Techno-economic analysis of serial-parallel and turbine extraction organic Rankine cycle configurations utilizing low to medium-temperature geothermal energy sources for multi-generation

Low to medium-temperature geothermal resources (temperatures below 150 °C) are abundant but remain largely underutilized due to their low efficiency in power generation. Small to medium-scale systems powered by low to medium-temperature geothermal sources, typically with thermal capacities below 20 MWth, are often not economically viable when used solely for power generation. However, by designing multi-generation plants, the overall energy utilization factor can be significantly improved compared to single-output systems. The objective of this paper is to identify the optimal design for multi-generation plants powered by low to medium-temperature geothermal resource. A techno-economic analysis of two different configurations of such a plant was performed. A geothermal resource with a heat source temperature of 143 °C in the Olkaria field, Kenya was considered for the analysis. The main innovation of our work is that we propose novel plant configurations that optimally aligns the heat source to meet the different requirements of multiple utilities. The system produces electricity using an organic Rankine cycle system with and without turbine extraction, provides cooling using a lithium bromide-water vapor absorption system, and generates hot air for drying. We investigated a combined serial-parallel configuration (configuration 1) and a configuration including an organic Rankine cycle with turbine extraction (configuration 2) to meet intermediate temperature requirements. A model to predict the techno-economic performance of the geothermal energy powered multi-generation system was developed. The results indicate that, under the base case assumptions, electricity priced at 150 €/MWh, cooling at 30 €/MWh, heating at 10 €/MWh, and a geothermal heat source cost of 4.5 m€, the minimum simple payback period for the investigated multi-generation system is 4.27 y when using R1233zd(E) and 4.69 y when using n-pentane, under configuration 1. Configuration 2, using n-pentane, achieves a comparable simple payback period of 4.73 y to that of configuration 1 with n-pentane, but only when the vapor absorption system cooling capacity is low. In configuration 1, the simple payback period increases only slightly as the vapor absorption system cooling capacity increases. In contrast, configuration 2 shows a significant rise in simple payback period as the vapor absorption system cooling capacity increases, indicating a high sensitivity to cooling demand.