## 4 Results and Discussion
In addition, this dimensionless number is greater than \(10^{9}\) for the PV section that consisted of six PV modules, which corresponds to turbulent flow. In particular, turbulent flow corresponds to higher values of the air velocity \(v_{\rm o}\) in accordance with Figure 3, as well as higher values of the average temperature of the PV section \(T_{\rm PV}\) in accordance with \[T_{\text{PV}}=\frac{(T_{\text{PVb}}+T_{\text{PVu}})}{2}, \tag{23}\]3 This is also confirmation that the proposed correlation (14) was used for the calculation during the iteration procedure. Figure 6 shows the air velocity \(v_{\rm o}\) and the average temperature of the PV section \(T_{\rm PV}\) depending on the height difference between the two openings of the ventilation channel \(L_{\rm TS}+L_{\rm AP}+L_{\rm PV}+L_{\rm BS}\) for two different numbers of PV modules per section, i.e., the PV  
\[T_{\text{PV}}=\frac{(T_{\text{PVb}}+T_{\text{PVu}})}{2}, \tag{23}\]4 Fundamental dimensionless number for free convection depending on solar irradiance for two different numbers of PV modules per section and \(L_{\rm TS}+L_{\rm AP}\approx 0.5\) m, \(L_{\rm TS}+L_{\rm AP}=1\) m, and \(L_{\rm TS}+L_{\rm AP}=1.5\) m.  
sections having the lengths \(L_{\text{PV}}=0.52\) m and \(L_{\text{PV}}=3.12\) m. The labels \"Roof\" and \"Facade\" have the same meanings as in the case of \[T_{\text{PV}}=\frac{(T_{\text{PVb}}+T_{\text{PVu}})}{2}, \tag{23}\]5 For all the considered cases, it is also assumed that the solar irradiance \(q_{\text{E,S}}\) and the solar chimney height \(L_{\text{TS}}+L_{\text{AP}}\) are 1000 W/m\({}^{2}\) and 0.5 m (approximately), respectively. It is evident from Figure 6a that the air velocity \(v_{\text{o}}\) increases with the increase in the height difference \(L_{\text{TS}}+L_{\text{AP}}+L_{\text{PV}}+L_{\text{BS}}\), as well as with the increase in the number of PV modules per section. In addition, according to Figure 6b, the average temperature of the PV section \(T_{\text{PV}}\) decreases with the increase in the height difference \(L_{\text{TS}}+L_{\text{AP}}+L_{\text{PV}}+L_{\text{BS}}\), and increases with the increase in the number of PV modules per section. Furthermore, both these dependencies are more pronounced in the case of \"Roof\" than in the case of \"Facade\". Based on the curves from Figure 6a,b, the increases in the air velocity \(v_{\text{o}}\) and the average temperature of the PV section \(T_{\text{PV}}\) (due to the increase in the number of PV modules per section) are, respectively, up to 42.79% and 23.24% for the case of \"Roof\", as well as 47.63% and 10.47% for the case of \"Facade\". It is now also necessary to demonstrate whether there are specific values of solar irradiance and number of PV modules per section at which laminar-to-turbulent flow transition occurs. For this purpose, Figure 7 is provided. Figure 7 illustrates the fundamental dimensionless number for free convection depending on the solar irradiance \(q_{\text{E,S}}\) for the PV sections consisting of one, two, three, four, five, and six PV modules and the solar chimney height of \(L_{\text{TS}}+L_{\text{AP}}\approx 0.5\) m.  
\[T_{\text{PV}}=\frac{(T_{\text{PVb}}+T_{\text{PVu}})}{2}, \tag{23}\]6 (**a**) The velocity of the air at the outlet of the solar chimney and (**b**) the average temperature of the PV section depending on the height difference between the two openings of the ventilation channel for two different numbers of PV modules. Note: For the case of PV modules integrated into the roof, the dimension \(L_{\text{TS}}+L_{\text{AP}}+L_{\text{PV}}+L_{\text{BS}}\) represents the sum of the projections of the corresponding individual lengths \(L_{\text{TS}}\), \(L_{\text{AP}}\), \(L_{\text{PV}}\), and \(L_{\text{BS}}\).