## 1 Introduction
[2] optimized the regenerative and recompression cycle of S-CO2 Brayton systems for a solar power application with a maximum operating temperature of 700 \({}^{\circ}\)C. The regenerative cycle achieved higher specific work and heat storage temperature difference, while the recompression cycle resulted in greater thermal efficiency. [PERSON] et al. [8] assessed a 100 MW solar tower CSP plant in Tibet, China, focusing on its technical and economic aspects. They compared two heat transfer fluids, solar salts and a mixture of 46.5% LiF, 11.5% NaF, and 42% KF, along with two power cycles, S-CO2 and Rankine. Using the System Advisor Model (SAM) [9], they calculated the net present value, payback period, and levelized cost of electricity. Their findings suggest that the S-CO2 cycle with the specified mixture is the more economically favorable option. Evaluating the economics of S-CO2 cycles is complicated due to a lack of economic data [10]. One approach is to compare different equipment sizes using specific parameters, assuming that smaller equipment offers greater economic benefits. [PERSON] et al. [11] used this method in their exergy analysis of a recompression S-CO2 cycle, including a preliminary cost analysis with size parameters (\(SP\)) and the total heat transfer coefficient (\(UA\)). Their study found that the turbine inlet temperature and split ratio are the most important for thermal efficiency. The precooler was highlighted as having the highest exergy destruction. Overall, as turbine and compressor inlet temperatures and pressures rise, total exergy destruction increases. While \(UA\) improves with better thermal efficiency, \(SP\) rises with higher inlet temperatures, showing a trade-off between cost and efficiency. This work compares two types of molten salts used in S-CO\({}_{2}\) Brayton cycles with a central solar receiver system: traditional solar salts and MgCl\({}_{2}\)-KCl. These two types of salts were selected to compare the current solar salts to one of the most promising alternatives for replacement due to their lower cost and higher operational temperature range. Energetic, energetic and equipment sizing analyses are performed in order to determine the advantages and disadvantages of each type of molten salt. Among the several alternative S-CO\({}_{2}\) cycles [12], the S-CO\({}_{2}\) recompression cycle has been selected because it achieves high efficiencies with a relatively simple configuration [13]. In this cycle, the recuperator is divided into two heat exchangers: a high-temperature recuperator (HTR) and a low-temperature recuperator (LTR). An extra compressor, the re-compressor (RC), is included to minimize the differences in heat capacity between the two sides of the recuperator [4]. The novelty of this work is the simultaneous analysis from the perspectives of energy, exergy, and equipment sizing for a solar tower-driven S-CO\({}_{2}\) recompression system utilizing two types of molten salts: solar salts and MgCl\({}_{2}\)-KCl. This approach enhances our understanding of how the choice of molten salt affects the overall performance of the system. An exergy analysis will help us assess which system achieves higher performance and how each molten salt contributes to the irreversibilities present in each equipment of the system. Additionally, the equipment sizing analysis will provide a preliminary estimate of how selecting one molten salt over another impacts plant costs. As noted in the previously cited works, the influence of the heat transfer fluid (HTF) in an S-CO\({}_{2}\) cycle is often studied primarily from an energy perspective, with efficiency, specific work, and the temperature differences of the HTF being the most commonly used parameters for comparison. Some studies extend this energy analysis by incorporating an economic analysis. This paper contributes to the existing literature by including an exergy analysis, which allows us to determine how the use of molten salts impacts the irreversibilities in various pieces of equipment within the S-CO\({}_{2}\) cycle.