Review and meta-analysis of Energy Return on Investment and environmental indicators of biofuels

This study reviews the state-of-the-art (2014–2020) of biofuels from all generation categories, collecting information from 150 case studies to address concerns about the environmental sustainability and the potential of biofuels to contribute to the energy system without compromising its viability. Levels of Energy Return on Investment for refined products (EROIfinal) are used as reference: <3:1 (net sink for society) and >8:1 (better performance than global-average oil products). First-generation biofuels (from edible crops): none of the reviewed studies reported EROIfinal>8:1; most of the reviewed studies reported EROIfinal<3:1. Second-generation biofuels (from non-edible crops & residues): The EROIfinal can be higher compared to first-generation biofuels, although with large uncertainties/range. EROIfinal>3:1 in the case of herbaceous crops (∼4:1), and for crop and forest residues for certain feedstocks or under certain conditions; EROIfinal>8:1 in the case of agricultural residues under certain conditions. Third-generation biofuels (from algae): the technological advancements are slow; several challenges need to be overcome to reach large-scale production; reported EROIfinal close to 1:1. The collected data on environmental aspects for all generation types are fragmentary and insufficient to reach robust conclusions. Only 5 % of the reviewed case studies are based on pilot/demonstration scale plants, raising the question of potential discrepancies between theoretical and actual values. System boundaries and assumptions have a key role in the obtained results; therefore, the utilisation of standard protocols in the calculation of EROI across studies is essential. Studies should consider additional environmental metrics to address all sustainability concerns related to biofuel production.