## 3 Results and Discussion
### Performance Parameters
The obtained model Equation (2) is:  
Figure 3.2  
where \(y\) is PV electricity in kWh, while \(x\) is the total POA radiation on PV array in kWh. This model, based on data obtained over 10 years of investigation, can be used for prediction PV electricity value for the known POA radiation value. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Location**} & **Power** & **PV** & **Final Yield** & \begin{tabular}{c} **System** \\ **(h/d)** \\ \end{tabular} & **PR (\%)** & **CF (\%)** & **Climate** & \
\begin{tabular}{c} **Year/Duration** \\ **(years)** \\ \end{tabular} \\ \hline
\begin{tabular}{c} Serbia—current \\ study \\ \end{tabular} & 2 & c-Si & 3.23 & 10.49 & 87 & 13.45 & Temperate/continental & 2022/10 \\ \hline Ireland & 1.72 & c-Si & 2.4 & 12.6 & 81.5 & 10.1 & Temperate/oceanic & / \\ \hline Norway & 2.1 & p-Si & 2.55 & 13-14 & 83.06 & 10.58 & Temperate/subarctic & / \\ \hline Brazil & 2.2 & p-Si & 4.6 & 13.3 & 82.9 & 19.2 & Tropical/subropical & / \\ \hline China & 3 & p-Si & 2.86 & 10.73 & 80.6 & / & Humid subtropical & 2009/3 \\ \hline Morocco & 2.4 & c-Si, p-Si & 4.34 & 11.67 & 76.7 & 18.16 & Hot semi-arid subtropical & 2018/4 \\ \hline Morocco & 2.04 & c-Si & 4.34 & 11.7 & 76.7 & / & Hot semi-arid subtropical & 2015/2 \\ \hline India & 2 & p-Si & / & / & 70 & / & tropical & 2019/1 \\ \hline Spain & 2 & / & & 7.11 & 64.5 & & Subtropical/Mediterranean & 1997/1 \\ \hline Turkey & 2.35 & c-Si, p-Si & / & 13.26 & 91 & / & Humid subtropical & 2014/1 \\ \hline Oman & 1.4 & p-Si & / & / & 84.6 & 21 & Hot desert & / \\ \hline Korea & 3 & c-Si & / & 7.9 & 63.3 & 11.5 & Humid subtropical & 2003/1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Performance comparison of grid-connected PV systems power of 1–3 kW with similar installation and crystalline-Si technology in different climatic zone [13; 22]. In order to test validity of the model, an ANOVA was conducted. The analysis of variance of the regression model is given in Table 2, while the parameter estimates are given in Table 3.  
The ANOVA showed that the model is statistically significant \(\alpha=0.05\) with a \(p\)-value less than 0.001, which means that the model provides significantly more information than the simple average. The T test was used to test the significance of the intercept and x variable, and both are statistically significant with the \(p\) value less than 0.001. Figure 9 considers POA radiation on PV array during the months measured over 10 years. In Figure 9, the black line is the mean of the data. The top and bottom of green diamonds represent the confidence interval for each year. The middle line across the diamond represents the mean of the POA radiation for each group (month). The circles represent the results of Tukey-Kramer test, and circles with the same color are statistically significantly different. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Source** & **DF** & **Sum of Squares** & **Mean Square** & **F Ratio** \\ \hline Model & 1 & 421,038.40 & 421,038 & 472.2001 \\ Error & 110 & 98,081.77 & 892 & Prob\textgreater{} F \\ C. Total & 111 & 519,120.17 & & \textless{}0.0001 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Analysis of variance of the regression model. Figure 8: Scatter plot of two numerical variables, PV electricity and POA radiation on PV array with fitted line—red line. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Term** & **Estimate** & **Std Error** & **t Ratio** & **Prob \textgreater{} |t| \\ \hline Intercept & 58.326117 & 7.002889 & 8.33 & \textless{}0.0001 \\ POA radiation on PV & 0.0685116 & 0.003153 & 21.73 & \textless{}0.0001 \\ array (kWh) & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameter estimates. The O'Brien test for checking equality of variances, with a \(p\)-value of 0.0692, shows that based on the data, there is no evidence that shows statistically unequal variances between the groups.