## 4 Results  
### Results of Unpowered Area  
Some results of the analysis of the tunnels and shaded areas where power generation is not possible on the Donghae expressway are shown in Figure 5. The grey line running from northwest to southeast is the expressway, the rectangular area with rounded corners is the tunnel section (only the approximate size is shown), and the black grid cells represent the shaded areas. The length of each section of the Donghae expressway, the length of the tunnel, and the percentage of road length that cannot be developed are presented in Table 4. As shown in Figure 4, the tunnel length of Section A is 4.56 km, the tunnel length of Section B is 11.28 km, and the tunnel length of Section C is 8.41 km. The area that could not be developed because of the tunnel is approximately 20% of the total length of the Donghae expressway.  
Generally, tunnel segments and shaded areas are separated, but as shown in Figure 5, they overlap in some areas. This is because the study extracted them separately during the analysis process, and calculating and summing their lengths can cause an overlap. Therefore, in cases where the tunnel and shaded areas overlapped, this study considered all shaded areas as tunnel sections and excluded the results of the overlapping shaded areas.  
In the case of shaded areas, unlike tunnels, the position of the sun changes daily; therefore, areas where power generation is not possible vary. During the summer solstice, when the sun's altitude is the highest, the shaded area is relatively large, and during the winter solstice, when the sun's altitude is the lowest, the shaded area is small. Therefore, this study presents the results of the shadow analysis on the summer and winter solstices, when the difference in the shaded area based on the hourly position of the sun is the largest, as presented in Table 5. At this time, only the results from 7 a.m. to 6 p.m. on the summer solstice and from 9 a.m. to 5 p.m. on the winter solstice are shown, excluding the time when power generation is not possible because of insolation conditions. Therefore, the average shadow area per day on the summer solstice of the Donghae expressway was 4.56 km (Section A: 1.60 km, Section B: 1.88 km, and Section C: 1.08 km), and the average shadow length per day on the winter solstice was 16.77 km (Section A: 6.15 km, Section B: 6.29 km, Section C: 4.33 km). The shaded area on the road was longer on solstice days than on equinox days because of the low altitude of the sun. Therefore, the amount of shading is significantly influenced by season.  
The length of the section that could not be powered due to the tunnel was 24.25 km along the entire section of the Donghae expressway (123.98 km long), and the average value of the road length that could not be developed due to shadow was 4.56 km at summer solstice and 16.77 km at winter solstice. Notably, tunnels in the study area cause approximately 1.4 to 5.3 times more sunlight obstruction than shadows caused by terrain. In addition, the average ratio of the area that could not be developed because of tunnels and shadows to the total length of the Donghae expressway was approximately 23% during the summer solstice and 33% during the winter solstice. This is calculated by entering the aforementioned length of the tunnel, the average length of shadows on the summer and winter solstice, and the length of the Donghae expressway into Equation (1).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Item** & **Section A** & **Section B** & **Section C** & **Total** \\ \hline Expressway length (km) a & 35.98 & 53.61 & 34.38 & 123.98 \\ Tunnel length (km) b & 4.56 & 11.28 & 8.41 & 24.25 \\ Ratio (\%) b/a & 12.67 & 21.04 & 24.46 & 19.56 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Length and ratio of tunnels on the Donghae expressway.