A computational model of a "solar thermal utilization system" was constructed, and a case study was conducted using simulation to evaluate the system from both the energy concept and the exergy concept. As a result, the following findings were obtained. It was confirmed that the exergy concept can quantitatively evaluate the difference in resource value (quality) due to the temperature of hot water. Even when the values and ratios of exergy supply and utilization were the same, there were cases where the exergy input to the power plant differed greatly. The importance of operating with the minimum necessary flow rate (flow velocity) when utilizing natural exergy was suggested.
