University of Illinois Urbana-Champaign study reveals which feedstocks perform best in specific regions
Researchers assessed the financial and environmental impacts of four biofuel crops used to create sustainable aviation fuels in the United States. They discovered that each feedstock—corn stover, energy sorghum, miscanthus, or switchgrass—performed best in specific regions of the United States. Their study, detailed in a recent University of Illinois news release, aims to assist growers and policymakers in selecting the most suitable feedstocks to reduce production costs, lower greenhouse gas emissions, and build soil carbon stocks.
The United States annually consumes 23 billion gallons of jet fuel, with aviation fuel contributing about 13% of domestic transportation carbon dioxide emissions, the researchers reported in the journal Environmental Science and Technology. Currently, only a few million gallons of sustainable aviation fuels are produced in the U.S. However, the Sustainable Aviation Fuel Grand Challenge aims to increase production to 3 billion gallons by 2030 and 35 billion gallons by 2050, with a 50% reduction in life-cycle greenhouse gas emissions intensity compared to conventional fuel.
“The mix of bioenergy crop feedstocks that will be produced to meet this challenge, their relative costs, and carbon intensities will depend on how the goals of the policy are specified,” said Madhu Khanna, a professor at the University of Illinois Urbana-Champaign and the director of the Institute for Sustainability, Energy and Environment. Khanna led the study with Xinxin Fan, a postdoctoral researcher at iSEE.
“It’s a huge task to weigh all the factors that make a particular biofuels feedstock economically or environmentally viable,” Khanna said in the release. “You have to consider all other potential uses for the land, the costs of establishing a new crop, and numerous other factors like weather, soil carbon, and productivity.”
“There’s also the cost of converting different feedstocks into biofuels and the greenhouse gas emissions associated with growing and transporting them to a refinery,” Fan added.
The study aimed to identify feedstocks with the lowest “break-even price” for growers switching from another viable crop, the lowest carbon intensity and cost of carbon abatement, and the highest biomass produced per unit of land.
Identifying these factors for each feedstock and growing region will help growers and policymakers determine which crops will perform best in each part of the country and which policies or incentives will be most successful, Fan said.
The researchers divided the rainfed zones of their study area—covering most of the continental U.S. from the Dakotas, Nebraska, Kansas, Oklahoma, and Texas eastward—into 1.5-mile-square plots. They focused on four zones: the Great Plains, Midwest, Northeast, and Southeast.
The team first determined the break-even costs for a grower switching from the next most viable crop to a biofuels crop. These include costs for seed, chemicals, fertilizing, storage, and all other expenses associated with planting, maintaining, and harvesting a crop. The scientists also modeled different growing conditions, carbon emissions, and the costs and benefits across the life cycle of each feedstock, including hauling it to a biorefinery and converting it to useable jet fuel. They also determined the average cost of greenhouse-gas abatement per feedstock.
“We show that the optimal feedstock for each location differs depending on whether the incentive is to lower the break-even price, carbon intensity or cost of carbon abatement, or to have higher biomass production per unit of land,” the researchers wrote.
The cost of abating greenhouse gas emissions with sustainable aviation fuels “was lowest with miscanthus in the Midwest, switchgrass in the South, and energy sorghum in a relatively small region in the Great Plains,” they reported. “While corn-stover-based SAF had the lowest break-even price per gallon, it has the highest cost of abatement due to its relatively high greenhouse gas intensity.”
Different policies would favor some feedstocks over others, Khanna said. Corn stover would be preferred if policymakers prioritized production volume over total greenhouse gas emissions reduction. However, using this feedstock would reduce soil carbon stores, making it more carbon-intensive than other energy crops. Miscanthus and switchgrass increase soil carbon and would significantly lower greenhouse gas emissions compared to corn stover. But these feedstocks are more expensive to produce, requiring incentives like a carbon tax credit to be economically viable.
Ultimately, the researchers concluded, “either carbon prices would need to rise or the cost of producing sustainable aviation fuels will need to fall to make SAFs an economically attractive alternative to jet fuel.”
Khanna also serves as a professor in the Center for Advanced Bioenergy and Bioproducts Innovation, the Carl R. Woese Institute for Genomic Biology, and the National Center for Supercomputing Applications at the University of Illinois. Fan is a postdoctoral researcher in CABBI.
Read the entire paper here: https://pubs.acs.org/doi/abs/10.1021/acs.est.4c01949
