## 3 Results and Discussion
### Performance Parameters
It should be noted that wind speed values for Ni\(\bar{\rm s}\) were taken from the website of the Hydrometeorological Institute of the Republic of Serbia ([[https://www.hidmet.gov.rs/ciril/meteorologija/klimatologija_godisnjaci.php](https://www.hidmet.gov.rs/ciril/meteorologija/klimatologija_godisnjaci.php)]([https://www.hidmet.gov.rs/ciril/meteorologija/klimatologija_godisnjaci.php](https://www.hidmet.gov.rs/ciril/meteorologija/klimatologija_godisnjaci.php)), accessed on 8 May 2023.). It was also observed that the ratio between the average monthly values of PR and the wind speed (v) follows the same trend over the 10-year measurements, as is the case with PV system efficiency. Performance comparison of grid-connected PV systems with similar installation, power (1-3 kW), and PV technology in the different climatic zone is given in Table 1[13; 22]. As the chosen PV systems, shown in Table 1, and PV system in Ni\(\bar{\rm s}\) have similar power and PV configurations, it can be concluded that PV system efficiency and PR are lower in countries with a subtropical climate due to the negative impact of higher ambient temperatures and, therefore, higher solar module temperatures. PV systems with other PV technology and higher powers, installed worldwide and shown in [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27], are not comparable to a given PV system in Ni\(\bar{\rm s}\). Figure 3.0 The ratio between the average monthly values of PV system energy efficiency (\(\eta_{\rm syst}\)) and the wind speed (\(v\)) for 10-year measurements. Statistical Analysis of PV System Electricity and Total POA Radiation Data during 10 Years of Measurements  
For statistical analysis of the results, the JMP Pro software is used [43]. The regression analysis is used for building a mathematical model for the prediction of PV electricity at a given POA radiation on a PV array. The model enables a specific value of POA radiation (independent variable) to calculate PV electricity (dependent variable) simply. The criterion for estimating the regression coefficients is a least square method. In order to assess the adequacy of a linear regression model, the statistical hypotheses about the model parameters are tested by \(T\)-test. To test hypotheses about the slope and intercept of the regression model, the error component in the model has to be normally distributed and also independently distributed. The significance of the regression is tested via Analysis of Variance (ANOVA). The existing significance shows that the model gives more information about the system than the simple average. The one-way ANOVA is also used for comparing the groups of data (groups is a categorical variables). The significance of the ANOVA shows that at least two groups have different means. ANOVA also uses to describe complex relationships between variables, as can be seen in the [36; 43; 44; 45; 46; 47]. As results in ANOVA do not identify which specific differences between pairs of means are significant, it is common to use post hoc tests to investigate differences between multiple groups' means while controlling for experimental error [47]. The PV and POA radiation are numerical variables. The relationship between numerical variables can be graphically shown via a scatter plot (Figure 8). A numerical representation that shows the strength of the relationship between numerical variables is the correlation coefficient. The resulting value of the correlation coefficient between two numerical variables, PV electricity and POA radiation on the PV array, is 0.90059, which shows that the relationship between these two variables is highly positive. The strong and positive relationship tendency between the two variables can also be seen in Figure 3.1 Such a high value of the correlation coefficient enables the formation of a regression model between the variables. A linear regression model, developed by the least squares method with R square and R square adjusted at 0.811062 and 0.809344, respectively.