recognizes that the cost of fuel and the greenhouse gas emissions from biofuels vary with feedstock. Because the purpose of the first set of analyses was to compare biochemical and thermochemical conversion, using one biomass feedstock in the analyses would better illustrate the differences between the conversion processes. Miscanthus, a high-yield perennial grass, was the biomass feedstock used for each conversion process (except those using only coal) because its cost and chemical composition are about the medians of the estimated costs and chemical composition of different cellulosic feedstocks. That analysis allowed the panel to estimate unit costs of each of the thermochemical and biochemical conversion processes on the assumption that Miscanthus was the biomass feedstock used for each process.

For the second set of comparisons, the panel chose two generic conversion processes—conversion of each of the lignocellulosic biomass feedstocks to produce ethanol, and thermochemical conversion of a combination of coal with each of the lignocellulosic biomass feedstocks (in a coal:biomass ratio of 60:40 on an energy basis) to produce synthetic diesel and gasoline. The estimated supply function for biomass provided information about feedstock quantities and costs. That information was combined with information about conversion costs to obtain supply functions for alternative fuels produced via either thermochemical or biochemical conversion and the assumed corn grain ethanol.

In its analyses, the panel made the following assumptions. Changes in the assumptions would normally change the estimated potential supply function. And because uncertainty is associated with each of the assumptions, the collection of uncertainties translates to important uncertainties in the potential supply curve.

  • All available land discussed in Chapter 2 will be made available for growing biomass for liquid fuels; none will be used for stand-alone electricity production. This assumption implies that renewable portfolio standards for electricity production will not result in the use of biomass to satisfy the requirements for renewable supplies of electricity.

  • Prices of biomass correspond to the costs of producing the biomass, including the opportunity cost of land. (See Chapter 2 for cost estimation.) All available biomass will be priced at those costs. As in Chapter 4, a coal price of $42/ton was used.

  • Conversion plants that use biomass as feedstock will have the capacity of using it at about 4000 dry tons per day, and all plants will run at 90 percent of capacity.

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement