Life cycle energy analysis for bioethanol: allocation methods and implications for energy efficiency and renewability

Increased use of biofuels for transport is emerging as an important policy strategy to substitute petroleumbased fuels. However, the extent to which biofuel can displace fossil fuels and net emissions of CO2 depends on the efficiency with which it can be produced. To demonstrate that biofuel has a positive energy balance – i.e. more energy is contained in than is used in the production – a life cycle approach must be employed, allowing quantification of the renewability of biofuel delivered to consumers. A novel indicator is proposed – the energy renewability efficiency – aiming at characterizing the renewability of (bio)energy sources. ERE measures the fraction of final fuel energy obtained from renewable sources. The LCEA for bioethanol in France has been investigated. Assessing the (fossil and non-fossil) energy used throughout the life cycle and calculating the renewability of two alternative bioethanol product systems are important goals. Physical and economic data was collected and a systemic description of the bioethanol chains has been implemented. Inventory results – calculated using four different allocation approaches and ignoring co-product credits – are analyzed in order to understand the effect of allocation in the overall energy efficiency and renewability of bioethanol. Sensitivity analysis shows that the choice of the allocation procedure has a major influence on the results. In fact, ERE values for ethanol can vary more than 50%, depending on the allocation used. Finally, we conclude that, in general, ethanol produced from sugar beet or wheat in France is clearly favorable in primary energy terms. In particular, a maximum ERE value of 55% was obtained for wheat based ethanol (mass allocation), meaning than 55% of the biofuel energy content is indeed renewable energy.