Newly published research from the University of Idaho and the U.S. Department of Agriculture (USDA) indicates that every unit of fossil energy needed to produce biodiesel returns 5.54 units of renewable energy, a higher trend than researchers said is found in regular diesel or other alternative fuels.
Researchers called this energy-in, energy-out ratio the "energy balance" or "fossil energy ratio." Biodiesel made from soybeans, for example, benefits from "free" energy from the sun. The study compared biodiesel with other alt fuels including liquefied propane and natural gas. Gasoline was also studied.
"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."
While NBB did not have data on the number of school buses nationwide running on biodiesel, the ability to directly mix the biofuel and diesel without the need for engine or vehicle alterations makes the alternative fuel an attractive option to operators. Initially, many school bus operators, especially those in colder states like Minnesota, experienced problems with gelling. But those challenges have abated over the past several years following more stringent production and quality standards.
The results from the paper "Energy Life-Cycle Assessment of Soybean Biodiesel Revisited" compares the energy used from 1990 through 2006. Researchers discussed the findings during a webinar presented Thursday by NBB. Participating on that call were James Duffield, a senior economist at USDA and co-chair of the federal biodiesel program, and Dev Shrestha, an associate professor in the Department of Biological and Agricultural Engineering at the University of Idaho.
The objective of the study was to construct a new biodiesel energy life‐cycle with 2006 data that reflects current soybean production and biodiesel plants built after 2002, which constitute the majority of plants producing biodiesel today. In addition, a comparison of the three time periods from the past studies conducted in 1990, 2002 and 2006 showed how energy life cycles change over time.
"Using data from 2009 or 2010 would likely show an even greater gain in energy efficiency," added Scott.
The U.S. Department of Energy and USDA completed the first comprehensive life-cycle 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.
The latest study concluded that three primary triggers led to the increased energy balance number for biodiesel. Soybean crushing facilities and biodiesel production plants have become increasingly more energy efficient, and soybean farmers have adopted energy-saving farm practices, such has minimum tillage. Additionally, the overall yield of soybeans have increased.
"Biodiesel deserves some credit for this progress - the demand it creates is helping to drive the new technologies that make American agriculture more efficient," said Scott.