market (DOE, 2007). When fully operational, the total production of these six plants would be 8000 bbl/d. In addition, a number of companies are actively pursuing commercialization of cellulosic ethanol plants. The corresponding technologies will continue to evolve over the next 5–10 years as challenges are overcome and experience is gained in the first technology-demonstration and commercial-demonstration plants. As a result, the committee expects deployable and commercialized technology to be in place by 2020 if technology-demonstration plants continue to be built, despite the current economic crisis, and if they are rapidly followed by commercial-demonstration plants.

The committee developed a model, in collaboration with the Massachusetts Institute of Technology, that estimated costs and CO₂ emissions for converting the biomass feedstocks just discussed into ethanol via biochemical pathways. The model included the effects of enzyme cost (10–40 cents per gallon [¢/gal]),³ feedstock composition, solids loading (18–25 percent), and plants size (40 and 100 million gallons per year, corresponding to daily feed rates of 1400 and 3500 dry tons, respectively). The analysis also included the effects of pretreatment, hydrolysis, and fermentation yields. Three scenarios (representing low, medium, and high levels of improvements) were developed, in the form of process-cost estimates, representing current technology for the biochemical conversion of cellulosic feedstocks, reasonable evolutionary advancement of the technology, and the most optimistic advancement of the technology. (See NAS-NAE-NRC, 2009, for details on the analyses and results.)

The committee judges that the reasonable-improvement scenario best represents where the technology will be for 2020 deployment, and that the major-improvement scenario shows the considerable potential likely to remain. Results of the modeling for the woody biomass poplar, as an illustration of how technology improvements and the size of the ethanol plant could affect costs, are given in Table 5.3. The current costs of production are estimated for a biorefinery with a production capacity of 40 million gallons of ethanol per year; the committee accounted for the costs of production by 2020 by assuming reasonable technological advancements between now and then for the same-size plant. The estimated cost of production in 2020 at a biorefinery with a production capacity of 100 million gallons of ethanol per year is also shown to illustrate the economy of scale.

Table 5.3 shows that the cost of biomass (listed as “raw material-dependent