TABLE 4.3 Estimated Primary Solid Biomass Components Available in the United States in the Near Term and 2030 for Less Than About $65 per Ton (2007 dollars)

Source

Biomass Amount (million tons per year)

NRC Estimatea

Walsh et al. (2000)

Milbrandt (2005)

Perlack et al. (2005)

NRC 2030

Crop residues

160

50

173

179

315

Forest residues

55

44

62

136

55

Mill wastesa

5

90

88

106

 

Urban wood waste

30

37

34

37

30

Energy crops

85

188

99

100

Total

335

509

456

458

490

aNRC estimate includes only that fraction that is estimated as not already being used.

use of forest growth beyond lumber requirements. Agricultural biomass availability increased even more than forest residue availability. Under their moderate-yield growth case, crop residue yields were assumed to increase up to 50 percent for corn and 100 percent for soybeans, and the efficiency of recovery increases from 60 to 75 percent over the next 40 years. Thus, recoverable corn stover today is estimated at 75 million dry tons per year at 50 percent recovery. Total stover biomass is therefore 150 million dry tons per year. This increases by 50 percent to 225 million dry tons of total stover produced, and when 75 percent of this is recovered, corn stover available for biofuel production is 170 million dry tons per year. Estimates for small grains and soybeans increase from 6 million dry tons per year (many current residue levels are too low to recover economically) to 26 dry tons per year. Recoverable wheat straw was estimated to increase from 11 million dry tons per year to 35 million dry tons. Grain quantities for biofuel production increase about 70 percent. Perlack et al. (2005) project even more aggressive growth numbers in their high-yield version of this case. For example, corn stover increases to 256 million dry tons (versus 172 million) per year, and most other agricultural biomass sources increase similarly. Without perennial crops, the projected amount of sustainable agricultural-based biomass production ranges from 425 million to almost 600 million dry tons per year (including 56 to 97 million tons each year of grains to biofuels) by 2050, assuming the high-technology changes summarized above (Perlack et al., 2005). Perennial energy crop production is assumed on 60 million acres and woody energy crop production is assumed on 5 million acres, with significant yield increases for each included. These perennial energy crops contribute between 156 million and 377 million dry tons of biomass per year. Their high-technology case involves significant land use changes raising questions of storage or loss of carbon from the soil, which could affect the CO2 impacts of biofuels (see below). Figure 4.4 shows the projected maximum technically available biomass in the United States in 2050 under the high-technology scenario

FIGURE 4.4 Projected sustainable biomass technically available in the United States by 2050, with aggressive energy crops. SOURCE: Perlack et al. (2005).



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