Resource Study For The Direct Use Of Low Temperature Geothermal Heat In Uganda

Abstract

The use of geothermal energy is a rapidly growing sector around the world. The need to explore less popularly known renewable energy sources, as well as the necessity to curb the currently soring effects of the emission of greenhouse gases into the atmosphere are key drivers for this growth. Geothermal energy utilizes heat harnessed for within the earth to supply required heat for various processes, these processes range from electricity production to direct use of the heat in domestic and industrial applications. The advantages of using geothermal energy are diverse and include; minimal greenhouse gas emissions, high capacity factor, and a reliable heat supply, to mention but a few. However, the development of a geothermal project until its actual implementation and running is a costly venture. Uganda has potential for geothermal exploitation especially in the field of direct use. Many agro-based industries exist and could use this energy to supply heat to their processes in the stead of burning biomass, which has resulted in high rates of deforestation and land degradation. This study was done to assess the geothermal resource available within the country, and then follow through with a prefeasibility study for the implementation of low temperature geothermal heat for direct uses in Uganda. Geothermal fields from different locations of the country have been considered under this study. Each field was assessed on the basis of fluid temperature, geochemistry and status of market for the heat. Fluid temperature was obtained from available data for the different regions, whereas the geochemical assessment was included aspects such as; potential for scaling and corrosion. Results showed that the geothermal waters of most regions did not pose a threat of silica or calcite scaling except for Kanangorok that exhibited possibility for calcite scaling. The market status was focused on prevailing economic activities and the products and services they yield, and was used as a key parameter in the selection of a field for further study. Direct use applications were selected based on the fluid temperature and possible uses as per the market status. The selected uses included; agricultural drying, aquaculture, greenhouses, geo-bio energy synergy, apiculture, milk pasteurization, balneology and salt extraction. The selection of a geothermal field for further assessment was done using screening and scoring methods. Screening was based on the number of possible direct use applications that could possibly be carried out for a given geothermal field, whereas scoring was done on the basis of weights and ranks for criteria such as market status, fluid temperature, scaling and corrosion potentials and the field with the highest weights chosen. The Buranga geothermal prospect was assessed under three scenarios. Scenario A used brine from a binary power plant for cascade application with direct uses. Scenario B used brine directly from a drilled well, and scenario C used hot water from a geothermal hot spring. The direct uses analyzed were agricultural drying of cocoa and a geothermal spa in a multiple system arrangement where all cases showed profitability, and hence feasibility of the projects. Scenario A exhibited the lowest costs related to investment and operation and hence a lower levelized cost of energy (LCOE) compared to the other two scenarios which only had slightly higher values for the case of agricultural drying. LCOE is however differing considerably in the case of the geothermal spa.