## 1 Introduction
Considering that the variable \"years\" is a categorical variable and \"PV electricity\" and \"POA radiation\" are numerical ones, a one-way analysis was performed. In this regard, the conditions for applying ANOVA were tested, and the O'Brien test was used to check the equality of variances. Thus, the originality of this study compared to similar ones is particularly reflected in the statistical analysis of the results (PV electricity and POA radiation) and the determination of statistical significance in the prediction model. Related to this, this study aims to apply the obtained results in integrating PV systems into the country's electro-power system to increase commercial PV systems applications in Serbia. Besides, this study provides data necessary for increasing the PV modeling accuracy by analyzing the accurate data. On the other hand, the obtained data are useful as guidelines for predicting, planning, and applying PV systems in other locations with similar climates. Besides, the study findings are also useful for degradations analysis of long-term PV system operations, especially in moderate continental climate regions. BackgroundThe main meteorological parameter that impacts the PV system operation is solar irradiation. It is generally known that the PV module operating voltage is logarithmic-dependent while the current has linear dependence. The main problem is the assessment of solar irradiation effects, which stems from solar irradiation being related to other factors affecting PV performance, such as the clear sky or diffuse radiation due to cloudy sky, low radiation in the early morning or late afternoon (high AM), angle-of-incidence (AOI) radiation effects, spectral response, etc. On the other hand, global solar irradiation is generally measured on a horizontal surface, while the maximum amount of incident solar irradiation is measured on an inclined surface (POA radiation) [10]. Recently, many analytical models have been proposed to estimate the amount of solar irradiation on horizontal (GHI) and inclined surfaces (POA irradiation). These models have different ranges and applicability to specific surfaces and locations. To find the most suitable solar model for a given location, the hourly results predicted by the available models are usually compared with the experimental measurements for the given locations [10; 37; 38]. In general cases, solar irradiation is usually measured as long-term data on the horizontal surface worldwide, and based on these measurements, solar databases are created. These solar databases, containing solar resource data obtained from the ground and/or derived from satellite imagery, are widely available as open-source or paid datasets. Based on these solar datasets and analytical models for the estimates of solar irradiation on the inclined surface, new bases are formed. The availability of solar databases containing POA irradiation data is limited and very low [10]. In accordance with the reasons mentioned above, the special importance of this study is that it contains long-term measurements of POA solar irradiation and electrical parameters of a grid-connected PV system and provides a statistical analysis of the long-term PV system operation in real conditions.