Time and Scale Aspects in Life Cycle Assessment of Emerging Technologies: Case Study on Alternative Transport Fuels
Life cycle assessments (LCAs, including well-to-wheel studies) that are to support decisions that strive to change large technical systems need to consider time- and scale-related factors that are given little attention in standard LCA procedures. We suggest that it is important to look beyond the current situation and study many possible future states, what we call stylised states, to explore general technology differences. We choose to address three issues in this report. Our case study deals with alternative fuels for transportation, and relates to a recent well-to-wheel study performed by CONCAWE, EUCAR and JRC. The methodological results, though, could be of equal importance when studying other major technologies.
First, shifting time frame gives room for technical development that should affect not only the choice of performance data, but perhaps also the functional unit and the selection of technologies under study.
Second, background systems such as heat and power production change over time, and we exemplify by using three different systems, mainly based on coal, natural gas and short rotation forestry, respectively. Increased production volumes may for some technologies also change the background system, which is of particular importance for technologies that are used in their own production processes. We show that for biofuels changes in background systems have consequences not only for greenhouse gas (GHG) emissions and agricultural land use for each fuel chain, but also for the ranking order of e.g. wheat ethanol and RME, in terms of GHG emissions. We use what we call a net output approach, which implies that a fraction of the produced biofuel is used for its own production. Accordingly, the functional unit used in this study is 1 MJ fuel available for other purposes than producing fuel.
Finally, different types of feedstock are available in different quantities and different by-product markets vary in size. Allocation of environmental impact between product and by-products is here made through system expansion, and we study some possible markets for by-products. To give an example of by-product effects, current key markets for ethanol by-products in EU-15 correspond to an ethanol production that covers about 2 % of demand, and for RME about 3 %, that is, well below the 5.75 % EU biofuel target for 2010. Therefore, the GHG emissions and agricultural land use allocated to the fuels differ between a low and a high market penetration.
Combining the results, we show that time and scale are important factors for the ranking of wheat ethanol, RME and wood methanol in terms of GHG emissions and agricultural land use, as the results are dependent on assumptions regarding background system and by-product markets. We indicate that agricultural land use results can be weighted in GHG terms in several ways, e.g. by using short rotation forestry or solar panels as a reference, an approach that would require further research.
life cycle assessment