FIGURE 4.8 Growth in production of corn-based ethanol in the United States. SOURCE: Courtesy of Renewable Fuels Association.

is well ahead of mandated biofuel levels. However, the 10 billion to 12 billion gallons per year probably represents the limit with respect to corn availability, assuming that corn yields and acreage increase modestly. Production of ethanol from grain is not likely to see significant additional process cost reduction. Further, costs are not subject to economies of scale because current plant size is about at the limit and water use limitations will probably increase costs in future plants. Based on the previous analysis in this chapter, a forward projection of grain ethanol production is as follows:

  • 8 billion gallons in 2008,

  • 10 billion gallons in 2010, and

  • 12 billion gallons in 2015.

Production of ethanol from cellulose is yet to be demonstrated at a commercial scale, and significant questions remain about the economic and commercial viability of the technology. Within the next 3 to 5 years, four to five commercial demonstration plants are expected. These will provide valuable information on cost, technology robustness, and particularly, commercial viability at the scale required to achieve large-scale cellulosic ethanol production. This information should be available by 2010. The committee expects the commercial and economic viability of cellulosic ethanol to remain a key issue for some time.

Cellulosic ethanol or other alternatives (e.g., biomass gasification, liquid-fuel synthesis) will be required to meet biofuel demand beyond levels achievable with grain ethanol. If commercially successful, cellulosic ethanol production could approach the growth experienced for grain ethanol. Cellulosic ethanol plants are similar to grain ethanol plants although somewhat more complex, and because of the dispersed nature of biomass, they will be limited in size to

TABLE 4.5 Key Assumptions and Parameters Used in Biomass-to-Biofuels Scenarios


Probable Case

Upper-bound Case

Biomass potentially available in the near-term (dry tons/yr)a



Biomass available in 2050 (dry tons/yr)



Average ethanol yield on biomass, 2008 to 2030 (gallons/dry ton)



Average ethanol yield on biomass, 2030 to 2050 (gallons/dry ton)



aBiomass use starts with crop residues (corn stover) and then adds other sources including energy crops as they become available, driven by cost.

bSee Table 4.3 for primary biomass components that make up this number.

about two to four times that of ethanol plants. For the rest of this discussion, the committee assumes that cellulosic ethanol is commercially demonstrated by 2010 and capacity begins to grow.5 Two cases are considered; both assume that cellulosic ethanol is economically competitive or there are sufficient fuel subsidies to make it competitive with oil-based fuels so that production capacity is built with private capital. One case is considered to be a measured response to the need to replace oil-derived liquid transportation fuels and is called the probable case. The other case involves a more aggressive application of the technology to generate liquid transportation fuels and is called the upper-bound case. Table 4.5 summarizes the key assumptions and parameters used for the two cases.

The probable case assumes a more measured pace of application of the technology in view of all the issues including process cost, water availability, biomass cost, other competitive uses of biomass and the ability to build plants and to increase biomass availability. For this case, the capacity build followed the grain ethanol capacity build experience, in which over a several-year period about 1 billion gallons of capacity was added per year. For this case (see Table 4.5 for details), the key assumptions are that the technology is commercially ready and there are 335 million dry tons of biomass available in the near term, increasing to 500 million dry tons available per year for conversion to biofuels by 2050. The upper-bound case also starts with 335 million dry tons of biomass available per year and assumes that by 2050,


The DOE roadmap on cellulosic ethanol is “to accelerate cellulosic ethanol research, helping to make biofuels practical and cost-competitive by 2012.” The three to five demonstration plants that DOE is funding should have achieved that goal by the end of 2010 or have identified the key remaining issues. If an economic business case can be made by that time, there is capital ready to build forward.

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