## 3 Results  
Monthly irradiation on the module plane at the considered location, in a warm summer continental climate according to [PERSON]'s climate classification, is shown in Figure 2. As can be seen, the most sunny period, beneficial for energy production from photovoltaics, was June to August in 2015. There are significant differences in the irradiation level in plane of module during the year: from a minimumof 20 kWh/m\({}^{2}\) in January to a maximum of 191 kWh/m\({}^{2}\) registered in August. The monthly average daily irradiation on module plane ranged from only 0.67 kWh/m\({}^{2}\) in January to 6.18 kWh/m\({}^{2}\) in August. In general, about 80% of yearly solar irradiation in Poland is received during the sunny and warm half of the year, from April to August. In order to better explain the on-site solar irradiance conditions, Figure 3 shows the accumulated irradiance distribution of incident global irradiation measured for period under study. As can be seen, irradiance conditions characterized by low values were the most frequent ones, resulting in median equal to 193 W/m\({}^{2}\). About 36% of the measurements have an irradiance lower than 100 W/m\({}^{2}\) and almost 98% of registered values are below 1000 W/m\({}^{2}\), however, about 17% of the results were characterized by a good or very good irradiance conditions, which varied from 700 W/m\({}^{2}\) to 1200 W/m\({}^{2}\). Simultaneously to irradiance measurements, the temperature of the modules was monitored in the given location (Figure 4). The values of temperature of the modules depend mainly on the irradiation and ambient temperature and have a great impact on the efficiency of the modules. Registered values of the modules temperature varied from about 0 \({}^{\circ}\)C in cloudy winter days to 60 \({}^{\circ}\)C in summer sunny days. The median of the module temperature for the studied period is equal to 30 \({}^{\circ}\)C.  
Figure 3: Accumulated percentage of collected incident global irradiation distribution according to irradiance levels measured in 2015. Figure 2: Monthly irradiation on module plane measured in 2015. The obtained results (Figures 2-4) indicate that due to seasonal variations, in considered location under moderate climate, STC used by manufacturers are rarely met. Only a small portion of instantaneous irradiance measurements are around 1000 W/m\({}^{2}\) and module temperature values quite often reach 15-48 \({}^{\circ}\)C in the analyzed period. An example of a hot sunny day, characterized by the high solar irradiance level reaching 1000 W/m\({}^{2}\) when the modules are heated by solar radiation up to 55 \({}^{\circ}\)C, shows that under this kind of real conditions, the power generated by pc-Si installation is lower compared to thin film technologies (Figure 5). For different analyzed PV technologies, the dependency of daily energy output as a function of daily average module temperature was shown in Figure 6. The increase of modules temperature caused by high incident solar irradiance during sunny days results in the decrease of energy production for all investigated technologies. As can be seen, thin film modules exhibit higher energy yield values than polycrystalline silicon ones. In particular, CIGS modules were characterized by the highest energy production in these specific--high temperature--conditions. The difference in daily energy production between CIGS and pc-Si modules during summer sunny days varies from 3.7% to 8.4%, while the CdTe modules produced from 1.7% to 6.1% more energy than pc-Si modules. The reason why CIGS installation exhibits better performance on sunny days can be explained as a result of double effect. Firstly, the temperature coefficient of power is lower than in case of pc-Si modules. Secondly, power  
Figure 4: Percentage distribution of module temperature measured in 2015. Figure 5: Normalized DC power generated by the PV systems of each studied technology. Maximum irradiance and temperature recorded for that day were 1000 W/m\({}^{2}\) and 55 \({}^{\circ}\)C, respectively.