## 4 Results and Discussion  
First of all, the proposed model is validated using experimental data and simulated results from [39]. Two simulation exercises are organized according to the description of the used experimentation [39]. The solar chimney model for cooling one PV module of type BP SX320P was made using a wooden channel that was thermally insulated from the surroundings. BP SX320P is a 20 W module with standard polycrystalline PV cells that can be used efficiently in any climate [45]. The experimental circuit consisted of three sections, as described in Section 2. Two identical PV modules were used in this experimental circuit. The first PV module was mounted on the inclined section of the solar chimney just below the absorber, while the second one was mounted on a separate steel frame next to the solar chimney created. This was carried out to maintain the uniformity of the experimental results for the purpose of comparing them to each other. The experimental circuit was tested on 20 October 2010 in Melbourne (Australia) at 37\({}^{\circ}\)47\({}^{\prime\prime}\) south latitude, which roughly corresponds to the northern latitudes where Serbia is located. For this reason, the experiments with PV modules inclined at an angle of \(\theta=37^{\circ}\) relative to the horizontal are considered. The temperatures of the ambient air and the bottom surfaces of the PV modules with and without the solar chimney were measured with type K thermocouples. These thermocouples are connected to the Data Taker-DT800 for recording and storing data. During the 90 min test, the maximum solar irradiance was 1000 W/m\({}^{2}\), and there was no wind. The ambient air temperature was around 22 \({}^{\circ}\)C. The average difference between temperatures of the bottom surfaces of the PV modules with and without the solar chimney was approximately 7 \({}^{\circ}\)C.  
Specifically, the same experimental circuit as in [39] is reconsidered, and the analytical model from [36], in which empirical correlations for free convection from a vertical flat plate (13) and (14) were included, is used for verification. The first simulation is performed with the following parameters: an inclination angle of \(\theta=37^{\circ}\) to the horizontal plane; \(L_{\rm TS}=0.187\) m; \(L_{\rm{AP}}=0.313\) m; \(L_{\rm PV}=0.52\) m; \(S_{\rm{AP}}=S_{\rm{PV}}=0.234\) m\({}^{2}\); \(L_{\rm{BS}}=0\) m; \(T_{\rm i}=T_{\rm a}=22\)\({}^{\circ}\)C; \(q_{\rm{ES}}=1000\) W/m\({}^{2}\); \(\alpha_{\rm{PV}}=0.97\); \(\varepsilon_{\rm{PV}}=0.91\); \(\alpha_{\rm{A}}=0.9\); \(\tau_{\rm{AP}}=0.91\); \(\eta_{\rm{el}}=0.14\); and \(K_{\rm{i+o}}=2.7\). The required remaining inputs can be found in the previous sections. In addition, it should be emphasized that the sum of \(L_{\rm TS}+L_{\rm{AP}}\) represents the height of the solar chimney, which should be distinguished from the total length of the ventilation channel. The results of the first simulation are given in Table 1. According to the Rayleigh number \(\text{Ra}=1.3257\times 10^{8}\), it is obtained that the free convection from the upper surfaces of the PV section and the acrylic plate is laminar. This means that the Nusselt number correlation for an inclined flat plate from [36] reduces to the empirical correlation (13). These results were obtained after the ninth iteration.