Researchers are finding that sugar content is as important as size when it comes to producing biofuels from woody biomass.

Scientists from the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) and Oak Ridge National Laboratory (ORNL), have been studying the size and growth rate of trees, as well as the amount of sugars that can be produced from the ligno-cellulosic biomass that can be converted into fuels. The researchers analyzed 900 samples of black cottonwood trees grown in Oregon to determine how variations in their size and composition affect feedstock quality and biorefinery economics.

The amount of fuel produced per acre each year and the minimum fuel selling price (MFSP) are most strongly connected to the size of a tree. But when considering the largest 25% of trees, the size and sugar content were of nearly identical importance to the MFSP, the researchers found.

The scientists chose the black cottonwood tree to study because of its fast growth and its prevalence across North America. The tree can be ready to harvest after about seven years from planting. In addition to the sugar content, the researchers also analyzed the amount of lignin, which forms rigid cell walls and bark that is difficult to break down. The analyses informed a techno-economic analysis of using the black cottonwood as a biofuel feedstock.

The findings are detailed in a new paper, “Economic Impact of Yield and Composition Variation in Bioenergy Crops: Populus trichocarpa,” published in the journal Biofuels, Bioproducts & Biorefining.