Study Area
The study area of this research is the Mashhad County of Khorasan Razavi Province of Iran located between 35º 43′ 9″ to 36º 58′ 4″ N and 59º 3′ 48″ and 60º 36′ 21″ E, with a total area of 10326 km2 (Figure 1). Elevation ranges between 950 m and 1150 m above sea level. The region is characterized by a semi-arid climate going under annual precipitation of 1509 mm with an annual average temperature of 15.7 ºC. The temperature reaches its maximum of 43ºC in July and its minimum of -23 ºC in January. Most of the precipitation is concentrated in the Winter and Early Spring, indicating a Mediterranean Climate. Mashhad county has a complex geological setting with several active faults within its boundaries. Mashhad is bounded to the north by the Kalat and Dargaz, to the east by the Sarakhs plains, to the south by the Torbat Heidarieh, and to the west by Neishabour. Based on the results of the census conducted in 2010, Mashhad is home to 3070000 people mostly concentrated in cities. Mashhad plain is a surrounded valley 100 km in length and 25 km in width as part of the Kashafroud Watershed. Geologically, the region is mostly covered with the Karstic and evaporative Mozdouran Sedimentary Carbonates with suitable underground reservoirs. The water table has been dropping over the past decade and most of the rivers and streams have dried out. The location of the study area is illustrated in Figure 1.
Iran is geographically located in a suitable area for photovoltaic power generation. The data from the global solar energy atlas https://globalsolaratlas.info/ for the monthly and hourly distribution of solar energy in the study area in figures 2 and 3 shows that most months of the year enjoy 12-15 hours of sunshine which make them ideal for energy production.
The monthly distribution of solar energy output for the study area also shows that spring and summer are the ideal months for energy production. The highest solar energy output belongs in August by 181.9 MW.h solar energy output.
Methodology
Site Suitability Analysis
To locate suitable areas for solar panel installation, the following set of indicators (table 1) and thresholds were adopted. In this research, we have developed a tool for solar panel installation in Mashhad County of Iran. The first stage of the work includes removing unsuitable areas for the installation. These areas included built-up and environmentally protected areas. Since there is no special water body in the study area, we excluded this indicator from the data analysis. We also excluded slopes greater than 10% and elevations above 2000m since they induce limitations for site preparation and installation. The remaining area is evaluated using a multi-criteria decision-making method.
Table 1. Criteria and indicators for selecting suitable sites for wind energy production According to (Sánchez-Lozano et al., 2013)
|
Criteria
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Range
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Environmental
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Residential areas
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>2000 m
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Highways and roads
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>500
|
Railways
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>300
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Rivers
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>500
|
Environmental Protected Areas
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>2000
|
Faults
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>500m
|
|
Land Cover
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Bare lands/Rangelands
|
Physiographic
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Elevation
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<2000
|
Slope
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<15%
|
|
Direction
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Flat areas, southern and eastern aspects
|
Climatic
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Solar Irradiation
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No limitation
|
|
Temperature
|
Lower average maximum temperatures
|
Data Collection
To combine different criteria and indicator layers, data were processed as indicated in the diagram below. Data for topography was downloaded from Alos DEM 12.5 m from Alaska State Data Hub at asf.alaska.edu. Data for environmentally protected areas was obtained as shapefiles from the local environment protection office. Data for railways and roads and residential areas were downloaded from https://mapcruzin.com/free-iran-arcgis-maps-shapefiles.htm. Data for fault lines were obtained from the Department of Geology Surveys and Mineral Exploration of Iran. Data for windspeed was obtained from Global Wind Atlas available at https://globalwindatlas.info/ for the altitudes of 50 m and 80 m. To generate buffer layers for thematic layers, the Euclidean Distance Tool in ArcGis 10.3 was used.
Methodology
We used a combination of the MCDM-AHP model for locating suitable spots for solar panel installation. The following diagram was used for suitability analysis. The thematic layers were separated into limiting and factor layers. The decision-making criteria were defined based on expert knowledge and group discussions. The layers were standardized, weighted, and combined to find the final suitable areas. The detail of each step is given in the following sections.
Normalization
To combine the RS thematic layers, they must have a common scale of measurement. The process of converting data into a comparable range of values is called standardization. There are several standardization procedures such as Min-Max, Z-score, Median Normalization, Fuzzy Transform, etc. (Jain et al., 2005). We used the Fuzzy transform method for data normalization into a range of 0 and 1. The Fuzzy Transform was first introduced by Zadeh (1996) to convert verbal expressions into mathematical equations. The fuzzy set X has its fuzzy subset A which is defined by a membership function which maps each element in A onto a real number between 0-1. Since we were only interested in the lower and upper part of the data, indicating severe conditions conducting for desertification, the Large and Small fuzzy membership functions in ArcGIS were applied. The Large fuzzy membership function is defined as:
Whereis the spread parameter defining the shape and character of the transition zone and is the midpoint, after which numbers have a higher possibility of becoming a member of the set (Jafari Shalamzari et al., 2019).
And the Small fuzzy membership function is defined as:
In the small function, numbers after the midpoint have a lower possibility of becoming a member of the set. Here, TCI, SDI, VCI, and salinity layers were standardized using the large function, while EVI and Precipitation layers were standardized using the small function.
Combination
The final desertification intensity was calculated using the weighted overlay combination as (eq. 7):
Whereis the weight assigned to each layer, andis the fuzzy layer.