modeled on the maximum practical deployment scenario from Transition to Alternative Transportation Technologies: A Focus on Hydrogen (NRC, 2008). There are two runs with the midrange vehicle fuel efficiencies, each with a different assumption about the GHG impact of the hydrogen production. Finally, there are two additional runs with optimistic assumptions about the fuel efficiency of FCVs, each with the different assumptions for the GHG emissions from hydrogen production. The hydrogen produced from a mix of low-GHG-emitting sources is assumed to come from production facilities, because they might operate under a sufficiently high carbon price. The CO2 emissions are about one-fifth of those from the alternative, low-cost hydrogen fuel generation (2.6 g CO2e/gge H2 compared to 12.2 g CO2e/gge H2; see Table 3.15).
• Emphasis on electric vehicles. There are four VISION runs for this case that account for differences in assumptions about vehicle efficiency as well as the GHG emissions of the fuel. It is assumed in all runs that the share of BEVs and PHEVs increases to about 35 percent of new car sales by 2030 and 80 percent of new car sales by 2050, in line with the rates put forth in Transitions to Alternative Transportation Technologies: Plug-In Hybrid Electric Vehicles (NRC, 2010), and this case assumes relatively greater sales of PHEVs than BEVs in all years. The first two runs assume midrange vehicle efficiency, each with a different assumption about GHG emissions from the electricity grid. These forecasts for the make-up of the grid are derived from the two cases put forth in AEO 2011 (EIA, 2011). The first is the BAU Case, and the second is the GHG price economy-wide case, where a low-GHG emissions grid is achieved by a tax on carbon that is first assessed in 2013 and increases at 5 percent per year (further details of the two grid scenarios can be found in Chapter 3). The second set of runs both use the optimistic assumptions about vehicle efficiency for the BEVs and PHEVs, again, with the two differing only in their assumptions about the GHG emissions from the grid. The low-GHG emissions grid is assumed to emit 111 g CO2 per kWh of generated power by 2050, reduced to just 21 percent of the BAU grid (541 gCO2e/kWh; see Table 3.8 and discussion).
• Emphasis on natural gas vehicles. This case has a set of runs that assumes an increasing penetration of compressed natural gas (CNG) vehicles into the market. The new car sales of CNG vehicles are assumed to be 25 percent by 2030 and 80 percent by 2050, as in the case for HFCVs due to a comparable level of current technological deployment. In the first run, the committee assumed that all vehicles attain the midrange efficiencies. The second run assumes optimistic fuel efficiency for CNG vehicles and midrange for the other vehicles in the fleet. CNG fuels rise over time to fuel the vehicles, and very little liquid fuel is needed by 2050. The committee continued to assume that RFS2 must be met by 2030, so the liquid fuel that is used is primarily biofuels in both of these runs. So little liquid fuels are needed in these runs that the committee assumed no CTL and GTL comes into the market—the plants are never built. CO2 levels are about 82 percent of conventional gasoline, on an energy basis (gCO2e/MJ, see Chapter 3).