Open access publications in the SLU publication database

Abstract

An important aspect that must be evaluated concerning biofuels is their efficiency in converting solar energy into biomass. This evaluation is important in reaching the right decisions about which crops are to be preferred in any specific situation. Another important factor is whether or not the cultivation is profitable from an energy point of view, i. e. if we get as much energy out of the cultivation, such as salix chips, as we invest in it, e. g. as fuels, nutrients, etc. This type of evaluation may be done from different viewpoints and in this report three different methods have been used, energy-, exergy-, and EMERGY analyses. The energy and the exergy methods are both based upon the laws of thermodynamics. The energy analysis has its roots in the first law of thermodynamics and therefore only concerns the amount of energy put into a product throughout the manufacturing but not how physical valuable the used energy was. The exergy analysis is based upon both the first and the second laws of thermodynamics, which results in not only the amount of energy used but also the energy quality is taken into consideration. EMERGY analysis, in contrast, is based upon H T Odum’s theory and has its roots in systems ecology and the maximum power principle. EMERGY is a record of previously consumed available energy that is a property of the smaller amount of available energy in the transformed product. The transformities are the "keys" in the EMERGY analysis. They describe the amount of energy, expressed in one and same unit, that has been used to create a flow or resource. In this report, results from analyzing salix-, winter wheat-, and winter rape cultivations from energy, exergy, and EMERGY perspectives are presented. The exchange in terms of energy for this Salix cultivation is 28 times, but if instead an exergy analysis is done the exchange for exactly the same process is 36 times. The energy analysis gives an energy exchange of 8.1 for winter wheat cultivation, and 5.7 for winter rape cultivation. Corresponding exchanges for the exergy analysis are 9.3 for winter wheat and 6.6 for winter rape. The EMERGY analysis gives a transformity for salix of 1.04E+l1 sej/kg DM, for winter wheat 3.85E+11 sej/kg DM, and for winter rape 1.03E+12 sej/kg DM. Thus, the EMERGY need is bigger for rape cultivation than for winter wheat and salix cultivation. The NEYR is the ratio between the EMERGY yield and the EMERGY invested from society (economy, services and other resources), and it is 1.10 for this salix cultivation, and 0.66 for both the winter wheat and the winter rape cultivations. The EIR is the ratio between the EMERGY invested from society and the EMERGY invested from the environment, and it is 2.23 for this salix cultivation, 11.5 for the winter wheat cultivation, and 11.8 for the winter wheat cultivation.