to sequester about 10 billion metric tons of CO2, cumulatively, if hydrogen was generated using natural gas as a feedstock, and about twice as much with coal as a feedstock. These figures also suggest that, except for biomass-based hydrogen, there is relatively little difference in the amount of sequestration needed between current and possible future technologies. Both the rate of sequestration and the cumulative amount of sequestration needed can be expected to pose very great challenges.
These estimates can be compared with the available estimates of the geological sequestration capacities of potential locations. North American storage capacity is estimated at between 5 and 500 gigatons (GT) CO2 in Holloway (2001), and the same review article notes that the capacity of a single aquifer has been estimated at 9 to 43 GT CO2.
To put the annual volumes of sequestration in context, one can compare them with the movement of natural gas. The EIA (2003) projections for the year 2025 of natural gas consumption at 36 quadrillion Btu per year translates to roughly 0.7 billion metric tons of natural gas moved per year. Thus, sequestration of CO2 from coal-based or biomass-based hydrogen production in 2050 (see Figures 6-16 and 6-18) would require the movement of a mass of CO2 twice the amount that the EIA projects to be the mass of natural gas moved in 2025.
Finally, the committee considered the economic impacts of the alternative hydrogen production technologies. Taking into account the estimate of the consumption of gasoline over time, the consumption of hydrogen over time, the cost of gasoline,10 and the cost of hydrogen from the various technologies, estimates were made of the total cost per year of fueling the fleet of automobiles. Under the assumption that hydrogen-fueled vehicles have the same production and maintenance costs as those for gasoline-fueled vehicles, differences in the total cost per year of fueling the fleet of automobiles translates directly into differences in the total economic costs of the transition to hydrogen.
Figures 6-20 and 6-21 provide these total annual costs for the current technologies, for fossil fuels, and for renewables and distributed electrolysis, respectively. Figures 6-22 and 6-23 provide similar data for future technologies for fossil fuels and nuclear thermal energy and for renewables and distributed electrolysis, respectively. In each of Figures 6-20 through 6-23, there is a curve displaying an estimation of the annual fuel cost with only conventional vehicles, with no