2.2. Methodology
In order to determine a solar farm location, it is necessary to evaluate, combine and analysis many important criteria according to their different characteristics. These operations require a very complex process. Firstly, specific factors for the study area must be determined. As a multi criteria decision, solar farm location selection cannot be made based on a single factor; several factors must be taken into account in order to achieve the main goal. In general, defined criteria are divided into two groups as factors and constraints. A factor increases or decreases the suitability of an alternative considered, while a constraint limits the alternatives in question. In other words, restrictions are applied to determine which areas are not allowed for a particular activity (Afzali, et al., 2014; Reisi, et al., 2018). Current literature and legal regulations are very important for determining factors and constraints.
Table 2
Factors and sub-factors of solar farm site selection.
Goal | Factors | Sub-factors |
Land Suitability | (F1) Slope (%) | 1> |
| 1–2 |
| 2–3 |
3< |
(F2) Distance from transmission lines (m) | 2000> |
2000–5000 |
5000–8000 |
8000–10000 |
10000< |
(F3) Distance from surface waters (m) | 500–2000 |
2000–5000 |
5000–7000 |
7000< |
(F4) Distance from transformer center (m) | 3000> |
| 3000–6000 |
| 6000–9000 |
| 9000–12000 |
| 12000< |
(F5) Distance from residential areas(m) | 1000–2000 |
2000–3000 |
3000–5000 |
5000< |
(F6) Distance from roads and railways (m) | 100–1000 |
1000–2000 |
2000–5000 |
5000–8000 |
| 8000< |
Evaluation criteria including the factors and constraints were determined (Table 2 and Table 3). A factor is a criterion that increases or decreases from the suitability of a particular alternative for the activity under consideration (Motlagh and Sayadi, 2015).
Table 3
The constraints of solar farm site selection.
Constraints | Buffer of residential areas distance = 1000 m |
Buffer of roads and railways distance = 100 m |
Buffer of surface waters distance = 500 m |
Buffer of protection areas (archaeological sites, forest land and environmental protection area) distance = 1000 m |
Agricultural land classification = Grades I-II |
Six factors were determined for the study area based on various reasons such as literature review and expert opinions (Uyan, 2013; Uyan, 2017b; Watson and Hudson, 2015; Doorga, et al., 2019; Tahri, et al., 2015; Finn and McKenzie, 2020 ). Solar radiation value was not evaluated as a factor, because of the same values as 1650–1700 KWh/m2/year for all of the study area. Considered factors were listed below for this study and shown with buffer scores at Fig. 6 (Uyan, 2017b):
(F1) Slope (%)
Land levelling is required for the deployment of solar farms and a low slope topology is ideal for minimizing costs of land levelling (Ruiz, et al., 2020). Slope factor was grouped into four parts (< 1%, 1–2%, 2–3%, > 3%) and buffer zone scored as 1, 2, 3 and 4, respectively.
(F2) Distance from transmission lines (m)
Generated electric from a PV park must be connected to transmission lines. Therefore, a connection must be established between the solar farm and the transmission line. The proximity of the renewable energy facilities to be established to the transmission lines will both reduce the cost of establishing new lines and prevent transmission losses (Mensour, et al., 2019). Distance from transmission lines is divided < 2000 m, 2000–5000 m, 5000–8000 m, 8000–10000 m and > 10000 m buffer zone scored as 1, 2, 3, 4 and 5, respectively.
(F3) Distance from surface waters (m)
Proximity to surface waters is important in terms of environmental effect. Distance from surface waters is divided 1000–2000 m, 2000–5000 m, 5000–7000 m and > 7000 m buffer zone scored as 1, 2, 3 and 4, respectively.
(F4) Distance from transformer center (m)
Positioning solar power plants close to transformer centers both reduces the installation cost and prevents energy loss. In the study, for distance from transformer center < 2000 m, 2000–5000 m, 5000–8000 m, 8000–10000 m and > 10000 m buffer zone scored as 1, 2, 3, 4 and 5, respectively.
(F5) Distance from residential areas
It is undesirable for economic investments to be very close to residential areas due to many social and environmental negative impacts. Therefore, in this study, it was decided to establish solar farms at least 1000 m away from the residential areas. Residential areas with 1000–2000 m, 2000–3000 m, 3000–5000 m and > 5000 m buffer zone scored as 1, 2, 3 and 4, respectively.
(F6) Distance from roads and railways
The proximity to roads and railways will reduce the additional costs of infrastructure construction for the power plants to be established. In addition, being close to the roads for the operation and maintenance of these power plants is important in terms of ease of transportation. Distance from roads and railways with 100–1000 m, 1000–2000 m, 2000–5000 m, 5000–8000 m and > 8000 m buffer zone scored as 1, 2, 3, 4 and 5, respectively.
Economic investments are not desired to be too close to residential areas due to some social and environmental negative effects. Hence, a buffer of 1000 m was applied from residential areas. A buffer of 100 m was applied from roads and railways against the possibility of widening the roads and railways. Proximity to surface waters is important in terms of environmental effect. For this reason, a buffer of 1000 m was applied from surface waters. A buffer of 1000 m was applied in order not to damage the protected areas from solar field investments. The lands are evaluated between I and VIII classes according to their land use ability in Turkey. first class lands are the lands that can be cultivated in the best, easiest and most economical way without causing erosion. On the other hand, eighth class lands are areas that are not suitable for any agriculture (Tercan and Dereli, 2020). For this reason, grades I and II were constrained due to their high arable value. Grades III, IV, V, VI, VII and VIII were not constrained due to the lower fertility of the land.
GIS data sets of study area were conducted through collecting 1:50000 and 1:100000 maps from different organizations. Data collected from various institutions regarding the above-mentioned factors were converted into digital format using GIS. Slope maps were prepared based on SRTM (Shuttle Radar Topography Mission) data.
2.2.1. Multi-criteria decision making and Analytic Network Process (ANP)
In this study, using the ANP method, which is a component of MCE methods, a model for solar energy field location selection was created. MCE is a combination of analytical methods that help decision makers to solve problems by combining determined weighted criteria by experts. Various MCE approaches such as AHP, ANP, Best worst method, ELECTRE, VIKOR have been developed to assist in decision making and planning (Afzali, et al., 2014).
ANP is a MCE method that an improved form of AHP presented by Thomas L. Saaty (1996). Uyan (2013) explained AHP method, widely. The ANP method can significantly simplify decision-making processes where criteria have complex relationships. It also provides the evaluation of all relationships by adding interdependencies and feedbacks to the decision system (Aghasafari, et al., 2020). ANP models the problem as a network where nodes are grouped into clusters and the directed arcs correspond to relationships between the nodes. The purpose of the process is to prioritize all the nodes in a cluster. Normally, there is a set of corresponding alternatives for a decision problem, so the process prioritizes these alternatives to support decision making (Quezada, et al., 2021). ANP differs from AHP in that it uses a hierarchical structure rather than a top-down hierarchical structure. Steps of the ANP method are as follows (Özder, et al., 2019):
Step 1
Identifying the problem
Step 2
Determining relationships between factors
Step 3
Performing pairwise comparison
Step 4
Calculating of consistency ratio (CR)
Step 5
Creating Super Matrices in Order (Ozkaya and Erdin, 2020)
Unweighted Super Matrix: A supermatrix is actually a partial matrix, and each matrix section shows the relationship between two factors in a system. Each element is represented at one row and one respective column.
Weighted Super Matrix: If the column sum of any column in the composed supermatrix is greater than 1, that column will be normalized.
Limit Super Matrix: The weighted super matrix is then raised to a significantly large power in order to have converged or stable values. The values of this limit matrix are the desired priorities of the elements with respect to the goal. Therefore, the importance weights of alternatives or comparable factors are determined by the limit super matrix.
Step 6
Determination of the Best Alternative