To reach the 2050 goals for reducing petroleum use and greenhouse gases, vehicles must become dramatically more efficient, regardless of how they are powered. In addition, alternative fuels to petroleum must be readily available, cost-effective and produced with low emissions of greenhouse gases. Such a transition will be costly and require several decades.

The committee’s model calculations, while exploratory and highly uncertain, indicate that the benefits of making the transition, i.e. energy cost savings, improved vehicle technologies, and reductions in petroleum use and greenhouse gas emissions, exceed the additional costs of the transition over and above what the market is willing to do voluntarily.

—Douglas M. Chapin

Summary of the findings of potential reductions of petroleum use (left) and GHG (right) under a series of scenarios. Horizontal bars mark the respective reduction targets. Source: NRC. Click to enlarge.

Background. In response to a Congressional mandate in 2010, the National Research Council (NRC) convened the Committee on Transitions to Alternative Vehicles and Fuels to assess the potential for vehicle and fuel technology options to achieve substantial reductions in petroleum use and GHG emissions by 2050 relative to 2005.

The statement of task specifically asks how the on-road LDV fleet could reduce, relative to 2005, petroleum use by 50% by 2030 and 80% by 2050, and GHG emissions by 80% by 2050.

Broadly, the committee found that four general pathways could contribute to attaining both goals of petroleum and GHG reduction:

• Highly efficient internal combustion vehicles
• Vehicles operating on biofuels
• Vehicles operating on electricity
• Vehicles operating on hydrogen

While natural gas vehicles would reduce petroleum use, they would have limited impact on GHG emissions. An important caveat to the use of biofuels, electricity and hydrogen is that their GHG benefits depend on their being produced without large GHG emissions. This expands the need for controlling emissions beyond the transportation sector, the committee noted, and thus calls for a broader policy implementation.

For vehicle technologies, the committee used two sets of assumptions for cost and performance:

1. Midrange estimates that are ambitious but reasonable goals in the committee’s assessment;

2. Optimistic estimates which are potentially attainable, but will require greater successes in R&D and vehicle design.

Again, both sets are predicated on the assumption that strong and effective policies are implemented to continually increase requirements or incentives (at least through 2050) to ensure that technology gains are focused on reducing petroleum use and GHG emissions (rather than enhancing performance, as has occurred in the past).

The committee also developed alternate assumptions for fuels to aid in assessing uncertainties. For example, several production processes were considered for hydrogen and biofuels, and both conventional generation and low-GHG-emission scenarios were considered for electricity.

The committee also considered crosscutting technologies. For vehicles, these included weight reduction and improvements in rolling and aerodynamic resistance; for fuels, carbon capture and storage (CCS). In addition, the analysis took into account sector-wide effects such as consumer preferences and potential changes in vehicle miles traveled (VMT).

The committee then analyzed the performance and cost impacts of the various options in different scenarios. Vehicle and fuel data were then used to forecast future LDV fleet energy use and GHG emissions using two models, as well comparing different policy-driven scenarios.

By their nature, all models are simplifications and approximations of the real world and will always be constrained by computational limitations, assumptions, and knowledge gaps. All the models’ estimations depend critically on assumptions about technologies, economics, and policies and should best be viewed as tools to help inform decisions rather than as machines to generate truth or make decisions. The LAVE-Trans model in particular uses the committee’s assumptions about technological progress over several decades, how people behave, what things cost and what they are worth. It predicts, in a formal relational structure, how the vehicle fleet composition would then evolve and what the impact would be on petroleum use and GHG emissions. Some of the LAVE-Trans results were surprising, but the committee examined them and the model, fixed mistakes, and revised assumptions, until it was satisfied with the robustness of the outputs that resulted from the inputs. Even so, there is considerable uncertainty about the results presented here.

—“Transitions To Alternative Vehicles And Fuels”

Major Findings. Major findings of the committee as reported include:

• It will be very difficult to meet the goal of a 50% reduction in annual LDV petroleum use by 2030 relative to 2005, but with additional policies, the US might achieve a 40% reduction. An increasing number of efficient ICE vehicles, with an increasing share of HEVs will be responding to the CAFE requirements.

  Additional policy support may be required to promote increased sales of natural gas vehicles, battery-electric vehicles, and fuel cell vehicles. Even then the US is unlikely to reach a 50% reduction in petroleum use by 2030 because very little time remains for achieving the required massive changes in the on-road LDV fleet and/or its fuel supply. Many of the vehicles on the road in 2030 will have been built by 2015, and these will lower the fuel economy of the on-road fleet.

• The goal of an 80% reduction in LDV petroleum use by 2050 potentially could be met by several combinations of technologies that achieve at least the midrange level of estimated success. Continued improvement in vehicle efficiency, beyond that required by the 2025 CAFE standards, is an important part of each successful combination. In addition, biofuels would have to be expanded greatly or the LDV fleet would have to be composed largely of CNGVs, BEVs and/or FCEVs.

• Large reductions are potentially achievable in annual LDV GHG emissions by 2050, on the order of 60 to 70% relative to 2005. An 80% reduction in LDV GHG emissions by 2050 may be technically achievable, but will be very difficult. Vehicles and fuels in the 2050 time frame would have to include at least two of the four pathways: much higher efficiency than current vehicles, and operation on biofuels, electricity, or hydrogen (all produced with low GHG emissions). All four pathways entail great uncertainties over costs and performance. If BEVs or FCEVs are to be a majority of the 2050 LDV fleet, they would have to be a substantial fraction of new car sales by 2035.

• None of the four pathways by itself is projected to be able to achieve sufficiently high reductions in LDV GHG emissions to meet the 2050 goal. Further, the cost, potential rate of implementation of each technology, and response of consumers and manufacturers to policies are uncertain. Therefore, an adaptive framework that modifies policies as technologies develop and as conditions change is needed to efficiently move toward the long-term policy goals.

• Substantial progress toward the goals of reducing LDV petroleum use and GHG emissions is unlikely unless these goals are set and pushed on a nationwide basis through strong and effective policy intervention by the federal government.

• Even if the US falls short of the 2050 goals, there are likely to be environmental, economic and national security benefits resulting from the petroleum use and GHG emissions reductions that are achieved.

• The CAFE standard has been effective in reducing vehicle energy intensity, and further reductions can be realized through even higher standards if combined with policies to ensure that they can be achieved.

  The committee suggests that LDV fuel economy and GHG emission standards continue to be strengthened to play a significant role after model year 2025 as part of efforts to improve LDV fuel economy and reduce GHG emissions.

• “Feebates,” rebates to purchasers of high-fuel-economy vehicles balanced by a tax on low-mpg vehicles is a complementary policy that would assist manufacturers in selling the more-efficient vehicles produced to meet fuel economy standards.

  The committee suggests that the U.S. government include “feebates” as part of a policy package to reduce LDV fuel use.

• Several types of policies including a price floor for petroleum-based fuels or taxes on petroleum-based fuels could create a price signal against petroleum demand, assure producers and distributors that there is a profitable market for alternative fuels, and encourage consumers to reduce their use of petroleum- based fuels. High fuel prices, whether due to market dynamics or taxes, are effective in reducing fuel use.

• Fuel cells, batteries, biofuels, low-GHG production of hydrogen, carbon capture and storage, and vehicle efficiency should all be part of the current R&D strategy. It is unclear which options may emerge as the more promising and cost-effective. At the present time, foreclosing any of the options the committee has analyzed would decrease the chances of achieving the 2050 goals.

  The committee supports consistent R&D to advance technology development and to reduce the costs of alternative fuels and vehicles. The best approach is to promote a portfolio of vehicle and fuel R&D, supported by both government and industry, designed to solve the critical technical challenges in each major candidate pathway. Such primary research efforts need continuing evaluation of progress against performance goals to determine which technologies, fuels, designs, and production methods are emerging as the most promising and cost-effective.

• Demonstrations are needed for technologies to reduce GHG emissions at appropriate scale (for example, low-carbon hydrogen and CCS) to validate performance, readiness, and safety. Integrated demonstrations of vehicles and fueling infrastructure for alternative vehicle and fuel systems will be necessary to promote understanding of performance, safety, consumer use of these alternatives, and other important characteristics under real-world driving conditions.

  The committee supports government involvement in limited demonstration projects at appropriate scale and at appropriate times to promote understanding of the performance and safety of alternative vehicles and fueling systems. For such projects, substantial private sector investment should complement the government investment, and the government should ensure that the demonstration incorporates well-designed data collection and analysis to inform future policy making and investment. The information collected with government funds should be made available to the public consistent with applicable rules that protect confidential data.

• Commercialization of fuel and vehicle technologies is best left to the private sector in response to performance-based policies, or policies that target reductions in GHG emissions or petroleum use rather than specific technologies. Performance-based policies for deployment (e.g., CAFE standards) or technology mandates (e.g., RFS) do not require direct government expenditure for particular vehicle or fuel technologies. Additional deployment policies such as vehicle or fuel subsidies, or quantity mandates directed at specific technologies are risky but may be necessary to attain large reductions in petroleum use and GHG emissions. For alternative-vehicle and fuel systems, government involvement with industry is likely to be needed to help coordinate commercial deployment of alternative vehicles with the fueling infrastructure for those vehicles.

  The committee suggests that an expert review process independent of the agencies implementing the deployment policies and also independent of any political or economic interest groups advocating for the technologies being evaluated be used to assess available data, and predictions of costs and performance. Such assessments could determine the readiness of technologies to benefit from policy support to help bring them into the market at a volume sufficient to promote economies of scale. If such policies are implemented, there should be specific goals and time horizons for deployment. The review process should include assessments of net reductions in petroleum use and GHG emissions, vehicle and fuel costs, potential penetration rates, and consumer responses.

Vehicle-specific findings.

• Large increases in fuel economy are possible with incremental improvements in currently known technology for both load reduction and drivetrain improvements. The average of all conventional LDVs sold in 2050 might achieve CAFE test values of 74 mpg (3.18 l/100 km) for the midrange case. Hybrid LDVs might reach 94 mpg (2.5 l/100 km) by 2050. On-road fuel economy values will be lower.

• The unit cost of batteries will decline with increased production and development; in addition, the energy storage (in kilowatt-hours) required for a given vehicle range will decline with vehicle load reduction and improved electrical component efficiency. Therefore, battery pack costs in 2050 for a 100-mile real-world travel range are expected to drop by a factor of about 5.

  However, even these costs are unlikely to create a mass market for BEVs, because a battery large enough for a 300-mile real-world range would still present significant weight and volume penalties and probably could not be recharged in much less than 30 minutes. Therefore, BEVs may be used mainly for local travel rather than as all-purpose vehicles.

• BEVs and PHEVs are likely to use lithium-ion batteries for the foreseeable future. Several advanced battery technologies (e.g., lithium-air) are being developed that would address some of the drawbacks of lithium-ion batteries, but their potential for commercialization by 2050 is highly uncertain, and they may have their own disadvantages.

• PHEVs offer substantial amounts of electric-only driving while avoiding the range and recharge-time limitations of BEVs. However, their larger battery will always entail a significant cost premium over similar HEVs, and their incremental fuel savings will decrease as the efficiency of HEVs improves.

• The technical hurdles that must be surmounted to develop an all-purpose vehicle acceptable to consumers appear lower for FCEVs than for BEVs. However, the infrastructure and policy barriers appear larger. Well before 2050 the cost of FCEVs could actually be lower than the cost of an equivalent ICEV, and operating costs should also be lower. FCEVs are expected to be equivalent in range and refueling time to ICEVs.

• Although fundamental technology breakthroughs are not essential to reach the mpg, performance, and cost estimates, new technology developments would substantially reduce the development cost and lead time. In particular, continued research to reduce the costs of advanced materials and battery concepts will be critical to the success of electric vehicles.

Fuel-specific findings.

• Meeting the GHG and petroleum reduction goals requires a massive restructuring of the fuel mix used for transportation. The use of petroleum must be greatly reduced, implying retirement of crude oil production and distribution infrastructure. Depending on the progress in drop-in biofuels versus non-liquid fuels, refineries, pipelines, and filling stations might also become obsolete. For BEVs to operate with low GHG emissions, coal- and natural gas-fired electricity generation might have to be greatly reduced unless CCS proves cost-effective. Reliance on natural gas or hydrogen for transportation would require additional infrastructure. With currently envisioned technology, sufficient biofuels could be produced by 2050 to meet the goal of 80% reduction in petroleum use if the committee’s vehicle efficiency estimates are attained.

• With increasing economic natural gas reserves and growing domestic natural gas production mostly from shale gas, there is enough domestic natural gas to greatly increase its use for the transportation sector without significantly affecting the traditional natural gas markets. Environmental issues associated with shale gas extraction (fracking) must be resolved, including leakage of natural gas, itself a powerful GHG, and potential contamination of groundwater.

  There are several opportunities, direct and indirect, to use natural gas in LDVs, including producing electricity for PEVs and producing hydrogen for FCEVs. The fastest way to reduce petroleum use is probably by direct combustion in CNGVs coupled with efficiency improvements, but that approach is likely to interfere with achieving the GHG goal in 2050.

• Making hydrogen from fossil fuels, especially natural gas, is a low-cost option for meeting future demand from FCEVs, but such methods, by themselves, will not reduce GHG emissions enough to meet the 2050 goal. Making hydrogen with low GHG emissions is more costly (e.g., renewable electricity electrolysis) or requires new production methods (e.g., photoelectrochemical, nuclear cycles, and biological methods) or CCS to manage emissions. Continued R&D is needed on low-GHG hydrogen production methods and CCS to demonstrate that large amounts of low-cost and low-GHG hydrogen can be produced.

• Natural gas and coal conversion to liquid fuel (GTL, CTL) can be used as a direct replacement for petroleum gasoline, but the GHG emissions from these fuels are slightly greater than those from petroleum-based fuels even when CCS is employed at the production plant. Therefore, these fuels will play a small role in reducing petroleum use if GHG emissions are to be reduced simultaneously.

• Carbon capture and sequestration is a key technology for meeting the 2050 goal for GHG emissions reductions. Insofar as fossil fuels are used as a source of electricity or hydrogen to power LDVs, CCS will be essential. The only alternatives are nuclear power and renewable energy sources, including biofuels. Applying CCS to biofuel production could result in slightly negative net emissions.

The study was sponsored by the US Department of Energy’s Office of Efficiency and Renewable Energy. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies. The Research Council is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering.

Resources

• National Research Council (2013) Transitions to Alternative Vehicles and Fuels