(d) (e)
Figure 6. Computed performance: a) Steam generated; b) Steam power turbine output; c) ISCC output; d) ISCC efficiency; e) Solar electric ratio
In order to estimate the sensitivity of ISCC power plant vis-à-vis the ambient temperature through the whole year; the average ambient temperature of each month (Table 12) is introduced. Also, the values of DNI were evaluated for monthly periods based on the daily average values which were averaged over one month. The obtained results are shown in Fig. 7 based on monthly average ambient temperatures during days. As shown, the output and thermal efficiency of ISCC plant exhibit a drop as the ambient temperature gets to its highest value. If the plant works as a conventional CC there is a significant drop in the output around 1 MW compared to ISCC and this is explained by the negative impact of high ambient temperature on GT. The slight decrease in performance of ISCC in hot periods is explained by the advantage of converting solar energy in producing additional steam in HSSG. Fig. 7(a) and Fig. 7(b) reveal that the additional steam generated by coupling the CC with the solar field compensates for the loss in power during the hot days, and hence the solar integration with CC is a good solution. It can be concluded that during high ambient temperatures coinciding with the period of higher normal radiation, the steam produced by the solar collectors alleviated the drop in electricity production by CC plants during the peak demand periods and improved the overall efficiency. Fig. 7(c) displays the impact of ambient temperature on the produced electricity by the solar field as quantified by the solar electric ratio which seems decreasing slightly with the ambient temperature such as the case during the summer.
Fig. 8 displays the response of ISCC plant to the variation in the ambient temperature during nights or cloudy periods depicted in Table 13. As shown the power output drops significantly from cold to hot periods such as in summer. Since ISCC works as CC and due to negative impact of ambient temperature the power drops for about 1 MW (Fig. 8(a)) as well as the thermal efficiency about 0.3 % as depicted in Fig. 8(b).
Table 12. Average ambient temperatures during the day [32]