Economic performances optimization of the transcritical Rankine cycle systems in geothermal application

• The optimal economic performance of the TRC system are investigated.
• In economic evaluations, R125 performs the most satisfactorily, followed by R41 and CO2.
• The TRC system with CO2 has the largest averaged temperature difference.
• Economic optimized pressures are always lower than thermodynamic optimized operating pressures.

The aim of this study is to investigate the economic optimization of a TRC system for the application of geothermal energy. An economic parameter of net power output index, which is the ratio of net power output to the total cost, is applied to optimize the TRC system using CO2, R41 and R125 as working fluids. The maximum net power output index and the corresponding optimal operating pressures are obtained and evaluated for the TRC system. Furthermore, the analyses of the corresponding averaged temperature differences in the heat exchangers on the optimal economic performances of the TRC system are carried out. The effects of geothermal temperatures on the thermodynamic and economic optimizations are also revealed. In both optimal economic and thermodynamic evaluations, R125 performs the most satisfactorily, followed by R41 and CO2 in the TRC system. In addition, the TRC system operated with CO2 has the largest averaged temperature difference in the heat exchangers and thus has potential in future application for lower-temperature heat resources. The highest working pressures obtained from economic optimization are always lower than those from thermodynamic optimization for CO2, R41, and R125 in the TRC system.