Energy and Greenhouse Gas Balance of Decentralized Energy Supply Systems based on Organic Agricultural Biomass

More and more farms apply organic production methods to reduce their environmental impact, but currently even organic farms are mainly using fossil fuels. Technologies available today or in the near future make it possible to produce heat, electricity and fuels from agricultural residues or woody biomass. The agricultural sector can thereby contribute to the fulfillment of climate goals and energy security without reducing the output of food products. The thesis describes and assesses possible energy supply systems based on biomass from an organic arable farm, using life cycle assessment (LCA) methodology. The impact categories used are energy balance, resource use and greenhouse gas (GHG) emissions. Technical systems are described for the supply of heat and power to a village near the farm, and for energy self-sufficiency at the farm. The systems utilize ley used as green manure, Salix and/or straw as the substrate for energy production, and are compared with a reference system based on fossil fuels. The emission calculations included field operations, processing and soil emissions, with a special model developed for estimating the impact on soil C concentration. The results show that it is possible to supply the village or the farm with energy through the systems described without competing with food production. Ley-based scenarios require higher energy input than scenarios based on Salix, but lower than the scenario based on straw. In the self-sufficient farm system, ley-based scenarios give the highest reduction in GHG, 33% compared with the reference scenario whereas the corresponding reduction from a completely straw-based energy system is 9%. In the village energy supply system, the ley-based system give the highest reduction in GHG with a total of -19 Mg CO2-eq./FU compared with 351 Mg CO2-eq./FU in the reference system. The Salix-based systems give 42 and 60 Mg CO2-eq./FU respectively.