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This study has attempted to compare two thermodynamic cascade cycles, which in this paper are presented as Systems A and B. System A was consisted of a steam Rankine cycle (SRC) as a top cycle and an organic Rankine cycle (ORC) as a bottom cycle. System B was consisted of the same SRC as the top cycle and a Kalina cycle as the bottom cycle. The comparison of both systems has been made by changing a number of parameters. The chosen parameters for this comparison were bottom cycle mass flow rate, aperture area of the collector, top cycle condensing pressure, and bottom cycle turbine inlet and outlet pressures. Also, a short economic evaluation has been made between two proposed cascade cycles (Systems A and B). The result indicated that the Kalina cycle shows superiority over the ORC as the bottom cycle in a solardriven SRC. Furthermore, it was determined that the most effective parameters on the overall efficiency of the systems are the condensing pressure of the top cycle and the outlet pressure of the bottom cycle turbine. Also, among the chosen parameters, the outlet pressure of the bottom cycle turbine had the highest effect on the efficiency of the bottom cycles.Considering the economic aspect, the results showed that the levelized costs of energy for both systems are quite equal at 0.011 ($/kWh).

In this paper, a new configuration of a solar combined cooling, heating, and power (CCHP) system is proposed to recover the waste thermal energy of a steam power plant, which provides the cooling and heating needs of an apartment complex located in Tehran. The required energy of the system is supplied by the parabolic trough solar collectors (PTCs) and, if necessary, an auxiliary heater is also used. An ejector refrigeration cycle (ERC) and a steam Rankine cycle are used for cooling and power generation, respectively. The cycle is dynamically modeled over a year using a TRNSYS‐EES co‐simulator. It is found that the highest Rankine cycle efficiency is obtained in the cold months (January) because of the decrease of turbine backpressure. With increasing the turbine inlet temperature from 190 to 210°C, the Rankine cycle and the overall cycle efficiencies increased about 1% and 2%, respectively. The maximum cooling, heating, and power generation, as well as the maximum solar fraction, are obtained at the turbine inlet temperatures of 210°C, which are 185.46, 598.65, 680.49 kW, and 70%, respectively. The annual overall performance and the solar fraction of the proposed CCHP system are 32.5% and 9.5%, respectively, based on 3000 m2 collector aperture area. The exergy analysis indicated that the maximum annual exergy destruction is related to the solar collectors, which have comprised 27% of the total exergy destruction. In addition, the yearly exergy efficiency of the proposed system is 39.9%.

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