Alternative Transportation Technologies:Hydrogen, Biofuels, Advanced Efficiency and Plug-in Hybrid Electric Vehicles

摘要

The National Academy of Sciences/National Research Council released a report in 2008, Transitions to Alternative Transportation Technologies-A Focus on Hydrogen, that assessed the maximum plausible growth rate of hydrogen fuel cell vehicles (HFCV) and the associated costs and impacts. It also compared the potential reductions in oil use and carbon emissions to those that might be achieved with a focus on biofuels or advanced fuel efficiency measures in conventional vehicles. The latter included hybrid electric vehicles, but not plug-in hybrid electric vehicles (PHEV). The U.S. Department of Energy requested the NRC to evaluate PHEVs on the same basis. This report was released in late 2009. This paper describes the analyses and results in the two reports, in particular comparing HFCVs with PHEVs. For the hydrogen study, the committee reviewed the technologies involved for vehicles and hydrogen supply and concluded that HFCVs could become the dominant technology for the light-duty vehicle fleet, but that it would take several decades. Achieving such a projection would depend on R&D success, continued and substantial government support, and consumer acceptance of the new technology. If achieved, oil consumption and carbon emissions could be greatly reduced by 2050. In comparison, biofuels and advanced fuel efficiency can achieve relatively rapid results, but these are likely to level out while HFCVs can keep growing. If all three options are pursued simultaneously, oil use in the light-duty fleet can be essentially eliminated by 2050 and carbon emissions reduced by almost 90 percent. PHEVs differ from the biofuels and advanced efficiency options in that they cannot be simply mandated by standards because, like HFCVs, they will be very expensive at least at first. Federal Government subsidies will be required to push them into the mass market. Batteries are by far the costliest component of PHEVs, and the rate at which costs can be reduced is uncertain. PHEVs also will require significant changes in driver behavior. They must be charged essentially every day to deliver their promised fuel savings, requiring a safe source of power and a commitment by the driver. PHEVs can get an earlier start than HFCVs because batteries are more nearly ready for mass production than fuel cells and fewer infrastructure changes are required, but the necessary cost drop is likely to be slower. Therefore the cumulative subsidies before reaching cost competitiveness are likely to be as high or higher for PHEVs unless currently unpredictable technology breakthroughs are achieved. HFCVs directly reduce gasoline use because the hydrogen will be produced from natural gas or other non-oil sources. PHEVs still use some gasoline, depending on driving and charging patterns. PHEVs with relatively small batteries that can deliver about 10 miles on electricity will use only slightly less oil than non-plugin hybrid electric vehicles. Larger batteries save more oil, but cost considerably more. PHEVs will reduce carbon emissions than oil consumption because the electricity must be produced at generating stations that use fossil fuel. If the power system can be decarbonized, the savings would be much greater.