Production and energetic utilization of wood from short rotation coppice-a life cycle assessment

Ambitious targets for the use of renewable energy have recently been set in the European Union. To reach these targets, a large share of future energy generation will be based on the use of woody biomass. Therefore, there is an increasing interest in the cultivation of fast-growing tree species on agricultural land outside forests. Intensive crop production is always considered to harm the environment. The study explores the environmental burdens of the cultivation of fast-growing tree species on agricultural land and their subsequent energetic conversion in comparison to the fossil reference energy system. Life cycle assessment (LCA) methodology according to the ISO 14040 and 14044 is used. Input data were partly collected within the German joint research project AGROWOOD. Two utilization paths of short rotation poplar chips are analyzed: heat and power generation in a cogeneration plant and the production of Fischer-Tropsch (FT) diesel. Subsequently, the bioenergy systems are compared with their fossil references. The production and distribution of 1 oven dry tonne (odt) of short-rotation poplar chips require 432 MJ non-renewable energy. This equals an output-input ratio of 43:1, which includes all process steps from field preparation to road transport. Emissions of this energy use amount to a global warming potential of 38.4 kg CO(2) eq odt(-1), an acidification potential of 0.24 kg SO(2) eq odt(-1), and a eutrophication potential of 0.04 kg PO(4) eq odt(-1). The greatest reductions of environmental impacts can be achieved by substituting power from lignite with cogenerated power from short-rotation coppice (SRC). Compared with the average German power generation mix GWP and AP of power generation from short rotation poplar chips are lower by 97% and 44%, respectively, while eutrophication potential is about 26% higher. FT diesel made from short-rotation poplar chips has an 88% lower global warming potential and a 93% lower acidification potential than fossil diesel. But, the eutrophication potential of FT diesel is twice as high as of fossil diesel. It was found that even intensively produced wood from SRC can reduce environmental burdens if it is used for biofuel instead of fossil fuel. The utilization of the same amount of short-rotation poplar chips for heat and power production causes fewer environmental impacts than its use for FT diesel.