Study shows environmental benefit of ethanol vehicles

By Matt Thompson | March 23, 2020

A recently released study by researchers at the Great Lakes Bioenergy Research Center explores the environmental benefits of decarbonizing the U.S. light duty transportation fleet, and the role ethanol can play in limiting global temperature increase to 1.5 degrees Celsius by 2100.

The study evaluated four cellulosic ethanol feedstocks produced from biomass, conversion of biomass to ethanol or electricity, and adding carbon capture and storage (CCS) to both those strategies. Biomass sources studied included miscanthus, switchgrass, native grasses and corn stover, among others. According to the study, reductions of 204 to 416 percent in CO2 emission intensities for ethanol vehicles could be achieved when coupled with carbon capture and storage, depending on the feedstock. “Together with other land management mitigation strategies, decarbonizing U.S. light-duty vehicle transport with bioenergy production coupled with CCS could meet a significant fraction of the negative emissions needed in the United States to help ameliorate further global temperature increases,” the study says.

G. Philip Robertson, science director of the Great Lakes Bioenergy Research Center and one of the study’s corresponding authors, said this research differs from previous decarbonization studies. Earlier studies, he said, “assumed rates of carbon sequestration and nitrous oxide emissions and the like. What makes this study different is that all greenhouse gas components were measured and for a long period. So the study encompassed enough climate variability that we have a lot of confidence that what we found was what would actually be reflected in a real field setting.” He added that while the approach the study took was novel, the results confirmed what many previous models had predicted. “That’s important,” he noted.

The results of the study, Robertson said, showed that all feedstocks studied—when used either to produce cellulosic ethanol or electricity to power electric vehicles- had the ability to substantially benefit the environment when compared with gasoline. “In all cases, the equations were great enough to certify these feedstocks as advanced biofuels, that is over the 66 percent better than gasoline legislative target—including corn stover, which has not yet been empirically shown in field studies,” Robertson said. “In fact, it had about an 80 percent better carbon efficiency than gasoline,” Robertson said.

The study also notes that the greatest climate benefit is seen when cellulosic ethanol or biomass-produced electricity are coupled with carbon capture and storage (CSS) technologies. “We know we get a lot of climate benefit from simply using the fuels made from biomass to power ethanol and electric vehicles,” Robertson said. “But we get the most bang for our buck when we also capture the carbon that is produced as CO2 while we’re refining the biomass or while we’re using it to generate electricity. If that carbon can be captured and stored below ground, it provides an even greater benefit than simply offsetting fossil fuel use,” Robertson said, acknowledging that further infrastructure development is required to make CSS a wide-spread and viable option.

“Another interesting finding was that the emissions intensity for electric vehicles was no greater than it was for the liquid vehicles, which was a bit of a surprise for us because we had this mindset that electric vehicles are necessarily going to be better than ethanol vehicles,” Robertson said. “But when you run the numbers you discover that the conversion of biomass to electricity has about the same efficiency as the conversion of biomass to liquid fuels, plus batteries have a significant embedded carbon cost.”