## 4 Discussion  
The research results can be divided into two parts. In the first part the effect of the tilt angle changes will be discussed. The second part of presented research aimed to determine the influence of the azimuth orientation on the resulting energy balance of the PV system. The results mentioned in the previous chapter take into account not only experimental data but also mathematical models which were created. The mathematical evaluation of the final function relations was done by software Matlab(r). The polynomial function pointed to the fact that the tilt angle 34.5\({}^{\circ}\) is the best for PV module installed in the southern Slovakia region. The obtained result was verified by analytical model, which confirmed that optimal tilt angle of PV module installed in the Southern Slovakia regions is 34,405\({}^{\circ}\), which agrees with the result calculated by using the model polynomial equation. The tilt angle difference between models was 0.095\({}^{\circ}\). Presented results are also in good agreement with the information presented in literature [65] and values of energy production amounts for every month are consistent with the results reported by research in the articles [20,21]. From numerical assessment of results for azimuth angle orientation in the southern Slovakia, it is evident that maximal power and energy production of PV system was obtained for azimuth angle in the range (\(-\)20-15\({}^{\circ}\)). This fact is in agreement with information presented in the literature [66], but the best energy production is detected if the azimuth angle is \(-\)5\({}^{\circ}\), which means the South-East orientation. The average energy losses if the PV modules have South (0\({}^{\circ}\)) azimuth orientation were 0.12%. The fact is known also from the literature [13] where general information is presented. Our research confirmed significant influence of azimuth angle and tilt angle on PV system energy production, which is in accordance with results presented by authors [11,17,27,37,53,56]. For verification and evaluation of the experimental results and the created mathematical models special photovoltaic software was also used, which enabled the simulation of the operating conditions of the PV system for the selected area. In this software the simulation of solar radiation and PV system energy production was performed. Software  
Figure 15: Three-dimensional dependence after polynomial approximation—the influence of azimuth angle on the electric energy production of PV system for calendar months. calculates the solar radiation from satellite according to the methodology described in publications [62; 63; 64]. The calculation of PV system power is based on Equation (14),  
\[P=\frac{G}{1000}\cdot A\cdot eff(I_{G},T_{m}) \tag{14}\]  
where \(P\) is power of PV module (W), \(I_{G}\) is solar radiation (W.m\({}^{-2}\)), \(A\) is area of PV system (m\({}^{2}\)), \(eff\) is efficiency of PV system (%), and \(T_{m}\) is temperature of PV module (\({}^{\circ}\)C) [62]. The total amount of energy PV system production was identified as a product of the PV system power by using Equation (14) and selected time range. The dependencies found in the experimental work were summarized and made a contribution to a comprehensive basis for the creation of a final mathematical model. The final model will be a platform for creation of smart application. Part of the flowchart is presented in Figure 16. Due to the applicability of the mathematical model in practice and the possibility of its use by the target group, which will be ordinary users, the model had to be simplified. It contains easily identifiable parameters. The created mathematical model allows for the prediction of power or energy of a PV system installed in southern Slovakia region.