Geothermal energy is considered a comparatively abundant renewable energy resource. The geothermal power generation system has negligible environmental impact (approximately 0.015kg-CO 2 /kWh), and it is expected to help prevent carbon dioxide emissions to the atmosphere. On the other hand, in our institute, we have developed general purpose software (EnergyWin™) to analyze the thermal efficiencies of power generation systems easily and rapidly. Such software can not only analyze the plant performance but also investigate the effect of the performance-deteriorated equipment or air condition change on power output quantitatively. Using this software, we have developed a new plant performance analysis system based on actual operation data for geothermal power plants. Then, applying the system to existing facilities, we have analyzed the plant performance and evaluated the effectiveness of the plant maintenance strategy during periodic inspection for consistency.

Recently, it is more necessary to maintain or improve the thermal efficiency of actual thermal power plants to reduce CO 2 emission and energy consumption in the world, and it is also important to reduce the maintenance cost of commercial thermal power plants. Thus, it is crucial to investigate power plant performance deterioration factors and solve problems related to these factors promptly when the thermal efficiency decreases. However, it is difficult to understand the internal state of power plants sufficiently and to determine power plant performance deterioration factors only from operation data because actual thermal plants are composed of many components and are very complex systems. In particular, it is more difficult to understand performance deterioration in gas turbine combined cycle (GTCC) power plants than in steam power plants because the performance changes markedly in GTCC power plants depending on atmospheric conditions (temperature, pressure, humidity). In other words, when thermal efficiency changes, it is difficult to determine whether the cause is the change in external factors or that in the performance of the component. Therefore, we develop a method based on heat balance analysis to calculate the immeasurable quantity of state and the efficiency of each component in GTCC power plants, and to correct the performance of each component in a plant to a standard state using the performance function obtained from long-term operation data. Through the method, the analysis of the effects of deterioration factors on thermal efficiency becomes possible, and the performance of a plant can be simulated when the operation conditions are changed. Thus, we can determine the main factor that affects thermal efficiency using our method.

We have developed a general-purpose software by which static thermal characteristics of a power generation system can be analyzed easily. This software has following notable features. - It has new algorithm that can solve non-linear simultaneous equations used in analyzing static thermal characteristics of various power generation systems, namely the heat and mass balance and the efficiency. - It has flexibility over setting calculation conditions. - It can be executed on a personal computer easily and quickly. We have ensured that it can produce the heat and mass balance diagrams of a nuclear power plant’s main steam system and then it can calculate power output and efficiency of the system. Furthermore, we have evaluated various measures to recover heat from steam generator blowdown water and proved that this software is a useful operation aid for planning effective changes in support of power stretch.