Energy Life-Cycle Assessment of Soybean Biodiesel Revisited

Abstract

The first comprehensive life cycle assessment (LCA) for soybean biodiesel produced in the U.S. was completedby the National Renewable Energy Laboratory (NREL) in 1998, and the energy inventory for this analysis was updated in2009 using 2002 data. The continual adoption of new technologies in farming, soybean processing, and for biodieselconversion affects the life cycle energy use over time, requiring that LCA practitioners update their models as often aspossible. This study uses the most recently available data to update the energy life cycle of soybean biodiesel and makescomparisons with the two past studies. The updated analysis showed that the fossil energy ratio (FER) of soybean biodieselwas 5.54 using 2006 agricultural data. This is a major improvement over the FER of 3.2 reported in the 1998 NREL studythat used 1990 agricultural data and significantly better than the FER of 4.56 reported using 2002 data. The improvementsare primarily due to improved soybean yields and more energy efficient soybean crushing and conversion facilities. Theenergy input in soybean agriculture was reduced by 52%, in soybean crushing by 58% and in transesterification by 33% perunit volume of biodiesel produced. Overall, the energy input reduction was 42% for the same amount of biodiesel produced.The addition of secondary inputs, such as farm machinery and building materials, did not have a significant effect on the FER.The FER of soybean biodiesel is likely to continue to improve over time because of increases in soybean yields and thedevelopment of increasingly energy efficient technologies.