GIS-based multi-criteria decision making under Silica Saturation Index (SSI) for selecting the best direct use scenarios for geothermal resources in Central and Southern Rift Valley, Kenya

Abstract

Direct use (DU) of geothermal energy is site-specific and majorly dictated by economics. Even with the availability of high enthalpy geothermal fluids, DU could still be curtailed by fluid pH, salinity, and silica content. Selecting economically viable best direct use (DU) scenarios for a given geothermal resource needs meticulous matching of geothermal resource characteristics to the nearby economic activities and local infrastructure. Silica saturation index (SSI) analysis should also be factored in to avoid silica scaling of DU facilities and reinjection well. There is a lack of a visual framework for incorporating all the necessary criteria for selecting the best DU scenarios, hence the motivation of this research. The current study employed a GIS-based multi-criteria decision making (MCDM) method: a hybrid of the analytical hierarchy process (AHP) method with the weighted aggregated sum product assessment (WASPAS) method. The model analyzed nine utilization scenarios against eleven criteria to select the best DU scenarios for six high-enthalpy quaternary volcanoes in the central and southern Kenyan rift: Menengai, Elementaita, Eburru, Olkaria, Longonot, and Suswa. The best typical DU schemes identified were horticultural greenhouse warming, spa, and crop drying. The model was validated with existing DU case studies to gauge its ability to predict suitable utilization methods. There was a good matching between the model's selection and existing case studies implicating the synergistic merger of GIS-based MCDM methods and SSI as a robust tool for planning and carrying out the feasibility study for DU of geothermal energy.