Biodiesel and Bioethanol: Energy and Carbon Balances of Biofuels Production

Keywords: Biofuels, Biodiesel, Bioethanol, Life Cycle Analysis, Energy cycle, Carbon cycle, Greenhouse gases.

The need to determine the life cycle energy, carbon and greenhouse gas impacts of three scenarios for biofuel production, namely biodiesel from oilseed rape, and bioethanol from sugar beet and wheat respectively, is set within the established framework of LCA, as specified by the International Standard ISO 14040 series.

The basic principles, definitions, conventions and methods of calculation of LCA are summarised. Against this background, existing studies relating to the evaluation of energy and environmental aspects of biodiesel and bioethanol production are reviewed.

As a result, suitable reference studies are selected, and detailed calculations of energy inputs and carbon and other greenhouse gas outputs are undertaken and presented for each scenario, using a standardised methodological approach based on clarity, transparency and completeness.

While there are differences between the three typical biofuel scenarios examined, it is clear that all produce positive net energy and greenhouse gas balances. The scenario calculations also point to key users of primary energy and producers of greenhouse gases within each production system. Amongst these are included the direct use of electricity/steam in crop processing, and the indirect energy and feedstock required for nitrogen fertiliser manufacture, resulting in comparatively major emissions of greenhouse gases.

Dr Ralph E Horne, Prof Nigel D Mortimer and M A Elsayed, Resources Research Unit, Sheffield Hallam University, Sheffield S1 1AB, United Kingdom.

55 Pages, 4 Figures, 25 Tables, 44 References.