Operational power performance of south-facing vertical BIPV window system applied in office building

•Operational power performance of a-Si transparent vertical BIPV window is investigated.•Big decrease of final yield in vertical BIPV was shown between April and August in Korea.•Even short extrusion of louver next above BIPV can cause decrease in PV performance.•PR can be decreased even by the effect of diffuse radiation due to adjacent obstructions. The purposes of this study are to analyze the power efficiency of BIPV system under actual operating condition and to reveal the factors of performance decrease through annual monitoring of the south-facing vertical BIPV window system (the capacity of 10.6kWp) whose performance was affected by partial shading. The study first investigated the monthly PR of each inverter to verify what caused the decrease in power performance by analyzing PR variation. Then, the shading analysis was performed using a simulation to analyze the capture loss of measured power performance and ultimately to find out the effect by partial shading components such as small overhang louvers of each floor, obstructions of adjacent building, and nearby hillock. The one-year measurement of the power performance showed that the annual average reference yield was 2.15h/day and the final yield was 1.52h/day; moreover, it was analyzed that the annual average capture loss was 0.49h/day and the system loss was 0.14h/day. Monthly average reference yield in summer (between April and August) showed only 1.28h/day which was 54% lower than the other seasons with average 2.77h/day. The annual average of PR was 0.69 (the monthly maximum of 0.77 and minimum of 0.58); the average PR in the summer with low reference yield was 0.64, while the average PR for other seasons was 0.73. Whereas monthly variation of LS (system loss) did not show big difference of under 9%, monthly LC (capture loss) highly varied with fluctuation. These primarily arise from the effect of the partial shading and vertically installed angle of south-facing BIPV modules. The BIPV system consisted of four arrays and installed on the same south façade. However, the power performance analysis per array showed that each array had different performances. The arrays located above the facade had the highest PR, from 0.74, 0.75, 0.66, and 0.62 respectively in order. In addition, LS and LC analysis of each array showed that there was performance difference mainly by LC, due to the influence of an adjacent building located in the south. The analysis using the simulation showed the adjacent bui