Indonesia has a predicted geothermal potential of 29 GWe, which is the biggest in the world. With this potential, the government has the ambitious target to generate as much as 7 GWe of electricity in 2025 from geothermal energy. However, the installed capacity of geothermal power plant in Indonesia until 2019 is only 1.9 GWe. Enhancements in already-installed geothermal power plants with a binary power plant can be considered to achieve the 2025 target. In this research, a thermo-economic analysis is carried out to assess the feasibility of binary power systems to enhance the existing geothermal power plants in Indonesia. The Wayang Windu site is selected as the case study. Three working fluids, i.e., n-Pentane, isopentane, and R245fa, are compared. Two different optimization objectives are considered and compared. First, the thermal efficiency is optimized to maximize the thermodynamic performance. In the second scenario, the heat exchanger area is optimized to maximize the economic performance. Analysis of the economic profitability variables, namely the payback period and internal rate of return, shows that optimizing the heat exchangers gives better economic results when compared to optimizing the thermal efficiency. The results also show that the type of working fluid significantly affects both the thermal efficiency and economic profitability of the binary power plant. Moreover, n-Pentane has the most preferred thermo-economic performance for the geothermal conditions at Wayang Windu with the smallest payback period of 13 years and the highest internal rate of return of 11.28%.
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