## 4 Results and Discussion
In addition, the height of the solar chimney remained approximately the same (equal to the dimension \(L_{\rm AP}=0.52\) m), so no significant increase in the velocity of air at the outlet of the solar chimney can be expected. Such results are obtained in the second simulation. This  
Figure 2: Comparisons between measured values of temperatures \(T_{\rm PV}\) and \(T_{\rm a}\) and simulated values of temperatures \(T_{\rm PV}\), \(T_{\rm PVu}\), \(T_{\rm PVb}\), and \(T_{\rm a}\). was a way to validate and verify the accuracy of the used analytical model based on the available experimental and simulated data. Figure 3 shows the dependence of the air velocity \(v_{\rm o}\) on the solar irradiance \(\vartheta_{\rm E,S}\) for the PV sections consisted of 1 and 6 PV modules (having the lengths \(L_{\rm PV}=0.52\) m and \(L_{\rm PV}=3.12\) m, respectively) and the following heights of the solar chimney: (a) \(L_{\rm TS}+L_{\rm AP}\approx 0.5\) m; (b) \(L_{\rm TS}+L_{\rm AP}=1\) m; and (c) \(L_{\rm TS}+L_{\rm AP}=1.5\) m. In this figure, the labels \"Roof\" and \"Facade\" refer to the inclination angles of \(\theta=37^{\circ}\) and \(\theta=90^{\circ}\) to the horizontal plane, respectively. All curves are obtained assuming that the walls of the ventilation channel are adiabatic (i.e., thermally insulated). The three curves represented with dashed blue lines (and marked as \"Roof\") are obtained using the proposed model for the case of the experimental circuit from [39], while the three curves represented with solid red lines (and marked as \"Roof\") are generated for the geometry of the roof-integrated PV modules considered in [36]. In addition, the remaining six curves are obtained for the geometry of facade-integrated PV modules from Figure 1.  
It can be seen from Figure 3 that the air velocity \(v_{\rm o}\) increases with the increase in the solar irradiance \(\vartheta_{\rm E,S}\), as well as with the increase in the height difference between the outlet and the inlet of the ventilation channel. By comparing each curve generated for one PV module with the corresponding curve obtained for six PV modules, it can be noted that the heat transferred from the PV section to the air in the ventilation channel also contributes to the increase in the air velocity \(v_{\rm o}\). For the curves from Figure 3, that increase ranges between 41.05% (for \"Roof\" in Figure 3c) and 141.14% (for \"Facade\" in Figure 3a) when \(\vartheta_{\rm E,S}\) ranges from 200 W/m\({}^{2}\) to 1200 W/m\({}^{2}\), respectively. It can also be noted that the red solid lines or red circles almost coincide with each other, and that there are significant discrepancies between the dashed blue lines or blue squares. This means that the effect of the increase in the height of the solar chimney \(L_{\rm TS}+L_{\rm AP}\) on the air velocity \(v_{\rm o}\) is almost negligible for the case of the PV section composed of a larger number of PV modules, that is, a larger amount of heat transferred between the PV section and the air in the ventilation channel. The effect of the height of the solar chimney is the same as that of the height difference between the two openings of the ventilation channel. This effect is also presented in Figure 3,  
Figure 3: The velocity of the air at the outlet of the solar chimney depending on the solar irradiance for two different numbers of PV modules per section and (a) \(L_{\rm TS}+L_{\rm AP}\approx 0.5\) m; (b) \(L_{\rm TS}+L_{\rm AP}=1\) m; and (c) \(L_{\rm TS}+L_{\rm AP}=1.5\) m.  
and it is of importance only for the cases with one PV module. According to Figure 3a,b, in the range of the considered values for \(q_{\rm E,S}\), an increase in the height difference of 0.5 m leads to an increase in the air velocity \(v_{\rm o}\) by 22.53-23.51% and 12.7-12.93% for the cases of \"Roof\" and \"Facade\", respectively.