# Energy and Exergy Analyses of an Existing Solar-Assisted Combined Cycle Power Plant
## 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 anddemand. Also, to increase the profitability of the CSP plants, CSP technologies have been integrated with conventional plants. The high thermodynamic efficiency of the CCPPs has attracted the construction of these power plants worldwide. On the one hand, the nominal process efficiency of a large-scale CCPP with a net electrical power of about 605 MW\({}_{\rm el}\) per unit can reach levels greater than 60% [3; 4; 5; 6]. On the other hand, state-of-the-art coal-fired power plants reach a net thermal process efficiency 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 effective 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 efficiency [8; 9; 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 CO\({}_{2}\) emissions [11]. [PERSON] et al. [12] demonstrated that the ISCC power plant concept presents an effective path for the continued development of PTC technology regarding the solar thermal-to-electric conversion efficiencies and the solar energy levelized energy cost (LEC). [PERSON] 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. [PERSON] et al. [13], [PERSON] et al. [14], [PERSON] et al. [15], and [PERSON] and [PERSON] [16] implemented exergetic analyses of ISCC power plants. [PERSON] 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 CO\({}_{2}\) emissions were reduced by 9%. [PERSON] et al.