Marijan Šušnjar

Energy Return on Investment (EROI) of Different Wood Products

Energy cannot be produced without consumption of some part of the energy, and the proportions in which this occurs are a key indicator of the efficiency of the production process. Energy return on investment (EROI) of energy production shows the relationship between obtained and invested energy in the production process. This relationship is a key factor in sustainable global energy supply. Wood chips and one-metre firewood are used to produce thermal energy. Amount of energy obtained by burning depends on the moisture content and the features of the energy plant. This chapter deals with the issue of the amount of energy required to produce in the process of wood chips and one-metre firewood production and its transport to the heating plant. When calculating the energy balance, it is important to include as many input parameters as possible (parameters of energy consumption), which represents an almost impossible task because one parameter directly binds several others. According to several authors, the relationship between obtained and invested energy or EROI for energy wood is 30:1 which is a better ratio than the production of oil, for which relationship between obtained and invested energy is about 20:1. The results of study show that most of the energy during the production and supply of energy wood products from final felling of oak stands is used for fuel for machinery and vehicles in the production process. Ultimately, the relationship between obtained and invested energy is approximately 25:1 in the case of moisture content in the wood chips in the limit (market) value of 35% and the mean distance truck transportation of wood chips of 50 km. The relationship of obtained and invested energy used for one-metre firewood is bigger than 25:1 because of less invested energy which does not include machines like wood chipper. This is a satisfactory relationship, but it decreases with a greater transport distance. Such is the case when chips manufactured in Croatia, due to the lack of heat plants, are transported over long distances to neighbouring countries.