Decentralised energy systems based on biomass : a life cycle perspective on climate impact and energy balance

Sammanfattning: Replacing fossil fuels with renewable energy sources is recognised as an important measure to mitigate climate change. Residual biomass from agriculture and forestry and short-rotation coppice grown on unused land can be converted to heat, power and fuel without directly compromising production of edible crops. As biomass is mainly produced in rural areas, increased use of biomass-based energy could contribute to job creation and rural economic development. This thesis investigated whether farmers can generate energy from their own on-farm agricultural and forestry residues for energy self-sufficiency on the farm or for commercial production of district heating or combined heat and power production, with reduced greenhouse gas emissions compared with fossil alternatives. Consequential life cycle assessment methodology was used, with the focus on greenhouse gas emissions and energy balance. The results showed that arable and dairy organic farms in Sweden can both become self-sufficient in energy by using on-farm biomass residues. Furthermore, decentralised bioenergy systems proved superior to central production based on fossil fuels or large-scale biomass in terms of both greenhouse gas emissions and production costs. The results also revealed large variations (9-97%) in greenhouse gas emissions reduction potential compared with fossil fuels. This variation is partly due to the impact on soil carbon content in soil management systems, where crop residue removal has a negative effect and willow coppice production a positive effect. The input energy requirement for biomass systems is generally higher than for fossil systems, but is typically generated from renewable energy.

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