FIGURE G-13 Efficiency of biological conversion of solar energy (adapted from Hall and Rao, 1999).

forest residues. At a cost of $30 to $40/t, available biomass can be estimated to be between 220 million and 335 million dry tons per year.22 This biomass consists mainly of urban residues, sludge, energy crop, and wood and agricultural residues. A significant fraction of this biomass, especially forest residues, is already used by industry or in other competing processes, such as energy generation directly. However, if all of this theoretically available biomass could be converted to hydrogen, the annually available amount would be on the order of 17 million to 26 million t H2. As Figure 6-3 indicates, in an all-fuel-cell-vehicle scenario in the year 2050, 112 million t H2 would be required annually. Considering this demand and the competing demands for other uses of biomass, the currently available biomass is insufficient to satisfy the entire demand in a hydrogen economy, and new sources for biomass production would need to be considered.

Primary biomass in the form of energy crops is expected to have the quantitatively most significant impact on hydrogen production for use as transportation fuel by 2050.23 Estimates of energy that can potentially be derived from energy crops to produce biomass by 2050 range between 45 and 250 exajoules (EJ) per year. Bioenergy crops are currently not produced as dedicated bioenergy feedstock in the United States. Therefore, crop yields, management practices, and associated costs are based on agricultural models rather than on empirical data (Milne et al., 2002; de la Torre Ugarte et al., 2003; Walsh et al., 2000).

Land Use for Additional Biomass Production

In the most aggressive scenario for a hydrogen economy as considered in Chapter 6, a land area between 280,000 and 650,000 square miles is required to grow energy crops in order to support 100 percent of a hydrogen economy. The magnitude for this demand on land becomes apparent when comparing these numbers with the currently used cropland area of 545,000 square miles in the United States. Consequently, bioenergy crop production would require a significant redistribution of the land currently dedicated to food crop production and/or the development of a new land source from the U.S. Department of Agriculture’s (USDA’s) Conservation Reserve Program (CRP).

Although bioenergy crops can be grown in all regions of the United States, regional variability in productivity, rainfall conditions, and management practices limit energy crop farming to states in the Midwest, South, Southeast, and East (see Figure G-14) (Milne et al., 2002; de la Torre Ugarte et al., 2003; Walsh et al., 2000). Considering all cropland used for agriculture, as well as cropland in the CRP, in pasture and idle cropland, de la Torre Ugarte et al. (2003) considered two management scenarios for profitable bioenergy crop production: one to achieve high biomass production (production management scenario, or PMS), and another to achieve high levels of wildlife diversity (wildlife management scenario, or WMS). The production management scenario would annually produce about 188 million tons of dry biomass, which would be equivalent to 15 million tons of H2, requiring 41.8 million acres of cropland, of which about

22  

Mark Pastor, Department of Energy, “DOE’s Hydrogen Feedstock Strategy,” presentation to the committee, June 2003; Roxanne Danz, Department of Energy, Office of Energy Efficiency and Renewable Energy, “Hydrogen from Biomass,” presentation to the committee, December 2, 2002.

23  

M.K. Mann and R.P. Overend, National Renewable Energy Laboratory, “Hydrogen from Biomass: Prospective Resources, Technologies, and Economics,” presentation to the committee, January 22, 2003.



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