Life Cycle Assessment of Biomass-based Combined Heat and Power Plants

Abstract

Norway, like many countries, has realized the need to extensively plan its renewable energy future sooner rather than later. Combined heat and power (CHP) through gasification of forest residues is one technology that is expected to aid Norway in achieving a desired doubling of bioenergy production by 2020. To assess the environmental impacts to determine the most suitable CHP size, we performed a unit process-based attributional life cycle assessment (LCA), in which we compared three scales of CHP over ten environmental impact categories—micro (0.1 megawatts electricity [MWe]), small (1 MWe), and medium (50 MWe) scale. The functional units used were 1 megajoule (MJ) of electricity and 1 MJ of district heating delivered to the end user (two functional units), and therefore, the environmental impacts from distribution of electricity and hot water to the consumer were also considered. This study focuses on a regional perspective situated in middle-Norway's Nord- and Sør-Trøndelag counties. Overall, the unit-based environmental impacts between the scales of CHP were quite mixed and within the same magnitude. The results indicated that energy distribution from CHP plant to end user creates from less than 1% to nearly 90% of the total system impacts, depending on impact category and energy product. Also, an optimal small-scale CHP plant may be the best environmental option. The CHP systems had a global warming potential ranging from 2.4 to 2.8 grams of carbon dioxide equivalent per megajoule of thermal (g CO2-eq/MJth) district heating and from 8.8 to 10.5 grams carbon dioxide equivalent per megajoule of electricity (g CO2-eq/MJel) to the end user. Supporting Information S1: This supplement contains further details on life cycle assessment (LCA) methodology and the assumptions used for the case system, along with tables of the foreground life cycle inventories, contribution analysis for each product (1 megajoule [MJ] electricity and 1 MJ district heating to end user) for each impact category, and total environmental impacts at the combined heat and power plant (1 MJ useful energy at the plant). Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.