Life cycle assessment of biomass pellets: A review of methodological choices and results

The use of biomass pellets as fuel is emerging as a suitable alternative to fossil resources for mitigating climate change. A considerable number of articles have applied Life Cycle Assessment (LCA) to quantify and to compare the environmental performance of biomass pellets but a wide variation of results can be found in the literature. This work reviews 84 articles on LCA of biomass pellets, focusing on identifying trends in methodological choices and on understanding the influence of those choices on life cycle impacts, in particular global warming and nonrenewable primary energy. Most of the reviewed articles assess woody pellets and most of the cradle-to-grave studies focus on heat generation. The methodological choices vary widely between articles with respect to approach (attributional or consequential), functional unit, system boundaries, procedure to deal with multifunctionality and allocation, biogenic carbon modelling, inclusion of greenhouse gases other than carbon dioxide, life cycle impact assessment method, impact categories, and presence of sensitivity analysis. The results for global warming and non-renewable primary energy were assessed, showing a correlation between them. Moreover, a high variability is found for global warming, with impacts ranging from -18 to 488 g CO2 eq/ MJ(pellets). The main causes (technological features, assumptions, methodological choices) for this high variability are analysed and discussed.