# GIS-Based Solar Radiation Mapping, Site Evaluation, and Potential Assessment: A Review
## 4 Solar Potential Assessment Using GISs
### Shading Analysis Tool  
Surfaces and rooftops are shaded if the direct path of the light from the sun is obstructed. Shading of PV modules is a common phenomenon that can affect the performances of PV systems. As such, shading analysis is essential during solar PV project design or analysis since it is associated with solar access or unobstructed solar gains. In PV systems, it is important to analyze shading caused by surrounding objects (buildings) and/or vegetation. Several authors have employed the hillshade algorithm and analysis to compute shadow areas and sunshine hours. [PERSON] et al. [75] determined the shadow areas on rooftops to obtain the hourly sun and shade grayscale values to evaluate rooftop solar PV potential in Taiwan. A national-scale hillshade map was generated as a sun-shadow model showing the illuminance of each grid of the surface by setting the location of the assumed light source and calculating the related illuminance value between each grid and its neighboring grids. The preset conditions ranged from 0 (black; more shadowing) to 255 (white; less shadowing). The grayscale values were then integrated into binary images to calculate the shadow areas on rooftops. [PERSON] et al. [76] and [PERSON] et al. [77] analyzed shadows based on the location of the sun via hillshade analysis to examine the available building rooftop areas for solar PV installation. The altitude and azimuth of the sun were calculated every hour from 6 a.m. until 7 p.m. (when the sun is over the horizon) on the 15 th (when the sun is at the average position for the present month) of each month from January until December in Seoul. Using these input data, hillshade analysis was conducted on 12 days (on the 15 th of each month from January until December) in hourly intervals (from 6 a.m. to 7 p.m.), for a total of 156 times. Thereby, the unshaded rooftop area in which the solar PV system could perform at the optimal level without any disturbances by building shadows was extracted. Many researchers have used DSMs (or 3D building models) to examine regional shadow characteristics. [PERSON] and [PERSON] [78] conducted a simple shadow analysis to evaluate rooftop PV electricity generation systems to establish a green campus in a GIS environment. Prior to shadow analysis, 3D modeling of the study area was performed using a DEM (0.1 m grid spacing) easily accessed and building height data. As mentioned above, since the DEM data only describe the relief of the natural terrain, the DEM and building height data were integrated to create 3D building data. Subsequently, shadow analysis was conducted using the solar radiation tools in ArcGIS to analyze the yearly shadow patterns based on the changes in the angle of the sun (Figure 8). Locations, that were unaffected by shadows for more than 9 h/day, were regarded as usable areas for a rooftop PV system at the university. [PERSON] et al. [1] developed a PV analyst that couples ArcGIS with a transient systems simulation (TRNSYS) to assess the distributed PV potential in urban areas. In this study, a DSM was input into the area solar radiation model of the solar radiation tools in ArcGIS to calculate the sun hours, which is the duration (in hours) of direct solar irradiation at each grid cell in the DSM. The duration of direct incoming solar irradiance from 9 a.m. until 3 p.m. (solar time) at the winter solstice was analyzed to fulfill the requirement that the PV systems to be installed in the study area would work solar time throughout the year without shading effects. The areas satisfying this requirement were regarded as usable areas for rooftop PV systems on each building in the study. In a few studies, detailed field investigations using fish-eye lens cameras as well as regional shadow analysis using DSMs were performed. [PERSON] and [PERSON] [79] analyzed the usable area for installing a PV system, considering the surrounding topography, for PV potential assessment at the tailing dam of an abandoned mine.