Life-cycle assessments (LCA) of biodistillate fuels are becoming increasingly important for policy decisions regarding alternative fuels. However, due to the data-intensive and assumptive nature of LCAs, rarely do two different studies produce comparable results. To add to the complexity, effects of indirect land use changes are now being incorporated into LCA models. This development is influencing policy decisions and generating much controversy.
A literature survey of 55 different LCA studies of bio-distillate fuels was conducted. The comparison of energy requirements and global warming potential (GWP) impacts of these studies help to illustrate which data inputs and assumptions most strongly affect the results, and wherein the major discrepancies lie.
Life-cycle energy results are typically reported as energy return (ER), meaning the heating value of the biofuel divided by the total fossil energy inputs to produce the fuels. Most studies report significantly higher ER values for biodistillates (both biodiesel and renewable diesel) compared to conventional diesel fuel. Similarly, most LCA studies show significant GWP reductions for biodistillates compared to conventional diesel. However, due to lack of consistency in LCA approaches and assumptions, considerable uncertainty still exists regarding the accuracy of most LCA results.
