## 4 Design
### Kinetic Photovoltaic Facade System  
To increase the energy self-sufficiency of a car park building, photovoltaics are installed on the building facade. Photovoltaics are located on the east, west, and south sides, excluding the north, where there is no direct sunlight. The vertical spacing of the photovoltaics on the southern building facade is 650 cm to avoid shadow interference between the panels. The standard size of a single photovoltaic panel is 20 cm in width and 100 cm in length. Photovoltaic panels of this standard are placed on an area measuring 68 m in width and 13 m in height on the south facade of the building (Figure 4). The photovoltaic system is designed to move monthly according to the optimal tilt angle (\(\beta\)) to maximize the efficiency of renewable energy generation. Equation (1) is a formula that derives the optimal tilt angle of the photovoltaic depending on the latitude of the target location [47]. \(\beta\) represents the optimal photovoltaic slope value, \(\varphi\) is the  
Figure 4: Principle of the kinetic photovoltaic facade system to be placed on the south side of the car park building (source: designed by the author). Figure 3: First floor plan (**top**) and section B-B (**bottom**) of a car park building with a 2.5% slope (source: designed by the author). latitude of the study area, and \(a_{1}\) and \(a_{2}\) are coefficients derived from the solar declination determined monthly according to the Earth's latitude. \[\beta=a_{1}+a_{2}\,\times\,\varphi \tag{1}\]  
This study was conducted in Seoul, the capital of South Korea (\(\varphi=37.5\)). The optimal tilt angles (\(\beta\)) from January to December according to Equation (1) are as shown in Table 1.  
The car park building has a total of four floors, with the east and west facades each measuring 28 m in width and 13 m in height. The size of the photovoltaic to be placed on the east and west building facades is the same as that placed on the south side (20 cm wide and 100 cm long) and is placed vertically in a unit module 1 m wide and 1.3 m long on the exterior wall of the building (Figure 5, left). To maximize the generation of renewable energy from photovoltaics, first, photovoltaics are placed according to the monthly optimal tilt angle (\(\beta\)) derived by Equation (1). Second, the photovoltaics should be tilted towards the south at an angle of \(\alpha\) to ensure maximum exposure to direct sunlight (Figure 5, right). The angle \(\alpha\), at which the east and west photovoltaics are tilted toward the south by the optimal tilt angle, was derived by a parametric algorithm built with Dynamo (Figure 6). The angle \(\alpha\) of the southward direction was input as a variable of the algorithm, and the amount of renewable energy generated by photovoltaics placed on the south and west facades was measured using Insight, a renewable energy generatio \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Month**} & \multirow{2}{*}{
\begin{tabular}{c} **Solar** \\ **Declination (deg)** \\ \end{tabular} } & \multicolumn{2}{c}{**Coefficients**} & \multicolumn{2}{c}{**Optimal Tilt Angle (deg)**} \\ \cline{3-5}  & & \(a_{1}\) & \(a_{2}\) & \(\beta\) \\ \hline January & \(-21.269\) & \(31.33\) & \(0.68\) & \(56.8^{\circ}\) \\ February & \(-13.289\) & \(16.25\) & \(0.86\) & \(48.5^{\circ}\) \\ March & \(-2.819\) & \(6.80\) & \(0.84\) & \(38.3^{\circ}\) \\ April & \(9.415\) & \(-6.07\) & \(0.87\) & \(26.6^{\circ}\) \\ May & \(18.792\) & \(-14.95\) & \(0.87\) & \(17.7^{\circ}\) \\ June & \(23.314\) & \(-19.27\) & \(0.87\) & \(13.4^{\circ}\) \\ July & \(21.517\) & \(-15.65\) & \(0.83\) & \(15.5^{\circ}\) \\ August & \(13.784\) & \(-4.23\) & \(0.75\) & \(23.9^{\circ}\) \\ September & \(2.217\) & \(6.42\) & \(0.77\) & \(35.3^{\circ}\) \\ October & \(-9.599\) & \(15.84\) & \(0.83\) & \(47.0^{\circ}\) \\ November & \(-19.148\) & \(23.61\) & \(0.84\) & \(55.1^{\circ}\) \\ December & \(-23.335\) & \(30.56\) & \(0.76\) & \(59.1^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}