*3.1. Power Generation Interdependence on Solar Irradiance*

The power generation performance of the BIPV system and solar irradiance were examined for 2.5 years. To elucidate the diurnal cycles of the two parameters, Figure 3 represents two selected days, namely 14 February and 2 June 2021, with the graphs depicting the data on a minute basis. Power generation generally followed the solar irradiance trend, as PV modules use solar irradiance as their energy source to generate electricity. The different solar irradiance values between the two days are mainly due to seasonal differences. In South Korea, February is winter, and June is summer, characterized by different sun paths and, thus, different irradiance intensities [8]. The total generated power and solar irradiance for each month are shown in Figure 4, with more detailed data from 2020 until the middle of 2022 shown in Table 2. Power generation and solar irradiance exhibited similar trends, with fluctuations in solar irradiance being accompanied in most cases by proportional fluctuations in generated power. The detailed power generation and solar irradiance values in Table 2 reveal that the highest power generation occurred in the earlier part of each year, with the highest power generation being evident in April or May. Total solar irradiance exhibited a slightly shifted trend, with the highest solar irradiance observed in the months of May to July of each year except in 2020.

**Figure 3.** Daily power and solar irradiance on (**a**) 14 February 2021 and (**b**) 2 June 2021.

**Figure 4.** Total generated power and solar irradiance in (**a**) 2020, (**b**) 2021, and (**c**) 2022.


**Table 2.** Total average generated power and solar irradiance from January 2020 to June 2022.

Solar irradiance variations throughout the year were attributed to changes in the solar position. The path of the sun is longer in spring and summer, resulting in longer days and higher total solar irradiance values [8]. The uncertain nature of the weather resulted in several cloudy and rainy days affecting the amount of solar irradiance throughout the observation period, with the relatively lower values in July 2020 and June 2022 being attributed to increased occurrences of such uncertain weather conditions. As solar irradiance is among the main influences on a PV system's power output, the power generation data followed the fluctuations in solar irradiance input throughout the observation period, and this agrees with Tina et al., whose floating PV system produced power generation values proportional to the solar irradiance values during optimal PV system operation [8]. However, the highest generated power value was not produced during the solar irradiance peak, as observed in May 2020 and July 2021, and this was due to another factor, namely system temperature, influencing the power generation of the PV modules [7,8,14]. The effect of temperature on the BIPV system's performance is discussed in the following section.
