Biodistillate Transportation Fuels 3 – Life Cycle Impacts

Life-cycle assessments (LCA) of biodistillate fuels are becoming increasingly important for policy decisions regarding alternative fuels. However, due to the dataintensive 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 biodistillate 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. INTRODUCTION Global climate change and concerns about greenhouse gases, dwindling supplies of fossil fuels and national energy security are driving growth in production and use of biofuels. In the US and EU, alternative fuels use is becoming increasingly regulated through policy and mandates. A goal of these policies is to decrease greenhouse gas (GHG) emissions relative to fossil fuels. To ensure this is achieved, LCA models are being incorporated. For example, California recently adopted its Low Carbon Fuel Standard (LCFS) regulations to reduce the carbon intensity of transportation fuel used in California by 10% by 2020. The regulation is being supported by the GREET LCA model that has been modified for California (CaGREET model) to ensure that full cradle-to-grave production and use of the fuel will comply with reduced CO2 emission requirements. While data documentation and format are standardized by ISO, LCA methodology is often convoluted, and results are heavily dependent on data inputs and on numerous assumptions. To further complicate the matter, the effects of indirect land use change (iLUC) are becoming of increasing concern. In fact, results from the CaGREET model are paired with LUC results from the GTAP (Global Trade Analysis Project) economic model for LCFS regulations. Recently, LCA models are being termed as “attributional” or “consequential” depending on the inclusion of indirect effects.