Energy and exergy analyses are conducted at the Dieng Geothermal Power Plant to determine the energy loss of components by calculating the efficiency, rate of change in energy flow, and exergy loss of each component. The data were collected on each component, including production wells, turbines, the main condenser, inter-condensers, and cooling towers, with the data collection occurring from April 2017 to March 2018. Energy and exergy analyses begin by calculating the enthalpy and entropy of both input and output from the compiled temperature data, with the help of a steam table. The study results show that the lowest efficiency was 67% in the turbine, and the highest energy change rate seen was 5.8×10 4 kW, in the inter-condenser. In addition, the greatest exergy loss was 50 Mw, which occurred in the turbine, indicating it was the component most in need of repair. In summary, the study results clarified that the component that needed to be treated and repaired at the Dieng Geothermal Power Plant was the turbine.

The Geothermal power plant at PT Geodipa Dieng has been operating for more than 10 years. It has undergone for several improvements including the replacement of turbines where to increase turbine efficiency. Before changing the turbine, the efficiency of turbine has decreased due to several factors, such as decrease in load, maintenance, usage, the lifetime etc. Therefore it needs to be analyzed the effiency of the turbine to find out whether the turbine is still feasible or not, and to find out whether it has necessary to replace the turbine again. The result of the turbine generator efficiency are obtained in one year from April 2017 to March 2018 with an average value of 70-85%. Based on the literature, the value is still at the turbine efficiency standard in general, which is 60-80%. So the turbines can still be categorized reliably and do not need to be changed.