Some Biofuel Feedstock Estimates ‘Overstating’ Yields

- March 4, 2014. Source: Envi­ron­men­tal Leader

Esti­mates 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.