Some Biofuel Feedstock Estimates ‘Overstating’ Yields

by | Mar 4, 2014

bioEstimates for potential biofuel feedstock crop yields from some widely cited research studies may overstate those yields by as much as 100 percent, according to research by the International Council on Clean Transportation.

One key factor in developing a sustainable biofuels policy is to realistically estimate the amount of biomass that can on average be grown on a given amount of land to produce cellulosic biofuel. But Will energy crop yields meet expectations? found that the highest predicted yields, and associated expectations of how much biomass could be grown for energy, could not be supported by an overview of studies in this field.

The study, which was published in the journal Biomass and Bioenergy, examined reported yields of five important energy crops miscanthus, switchgrass, poplar, willow, and eucalyptus. A  handful of studies on biomass production report very high yields, but the ICCT found that these were all extrapolated from very small experimental plots, intensively irrigated and weeded, and carefully hand-harvested. These are conditions that would not be replicable at commercial scale. Studies that grew energy crops over larger areas and used conventional harvesting techniques have shown much more modest results, but these more realistic experiments are not always the ones highlighted by bioenergy researchers.

Not only are commercial-scale energy crop yields lower than often thought, but they are not likely to improve rapidly over time. The ICCT note that agricultural practices and achievements in plant breeding or genetic modifications that have increased yields of food crops over the past several decades, like intensive fertilization and increasing the ratio of grain to straw, generally do not work on energy crops. Miscanthus, for example, often considered a top candidate for large-scale biomass production, is a hybrid between two types of plants and cannot reproduce by seed, which significantly slows down research.

But the authors stressed that their findings should not be interpreted to mean that policies supporting cellulosic biofuel are misplaced insisting that, if the idustry is to thrive, we need more, not less support for cellulosic biofuels.

Lower biofuel feedstock prices could drive down the price of fermentable cellulosic sugar allowing bio-based chemicals and biofuels to be made from more plentiful non-food sources, helping them better compete with petroleum-based chemicals and fuels, according to a study by Lux research released in November.

Lower feedstock prices could drive down prices of fermentable cellulosic sugar to $0.26/kg, down from $0.32/kg to $0.36/kg, competitive with sugars from corn or sugarcane, according to Cellulosic Chemicals and Fuels Race to Compete with First-Gen Sugar Economics.

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