## 2 Materials and Methods  
The subject of the study is the dependence of the installation efficiency of vertical stationary solar PV-modules, equipped with a double-sided panel with an \"East-West\" orientation, on the time of the day. The main hypothesis of the study is that the combination of different installation systems of solar PV-modules can increase their efficiency of use. The main assumption and simplification adopted in the work is as follows: it was assumed that the Earth is in a parallel flow of the Sun's rays, and the phenomenon of cloudiness was ignored (it affects only the intensity of solar radiation, and the angle of incidence of the Sun's rays on the PV-module is not affected). The specific (per square meter) power of a photovoltaic module is determined by a simple well-known formula, and is  
\[P/S=I\;\eta\;\cos\theta_{z} \tag{1}\]  
where \(P\) is the specific power of the photovoltaic module, W; \(S\) is the area of the photovoltaic module, m\({}^{2}\); I is the intensity of solar radiation, W/m\({}^{2}\); \(\eta\) is the efficiency of the photovoltaic module, rel. units; \(\theta_{Z}\) is the angle of incidence of solar radiation (the angle between the direction of incidence of solar radiation and perpendicular to the photovoltaic module), degrees. This dependence, by its structure, yields three main directions for improving photovoltaic modules, namely, studying the nature of the intensity of solar radiation, increasing the efficiency of the photovoltaic module itself, and increasing the installation efficiency (reducing the angle between the direction of incidence of solar radiation and the angle perpendicular to the photovoltaic module). It is also well known that the intensity of solar radiation is a natural phenomenon, and therefore it is impossible to influence its value. It is possible to influence the value of the specific power of photovoltaic modules by improving the semiconductors involved, and this is a separate approach to their improvement. An important factor influencing the specific power of a photovoltaic module is the angle of incidence of solar radiation on the photovoltaic module, except in cases where a photovoltaic module that tracks the Sun is used. However, photovoltaic modules that track the Sun are rarely used due to their relatively high cost. Therefore, the task associated with determining the angle of incidence of solar radiation on a photovoltaic module (not energy efficiency, but the installation efficiency of the photovoltaic module) remains important and relevant. Based on the above, we can talk about three areas of research in terms of analyzing the efficiency of photovoltaic systems, as follows:  
1. Determining the intensity of solar radiation as a natural phenomenon depending on the temperature of the Sun, the radiation spectrum, etc. ;
2. Improving semiconductors for photovoltaic modules (increasing the energy efficiency of semiconductors);
3. Determining the angle of incidence of solar radiation on a photovoltaic module (installation efficiency of photovoltaic module). The task of synthesizing photovoltaic systems involves the need to combine the results obtained in the above three areas to create new systems and determine their energy efficiency in terms of power or the amount of electricity generated. The results obtained in the third area, namely, determining the angle of incidence of solar radiation on a photovoltaic module, will reduce the number and complexity of experimental studies, reduce the time and financial investment in design work, and help to quantitatively assess the installation efficiency of the solar photovoltaic modules at different latitudes with different installation methods. To model the installation efficiency of the panel, this study used the basic theoretical principles outlined in [17], which are built on the basis of a physical model of the Earth's illumination by a parallel stream of sunlight.