Abstract
Nowadays, due to the continuously increasing global demand for energy and the depletion of fossil resources, renewable energies have gained greater importance. Accordingly, investigating the feasibility of utilizing renewable energy sources in various conventional systems is of significant interest. The objective of this paper is to perform agent-based simulation, thermodynamic analysis, and exergy analysis of the integration of a supercritical gas turbine Brayton cycle with an organic Rankine cycle using biomass and solar energy in off-grid regions of Iran. In this study, the effects of various parameters—including temperature, compressor pressure ratio, and solar irradiation intensity—on the energy and exergy efficiencies of the system, the amount of heat generation in the solar collector, the input, output, and destroyed exergy of the system, as well as the total power output of the overall system, were investigated. The results indicate that with increasing compressor pressure ratio, the net power output and the energy and exergy efficiencies of the system initially increase by 4% and 5%, respectively, and then decrease, while the exergy destruction of the system increases continuously. Furthermore, the results show that the total input exergy to the system is 51,672 kW, whereas the rates of exergy destruction and exergy output from the system are 33,756 kW and 17,717 kW, respectively. The highest exergy destruction occurs in the solar collector, followed by the heat exchanger, while the lowest exergy destruction occurs in the pump.
EXTENDED ABSTRACT
Introduction 
The use of solar radiation energy in gas turbine cycles is one innovative method to increase the efficiency of these cycles. The use of heliostat solar reflectors and the placement of a solar receiver upstream of the combustion chamber can increase the temperature of the air entering the combustion chamber, thereby reducing fuel consumption. The reduction of fuel injection into the combustion chamber, in turn, enhances efficiency, reduces pollution, and decreases the irreversibility rate in the cycle. In this system, the solar collector is installed at the top of a tower and absorbs the energy emitted from the solar panels installed on the ground surface. Compressed air is sent through pipes to the top of the tower, where it is heated in these collectors and then directed to the combustion chamber. Along the path between the compressor and the solar collector, due to the increase in air volume, the air temperature rises while its pressure decreases. In the path from the collector’s outlet to the combustion chamber, there is a slight decrease in temperature and pressure, which does not significantly affect the system's performance. Insulating the return air pipes from the tower can compensate for this temperature reduction to some extent. In cases of high solar radiation intensity, the combustion chamber can be completely removed, and a solar receiver can be used as an alternative. In this case, the system's efficiency will increase significantly, and the irreversibility rate will reach its minimum possible value.
Material and Methods 
In this study, an effort was made to utilize biomass fuel to generate the heat required for the Brayton cycle. The proposed system consists of several subsystems. A brief description of the overall system and its components is provided below. Based on the advantages and findings of previous research on the supercritical Brayton cycle with CO₂ as the working fluid, this cycle was selected as the secondary cycle to recover waste energy from the heat generation system using biomass fuel.
Subsequently, the exhaust gases from the first turbine are reheated using a solar source and directed toward the second turbine to generate additional power. The exhaust gases from the second turbine are then directed to the Organic Rankine Cycle located at the end of the system.
Furthermore, considering the thermodynamic requirement for the main compressor inlet temperature in the S-CO₂ cycle to be low, a significant amount of energy is lost to the environment in this section. For the system analysis, a computer program was developed in EES software, and the thermodynamic and exergetic performance of the system was evaluated.
Results and Discussion 
The power output of the gas turbine system and the net total power initially increase with the rise in the compressor pressure ratio, reaching a maximum at a pressure ratio of 6 to 7, and then decrease. Increasing the compressor pressure ratio leads to an increase in the power generated by the turbine. However, within the pressure ratio range of 6 to 20, the work consumed by the compressor increases, which results in a reduction in the system's power output. The variations in energy efficiency and exergy efficiency follow a trend similar to the changes in the system’s power output. As the compressor pressure ratio increases, both the energy efficiency and exergy efficiency of the system initially rise, reach a maximum point, and then begin to decrease. With an increase in the compressor pressure ratio, the exergy input to the system increases. As the compressor pressure ratio increases, more air enters the system, and consequently, more fuel is introduced for combustion, resulting in higher exhaust gas temperatures from the combustion chamber. These gases then enter the turbine, resulting in an increase in the power generated by the turbine. On the other hand, the exergy input to the system also increases with the rise in the compressor pressure ratio. With an increase in solar radiation intensity, the amount of heat input to the system rises, leading to an increase in the power generated by the S-CO₂ turbine and, consequently, an increase in the total power output of the system. As the system's power output increases, its energy efficiency also improves.
The rise in solar radiation intensity results in an increase in both the heat and exergy input to the system, which in turn enhances the overall exergy efficiency of the system. Therefore, increasing solar radiation intensity directly contributes to higher heat and exergy input to the system. As solar radiation intensity increases, the heat and exergy input to the system rise. As mentioned earlier, one of the components of the system that contributes to exergy destruction is the solar collector. The irreversibility in the solar collector leads to exergy destruction. With an increase in solar radiation intensity, the exergy input, exergy output, and exergy destruction also increase due to the higher heat input to the system. Additionally, as the temperature of the gases entering the turbine rises, the power generated in the Rankine cycle and the overall system power output also increase.
Conclusions 
As the compressor pressure ratio increases, the exergy efficiency initially rises and then decreases. At a pressure ratio of 7, the exergy efficiency reaches its maximum value of 64.7%.
•With an increase in the compressor pressure ratio, the exergy input, exergy output, and exergy destruction also increase. For instance, the exergy input to the system rises from 48,000 kW to 55,000 kW.
When solar radiation intensity increases, both energy efficiency and exergy efficiency improve. Specifically, the energy efficiency increases from 53% to 57%, while the exergy efficiency rises from 64% to 69%.
•As solar radiation intensity increases, exergy destruction, along with the exergy input and output of the system, also grows. The exergy input to the system increases from 45,000 kW to 62,000 kW. Additionally, the amount of energy entering the system from the solar collector increases from 300 kW to 3,800 kW.
The highest exergy destruction occurs in the solar collector, followed by the heat exchanger, while the lowest exergy destruction takes place in the pump.
Author Contributions
Moez Behrouz: Methodology 
Pourdarbani Raziyeh: Supervisor 
Ghaebi Hadi: Validation
Data Availability Statement
"Not applicable" 
Acknowledgements
The authors would like to acknowledge the Bu-Ali Sina University for finantcial support 
Ethical Considerations
This section states ethical approval details (e.g., Ethics Committee, ethical code) and confirms adherence to ethical standards, including avoidance of data fabrication, falsification, plagiarism, and misconduct.
Conflict of Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper
Funding Statement
The author(s) received no specific funding for this research