How do we know the energy use when producing biomaterials or biofuels?

How much fossil energy that is used in the production of biomaterials or biofuels (e.g. fuel used in harvesting) is a parameter of obvious interest when optimizing the production systems. To use more fossil fuels in the production of a biofuel than what will be available as the biofuel product is obviously a bad idea. With increasing interest in biomaterials and biofuels, a shift from a sole focus on fossil energy will be necessary. Optimized use of energy over the whole life cycle is one important parameter to ensure sustainability. However, to report and interpret values on life cycle energy use is not as straight forward as what might immediately be perceived. The impact category ‘energy use’ is frequently used but is generally not applied in a transparent and consistent way between different studies. Considering the increased focus on biofuels, it is important to inform companies and policy-makers about the energy use of biofuels in relevant and transparent ways with well-defined indicators. The present situation in how energy use indicators are applied was studied in a set of LCA studies of 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 a test, we applied these five energy use indicators to the same cradle-to-gate production system and they give 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. Direct comparisons between different energy use results could lead to misinformed policy decisions