## 2 Materials and Methods
The developed calculation algorithm makes it possible to determine the installation efficiency of vertical stationary PV-modules equipped with a double-sided solar panel with an \"East-West\" orientation at the geographic latitudes of the Earth's surface from the equator to the latitude of 66.55\({}^{\circ}\). Comparison of the Installation Efficiency of the PV-Modules Equipped with a Solar Panel with \"East-West\" and \"South\" Orientations  
Based on the received data, regarding the cosine changes of the horizontal and vertical azimuths of the Sun's rays falling on a double solar panel with an \"East-West\" orientation on a vertical stationary PV-module, further calculations were carried out during the day. Thus, according to Formula (3), the cosine of the Sun's rays falling on a double panel with an \"East-West\" orientation on a vertical stationary PV-module during the day was calculated (Table 2). \begin{table}
\begin{tabular}{c c c c} \hline
**Moment of Time** & **Sunrise** & **At Noon** & **Sunset** \\ \hline \multicolumn{4}{c}{The cosine square of the Sun’s rays falling on the panel of a PV-module, cos\({}^{2}\theta_{Z}\)} \\ March 21 & 0.99997 & 0.00000 & 0.99997 \\ June 21 & 0.84164 & 0.00000 & 0.84164 \\ December 21 & 0.84164 & 0.00000 & 0.84164 \\ \multicolumn{4}{c}{Cosine of the angle of the Sun’s rays falling on the panel of the module, cos\(\theta_{Z}\)} \\ March 21 & 0.99998 & 0.00000 & 0.99998 \\ June 21 & 0.91741 & 0.00000 & 0.91741 \\ December 21 & 0.91741 & 0.00000 & 0.91741 \\ \end{tabular}
\end{table} 
Table 2: Calculation of the angle of incidence of the Sun’s rays on a double-sided panel with an “East–West” orientation on a vertical stationary PV-module. Figure 5: The change in the cosine of the vertical azimuths of the Sun’s rays falling on a double-sided solar panel with an “East–West” orientation on a vertical stationary PV-module during the day. The weighted average daily installation efficiency of vertical stationary PV-modules with a double-sided solar panel with \"East-West\" orientation is determined by expression (4), and is given in Table 3.  
The results of a comparison of the weighed annual daily installation efficiencies of vertical stationary PV-modules with a double-sided solar panel with \"East-West\" orientation and PV-modules with \"South\" orientation are shown in Figure 7. \begin{table}
\begin{tabular}{c c c c} \hline
**Moment of Time** & **Sunrise** & **At Noon** & **Sunset** \\ \hline \multicolumn{4}{c}{Cosine of the Sun’s horizontal azimuth, \(\text{cos}\theta_{H}\)} \\ March 21 & 0.000 & 0.99998 & 0.000 \\ June 21 & 0.000 & 0.917 & 0.000 \\ December 21 & 0.000 & 0.917 & 0.000 \\ The angle of the Sun’s rays (the angle between the Sun’s rays and the axis z), \(\theta_{Z}\) \\ March 21 & 0.31 & 90 & 0.31 \\ June 21 & 23.45 & 90 & 23.45 \\ December 21 & 23.45 & 90 & 23.45 \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 6: Change in the cosine of the Sun’s rays falling on a double-sided panel with an “East-West” orientation of a vertical stationary PV-module during the day. \begin{table}
\begin{tabular}{c c c c} \hline
**Day of a Year** &
\begin{tabular}{c} **December** \\ **21** \\ \end{tabular} & **March 21** & **June 21** \\ \hline PV-modules with a double-sided solar & 45.87 & 50.00 & 45.87 \\ panel with the “East–West” orientation & 45.87 & 50.00 & 45.87 \\ PV-modules with the “South” orientation [10] & 45.87 & 50.00 & 45.87 \\ \hline \end{tabular}
\end{table} 
Table 3: The weighted average daily installation efficiency of solar PV-modules at the latitude of 50\({}^{\circ}\). The obtained data indicate that the weighted average annual daily installation efficiencies of vertical stationary PV modules with a double-sided solar panel with an \"East-West\" orientation and PV-modules with a \"South\" orientation have the same values. However, a change in the cosine of the Sun's rays falling on the surface of the module panels leads to mutually opposite values throughout the day.