## 4 Discussion  
Locating suitable regions for installing PV plants is a pivotal step in planning energy management in infrastructure construction. This research proposes a geo-spatial analysis-based optimal-site selection approach considering unused sites near highway networks. It uses digital numerical maps and raster image-based PV power output maps with a GIS. In addition, the installation of PV plants in suitable areas is visualized in a BIM environment to apply the concept of energy management to managing civil infrastructure (i.e., highway networks). Previous studies could only investigate potential areas for PV plants nationwide using GIS and decision-making techniques (e.g., AHP). For instance, [PERSON] et al., 2020 [26] presented optimal site selection for PV plants using GIS and AHP techniques in the case of Turkey province. They dedicated that ten variables (e.g., solar energy potential, land cover, aspect, transformer centers, energy transmission lines, etc.) affect the site selection of PV plants, and they finally selected the candidate sites by restricting to the less clustered areas (i.e., area <20,000 m\({}^{2}\)). Also, [PERSON] et al., 2017 [27] searched the optimal sites for PV power plants using GIS and decision-making methods in four candidate sites in China. They considered economic profit (e.g., initial investment, total revenue, maintenance cost, outage cost), solar radiation, elevation, and temperature to execute the sensitivity analysis for site selection. On the other hand, this proposed approach uses PV power-output maps and thus, evaluates the potential production of PV power in suitable regions using the proposed geo-spatial analysis. The experimental results show that, by using PV power output maps, the proposed method can investigate suitable regions and evaluate the potential production values (e.g., a total value of 6,783,725 MWh) of PV power output  
Figure 10: Visualization of a suitable solar site in the BIM environment. in the vicinity of highway networks. The result also demonstrates that the differences of regional scales can affect the production of PV power (e.g., reduce the range of available production from 9.4-15.4 MWh to 11.2-14.4 MWh) in Table 2. This study also focused on the case study area of Ucheon-myeon (the total potential production value was 8227 MWh) to investigate the candidate sites analyzed on a nationwide scale in more detail. In addition, unlike recent studies that estimate and assess the solar power generation in a limited area such as roof [19] using BIM, this paper visualizes as families of solar panels generated from geo-spatial analysis on a 3D terrain map (toposurface map) with a BIM environment. In particular, this study visualized the installation of solar panels in the same environments as the realistic 3D terrain (including x, y, and z positions) near the highway by importing the amount of potential electricity that can be produced in the suitable sites by spatial analysis from GIS to BIM and documented the information of potential electricity generation in virtual space (i.e., BIM environment). The results show that the proposed approach enables the evaluation of power generation in the vicinity of highways as unused areas and explores suitable areas with high production efficiency from the distribution map and heatmap (Figure 8a,b), where the concentration of suitable regions for the construction of PV plants minimizes the additional installation of electrical facilities. In addition, visualizing the installation of solar PV plants near highway networks in BIM environments may help the energy management and planning of highway management by balancing the energy consumption during highway maintenance and solar power generation produced on the selected suitable sites for PV plants in this paper as building an independent smart grid system in BIM and GIS.