Energianalyser av biobränslen från höstvete, raps och salix

Growing various crops on surplus arable land as a source of energy has become a matter of discussion in Sweden. One reason for that is that there are a lot of different priorities depending on what interest you have in agriculture and society as a whole. The farmers want to stay farmers and are looking for a crop that can replace food producing crops and give a reasonable profit. The users of the bioenergy want a fuel which is better than fossil fuels both technically and economically. There is also an environmental view of energy production. Using bioenergy instead of fossil fuels is a way to diminish the greenhouse effect. Regarding the interest of society there can be of value to cultivate a crop with maximum yield of energy and a minimum of environmental effects. Following of what is said above, the matter of choosing an energy crop is very complex. No matter what crop you choose, one or more of the priorities mentioned above will be set aside. This study is carried out for the Department of Agricultural Engineering at the Swedish University of Agricultural Sciences at the request of NUTEK. The purpose of my work is to establish energy balances for three of the energy crops that have been under evaluation. These crops are: ¤ Salix, for heat production or for producing ethanol as a fuel for Otto engines. ¤ Rape seed for production of oil as a fuel for modified diesel engines, or processed oil for ordinary diesel engines. ¤ Winter wheat, for heat production or for producing ethanol as a fuel for Otto engines. The method used is that I have presupposed all the conditions for the cultivation. With those conditions known I calculated the number of machine hours and the consumption of fuels and fertilizer etc. The machine hours where needed in computing how much of the energy used in manufacturing the machines that should charge the cultivation. Data on specific energy amounts in machines and materials include the energy needed for mining, transport and manufacture. Energy used in buildings are not included in the analyses, neither is energy in form of human labour. After calculation the total input, I have calculated the energy ratio. Energy ratio=energy out/energy in. The energy ratio for different crops and products, below, is the result of the study. ¤ Salix for heat production: 19.3 ¤ Ethanol from salix: 1.82 ¤ Rape seed oil: 3.08 ¤ Rape methyl ester: 2.74 ¤ Winter wheat for heat production: 3.79 ¤ Ethanol from winter wheat: 1.25 All analyses are made on specific assumptions. The results are therefore not valid in general. According to the ratios above it seems quite simple to choose an energy crop. But as mentioned above, it is a complex matter, depending on what priorities you have. And the energy ratio is not the only measure of efficiency in cultivation. You can compute the surplus energy per hectare as well, or the ratio between input of fossil fuels and electricity and output of biofuel. That last ratio, the fuel ratio is highest for wheat for ethanol production. That is an example on the complexity in this matter.