"There are major technological challenges in realizing these goals. Genetic improvement of energy crops such as switchgrass, poplar, and jatropha has barely begun. It will be important to increase the yield and environmental range of energy crops while reducing agricultural inputs. Plant development, chemical composition, tolerance of biotic and abiotic stresses, and nutrient requirements are important traits to be manipulated. The combination of modern breeding and transgenic techniques should result in achievements greater than those of the Green Revolution in food crops, and in far less time."
"The cost of biomass transport determines the supply area of a biofuels processing facility and thus its scale and economics. But unlike most food crops, there is no need to keep biomass intact. That means that in-field densification, pelletization, drying, and pyrolysis are among the technology opportunities to reduce transport costs. Fuel production from the lignocellulosic component of biomass will be a very important improvement. Its particular challenges of chemical recalcitrance and utilization of the constituent sugars to produce optimal fuel molecules and co-products are not intractable to current biotechnology. Similarly, process integration comparable to that of a modern petroleum refinery is a plausible chemical engineering goal."
"In a sophisticated journal such as Science, we expect the topic of energy policy to be illuminated by use of arithmetic and other analytical tools. The Review "The path forward for biofuels and biomaterials" (A. J. Ragauskas et al., 27 Jan., p. 484) presents its most important datum, 1020 joules per year of sustainable biomass energy, without any attempt to relate it to energy consumption. The United States uses more than 400 million kilowatts of electrical power, or a little more than one kilowatt per capita. If we multiply this quantity by the number of seconds in a year (3600 24 365), the result is 1.26 1019 joules per year. Production of one unit of electrical energy requires three units of fuel energy; thus, the corresponding demand on biomass energy would be 0.38 1020 joules per year. For itself, the United States would use approximately 40% of the world's biomass energy just for electricity. The remainder of the energy, and more besides, would be consumed by transportation, space heating, and manufacturing. Nothing would be left over for the rest of the world."
"Harvesting our Fields and Meadows for Transportation Fuels" - 10.1126/Science.1124886