The study was completed by the University of Idaho and U.S. Department of Agriculture (USDA). The energy-in, energy-out ratio is called "energy balance" or "fossil energy ratio."
"This study shows the clear trend that biodiesel production continues to improve when it comes to efficient use of resources," said Don Scott, director of sustainability for the National Biodiesel Board (NBB). "No other fuel available in the U.S. comes close to such a high energy balance."
Scott noted the most recent data available for this study was from 2006.
"Using data from 2009 or 2010 would likely show an even greater gain in energy efficiency," he said.
Biodiesel, made from agricultural co-products and byproducts, has always had a relatively high energy balance. This is partly because the main energy source used to grow crops is the sun, which is "free energy."
The U.S. Department of Energy and USDA completed the first comprehensive lifecycle assessment for biodiesel produced in the U.S. in 1998. That study found a 3.2-to-1 energy balance. The energy inventory for this analysis was updated in 2009 using 2002 data, finding the ratio had improved to 4.56-to-1.
In the new study, three things are primarily responsible for the leap in biodiesel's energy balance number:
• New data from USDA and the National Biodiesel Board show that soybean crushing facilities and biodiesel production plants have become increasingly energy efficient.
• Soybean farmers have adopted energy-saving farm practices, such has minimum tillage.
• Increases in soybean yields.
"In addition to improved energy efficiency at processing facilities, soybean growers have accomplished greater yields with lower inputs of water and fertilizer per bushel, even as cropland has declined," said Jim Duffield, USDA senior agricultural economist, who co-authored all three life cycle analysis studies. "Biodiesel deserves some credit for this progress — the demand it creates is helping to drive the new technologies that make American agriculture more efficient."
Specifically, in comparison to the 2009 study, the new study finds:
• The energy input in soybean agriculture was reduced by 52%.
• The energy input in soybean processing was reduced by 58%.
• The energy input in biodiesel production (transesterification) was reduced by 33%, per unit 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 fossil energy ratio.