## 6 Discussion and Conclusions  
This study examined the power generation performance of a BIPV system depending on the installation conditions (horizontal, south-inclined, south-vertical, west-vertical), and the power  
Figure 14: Power conditioning system (PCS) conversion efficiency-corrected performance ratio (PR) of each array. Figure 13: PCS conversion efficiency of each array. loss factors based on the long-term measured data of a BIPV system located in Korea. The power performance loss factors were analyzed by the module surface temperature, dust and soiling, PCS standby loss, and DC-AC conversion loss. Power performance analysis was conducted through a performance ratio of IEC 61724. The analysis of the final yield showed that the final yield of HR 0\({}^{\circ}\) was 3.03 h/day. This was 2.2 times larger than that of WV 90\({}^{\circ}\), which showed the lowest final yield (1.36 h/day). In addition, the PR ranged from 66.8(%) to 69.5(%) depending on the installation conditions, and HR 0\({}^{\circ}\) showed the highest power generation performance. Compared to the results of a previous study of the power generation performance of the BIPV system composed of the same module and PCS [7], the system loss was relatively higher and the PRs of all arrays were less than 70(%). An analysis of the power performance loss factors showed that the annual power performance loss due to the increase in module surface temperature ranged from 2.2(%) to 6.0(%). Regarding the losses due to the temperature rise, SI 30\({}^{\circ}\) showed the highest loss ratio of 6.0(%), followed by HR 0\({}^{\circ}\) (4.6(%)), SV 90\({}^{\circ}\) (3.9(%)), and WV 90\({}^{\circ}\) (2.2(%)). HR 0\({}^{\circ}\) showed a distribution of low temperatures throughout the year in the module surface temperature, but it showed the second highest power generation performance loss after SI 30\({}^{\circ}\). Based on the analysis results, this large power performance loss was because although the average monthly temperature was low, the time when the temperature was 50 \({}^{\circ}\)C or higher was longer in HR 0\({}^{\circ}\) than in the other PV arrays. The effects of dust and soiling on power performance losses were analyzed by comparing the power generation efficiencies before and after cleaning on the representative day. The efficiency of each PV array before cleaning was 3.9(%) HR 0\({}^{\circ}\), 3.5(%) for SI 30\({}^{\circ}\), 4.5(%) for SV 90\({}^{\circ}\), and 3.5(%) for WV 90\({}^{\circ}\). After cleaning, the efficiency of PV array was increased to 4.8(%) for HR 0\({}^{\circ}\), 4.0(%) for SI 90\({}^{\circ}\), 4.6(%) for SV 90\({}^{\circ}\), and 3.7(%) for WV 90\({}^{\circ}\). Compared to the efficiency values before cleaning, the performances of SV 90\({}^{\circ}\) and WV 90\({}^{\circ}\) were improved by approximately 5.7(%) and 2.2(%), respectively, whereas that of HR 0\({}^{\circ}\) and SI 30\({}^{\circ}\) were improved by 23.1(%) and 14.3(%), respectively. These results suggest that continuous management is required to maintain the initial power generation performance of PV systems installed on a horizontal or inclined plane. An analysis of the power performance losses due to the PCS standby loss was conducted using the accumulated irradiation of the time when the PCS would not operate. The total ratio of the irradiation that was not used for power generation because the automatic start/stop function of the PCS was analyzed 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 was excluded, the ratio was reduced to 5.1(%) for HR 0\({}^{\circ}\) and to 4.6(%) for SI 30\({}^{\circ}\). These results show that 4.6-15.7(%) of the annual irradiation is not utilized for power generation due to the PCS standby mode. The BIPV system investigated in this study was connected to a PV array with a capacity of 17.6(%) of the rated capacity of the PCS.