Energy Issues for Vehicles: R&D, Carbon Sequestration, Fuel Conversion

Abstract

Ogden replies: Dan Cohn and John Heywood raise the issue of allocation of R&D resources among short-term and long-term concepts. Analysis by our group at Princeton University and other researchers suggests that, even under optimistic assumptions about, it would be several decades before hydrogen fuel-cell vehicle technologies could make a globally significant impact on reducing emissions. We agree that it is very important in the near term to encourage use of more efficient, less polluting internal combustion engine technologies using conventional fuels.Still, hydrogen holds the greatest long-term promise for dealing simultaneously with air pollution, greenhouse gas emissions, and energy supply diversity. With hydrogen fuel-cell vehicles, emissions could be reduced significantly compared to those from advanced internal combustion engine vehicles. It is highly uncertain today what economic values should be assigned to external costs of energy (such as climate change, health effects from air pollution, oil supply insecurity). However, the trend of the past few decades has been toward ever-increasing regulation of emissions, and integrated assessment models of global climate change suggest that deep reductions in carbon emissions from energy use will be required to stabilize atmospheric carbon dioxide at acceptable levels. Depending on how we ultimately value the external costs of energy, hydrogen might become the long-term fuel of choice.Should long-term concepts like hydrogen and fuel-cell vehicles have high priority, given that relatively modest improvements in more traditional internal combustion engine technologies could help address environmental and energy supply problems much sooner? In my view, hydrogen and fuel-cell technologies, although high-risk and long-term, have a potentially very high payoff. Therefore, they deserve significant government support now, as “insurance,” so that they will be ready in a few decades, if and when we need to deploy them widely.Rather than curtailing research on long-term technologies, I encourage a comprehensive strategy: Develop clean, efficient internal combustion engine vehicles in the near term, coupled with a long-term strategy of R&D on hydrogen and fuel cells. Consistent policies to encourage use of cleaner transportation systems with lower carbon emissions and to move away from our almost exclusive dependence on crude-oil–derived transportation fuels would encourage adoption of advanced internal combustion engine vehicles in the near term and, eventually, of hydrogen vehicles. Ramesh Gopalan makes a good point about carbon sequestration. However, removing CO2 from small sources (such as small engines), collecting it, transporting it, and sequestering it are daunting tasks. Building a CO2 disposal infrastructure for small-scale carbon capture and collection could be as difficult and costly as implementing a hydrogen infrastructure. Carbon sequestration is better suited to large energy complexes that produce decarbonized energy carriers (electricity or hydrogen).Vladislav Bevc questions whether large-scale use of hydrogen would be feasible, given that large-scale conversion of primary energy resources would be required. Studies have found that sufficient hydrogen to supply foreseeable demands for fluid fuels could be produced from a variety of primary resources including fossil resources (possibly with carbon sequestration), renewables (wind, biomass, or solar), and perhaps nuclear.To illustrate this point, consider energy use for US automobiles. An efficient, four- to five-passenger hydrogen car is projected to have a fuel economy equivalent to about 60–80 miles per gallon of gasoline. If such a car were driven 11 000 miles per year (the US average), and if one assumes that gasoline has a lower heating value of 122 megajoules per gallon, such a vehicle would use 17–22 gigajoules of energy per year. If all 132 million US passenger cars used hydrogen, the total energy use would be perhaps 2.2–3.0 exajoules per year. If the hydrogen is made from fossil fuels or biomass at 60–80% efficiency (depending on the feedstock), the primary energy use would be 3–5 EJ per year. This contrasts with current primary energy use of about 10 EJ for US automotive transportation. 1 1. For a discussion of primary energy resources for hydrogen production, see J. Ogden, Annu. Rev. Energy Environ. 24, 227 (1999). https://doi.org/10.1146/annurev.energy.24.1.227 REFERENCESection:ChooseTop of pageREFERENCE <<1. For a discussion of primary energy resources for hydrogen production, see J. Ogden, Annu. Rev. Energy Environ. 24, 227 (1999). https://doi.org/10.1146/annurev.energy.24.1.227 , Google ScholarCrossref© 2002 American Institute of Physics.