How much energy is used when producing biofuels?
Conference poster, 2012
Considering the increased focus on biofuels, it is important to inform companies and policy-makers about the energy use for production of biofuels in relevant and transparent ways, using well-defined indicators. The amount of fossil energy used in the production of a biofuel (e.g. diesel fuel used in harvesting) is a parameter of obvious interest when comparing different biofuels or when optimizing the production systems. With increasing worldwide production of different biofuels, a shift in focus from fossil energy to the entire energy use will also be necessary. In that context, not only reducing the use of fossil fuels in biofuel production, but also optimizing the use of all energy sources over the whole life cycle becomes an important to ensure the sustainability of biofuels.
However, to report and interpret values on life cycle energy use is not straight forward due to methodological difficulties. The impact category ‘energy use’ is frequently used in life cycle assessment (LCA). But the term ‘energy use’ is generally not applied in a transparent and consistent way between different LCA studies of biofuels. It is often unclear whether the total energy use, or only fossil energy, has been considered, and whether primary or secondary energy has been considered. In addition, it is often difficult to tell if and how the energy content of the fuel or the biomass source was included in the energy use.
This study presents and discusses the current situation in terms of energy use indicators are applied in LCA studies on biofuels. It was found that the choice of indicator was seldom motivated or discussed in the examined reports and articles, and five inherently different energy use indicators were observed: (1) fossil energy, (2) secondary energy, (3) cumulative energy demand (primary energy), (4) net energy balance, and (5) total extracted energy. As an illustration, we applied these five energy use indicators to the same cradle-to-gate production system (production of palm oil methyl ester), resulting in considerably different output numbers of energy use. This in itself is not unexpected, but indicates the importance of clearly identifying, describing and motivating the choice of energy use indicator. All five indicators can be useful in specific situations, depending on the goal and scope of the individual study, but the choice of indicator needs to be better reported and motivated than what is generally done today. Above all, it is important to avoid direct comparisons between different energy use results calculated using different indicators, since this could lead to misinformed policy decisions.