## 3 Results
Formulas (5)-(7) [32] allow the calculation of the fundamental parameters of the I-V characteristics of the PV module for a specific temperature \(T_{M}\) in relation to the value at 25 \({}^{\circ}\)C (in STC), given by the manufacturer (Table 1). These formulas are based on three temperature coefficients (\(\alpha_{T}\), \(\beta_{T}\), and \(\gamma_{T}\)) from Table 1:  
\[I_{\text{SC}}(T_{M})=I_{\text{SC}}\Big{[}1+(T_{M}-25)\frac{\alpha_{T}}{100} \Big{]}, \tag{5}\]  
\[U_{\text{OC}}(T_{M})=U_{\text{OC}}\Big{[}1+(T_{M}-25)\frac{\beta_{T}}{100} \Big{]}, \tag{6}\]  
Figure 4: Verification results for measuring point P1 (see Table 2). \[P_{MPP}(T_{M})=P_{MPP}\bigg{[}1+(T_{M}-25)\frac{\gamma_{T}}{100}\bigg{]}. \tag{7}\]  
Only for the open circuit voltage \(U_{OC}\) (Table 4) model was the positive verification of the temperature model obtained (relative error is 3%). Other parameters (\(I_{SC}\) and \(P_{MPP}\)) calculated according to the models differ significantly in relation to the measurement results. The obtained results of model calculations assumed a simplification in the form of proportionality of the dependence of these three parameters on temperature without taking into account other weather conditions. Another temperature model [35] makes the value of the module temperature (\(T_{M}\)) dependent on the ambient temperature (\(T_{amb}\)) and solar radiation intensity (\(E\)) under NOCT (Normal Operating Cell Temperature) conditions, which are more similar to real ones in the considered location of the tests in relation to the STC conditions, represents Formula (8):  
Figure 3:0  
For the model from Formula (8) a result of 48.3 \({}^{\circ}\)C was obtained, which is also much higher than the measured value, which was equal to 35.5 \({}^{\circ}\)C. This model assumes NOCT conditions, in which a lower wind speed (1 m/s) is assumed than measured during measurements (5 m/s). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameters:** & **Model Calculations** & **Measurement** & **Relative Error of** \\  & **Results** & **Results** & **Comparison, (\%)** \\ \hline \(I_{SC}\), (A) & 10.21 & 8.23 & 19\% \\ \(U_{OC}\), (V) & 39 & 37.87 & 3\% \\ \(P_{MPP}\), (W) & 307.9 & 240 & 22\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of results of calculations of parameters according to models (5), (6), and (7) with the results of measurements for a 35.5 \({}^{\circ}\)C PV module temperature. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameters and** & **Measurement** & **Simulation** & **Relative Error of** \\
**Coefficients:** & **Results** & **Results** & **Comparison, (\%)** \\ \hline \(I_{SC}\), (A) & 8.23 & 8.09 & 1.7 \\ \(U_{OC}\), (V) & 37.87 & 38.28 & 1.1 \\ \(I_{MPP}\), (A) & 7.61 & 7.58 & 0.4 \\ \(U_{MPP}\), (V) & 31.58 & 32.98 & 4.4 \\ \(P_{MPP}\), (W) & 240 & 250 & 4 \\ \(FF\), (\%) & 77.1 & 80.7 & 4.7 \\ \(\eta\), (\%) & 17.8 & 18.6 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Relative errors in the comparison of the basic parameters of the current–voltage (I–V) characteristics and the values of the fill factor (\(FF\)) and \(\eta\) coefficients for the measuring point P1 graphically shown in Figure 4 (for \(E\) = 810 W/m\({}^{2}\), \(T_{M}\) = 35.5 \({}^{\circ}\)C, and \(T_{amb}\) = 23 \({}^{\circ}\)C). Figure 5: Verification results for measuring point P2 (see Table 2). Figure 6: Verification results for measuring point P3 (see Table 2). Figure 7: Verification results for measuring point P4 (see Table 2). Table 5 presented a comparison of the obtained results in relative values with the results of previous studies [23] for two partial shading cases that can be considered as corresponding. It has been assumed that the shading of two whole PV cells corresponds to the shading of four halves of cells, and the shading of four whole PV cells corresponds to eight halves of cells.