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The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs
TABLE 5-1 Combinations of Feedstock or Energy Source and Scale of Hydrogen Production Examined in the Committee’s Analysis
Feedstock or Primary Energy Source
Scale of Production
Grid-Based Electric Energy (from any source)
Central station plant
Thermal splitting of water
Gasifier or direct conversion
developing this analysis.4Appendix E contains the data for each technology case analyzed.5
The costs and energy requirements for distributing the hydrogen to the “filling” station and then dispensing it into the vehicle can be a significant fraction of the total. For central station plants, it is assumed that the distribution system uses pipelines. For midsize plants, it is assumed that distribution would be by cryogenic truck, because the low volumes of hydrogen involved would not justify a pipeline system. Distributed technologies generate hydrogen at the filling station itself and do not require a distribution system.
State of Technology Development
Almost all6 of the cost estimates are developed for two different states of technology development. One state, referred to as current, is based on technologies that could in principle be implemented in the near future. No fundamental technological breakthroughs would be needed to achieve the performance or cost estimates, although normal processes of design, engineering, construction, and system optimization might be needed to achieve costs as low as those estimated in this analysis.
The second state, referred to as possible future, is based on technological improvements that may be achieved if the appropriate research and development (R&D) are successful. These improvements are not predicted to occur; rather, they may result from successful R&D programs. Some may require significant technological breakthroughs. The nature of the improvements in each particular technology is discussed in Chapter 8; additional detail is provided in Appendix G. Generally these future technologies are assumed to be available at a significantly lower cost than that of the current technologies using the same feedstock.
Carbon Dioxide Sequestration
Some of the technologies in the analysis are further differentiated by whether carbon dioxide resulting from hydrogen generation is separated and sequestered. In particular, the midsize and the central station production facilities at which production is based on natural gas, coal, or biomass are examined both with and without the sequestration of carbon dioxide.
Summary of Technologies Considered
The hydrogen supply chain pathways that are considered in this chapter are identified in Table 5-2. They do not include all combinations of the factors listed above (e.g., coal as a feedstock in a distributed plant, or sequestration in a photovoltaic-driven electrolyzer plant). Intermittent technologies (wind, photovoltaics) can be used independently or in combination with the electric grid in order to allow hydrogen production when the renewable technology is not producing power. The results presented here are for the latter case, representing the average output of these intermittent technologies, as discussed later in this chapter. The cases for 100 percent renewables are presented in Appendix E. An all-grid-based system is included here.
CONSIDERATION OF HYDROGEN PROGRAM GOALS
Although the unit cost of producing and delivering hydrogen from the various technologies is critically important
In the graphs in this chapter (Figures 5-1 through 5-13), all of the combinations listed in Table 5-1 are included except midsize generation of hydrogen based on natural gas. The analysis suggests that this alternative would be dominated by either distributed or central station use of natural gas, and thus those estimates are not reported.
Solar-photovoltaic (PV) and wind technologies were examined by the committee only at distributed scale. These technologies do not benefit from scale economies to the same extent as do single-train processes, such as gasification (of biomass or coal) and steam methane reforming. For example, in the case of solar-PV, twice the structural supports will be required for a solar field of twice the generating capacity (watts)—a linear scaling. Wind farms require multiple turbines to reach capacities above a few megawatts.
Evaluation of a current nuclear thermal reforming of water is not included because no such technology exists at the present time.