# Energy and Exergy Analyses of an Existing Solar-Assisted Combined Cycle Power Plant
## 4 Results and Discussion
### The Exergetic Efficiency of the Main Components of the ISCC  
The exergetic efficiency of different components of the ISCC at different ambient temperatures for solar heat inputs 0 MW, 75 MW, and 50 MW is shown in Figures 6-8, respectively.  
Figure 6 depicts the exergetic efficiency of different components of the ISCC at different ambient temperatures in the absence of the solar field (solar heat input equal to 0 MW), i.e., under the combined cycle regime. Under the combined cycle regime, the condenser has the lowest exergetic efficiency except at ambient temperature 5 \({}^{\circ}\)C. That may be due to the decrease in the low-temperature reservoir which increases the heat dissipated to the condenser cooling water.  
Figure 5: Percentage of exergy destruction in each component of the ISCC out of the total exergy destruction of the plant at different ambient temperatures for solar heat input equal to 75 MW.  
The exergetic efficiency of the solar field decreased from 31.3% to 14.5% when the ambient temperature increased from 5 \({}^{\circ}\)C to 35 \({}^{\circ}\)C, as shown in Figure 7. The condenser exergetic efficiency also decreased from 75.5% to 19.3% when the ambient temperature increased from 5 \({}^{\circ}\)C to 35 \({}^{\circ}\)C for solar heat input equal to 50 MW. This may be due to the decrease in the temperature difference between the exhausted steam from the low-pressure turbine and the cooling water from the cooling tower.  
Figure 8 shows that the exergetic efficiency of the solar field decreased from 47% to 21.7% when the ambient temperature increased from 5 \({}^{\circ}\)C to 35 \({}^{\circ}\)C. The condenser exergetic efficiency also decreased from 65.8% to 19.3% when the ambient temperature increased from 5 \({}^{\circ}\)C to 35 \({}^{\circ}\)C for solar heat input equal to 75 MW.  
Figure 6: Exergetic efficiency of different components of the ISCC at different ambient temperatures for solar heat input equal to 0 MW.  
Figure 7: Exergetic efficiency of different components of the ISCC at different ambient temperatures for solar heat input equal to 50 MW.  
As shown in Figures 6-8, the exergetic efficiency of the HRSG decreased with increasing ambient temperature, and this may be due to the existence of the attemperators in the HRSG which limit the steam temperature to the setpoint value. In the HRSG installed in the Kureimat power plant, attemperators were installed at the surface of the superheaters to control the temperature at the inlet of the high-pressure steam turbine. These attemperators use water directly from the main feedwater pump of the power plant. An increase in the ambient temperature may lead to an increase in the flue gas temperature of exhaust from the gas turbine into the HRSG, and the attemperators limit the effect of this temperature increase on the temperature of the superheated steam going into the steam turbine using water directly from the main feedwater pump. This may be a reason for the decreasing exergetic efficiency of the HRSG with increasing ambient temperature as shown in Figures 6-8.  
Unlike the thermal efficiency [27], the exergetic efficiency of the solar field explicitly decreased with increasing ambient temperature, as shown in Figures 7 and 8. This may be due to the increase of the exergy destruction in the solar field with increasing ambient temperature, as shown in Figures 4 and 5.