## 3 Results
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Sum of Squares** & **1.735 \(\times\) 10\({}^{8}\)** \\
**Coefficient of** & & **0.8723** \\
**Determination** & & \\ \hline Standard error of & & 1.491 \(\times\) 10\({}^{3}\) \\ arithmeticaverage & & \\ Regression Equation & \(E_{m}(t,\ \beta)=A+B\cdot t+C\cdot\beta+D\cdot t^{2}+E\cdot t\cdot\beta+F\cdot\ \beta^{2}\) \\ \hline Coefficient & Value & Minimum of the & Maximum of the \\  & & Range & Range \\ \hline A (kWh) & \(-\)1438 & \(-\)3063 & \(-\)185.8 \\ B (kWh\(\cdot\)month\({}^{-1}\)) & 56.33 & 12.4 & 100.3 \\ C (kWh) & 4218 & 3785 & 4652 \\ D (kWh\(\cdot\)month\({}^{-2}\)) & \(-\)0.8993 & \(-\)1.315 & \(-\)0.4835 \\ E (kWh\(\cdot\)month\({}^{-1}\)) & 0.8507 & \(-\)2.278 & 3.979 \\ F (kWh) & \(-\)340.9 & \(-\)371.6 & \(-\)310.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The statistical and regression characteristics of approximated polynomial function for three-dimensional dependence on Figure 10.  
Figure 10: Three-dimensional dependence after polynomial approximation—the influence of tilt angle on the electric energy production of PV system for calendar months. determine the energy balance of a PV plant with an installed output of 100 kWp for any tilt angle and calendar month of the year in the southern Slovakia region. The second part of research was focused on identification of optimal azimuth angle for southern Slovakia region. Azimuth angle change was measured on PV power plant and the model PV system. The results are summarized as graphical dependencies. For clarity, results are presented in two figures. At first, dependencies were created in the range \(-\)90-5\({}^{\circ}\) shown in Figure 11 and then were made relations for azimuth angles 0-90\({}^{\circ}\) in Figure 12. The results were compared with values experimentally obtained from the model PV system for seven different azimuth orientations (\(-\)90\({}^{\circ}\), \(-\)60\({}^{\circ}\), \(-\)30\({}^{\circ}\), 0\({}^{\circ}\), 30\({}^{\circ}\), 60\({}^{\circ}\), and 90\({}^{\circ}\)). The difference between values obtained from the PV power plant and model PV system was approximately 0.58%. The measured data were statistically processed and the selected statistical characteristics for each data group were calculated. Especially, arithmetic average, deviations from  
Figure 11: Dependencies of energy produced by the PV system for azimuth angle from \(-\)90\({}^{\circ}\) to 0\({}^{\circ}\) in different calendar months. Figure 12: Dependencies of energy produced by the PV system for azimuth angle from 0\({}^{\circ}\) to 90\({}^{\circ}\) in different calendar months. Summary results for energy produced by PV system with different azimuth orientation are presented in Table 3. It is clear that the largest amount of electrical energy is produced for the azimuth orientation from \(-5^{\circ}\) to \(-35^{\circ}\), which represents the energy range (8420-8590) kWh. In the South orientation \(0^{\circ}\), the PV system produced 8580 kWh. In the Southwest orientation was the maximum energy production in range 8560-8450 kWh obtained for azimuth angles from \(+5^{\circ}\) to \(+20^{\circ}\). The comprehensive evaluation of the results for the azimuth angle that influenced the PV system energy production pointed to the fact that optimum energy is achieved at the azimuth angle \(-20\)-\(15^{\circ}\). However, the average difference is only 3.80% as compared with the orientation in the range (\(-35\)-\(35^{\circ}\)), which is presented as acceptable for the azimuth angle for the PV module orientation in literature [16; 63; 64; 65].