Comparative study on energy sustainability of biofuel production chains

Abstract
This paper is concerned with a comparative study of the energy sustainability of the production of biodiesel from oleaginous plants (rape and sunflower), of bioethanol from sugar crops (sugar beet and sweet sorghum) and of electricity from lignocellulose materials (miscanthus and short rotation forestry poplar). The results show the lignocellulose feedstock to perform best in terms of both net energy produced per unit area of cultivated land, from around 184 GJ/ha to more than 434 GJ/ha, and of energy ratio between energy produced and energy consumed, in the order of 12–19. Biodiesel and bioethanol production were found to be less advantageous in terms of energy sustainability, especially when residues and by-products are not used as feedstock. For bioethanol production, sweet sorghum exhibited the higher energy ratio of around 5.2, due mainly to the heat recovered from residue in cogeneration plants. As for biodiesel production, neither the rape nor the sunflower proved to be particularly sustainable with an energy ratio of around 1.3–1.4, but performance can be improved using the agricultural and industrial processing residues to produce energy, increasing energy ratios up to 3.4–4.2.