BIOEN
“High Beams” Approach Versão em português
We will never achieve a sustainable and secure future by extrapolating from the technologies and actions that have lead us to the unsustainable and insecure present. Thus the feasibility of large-scale bioenergy production is most informatively approached from a "high beams perspective" considering the world as it could be, rather than a "low beams" perspective considering the world as it is.
The dramatic difference between high beam and low beam perspectives on the feasibility of large-scale bioenergy production is illustrated by analysis presented in Figure 1, developed as part of the Role of Biomass in America's Energy Future (RBAEF) project. With status quo assumptions, the new land required to provide for total US mobility requirements is over 1 billion acres, representing over half the area of the lower 48 states.
Mature conversion technology as projected based on detailed analysis by the RBAEF project reduces the new land required to 410 million acres. Further 2.5-fold decreases are possible for future technology due to increased vehicle efficiency (miles per gallon) and increased productivity of cellulosic biomass production (tons per acre per year), lowering the new land requirement to 65 million acres.
Further decreases are possible by integrating feedstock production into existing land uses, which could and very likely would be practiced to a much greater extent than now in response to emergent demand for non-nutritive cellulosic biomass. One strategy among several for such integration is growing early-cut grass or alfalfa in lieu of soybeans, resulting in coproduction of animal feed protein and feedstock for cellulosic biofuel production. The quantity of coproduced feedstock is potentially large enough to reduce the new land requirement to zero.
The conclusion that it is possible - in the US at least - for biofuels to make a large mobility contribution with little or no requirement for new land is made more robust by the availability of a multiplicity of options for integrating biofuel feedstock production into existing land uses without displacing food production. Such strategies include double crops, sustainable harvest of agricultural residues and forest biomass, increased production from under-utilized land (particularly pasture land), and land-efficient feed rations. Achieving a large mobility contribution with little or no new land involves multiple, large, complimentary, and currently improbable changes. The same can be said of most if not all paths to a sustainable world.
Figure 1. New land required for current U.S. mobility with consideration of increases in processing yield, vehicle efficiency, biomass yield, and agricultural integration. Agricultural integration scenario I involves coproducing animal feed protein and biofuel feedstock from early-cut perennial grass in lieu of soybeans as described in Dale et al., 2009. Other agricultural integration scenarios include, but are not limited to, double crops, use of some agricultural residues (e.g. corn stover, wheat straw, etc.), increased production on under-utilized land, land efficient feed rations, and dietary changes.
At the end of a detailed chapter on the land availability issue, including review and analysis of the widely disparate conclusions reached by different studies, Lynd et al. (2007) comment:
Ultimately, questions related to the availability of land for biomass energy production and the feasibility of large-scale provision of energy services are determined as much by world view as by hard physical constraints... To a substantial degree, the starkly different conclusions reached by different analysts on the biomass supply issue reflect different expectations with respect to the world's willingness or capacity to innovate and change.
A high beams analysis, focusing on long-term potential and including mature conversion technology and multiple complementary changes that accommodate large-scale use of bioenergy, has not been undertaken at a global scale. Yet it is increasingly clear that such an analysis is sorely needed. Testimony to the need for a global-scale analysis is provided by concern over carbon emissions resulting from land clearing in one country in response to use of cropland for biofuel production in another country, and further by the impact of dietary changes in the third world on availability of land for biofuel production. In light of these and other issues, analysis on a less than global scale cannot adequately address the question of large-scale bioenergy feasibility.
Such a global bioenergy analysis would include a range of potential future scenarios, and may well result in some scenarios generating a large bioenergy contribution while feeding the world and honoring other important priorities. If this were shown, it would provide critically important guidance with respect to both overall the feasibility of a bioenergy-intensive future as well as policy and land use trajectories that foster this outcome.
References
- Dale, BE, MS Allen, M Laser, LR Lynd, 2009. Protein feeds coproduction in biomass conversion to fuels and chemicals. Biofuels, Bioproducts, & Biorefining, 3:219-230.
- Lynd LR, M Laser, J McBride, K Podkaminer, J Hannon, 2007. Energy myth three - High land requirements and an unfavorable energy balance preclude biomass ethanol from playing a large role in providing energy services. pp 75 to 101 In: B. Sovacool and M. Brown (eds) Energy and Society: Thirteen Myths About the Environment, Electricity, Efficiency, and Energy Policy in the United States. Springer.