## 3 Kinetic Facade Design and Operating Concept
### Kinetic Facade System Design and Solar Energy Generation  
In a kinetic facade system, for optimal solar energy generation, a solar panel is placed at the top and an aluminum panel with high reflectivity at the bottom. The upper solar panel is adjusted every month to the optimal tilt angle. With high reflectivity, the lower aluminum panel reflects indirect light to the solar panel (Figure 7).  
Figure 5: Example of solar energy generation (2691 kWh) of solar panel according to optimal tilt angle (59\({}^{\circ}\)) using Revit 2020 and Insight software.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Type** & **Parameter** & **Value** \\ \hline \multirow{4}{*}{Solar module} & Model & Q.PEAK DUO ML-G11.5/BFG \\ \cline{2-3}  & Length (mm) & 2000 \\ \cline{2-3}  & Width (mm) & 1000 \\ \cline{2-3}  & Power capacity (kW/unit) & 500 Wp \\ \cline{2-3}  & Efficiency (\%) & 21\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: Hanwha Q.PEAK DUO ML-G11.5/BFG solar module.  
Figure 6: Two types of solar panel.  
To determine the shape of the solar panel to be placed at the top of the kinetic facade system, Type A and Type B solar panels (Figure 6) were fitted to be suitable for the basic module (2 m \(\times\) 1 m) of the Won-Hyo and Cho-Rang Elementary School building facades. Using the Revit software, Type A (2 m \(\times\) 1 m) and Type B (1 m \(\times\) 2 m) kinetic facade systems were created on the south- and southeast-facing building facades, which receive optimal solar radiation. The amount of solar energy generated from January to December was calculated for the two types of kinetic facade systems using the Revit plug-in program Insight.  
Figure 8 shows a three-dimensional image of Won-Hyo and Cho-Rang Elementary school with Type A and Type B kinetic facade systems.  
In the case of Won-Hyo Elementary School, Type A solar panels placed on the south and southeast facades resulted in a total solar area of 420 m\({}^{-2}\). For Type B, the total solar area was 800 m\({}^{-2}\). The total solar energy generation from January to December 2021 was 5,663,989 and 10,143,682 kWh with Types A (420 m\({}^{-2}\)) and B (800 m\({}^{-2}\)) solar panels, respectively.  
In the case of Cho-Rang Elementary School, Type A solar panels placed on the south and southeast facades resulted in a total solar area of 820 m\({}^{-2}\). For Type B, the total solar area was 1640 m\({}^{-2}\). The total solar energy generation from January to December 2021 was 11,947,833 and 21,900,856 kWh with Types A (820 m\({}^{-2}\)) and B (1640 m\({}^{-2}\)) solar panels, respectively (Table 4).  
Figure 8: Simulation of solar energy generation in December 2021 with Type A and Type B kinetic facade systems installed on south- and southeast-facing building facades of Won-Hyo Elementary School in Seoul (upper image) and Cho-Rang Elementary School in Busan (lower image).  
Figure 7: Principle of kinetic facade system with solar panel according to optimal tilt angle (\(\beta\)o).  
For the case of Won-Hyo Elementary School, the energy generation per unit area (m\({}^{-2}\)) was 13,485 and 12,679 kWh-year\({}^{-1}\) for Types A and B solar panels, respectively. Whereas, for the case of Cho-Rang Elementary School, it was 14,570 kWh-year\({}^{-1}\) and 13,354 kWh-year\({}^{-1}\), respectively.  
In both elementary schools, Type A produced more energy than Type B.  
Figure 9 shows an image of the kinetic facade system installed on the Won-Hyo Elementary School and the installation process.