1 Department of Buildings and Energy, Technical University of Denmark2 Department of Management Engineering, Technical University of Denmark
The aim of the present project has been to establish an LCA methodology for assessing different biomass energy systems in Denmark and Ghana in relation to their emission of greenhouse gases. The biomass systems which have been studied are willow chips, surplus straw and biogas from manure for Denmark and energy forest and use of saved wood in the food preparation process for electricity production in Ghana.DenmarkThe life cycle analysis has been relatively well defined for the case of willow chips and straw as their system boundaries are relatively well-defined, whereas the definition of system boundaries are more difficult for the biogas case. For the willow chip production the uncertainty is the possible enhanced emission of N2O when the energy forest is fertilised. For the biogas study, the uncertainties are related to the definition of alternative uses and handling of the manure, and for the definition of reference technology. For all Danish case studies the reference technology has been energy produced by natural gas. The total emission for willow chips in Denmark is 99 g CO2-eq per kWh of electricity produced for willow chips, 68 g CO2-eq per kWh for surplus straw and 58 g CO2-eq per kWh for biogas. The CO2 reduction potential is determined as 310 g CO2 per kWh for willow chips, 340 g CO2-eq per kWh for surplus straw and 350 g CO2 per kWh for biogas, when they replace energy produced in a natural gas system. With a potential of 32 PJ energy forest (200,000 ha), 33 PJ of surplus straw and 20 PJ of biogas, the total CO2 reduction will be 3.8 million tonnes or 6% of present CO2 emission if biomass substitute natural gas. This relates to the use of present available technologies. In the decades to come new and more efficient technologies will be developed for biomass plants. This will increase the reduction potential for CO2. GhanaTwo different case studies have been carried out for Ghana. The first is a life cycle analysis of an energy forest plantation in Ghana which has been cultivated with modern equipment. The second LCA is extended with an energy end use chain to determine the energy conservation options in the food preparation process. The idea has been to use the saved wood in the food preparation process for electricity production.The results for the energy forest in Ghana are not very different from the willow forest in Denmark. Similar assumptions about energy consumption for use of machines have been made in the two cases. The main difference is that the energy forest in Ghana uses Nitrogen fixing species to avoid the use of fertilisers. The second Ghanaian case study was established so that one-third of the electricity produced at the power plant should be supplied by savings in the food preparation process to cover the domestic electricity consumption. The remaining two-thirds of the electricity has been produced in an energy forest to cover industrial demand.The saving options have been determined to be 65% by use of an improved woodstove and efficient cooking performances compared to the traditional cooking performance and the use of three-stone stove. The results indicate that the energy saving options are higher by changing habits than by changing cooking stove. This implies that it is better to use an efficient cooking performance on a three-stone stove than inefficient cooking performance on an improved stove. The efficiency options for the improved stove have also been compared with the use of LPG and electric stoves.The use of a life cycle analysis for the saved wood case indicate that the energy saving options have to be taken into account when assessing the different cooking options. This is an important issue as long as cooking is the main energy service in Ghana. Life cycle analysis can be a useful tool for assessing the different saving options and for identifying environmental impacts from the cooking process.To supply sufficient woodfuel to cover one-third of the electricity production two-thirds of the households would have to change into efficient cooking performance and to use improved stoves. This model is only theoretical, but it indicates that the amount of biomass which is wasted in the food preparation process is large. The assumed electricity consumption per household is 1,200 kWh per year.The biomass potential in Ghana is large. If degraded land were changed into energy forests, biomass could be the major energy source for decades in Ghana. Utilising 5% of the area for energy production will almost double the electricity capacity in Ghana today. The estimated saving potential of 65 % in the food preparation process will lead to a saving of a total of 3 million tonnes of wood throughout Ghana. If it was used for electricity production it could lead to an electricity production of 3.8 TWh per year or a capacity of 0.8 GW using the key figures of the power plant studied in this report. This is almost equal to the present power capacity in Ghana.Energy planning and LCA in GhanaDanish energy planing experiences have been developed in a educated population and in society with traditions for well-functioning institutions. Even though some energy programmes have been implemented, the institutional framework is relatively weak in Ghana compared to the severe and in some cases fundamental problems they are supposed to solve. Severe problems are present both in the traditional sector with increasing utilisation of biomass and in the modern energy sector which is challenged by the high population growth. The advanced energy planing used in Denmark today is only relevant for the modern energy sector, and it has to be adjusted in order to cope with the large rate of population growth in Ghana. The problems in Ghana are related to the general development of society, education of people, training of technicians, and creation of economic incentives for stimulating people to take the right decisions.A comparison of the two energy sectors illustrates the difficulties in using the advanced Danish energy planning experience in Ghana. The basic parameters are very different. Compared with Denmark the modern energy sector in Ghana is challenged by a high population growth whereas the population has stabilised in Denmark. Furthermore, the Danish energy planning has been supported by an educated population and strong public institutions. This is not the case in Ghana.