## 5 Power Generation Performance Loss Factor of the BIPV System
### PCS Standby Loss  
The PCS installed in the BIPV system examined in this paper operated only if the output voltage of the PV array exceeded 190 V. As can be seen in Figure 11, when the solar radiation was 0-100 W/m\({}^{2}\) \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Efficiency (\%)**} & \multicolumn{6}{c}{**Before Cleaning**} & \multicolumn{6}{c}{**After Cleaning**} \\ \cline{2-11}  & **1** & **2** & **3** & **4** & **Avg.** & **1** & **2** & **3** & **4** & **Avg.** \\ \hline HR 0\({}^{\circ}\) & 3.8 & 3.9 & 4.0 & 3.7 & 3.9 & 4.8 & 4.6 & 4.9 & 5.0 & 4.8 \\ SI 30\({}^{\circ}\) & 3.5 & 3.4 & 3.5 & 3.4 & 3.5 & 4.0 & 3.9 & 4.0 & 3.9 & 4.0 \\ SV 90\({}^{\circ}\) & 4.4 & 4.5 & 4.5 & 4.4 & 4.5 & 4.6 & 4.5 & 4.7 & & 4.6 \\ WV 90\({}^{\circ}\) & 3.3 & 3.5 & 3.5 & 3.6 & 3.5 & 3.7 & 3.7 & 3.6 & & 3.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: PV array efficiency before and after cleaning. Figure 10: PV array efficiency before and after cleaning. Figure 9: Irradiation and module temperature of each arrays during the analysis period (1 h). it can be confirmed that the DC power generation was 0 W. This means that the PCS operation commenced when the irradiation intensity of the array having an installation capacity of 0.528 kWp was 100 W/m\({}^{2}\) or more. Therefore, it is impossible to utilize solar irradiation if the solar radiation intensity is below the level that can satisfy the driving condition of the PCS. This irradiation during standby mode varies according to the meteorological and installation conditions of the PV array, and it occurs mainly when irradiation is low or when there is a barrier, such as snow on the PV array even if the irradiation intensity is high. The measured data of SI 30\({}^{\circ}\) was used to analyze the PCS standby loss according to the meteorological conditions. The analysis was conducted by selecting the representative day; one day of June was nominated according to the sky condition. The representative day was selected based on the cloud cover, as listed in Table 7.  
Figure 11 shows the irradiation and output of the PV array of SI 30\({}^{\circ}\) according to the sky conditions. In the case of an overcast sky, the irradiation intensity was 100 W/m\({}^{2}\) or less most of the time, and the PCS was repeatedly operated and stopped. For a clear sky, most of the irradiation intensity was 100 W/m\({}^{2}\) or more, the irradiation intensity satisfied the driving condition of the PCS, so the PCS operated continuously. The analysis results for overcast sky and clear sky showed that the array of the south vertical plane satisfied the driving condition of PCS when the solar radiation intensity was approximately 100 W/m\({}^{2}\). The monthly ratio of solar irradiation during the standby mode of each array as the PCS standby loss was calculated in the same way, and the results are shown in Figure 12 and Table 8.  
The total amount of irradiation not used for power generation due to the automatic start/stop function of PCS among the amounts of accumulated irradiation obtained for one year under each installation condition was estimated to be 6.8% for HR 0\({}^{\circ}\), 4.9% for SI 30\({}^{\circ}\), 8.4% for SV 90\({}^{\circ}\), and 15.7% for WV 90\({}^{\circ}\). When the influence of snow during winter in the horizontal and south-inclined planes was excluded, the ratio was reduced to 5.1% and 4.6% for the horizontal and south-inclined planes, respectively. This means that 4.6% to 15.7% of the annual irradiation is not used for power generation depending on the installation conditions, due to the PCS standby loss. In particular, in WV 90\({}^{\circ}\), a large loss of 15.7% of annual accumulated irradiation occurred due to the installation location characteristics.