Comparative thermoeconomic analysis of geothermal energy recovery via super/transcritical CO2 and subcritical organic Rankine cycles

Transcritical-CO2, supercritical-CO2, and organic Rankine cycles are numerically investigated and compared in simple Rankine, Rankine with internal heat exchanger, and regenerative Rankine configurations to assess their thermodynamic and thermoeconomic performance indicators. Subsequently, the systems are optimized using a multi-objective optimization method. Pareto optimal solutions are provided to present the trade-off between thermodynamic and thermoeconomic indicators. In addition, scatter plots of decision variables are presented to ascertain the optimal operating range of input variables. The results show that transcritical-CO2 systems can generate the highest power. The levelized cost of electricity for the studied configurations fall in the range from 0.12 to 0.16 $/kWh. Moreover, the transcritical-CO2 configuration has the lowest payback period of the studied cycles, with a payback period of 6.5 to 8.5 years. Optimization results show that the simple transcritical-CO2 system achieves the highest first- and second-law efficiencies while the simple organic Rankine cycle is preferred if economic criteria are more important.