Time-dependent climate impact of heat production from Swedish willow and poplar pellets – In a life cycle perspective

Abstract

Sweden has the potential to increase fuel pellet production from alternative raw materials, such as willow and poplar, and also to use former agricultural land for energy crop production. This study used a life cycle perspective to investigate district heat production from pellets produced from willow or poplar cultivated on fallow land in Sweden. The energy efficiency and global warming potential of the systems was evaluated, additionally was the climate impact, expressed in global mean surface temperature change, evaluated from annual greenhouse gas data, including the most relevant fossil and biogenic sources and sinks. The systems were also compared with a fossil fuel alternative in which coal was assumed to be used for heat production. The results showed that the systems investigated had a cooling effect on both global mean surface temperature and global warming potential within the 100-year study period owing mainly to an increase in live biomass and a more long-term increase in soil organic carbon (C), which shows the importance of land use. At the same time, the systems produced renewable energy. The poplar system contributed to a larger cooling effect than the willow system due to more C being sequestered in live biomass and soil in the longer growth periods between harvests and to higher yield. The energy efficiency of the willow and poplar systems used for pellet fuel production was about 11 times the energy input.