## 3 Results  
Table 2 presents a summary of the results of verification measurements and provides references to drawing numbers with comparative charts and adopted methods of shading of the tested PV module. The first measuring point P1 (first item in Table 2) was to verify the correctness of the adopted model structure without the shading effect. In the first column of Table 2, reference is made in brackets to drawing numbers with the results of verification tests for all five measuring points P1-P5. The third column of Table 2 gives references to the respective shading case shown in Figure 3, and the last fourth column gives the values of solar radiation intensity that were measured without shading and with partial shading (the last two cases do not concern the measuring point P1). Figures 4-8 present charts of current-voltage characteristics and power charts for all tested cases of verification tests. The quality of the modules under STC is determined by calculating the fill factor \(FF\) (3) of the I-V characteristic. In the case of partial shading, such an assessment would be unreliable, \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Measurement Points:**} & **PV Module** & **Number of Shaded PV** & **Solar Surface Irradiance** \\  & **Temperature** \(T_{M}\)**, (°C) & **Cell Halves (pcs.)** & **Unshaded/Shaded** \\  & & & **\(E_{\text{,}}\) (W-m-2)** \\ \hline P1 (Figure 4) & 35.5 & 0 \({}^{1}\) & 810/0 \\ P2 (Figure 5) & 36.9 & 4 (Figure 3a) & 809/444 \\ P3 (Figure 6) & 36.2 & 8 (Figure 3b) & 808/443 \\ P4 (Figure 7) & 33.5 & 12 (Figure 3c) & 805/442 \\ P5 (Figure 8) & 32.8 & 24 (Figure 3d) & 802/432 \\ \hline \hline \end{tabular} \({}^{1}\) Measurement without shading.  
\end{table} 
Table 2: List of parameters and conditions of verification measurements with links to relevant drawing numbers with the results of verification tests. Figure 3: Shading places of the PV module from half cells for the four considered cases verified: (**a**) shading of four halves of PV cells; (**b**) shading of eight halves of PV cells; (**c**) shading of twelve halves of PV cells; and (**d**) shading of twenty-four halves of PV cells. because the I-V characteristics are significantly deformed from the correct ones and the _FF_ would be greatly underestimated [32]:  
\[FF=\frac{P_{MPP}}{I_{\text{SC}}U_{\text{OC}}}=\frac{I_{MPP}U_{MPP}}{I_{\text{SC}}U _{\text{OC}}}, \tag{3}\]  
where signs in the Formula (3) are in accordance with that given in Table 1.  
There is also a relationship between the fill factor (_FF_) of the I-V characteristic and the efficiency (\(\eta\)) of the PV module according to Formula (4):  
\[\eta=\frac{P_{MPP}}{ES}=\frac{I_{MPP}U_{MPP}}{ES}=FF\frac{I_{\text{SC}}U_{ \text{OC}}}{ES}, \tag{4}\]  
where the surface area of the PV module (_S_) is calculated based on the external dimensions (shown in Table 1) and does not take into account the spacing between the halves of the PV cells. Figure 4 graphically presents the results of the verification of simulation tests in relation to the measurements of the modeled PV module without shadowing. In Table 3, relative errors in the comparison of fundamental parameters of I-V characteristics and the values of the _FF_ and \(\eta\) coefficients were calculated according to Formulas (3) and (4) for the first measuring point (P1 in Table 2). These calculations determine the accuracy of the method used to model the PV module from half cells, and the maximum relative errors were less than 5%. The comparison of the I-V characteristics in Figure 4 corresponds to the changes resulting from the temperature difference, and therefore this is due to the inaccuracy of the temperatures assumed in the model. The shape of the I-V characteristic made by the I-V 400 meter in relation to the one obtained as a result of the simulation suggests that the temperature was lower during the measurement. For the other measurement points (P2-P5 in Table 2) such calculations would not be correct because there are local extremes on the power graphs (Figures 5-8).