Energy use indicators in energy and life cycle assessments of biofuels: review and recommendations

In this study we investigate how indicators for energy use are applied in a set of life cycle assessment (LCA) and energy analysis case studies of biofuels. We found five inherently different types of indicators to describe energy use: (1) fossil energy, (2) secondary energy, (3) cumulative energy demand, (4) net energy balance, and (5) total extracted energy. It was also found that the examined reports and articles, the choice of energy use indicator was seldom motivated or discussed in relation to other energy use indicators. In order to investigate the differences between these indicators, they were applied to a case. The life cycle energy use of palm oil methyl ester was calculated and reported using these five different indicators for energy use, giving considerably different output results. This is in itself not unexpected, but indicates the importance of clearly identifying, describing and motivating the choice of energy use indicator. The indicators can all be useful in specific situations, depending on the goal and scope of the individual study, but the choice of indicators need to be better reported and motivated than what is generally done today.