**1. Introduction**

The world society actively supports measures aimed at facilitating flexible and low-carbon energy economy. These actions mainly include the promotion of renewable energy sources for power generation with possible electrification of the heating and transport sectors.

Concentrated solar power (CSP) plants use steam to produce energy, similar to the conventional steam power plants. They consist of a solar field and a power block, and they may have an energy storage system (optional).

Many types of collectors have been developed to be used in CSP technology. Parabolic trough collectors (PTCs) have been used in many CSP plants. Parabolic trough power plants are ready for use today because they were tested on a commercial basis [1]. This has been proven in California since 1985 with parabolic trough power plants, with 354 MW of installed capacity [2], which have succeeded in commercial operation and generate electricity using a steam turbine connected to a generator as conventional power plants.

However, the increasing share of renewables is raising awareness of a critical challenge. Renewables normally provide fluctuating feed-in into the electricity grid so that energy reserves, e.g., energy storage systems or conventional thermal power plants such as nuclear power plants and combined cycle power plants (CCPPs), are required to achieve a balance between current electricity supply and demand. Also, to increase the profitability of the CSP plants, CSP technologies have been integrated with conventional plants.

The high thermodynamic e fficiency of the CCPPs has attracted the construction of these power plants worldwide. On the one hand, the nominal process e fficiency of a large-scale CCPP with a net electrical power of about 605 MWel per unit can reach levels greater than 60% [3–6]. On the other hand, state-of-the-art coal-fired power plants reach a net thermal process e fficiency of about 46% with single reheat and several low-pressure and high-pressure feedwater preheaters [7]. According to the International Energy Agency (IEA) in 2018, gas-fired power generation accounted for approximately 24% of the total share of worldwide electricity generation, dominated by CCPPs.

The CCPPs have the advantage of absorption of the waste heat in the flue gas of a gas turbine using a heat recovery steam generator (HRSG) installed downstream of the gas turbine. The integration of solar energy into this technology is an e ffective method for cleaner and cheaper power generation.

CSPs integrated within CCPPs are known as integrated solar combined cycle (ISCC) power plants. ISCC power plants consist of a solar field and a solar steam generator integrated into a conventional CCPP. This ISCC system improves the solar-to-electricity conversion e fficiency [8–10] and the economic feasibility of the CSP plants. In addition, it increases the solar share, which leads to saving the fossil fuels used in these plants [10] while decreasing the CO2 emissions [11].

B. Kelly et al. [12] demonstrated that the ISCC power plant concept presents an e ffective path for the continued development of PTC technology regarding the solar thermal-to-electric conversion efficiencies and the solar energy levelized energy cost (LEC). J. Dersch et al. [11], in collaboration with the International Energy Agency SolarPACES (Solar Power and Chemical Energy Systems) organization, studied the advantages and disadvantages of ISCC systems compared with solar electric generation systems (SEGS) and conventional CCPPs. The study showed the environmental and economic benefits of each ISCC configuration.

G. Bonforte et al. [13], P. Iora et al. [14], M. Mehrpooya et al. [15], and A. Baghernejad and M. Yaghoubi [16] implemented exergetic analyses of ISCC power plants. G. Bonforte et al. [13] developed an exergo-environmental and exergo-economic model to analyze an ISCC power plant in Southern Poland under the design conditions. The results showed that the CO2 emissions were reduced by 9%. P. Iora et al. [14] presented a novel allocation method for the electricity produced in an ISCC based on the exergy loss approach by implementing internal exergy balances. They showed that this method is reliable and as good as the conventional Separate Production Reference method. M. Mehrpooya et al. [15] constructed a model using ASPEN HYSYS simulation software and MATLAB code to exergetically analyze an ISCC with a high-temperature energy storage system. It was found that the largest exergy losses were at the solar collector, the energy storage system, and the combustor.

A. Baghernejad and M. Yaghoubi [16] carried out energy and exergy analyses for an ISCC in Yazd, Iran using the design data of the power plant. The results showed that the energy and exergy efficiencies of this power plant are higher than those for a simple CCPP without a solar contribution and those for steam power plants with PTC technology. O. Behar et al. [17] simulated the performance of the first ISCC in Algeria, under HassiR'mel climate conditions. The results showed that the output power and the thermal e fficiency increased at daytime than at night by 17% and 16.5%, respectively.

S. Wang et al. [18] analyzed the performance variation of the solar field and overall ISCC using advanced exergy analysis methods and hourly analysis within a typical day. The results showed that increasing the solar energy input to the ISCC system decreases the exergy destruction of the Brayton cycle and increases the exergy destruction of the Rankine cycle.

In the literature, one can find several papers regarding the investigation of ISCC power plants applied to di fferent atmospheric conditions. The originality of this work is the parametric study of the energy and exergy analyses regarding an existing ISCC power plant in Egypt, under Kureimat climate conditions, as a whole and for the main components in the ISCC power plants. This work aims to identify the sites of major exergy destruction, clarify the reasons for exergy destruction in these sites, and attempt to clarify how to decrease the exergy destruction in this type of power plant. Besides this, given the challenges for the electricity market with the continuing expansion of intermittent renewables, in this work, we investigate the operational flexibility of ISCC power plants.

In this paper, we start with a description of the ISCC power plant under investigation, and we provide the method and the equation for the calculation of energy and exergy parameters. Then, we show the influence of ambient temperature and solar heat input on the plant performance. Finally, on the basis of these results, we investigate the sources of exergy destruction in the solar field and the combustion chamber to identify the possibility to enhance the performance of these components.
