|May 04, 2011|
New analysis of energy and environmental performance of biofuels
|New research identifies important influences on the energy and
environmental performance of biofuels made from agricultural crops.
Type of land use change, type of biofuel crop and the by-products
from the conversion process all influence performance.
The benefits of introducing biofuels in the transport sector or as feedstock in the chemical industry are widely debated. Research has produced contradictory results in terms of greenhouse gas (GHG) reductions, energy efficiency, impact on biodiversity and water pollution. There is also debate on the socio-economic benefits, especially for developing countries.
The study analysed the energy and environmental performance of six different agricultural crops: wheat, sugar beet, rapeseed, crops for livestock, maize and willow. It considered two possible direct land use changes: one from unfertilised grassland and the other from land producing wheat for food without the removal of straw. The biofuel production was assumed to take place in northern Europe with current cultivation practices and state-of-the-art technologies.
The researchers also considered whether to account for the impacts of indirect land use change caused by biofuel crop production, i.e. displacement of food and feed crop production to areas not used for cultivation previously. Some other studies have suggested that emissions from indirect land use change could completely offset the benefits of using biofuels.
The researchers argue that, ideally, it should therefore be included in environmental assessments of biofuels, but they were not satisfied with the reliability of any existing methodologies for its calculation, so did not include indirect land use change in this study.
Energy performance was based on the ratio of energy output, that is the energy produced by biofuels, to energy input, such as energy needed for fuel, fertilisers and electricity to grow and process crops. Environmental performance considered GHG emissions during the life cycle of production and the impact on eutrophication.
The energy output/input ratio of the different biofuel production systems varied from the worst performer of 1.3 for ethanol from grain, when by-products are excluded, to the best performer of 11 for methanol from willow. Although willow does not have the highest energy output (this comes from sugar beet and wheat), it has a very low energy input giving it the best energy balance.
The variation amongst systems also depends on the efficiency of the crop-to-fuel conversion process and the by-products. For example, the tops and leaves from sugar beet and straw from wheat contribute to the energy output of the biofuel production process.
If the best energy performer, willow, replaced fossil vehicle fuels, the reduction in GHG emissions would be approximately 80 to 85 per cent if the land used was previously unfertilised grassland.
The environmental performance of biofuels from agricultural crops depends a great deal on land use change, i.e. what the land was used for before the biofuel crops were grown.
If the best energy performer, willow, replaced fossil vehicle fuels, the reduction in GHG emissions would be approximately 80 to 85 per cent if the land used was previously unfertilised grassland. Eutrophication impacts depend on the crop type. Biofuels based on sugar beet, livestock crops and willow contribute roughly 2-3 times less than biofuels based on wheat.
The research highlighted several issues that could affect the analysis but which could contribute to improved sustainability assessments. As mentioned, indirect land use changes were not included. Also, only two types of land use change were considered. If peat soils are used to grow biofuel crops, then CO2 emissions from the soil could be 10-20 times higher.
Nevertheless, the research has identified important factors affecting the energy and environmental performance of biofuels made from agricultural crops.
Source:Börjesson, P. & Tufvesson, L.M. (2011) Agricultural crop-based biofuels - resource efficiency and environmental performance including direct land use changes. Journal of Cleaner Production. 19:108-120.Source: ec.europa.eu