A systematic review of bioenergy life cycle assessments

On a global scale, bioenergy is highly relevant to renewable energy options. Unlike fossil fuels, bioenergy can be carbon neutral and plays an important role in the reduction of greenhouse gas emissions. Biomass electricity and heat contribute 90% of total final biomass energy consumption, and many reviews of biofuel Life Cycle Assessments (LCAs) have been published. However, only a small number of these reviews are concerned with electricity and heat generation from biomass, and these reviews focus on only a few impact categories. No review of biomass electricity and heat LCAs included a detailed quantitative assessment. The failure to consider heat generation, the insufficient consideration of impact categories, and the missing quantitative overview in bioenergy LCA reviews constitute research gaps. The primary goal of the present review was to give an overview of the environmental impact of biomass electricity and heat. A systematic review was chosen as the research method to achieve a comprehensive and minimally biased overview of biomass electricity and heat LCAs. We conducted a quantitative analysis of the environmental impact of biomass electricity and heat. There is a significant variability in results of biomass electricity and heat LCAs. Assumptions regarding the bioenergy system and methodological choices are likely reasons for extreme values. The secondary goal of this review is to discuss influencing methodological choices. No general consensus has been reached regarding the optimal functional unit, the ideal allocation of environmental impact between co-products, the definition of the system boundary, or how to model the carbon cycle of biomass. We concluded that a higher level of transparency and a harmonisation of the preparation of biomass electricity and heat LCAs are needed to improve the comparability of such evaluations. (C) 2013 Elsevier Ltd. All rights reserved.