## 4 Results and Discussion
The daily average thermal energy achieved by air, water, and dual-fluid type PV/T systems are 569.2, 649.8, and 695.3 W, respectively. When a single-fluid heat exchanger is used, the excess heat from the PV module is lost into the surrounding air, whereas the dual-fluid heat exchanger did not allow excess heat to be trapped in cells or dissipate to the ambient air. Figure 7 demonstrates the effect of hourly solar radiation variations on the electrical performance of the PV/T system. Simply put, the relation between daytime solar radiation and electrical energy at different fluid operations has been evaluated. As shown, the air-based PV/T system has the lowest performance and the dual-fluid PV/T system achieves the maximum electrical productivity. It is observed that the daily average electrical energy for the dual-fluid PV/T systems is 227.8 W, followed by the water type PV/T system with an efficiency value of 219.1 W and the air type PV/T system at third with 205.9 W. The increased electrical efficiency with dual-fluid confirms that simultaneous application of two fluids is a good choice as it maximizes the heat exchange rate and hence reduces the PV module temperature. Fluctuation in daily solar radiation and ambient temperature causes inconsistency in production and also temperature non-uniformity across the PV module, which can be overcome by application of the dual-fluid heat exchanger. Exergy energy is considered an important part of engineering system analysis because it is helpful in achieving the maximum possible improvement in the PV/T performance. Exergy is a thermodynamic property that addresses both the quantity and quality of energy. In simple terms, the maximum useful work can be obtained until the system is brought to equilibrium with the surroundings or a reservoir. Figure 8 illustrates the effect of different fluid operations on the exergy efficiency of a PV/T system. Unlike thermal energy, the electrical energy is considered to be in the form of exergy energy, and therefore both follow the same trajectory when they are plotted in relation with solar radiation. The maximum exergy efficiency for the air, water, and dual-fluid PV/T systems are 11.5%, 12.9%, and 13.8%, respectively. The lower rate heat losses to ambient air and the higher rate of heat exchange between the PV module and circulating fluids can be attributed to an increase of exergy efficiency, especially in the case of dual-fluid PV/T systems. Furthermore, the monthly thermal and electrical efficiencies for the PV/T system with dual and single fluid heat exchangers were calculated for a period  
Figure 6: Daily thermal power of PV/T systems plotted against different fluid operations. of one year so that the impact of these parameters on the system's life cycle cost can be analyzed. The monthly data obtained from the energy analysis is given in Figure 9. It is evident that the thermal and electrical performance of the dual-fluid PV/T system for all months is better than the PV/T system using air and water independently. Figure 8: Daily exergy efficiency of the PV/T systems plotted against different fluid operations. Figure 7: Daily electrical power of PV/T systems plotted against different fluid operations. A payback period in real terms represents the economic analysis of any system, especially in the context of its performance assessment. The findings from the economic analysis can help to set a clear understanding for the selection of an appropriate system from the available options. In this study, the cash flow for the assumed years is used to calculate the total cost of air, water, and dual-fluid type PV/T systems over their lifespans. The initial investment of the PV/T system is calculated by summing up the cost of each component used in assembly. Table 3 shows the initial investment cost breakdown; the presented prices of all components were obtained from local suppliers. The annual maintenance cost is the sum of the PV module, heat exchanger, and pump costs.