## 3 Results and Discussion
Additionally, it presents the deviation between the two tools in each set of results. The temperature values are displayed as temperature differences relative to the inlet temperature, as this qualitative representation is more informative than quantitative values for visual analysis. Figure 5: Darcy friction factor: numerical and theoretical values and their deviation with regards to inlet temperature. In particular, the results in Figure 7 exhibit a remarkably close agreement between SolidWorks and COMSOL results. Also, it is demonstrated that the calculated temperature profiles for both the upper and the lower photovoltaic components are highly similar. The maximum deviation of 6.87% between the two tools highlights the consistency and accuracy of the simulations. This close correspondence leads further credibility to the reliability of the simulation tools employed in this study. From comparing Figure 7a with Figure 7b, it seems that the PV located on the lower part of the receiver consistently presents higher temperatures than the PV on the upper part throughout the entire range of operation. This observation can be attributed to the fact that the PV on the back side of the receiver receives a greater amount of solar irradiation. This discrepancy arises, also, because the solar radiation is focused in a narrower zone for the lower PV compared to the upper one, leading to higher temperatures, especially near the focal point. An intriguing observation is that the temperature delta involving the photovoltaic (PV) component and the temperature at the inlet tends to be larger at lower inlet temperatures. This happens because the convective regime inside the channels is being enhanced with the increment of the temperature at the inlet. Another purpose for this fact is that when the collector becomes warmer, it grows closer to the stagnation conditions in which the temperature fields converge with each other. Figure 8 further illustrates the above analysis by displaying the temperature allocation on the top and bottom PV. As described previously, the figure shows that as the working fluid warms up, a corresponding temperature rise is observed on the upper PV panel. Also, the focal point of the concentrator on the bottom side of the receiver is evident in the region characterized by the highest temperature at one end of the receiver. Figure 6: Thermal efficiency of ACPC-PVT: COMSOL and SolidWorks. Figure 7: Temperature delta of the (**a**) upper and (**b**) the lower PV by the inlet temperature. Figure 9 visually represents the temperature difference between the ambient and the enclosed to the gap air, resulting from the procedure outlined in Section 4. Furthermore, Figure 9 clearly demonstrates the close agreement between the two numerical models, with a maximum deviation of 5.36%. The negative values are explained, since for the low inlet temperatures, the enclosed air temperature is lower than the ambient one. Figure 8: Temperature profiles at the top (**left**) and the bottom (**right**) PV of the receiver for T\({}_{\mathrm{f}i}\) = 40 \({}^{\circ}\)C.  
Figure 9: Temperature of the air in the gap with temperature on the inlet. Figure 10 presents the air temperature within the collector's gap, as well as the temperatures of the receiver and the outlet. The objective is to assess the influence of the receiver and the outgoing temperature on the air temperature, as well as to observe the behavior of each one with respect to the rest temperatures. According to Figure 10, the increment of the absorber temperature and the corresponding temperature at the outlet leads to the increment of the enclosed air temperature. However, this increment happens at a lower rate since the enclosed air has contact with the \"cold\" cover. Additionally, the temperature delta between the absorber and the fluid highlights that the temperature on the absorber tends to converge towards the water temperature as the temperature at the inlet rises, resulting in a decrease in the useful heat gained at a system level.