Determining optimal solar power plant (SPP) sites by technical and environmental analysis: the case of Safranbolu, Türkiye

Solar energy is among the sustainable and renewable energy sources that has become an important and inevitable part of our lives today. It is of great importance to consider economic, environmental, and social factors in determining the installation locations of solar power plants (SPP). In this study, we aimed to determine suitable areas where SPP can be established in Safranbolu District by using the fuzzy analytical hierarchy process (FAHP), which is one of the multiple criteria decision making (MCDM) method together with Geographic Information Systems (GIS), to enable the decision-makers to express their preferences in approximate or adaptable ways. The criteria addressed in the technical analysis process were also determined by supporting the basic principles of impact assessment systems. Within the scope of the environmental analysis, the relevant national and international legal frameworks were also examined and the legal constraints were identified. Thus, in the process of determining the optimal areas for SPP, it has been attempted to produce sustainable solutions that are expected to have minimal impact on the integrity of the natural system. This study was carried on within a scientific, technical, and legal framework. According to the results obtained, the Safranbolu District had low, medium, and high sensitivity properties for SPP construction, and the areas suitable for SPP construction provided medium and high sensitivity of 10.86% and 27.26% correspondence detected according to the Chang (Eur J Oper Res 95(3): 649-655, 1996) and Buckley (Fuzzy Set Syst 17(3): 233-247, 1985) methods, respectively. There are very suitable areas for SPP installations in the central and western parts of Safranbolu District, and there are also areas suitable for SPP installation in the northern and southern parts of the district. Thanks to this study, suitable SPP establishment areas were determined for the under protection in a location in Safranbolu where clean energy is needed. It was also observed that these areas do not conflict with the basic principles of impact assessment systems.


Introduction
It is important to use alternative and renewable energy sources instead of fossil fuels in sustainable electrical energy production (Tasri and Susilawati 2014;Can 2019;Yalçınkaya 2022). In meeting and generating the everincreasing demand for electrical energy, fossil fuels, which have started to be depleted, are now being replaced by alternative economic, renewable, and environmentally friendly energy sources (Munteanu 2007;Wang et al. 2018;Can and Erbıyık 2020).
Within the framework of the sustainable development approach, the use of renewable energy resources in the process of meeting the electricity demand, problems such as destruction of natural system integrity, climate change, Responsible Editor: Philippe Garrigues and environmental pollution are considered within a certain framework. In other words, utilization of renewable energy resources in electricity generation does not mean zero environmental destruction. Of course, depending on the location of the study area, it is likely that there will be a loss of area of varying size and a negative impact on environmental components, natural and cultural landscapes, and the biological lives of local people. However, it should be emphasized at this point that the production of energy based on renewable resources supports a more sustainable supply of electricity to society. The use of renewable energy in the energy production reveals the necessity of conducting the relevant decision-making processes in an ecologically based framework. Thus, in addition to obtaining clean energy, natural, cultural, and social environmental components are considered during the site selection and determination of connection routes during the installation phase of the facilities (Al-Mulali et al. 2016;Jebli and Youssef 2017;Rehman and Khan 2017;Solangi et al. 2018;Wang et al. 2018;Yalçınkaya 2022). Solar energy, one of the renewable energy sources, is an inexhaustible and clean energy source. It does not contain environmental pollutants such as carbon monoxide (CO), sulfur, smoke, gas, radiation, odor, and sound (Çağlayan et al. 2014). The areas of use of solar energy can be summarized as electricity generation, heating, cooling, drying, lighting, energy supply to calculators, clocks and traffic signal lights, hot water production, water distillation, charging cell phone batteries and other portable devices, cooking, artificial satellites and solar towers, and solar cars and aircraft (Alternatürk 2022).
In this study, to increase the electricity generationinstalled capacity of the Safranbolu district of Karabük province located in the Black Sea Region of Türkiye and the share of solar power plants (SPP) in this installed capacity, it is aimed to find suitable SPP areas by using the geographic information systems (GIS)-based fuzzy analytical hierarchy process (FAHP) method, which is an effective tool for properly planning (Karabulut et al. 2022;Esmaeilpour Poodeh et al. 2022;Zhang et al. 2022) to utilize solar energy, one of the renewable energy sources.
The FAHP method was particularly preferred since the widespread use of the analytical hierarchy process (AHP) and FAHP methods in the creation of GIS-based suitability maps in the literature (Keskin Citiroglu and ARCA 2022) and since the decision-maker has a more flexible decision environment when analytical solutions are made with fuzzy logic. The selection of a suitable location for the potential SPP installation in the Safranbolu District was created with the GIS-based multiple criteria decision making (MCDM) method since it consists of a system that produces useful solutions in managing multiple selection criteria. In this context, solar radiation, distance to power distribution centers (PDCs), slope, aspect, land use, distance to road lines, distance to streams, geology, distance to fault lines, and distance to residential areas were used as data layers. All factors used in the study were produced in raster structure using GIS software, and fuzzy number equivalents and pairwise comparison matrix fuzzy numbers were obtained. The weight values of each factor were determined by the FAHP method. After this stage, the consolidation analysis and the classified criteria maps were combined to obtain a suitability result map showing the most suitable areas for SPP. Although there are many studies in the literature using FAHP, Bakır and Atalık (2021) integrated FAHP and fuzzy measurement of alternatives and ranking according to the compromise solution (FMARCOS) method in their study. Alosta et al. (2021) used AHP and ranking of alternatives through functional mapping of criterion sub-intervals into a single interval (RAFSI) model to choose the optimal location of emergency medical service in Libya. Karamaşa et al. (2021), on the other hand, used neutrophisophic AHP to prioritize factors to select the right logistics service provider. In the process of determining the optimal areas for SPP, the environmental approach was considered in the technical analyses, and the principle of environmental impact assessment (EIA) was also considered in determining the criteria in question. Solar energy, which is among the various alternative sources in Türkiye in terms of renewable energy resources, should be evaluated and used with an environmentalist approach in line with the sustainability principle as other renewable energy sources in terms of the country perspective. In this framework, EIA is a very effective legal tool and will contribute to the site selection for SPP by adopting the principle of sustainability. The optimal areas to be determined for the installation of the facility should have qualities such as the distance to residential areas, the absence of rare and endangered endemic species that may be damaged in the immediate vicinity, easy accessibility of the site, flat topography, and proximity to the energy transmission line. Impact assessment systems are the most effective tools for achieving sustainable development goals. "Impact assessment," conceptually investigated on the basis of "affectingeffect-affected," includes components that vary depending on space and time (Fig. 1).
The strategic environmental assessment (SEA), another legal instrument for environmental assessment in Türkiye for ensuring cumulative environmental management during sectorial planning processes, has been defined as an assessment process that guides sectorial investments and assesses the possible environmental impacts of decision-making mechanisms of up-scale policy documents. The SEA regulation published and enacted in the Official Gazette No. 30032 dated April 8, 2017 is currently effective in Türkiye (Yalçınkaya 2019(Yalçınkaya , 2022Geißler et al. 2021;Partidário 2021). According to the legal framework, SEA processes in the investment-based sectors such as the energy sector, which began to be implemented officially on January 1, 2023 under Provisional Article 2 of the SEA regulation. However, this practice is due to the lack of infrastructure and human resources. In another words, no SEA processes are experienced in the energy sector for solar power plants except for the EIA process in Türkiye.
EIA, which is legally applied to decision-making processes, is an instrument that aims at sustainability in sectoral land use decisions. For investment projects, an EIA application file must be prepared and submitted to the Directorate General of Environmental Impact Assessment, Permits and Inspections of the Ministry of Environment, Urbanization and Climate Change. The Regulation on Environmental Impact Assessment (EIA Regulation) currently in force in Türkiye was published and enacted in the Official Gazette No. 31907 dated July 29, 2022. Annex I of the Regulation, as amended (Official Gazette No. 30077 of May 26, 2017), includes "solar power plants with 20 hectares and above or with an installed capacity of 10 MWm or more" among the list of projects for which environmental impact assessments (EIAs) are to be implemented (EIA Regulation Annex 1). To be understood here, solar panel investments above a given threshold are subject to an EIA process.
The list of projects to which selection and elimination criteria are to be applied contained in Annex 2 of the EIA Regulation includes power plants with 2 hectares and above or with an installed capacity of 1 MWm or more among the list of projects. For such facilities, as well as for projects that fall outside the scope of the EIA Regulation (i.e., solar power plants with less than 2 hectares or an installed capacity of less than 1 MWm), a project presentation file must be prepared and submitted to the relevant units of the Ministry of Environment, Urbanization and Climate Change. Should an "EIA Not Required" decision be issued, the construction process can go ahead. However, if it is decided that an EIA is required, then the project is subjected to an EIA process in the same way as facilities that meet the criteria in Annex 1.
SPPs to be established in Safranbolu that is a touristic and historical city and at least meeting the residential energy needs from solar energy will provide a healthy environment and clean and cheap energy supply in Safranbolu.
A novelty of this article is that-thanks to this studysuitable SPP establishment areas were determined for the under protection in a location in Safranbolu where clean energy is needed. Additionally, re-evaluation of these areas with the basic principles of impact assessment systems is another innovation. In other words, this study was carried on within a scientific, technical, and legal framework. Another novelty of this article is that solar radiation and geology factors, which are not often used in such studies, are considered as parameters.

Study area
Safranbolu is one of the 6 districts of Karabük Province located in the Black Sea Region in Türkiye. Karabük Province and Yenice and Ovacik Districts are located in the south Kastamonu Province and Eflani District in the east and Bartın Province in the north and the west. Figure 2 shows the location map of Safranbolu District, which is the study area.
Safranbolu District, which has approximately 3000 years of historical past and historical architecture, was included in UNESCO's World Heritage List on December 17, 1994 and hosts 1125 of the approximately 50,000 cultural and natural assets that need to be protected in Türkiye. Therefore, it is a museum city. For this reason, Safranbolu is the most important settlement reflecting the culture of this region and attracts local and foreign tourists. Here, old buildings have been restored and preserved and brought to the society. Of the approximately 2000 traditional buildings, 1008 have been registered and taken under legal protection (Yeni et al. 2013). According to the December 31, 2021 address-based population registration system results, the total population of Safranbolu District is 69,449 (TURKSTAT 2022). With the interest of tourists, the creation of touristic facilities, the conversion of abandoned mansions into buildings such as hotels and restaurants, and the restoration of monumental monuments started in the early 1990s.
The total annual solar radiation of Safranbolu District, which is the study area, is between 1400 and 1500 kWh/m 2 / year. Additionally, the monthly average daily sunshine duration of Safranbolu is approximately 6.6 h, and the annual average total sunshine duration is approximately 2409 h. It is seen that the global radiation values of Safranbolu are the highest in June and July, the average daily radiation intensity is approximately 3.7 kWh/m 2 /day, and the annual average total global radiation value is approximately 1361 kWh/m 2 / year (MENRT 2022).
In the city center of Karabuk, to which the study area is connected, there is the Enerjisa Karabük SPP, which is the 5th largest power plant in Karabük and produces sufficient electricity to meet the energy needs of 3619 residences, with an installed capacity of 7 MWe, unlicensed SPPs (Energy Atlas 2022) installed by various companies with an installed capacity of 5.15 MWe and Karabük University SPP with an installed capacity of 0.022 MWe (Şevik 2017). Tema Trend Gayrimenkul SPP (Energy Atlas 2022) with an installed capacity of 0.67 MWe on the roof of a shopping mall in Safranbolu District not only meets the electricity needs of the businesses operating in the mall with annual electricity generation of 1 million kW/h but also sells the system. Additionally, Tema Trend Gayrimenkul SPP has two SPPs of one MW installed 300 m away from the same shopping mall in 2017. Their installed power is 2.67 MW, and, apart from these, there are 2 GES investments with an installed power of 1 MW each, which started production in 2019, belonging to two different companies in the Safranbolu District Sine village (Oral 2020). The installed power distribution according to the sources of all existing power plants in Karabük Province, where the study area is connected, shows that hydropower plants (HPP) and coalweighted electricity production are predominant (Şevik 2017). While the total share of thermal and hydroelectric power plants in the total installed power throughout the province is 92%, the share of SPPs is 8% (Oral 2020). Safranbolu District was selected as the study area by considering into account the presence of existing SPP and solar energy potential atlas (GEPA) data (MENRT 2022) for selecting appropriate SPP locations to increase the share of SPP in electricity production.

Materials and methods
The methodology of the study comprises eight steps as follows: (1) literature review and data collection of the study area and solar power plants; (2) determination of analytical instruments such as GIS, MCDM, FAHP; (3) environmental analysis including impact assessment systems principles and legal framework; (4) excluding the restricted areas while gathering together the data for technical analyses; (5) determination of the layers used in technical analyses based on different features suitable with impact assessment system principles as well; (6) application of the analytical instruments; (7) identification of the sensitive areas by technical and environmental analyses; and (8) achieving outcomes, outputs, and proposals (Fig. 3).

Site selection and determination of restricted areas
The criteria decisive in SPP site selection directly affect all processes and electricity generation costs from the installation phase to the operation phase of the power plants. Efficiency, legal regulations, and EIA criteria are effective on site selection (Şenlik 2017). In other words, the site selection for SPP is affected by three main factors: (i) technical, (ii) economic, and (iii) environmental. These factors depend on the geographical location, biophysical characteristics, and socioeconomic infrastructure of the areas being studied (Charabi and Gastli 2011).
Within the scope of this study, a comprehensive literature research (Wood 2003;Sadler 2005;Asakereh et al. 2017;Al Garni and Awasthi 2017;Noorollahi et al. 2016;Yücel 2016;Şenlik 2017;Wang et al. 2018;Yalçınkaya 2022) and institutional interviews were conducted in the process of determining the restricted areas for SPP installation. Figure 4 shows the indicators of restricted areas determined by literature research and institutional interviews for SPP installation (Sarsıcı 2020; Karabük Provincial Directorate of Culture and Tourism 2022; Karabük Regional Commission for the Protection of Natural Assets 2022; Ministry of Agriculture and Forestry, Karabük Provincial Branch Directorate 2022; SAYS 2022).
Buffer zone analyses were performed separately for each criterion; thus, restricted areas regarding the SPP installation were identified and these areas were combined (Fig. 5). In this combination process, if an area is restricted in terms of any criterion, it is considered as restricted regardless of other criteria. In the next step, the process of determining the suitability levels of the areas determined as suitable was started.

Determination of criteria
To provide the highest level of results in the studies carried out for SPP site selection and to perform an accurate analysis, the data, which is the most basic need, must be provided in an appropriate way (Memişoğlu 2014;Çolak et al. 2020;Shorabeh et al. 2022;Goh et al. 2022;Karipoğlu et al. 2022). In determining the areas suitable for SPP installation, layers representing the study area were selected because of both field and literature studies (Asakereh et al. 2017;Uyan 2013;Noorollahi et al. 2016;Al Garni and Awasthi 2017). These layers are the factors of solar radiation, distance to PDCs, slope, land use, distance to fault lines, geology, distance to the streams, distance to road lines, aspect, and distance to residential areas. Since Safranbolu District is not on a migratory bird route (URL-1 2022), the distance to migration routes parameter was not used in the analysis.
The design and performance analysis of solar energy systems depends on solar radiation data (Bulut and Büyükalaca 2007;Kaygusuz and Ayhan 1999). The most important criterion for the efficiency of solar energy systems is the solar radiation affecting that region. Solar radiation directly affects the energy obtained from a power plant to be installed. Solar radiation is a fundamental input to renewable energy applications (Nourani et al. 2019). For this reason, the solar radiation parameter has been examined in many studies (Charabi and Gastli  Kengpol et al. 2013;Sánchez-Lozano et al. 2013;Uyan 2013). Therefore, solar radiation data was used as a parameter in this study, and the solar radiation map (MENRT 2022) is given in Fig. 6a.
The distance to the substation center is economically critical to determining the optimal installation areas for SPP. The reason for this is that it is more costly to transmit the electricity generated as it moves away from the center. It is preferred that the areas where SPP will be installed are located less than 10 km from substations (Uyan 2017). The distance factor to the substation in the study area was evaluated under 5 classes (Fig. 6b).

Fig. 5 Restricted areas related to SPP installation
The topography of the land is among the most important factors in determining the optimal installation areas for SPPs. Slope and aspect, which are among the topographic factors, have a direct effect on the selection. It is desired to have a low slope where the SPP panels will be installed. Generally, areas with a slope above 11% are considered unsuitable, while slopes of 4% and less than 4% are considered quite suitable. A reason for this is that the solar panels shade each other when the slope is high. This has a negative effect on efficiency. The other is that the high slope increases the installation cost of the power plant (Noorollahi et al. 2016). Despite all these, on the other hand, completely flat lands without slopes are not preferred for SPP installation due to water accumulation and accumulated water drainage problems (Şenlik 2017). The slope data of the study area were produced from the digital elevation model of the region. The produced slope map is divided into 5 classes (Fig. 6c).

Fig. 6
Parameters (a solar radiation b distance to PDCs, c slope, d aspect, e land use, f distance to road lines, g distance to streams, h geology, i distance to fault lines, j distance to residential areas) Regarding this aspect, the slope of the land in the south direction has a significant effect on the duration and amount of insolation and increases the suitability of the land (Effat 2013;Noorollahi et al. 2016). For this reason, regarding the SPP site selection, it is necessary to prefer the southern facades that provide the most benefit from the sun during the day and provide high sun angle according to seasonal conditions (Yalçın and Yüce 2020; Sarsıcı 2020). The aspect map of the study area was evaluated to include 9 classes in the range of − 1 to 360° (Fig. 6d).
Existing land uses are very effective for determining the optimal locations for SPP. Settlement areas, military areas, areas with protection status (national parks, nature parks, wildlife development areas, etc.), transport networks, agricultural lands, forests, etc., within the administrative boundaries of the area where the research is carried out should be determined as a priority, and the physical and legal limitations of the study should be determined accordingly. SPPs should be at a certain distance from these regions according to the characteristics of these regions. Additionally, it should not be ignored that settlements grow in parallel with the population growth and even SPPs may stay within these regions.
Since the SPP will affect the natural life, cultural and natural protection areas in the environment where it is established should be at a certain distance from the protection areas. Areas such as forests, maquis, reeds, etc., are definitely not preferred in the selection of the location, since increasing the shading of natural vegetation will reduce the efficiency of electricity generation (Şenlik 2017). In this study, land use was analyzed in 5 classes under the headings of agriculture, forest, pasture, mixed vegetation, and settlement (Köseoğlu 2015), and the land use map is shown in Fig. 6e.
During the construction process (installation) of the SPP plant, being close to transport networks is an important criterion that ensures that both the cost of infrastructure installation and the maintenance and repair costs of the plant are low. Additionally, utilizing the existing transport routes will prevent the opening of new roads for transport purposes and will prevent the increase of different land uses in the immediate vicinity and cultural pressures on environmental components (Yücel 2016;Uyan 2017). However, SPPs should be more than 100 m away from the roads so that solar panels are not affected by the pollution caused by the traffic on the roads (Uzar and Koca 2020). Taking all these into consideration, the distance factor to the road lines in the study area was evaluated under 6 classes (Fig. 6f).
Hydrological structure is another effective factor in determining the optimal areas for SPP. When considering the criterion of proximity to the river, it is desired that SPPs should not be closer than 400 m to the rivers, considering all the changes that rivers and river beds will show in different seasons (Uzar and Koca 2020). There are 4 canyons in the study area, named Tokatlı, Düzce (Kirpe), Sırçalı, and Sakaralan (Yaci). Since the locations of these canyons are within the restricted area in terms of proximity to rivers, they are considered within the distance to river parameters and not discussed separately. In the study area, the distance to the river factor was evaluated under 5 classes (Fig. 6g).
The geological structure is another parameter used in determining SPP installation location alternatives (Uyan 2017) and affects the cost of the power plant projects (Eroğlu 2018). Additionally, it is desirable that the ground where the power plant is installed should present a geological structure that will allow the application of the hammer-mounting system. There are 12 different lithological formations and 4 members surfacing the study area. Stratigraphically, the formations in the study area are Aydos (Oa), Ereğli (ODe), Ferizli (Df), Yılanlı (DCy), Bürnük (Jb), Ulus (Ku), Safranbolu (Tes), Karabük (Teka), Soğanlı (Teso), Akçapınar (Tea), Örencik (Tplö) formations, and alluvium (Qal). Aydos formation (Oa) consists of quartzitic sandstone and conglomerate and is 50-to 200-m thick. Eregli formation (ODe), which consists of shale, sandstone, and limestone, has a thickness of 300-550 m. The Ferizli formation (Df) consists of dolomite, sandstone, algea, and oolitic ironstone and has a thickness of about 100 m. The Yılanlı formation (DCy), which consists of limestone, dolomitic limestone, and dolomite successions, is 1000-m thick. Bürnük formation (Jb) consists of conglomerate, sandstone, and carbonate sandstone and reaches a thickness of 200 m. Ulus formation (Ku), which consists of shale, claystone, marl, limestone, sandstone, sandy limestone, and conglomerate succession, is divided into 2 members, Ahmetusta (Kua) and Sunduk (Kus). The conglomerates within the Ulus Formation constitute the Ahmetusta Member (Kua), and the rocks are grey, yellow, brownish yellow, medium-thick layered and massive in appearance. The Sunduk Member (Kus) consists of grey, beige, medium-thick layered limestones. The thickness of the formation can reach up to approximately 2000 m. The Safranbolu Formation (Tes) starts with a thin conglomerate-sandstone level at the bottom and transitions to carbonate sandstone, sandy limestone, and limestone levels toward the top, and its thickness varies between 50 and 500 m. The Karabük Formation (Teka), which has a medium-thick layered characteristic, consists of marl at the lower levels and claystone and sandstone succession toward the top. There are also thin coal levels in the upper parts of the formation. The Çerçen Member (Tekaç), which is a member of the Karabük Formation, consists of conglomerate, sandstone, siltstone, claystone, and mudstone succession and is about 450-m thick. The Soğanlı Formation (Teso) consists of limestones, and there are marl layers between the limestone layers. There are abundant joints and deep karst structures within the limestones of the unit with an average thickness of 150 m. Akçapınar Formation (Tea) consists of dolomitic limestone, claystone, mudstone, and marl succession, mainly clayey limestone. The formation has a thickness of 150-200 m. The Örencik Formation (Tplö), the younger deposit in the study area, consists of terrestrial conglomerate, sandstone, and mudstone succession. It shows medium-thick stratification and offers a thickness of 50-100 m. Yörük Member (Tplöy), who is a member of this formation, consists of lacustrine limestones and has a thickness of approximately 100 m. The youngest unit of the study area is quaternaryaged alluvium (Qal) and consists of river beds, old pits and gravel, and sand and mud sediments developing on flat areas (Gedik and Aksay 2002;Timur and Aksay 2002).
Since the alluvium in the study area consists of uncemented sediments, it is not a suitable layer for installing SPP on it. However, if it is necessary to establish an SPP on the alluvium, it will be possible to implement it provided that the hammered mounting system is used and the system used is lowered until reaching to the foundation under the alluvium. Otherwise, it does not offer a secure feature for SPP installation. All geological units in the study area offer suitable features for the hammer-mounting system. The Safranbolu Formation (Tes) and the Sunduk Member (Kus), which is a member of the Ulus Formation, contain deep and widespread karst structures such as canyons and caves; therefore, detailed field work is required for SPP installation on them as they offer dissoluble property. Additionally, SPP should never be installed in karstic environments that are part of tourism activities and contain natural geological heritage elements that need to be protected. The geology map of the study area is given in Fig. 6h.
In this study, seismicity was also examined within the scope of the geological structure. As the proximity to the active fault lines increases the earthquake effect, in site selection analyses, the distance to fault lines is also a very effective factor. Areas with lower earthquake risk are more suitable for SPP installation. For this reason, the fault line data were obtained by digitizing from the fault map presented on the website of the General Directorate of Mineral Research and Exploration, MTA (MTA 2022; AFAD 2022), and five different buffer areas were created at 2500-m intervals to be used in the analysis (Fig. 6i).
The transmission of energy generated by SPP to remote consumption regions causes energy loss. For this reason, to avoid loss of efficiency in energy transmission, remote locations to residential and industrial areas should be avoided in SPP site selection (Şenlik 2017), provided that SPPs do not remain within the expanding residential areas over time (Uzar and Koca 2020). Considering all these, the distance factor to the residential areas was evaluated under 5 classes in this study (Fig. 6j).
Considering the data of the current situation given in Fig. 6 in terms of environmental-social and economic-based impact assessment principles for SPP establishment, (a) Safranbolu District is advantageous in terms of renewable energy potential since the annual total solar radiation data is in the range of 1400-1550 kWh/m 2 /year. (b) In the case of selecting SPP installation areas relatively closer to the substation (less than 10 km), there is no need to establish new transmission networks that require a costly process. By integrating the regions with these conditions into the technical process, it is aimed to control the occurrence of cultural pressures to a certain extent and to prevent additional negative impacts on economic, social, and natural bases. (c) By integrating areas with a slope ≤ 4% into the technical analysis process, it is aimed to prevent the generation of excavation waste to a certain extent by supporting minimal excavation-filling works. In such a situation, the change in the integrity of the natural soil system will be kept under control to a certain extent. (d) Because Türkiye is located in the northern hemisphere, the fact that the panels are positioned predominantly in the south direction in SPP systems increases the efficiency. This requirement has been integrated into the technical analysis process. (e) Among the land uses, there are dense flora such as trees, shrubs, vegetation cover, meadow pasture, etc., where the presence of flora is intense. Care has been taken to exclude such areas from the selection criteria to avoid the destruction of ecological integrity. (f) The activity is expected to have an easily accessible road, a railroad, an airway, and/or a maritime road network to provide the transport required, especially during the construction process. The fact that these roads are among the existing ones is not only economically preferable but also a matter that considers the integrity of the natural system. For this reason, areas in the range of 100-500 m have been integrated into the technical analysis process. Additionally, the connections to be made should not damage the existing village roads and should be planned in a way that will not prevent the traffic flow and endanger the lives and property safety of the people. (g) The fact that the facility area selection is close to the underground-ground water resources is a situation that poses a risk to the environment and public health. Within the scope of the Regulation on the Protection of Potable Water-Utility Water Basins published and enacted in the Official Gazette No. 30224 dated October 28, 2017, it is recommended to select it from the areas located at least 400 m away. This threshold was taken into account in the study. In the works to be carried out, necessary precautions should be taken by considering the water resources; no waste should be left in the water resources, no intervention should be made, and no wastewater should be discharged into the underground.
(h) In the study area, it is observed that geological and geomorphological formations with unique characteristics remain within restricted areas. (i) During the operation period in the project area, the site selections made among the areas far from active fault lines in accordance with the "Türkiye Building Earthquake Regulation" published and enacted in the Official Gazette No. 30364 dated March 18, 2018 will provide economic and environmentally based use in the long term. Considering the standards in the Official Gazette, 2500-m distance to active fault lines was taken as a basis in the analysis. (j) The effects of the noise and waste to be generated due to the activity during the installation and operation phase on the nearest settlements are an issue that should be considered in accordance with the "Regulation on the Assessment and Management of Environmental Noise" published and enacted in the Official Gazette No. 27601 dated June 4, 2010. For this reason, attention has been paid to the location of the areas integrated into the technical analysis at a distance from the dense residential areas.

Fuzzy logic and fuzzy decision making
In cases where a decision needs to be made with incomplete or uncertain information, fuzzy logic methods are preferred. It is possible to define decision-making as the determination of the opinions that must be finalized at all levels by addressing all aspects of the problem, sometimes as a single issue and sometimes as a series of issues, aiming to obtain the most accurate result (Harcar 1992). The presence of verbal information in decision-making processes may cause uncertainty, and this may create models with subjective thoughts. In other words, if the uncertainties cannot be eliminated, it is recommended to analyze by accepting the existence of uncertainty. Performing analytical solutions with fuzzy logic provides the decision-maker with a more flexible decision environment. Using fuzzy logic, it is possible to obtain the numerical equivalents of the verbally presented information and apply them to the solution process.
If personal data, such as questionnaire results and expert opinions, are included in the solution process, the solutions may differ according to the number of the respondent group and the change, which affects the optimal decision (Aydın 2009). Fuzzy logic is based on rating. Since there are fixed and precise rules in the measurability of variables, Zadeh (1965) proposed fuzzy models as an alternative approach. Fuzzy logic, which has been increasingly important since 1965, is defined as a mathematical order established to explain uncertainties and to work with uncertainties (Klir and Yuan 1995).

Fuzzy multi-criteria decision making (FMCDM) and fuzzy analytic hierarchy process (FAHP)
In MCDM problems, determining the weights of the criteria and choosing the appropriate model for the solution of the problem are two critical problems. There is no consensus in the literature on which model to apply to the problem and to determine the most appropriate method for weighting (Demir and Bircan 2020). MCDM models can be seen in which decision-makers are not objective in their judgments, express their judgments verbally, or their judgments do not contain precise and complete information. In such cases, analyses in decision models can be made with a fuzzy logic approach.
Applications of fuzzy logic in the decision-making process are usually carried out by blurring classical decision theories. In decision problems defined by fuzzy logic, just like in classical problems, it is aimed to reach a non-fuzzy "best" decision. However, fuzzy theory reveals in which probability each alternative can be optimal rather than the optimal decision reached. In other words, it is important to apply the methods developed with fuzzy theory in cases where there are no definite determinations in the problems; the parameters are not known precisely or the evaluations are verbal (Klir and Yuan 1995).
There are many criteria-weighting methods in the literature (Pöyhönen and Hämäläinen 2001). These weighting methods divide the criterion weights into three as subjective, objective, and mixed methods. There are simple multiattribute rating technique (SMART), AHP, Delphi, etc., methods of subjective weighting based on the decision makers' own evaluations. There are entropy weight method (EWM), technique for order of preference by similarity to the ideal solution (TOPSIS) methods, which are based on the analysis of raw data and use of objective weighting that includes mathematical algorithms and models without considering the preferences of the decision-maker. There are also varieties of mixed weighting obtained by the sum and multiplicative synthesis of other methods (Shemshadi et al. 2011).
AHP is an MCDM method based on binary comparisons, and comparisons can be made subjectively or objectively, depending on the definition of the criteria. It is necessary to determine the compared weights objectively, considering how important one alternative is compared to the other. However, when comparisons are made according to the criteria of expert opinions such as suitability, preferability, and importance, where personal evaluations come to the fore, subjective results arise. Although the subjectivity of expert opinions is seen as an advantage of the AHP method (Anderson et al. 1997), this personalization makes the results less precise. For this reason, FAHP, which was first proposed in the work of Laarhoven and Pedrycz (1983), is preferred in such cases. In this study, judgments and weights are expressed in triangular fuzzy numbers. Buckley (1985), on the other hand, argued that a single solution cannot always be obtained in the work of Laarhoven and Pedrycz (1983) and worked with trapezoidal fuzzy numbers based on arithmetic operations of fuzzy numbers. Different from these, Lee et al. (1999) introduced the concept of an interval for binary comparisons based on probabilistic optimization in fuzzy comparisons. Chang (1996) improved the method by using synthetic degrees.
Since the parameters are taken directly from the experts in the classical AHP method, the results may not be accurate because the indecision of the experts is not considered while creating the comparison matrix. For this reason, in this study, we preferred to use the fuzzy AHP method to determine the weights of the parameters instead of obtaining a value directly from the experts as in the classical AHP method.
The first step in FAHP is to express the problem in a hierarchical structure, showing the objective, criteria, sub-criteria, and alternatives (Awasthi et al. 2018). In the second stage, a numerical link is established between the objective and the criteria. The importance level of the linguistically expressed criteria was determined by the experts, and literature was determined and a comparison matrix was created. In this study, the geometric mean method (Buckley 1985) and the extended analysis method (Chang 1996) have been used from fuzzy analytic hierarchical process methods. In Table 1, the triangular fuzzy scale implemented in the current study has been introduced. After the fuzzy synthesis values are calculated, these values are compared with each other, and the priority values of the options and criteria are found. By normalizing this vector, the real priority vector is obtained.

Environmental impact assessment (EIA) process
The implementation of impact assessment systems for sectoral activities with spatial dimensions is important in terms of ensuring integrated environmental management. In this framework, when the direct or indirect relationship of the energy sector with other sectors and different land uses is considered, it is clear that decision-making processes need to be subjected to an impact assessment process. An EIA process focuses on the location and technical conditions of the planned project. Within the scope of this study, the determination of suitable locations for SPP is one of the most fundamental issues considered while conducting the EIA process. Therefore, in determining the criteria in the technical analysis process carried within the scope of the study, the principles of impact assessment systems have also been considered. The main reason for this is the fact that the areas determined to be suitable for installation and their immediate surroundings will be within the scope of the impact area during the installation and operation of the project.
In the process of determining the areas to be proposed for SPP facility, EIA principles observe that the most suitable areas in terms of environmental, social, and economic aspects are determined, and this situation is presented with a cause-effect relationship. In this direction, considering the solar energy data of Safranbolu District, electricity production can be supported by SPP systems; considering the population density, it has been determined that a systematic production process will support an efficient supply at the city level. Detailed and complete implementation of the legal framework for SPP facilities, of which location proposals have been developed to establish and operate in the city, prevents long-term negative effects on the environment. The establishment of SPP in Safranbolu will ensure that the rich natural resources of the city are utilized in accordance with their purpose. As a result, natural resources will be utilized as inputs to the national economy.
At the end of the technical analysis process, location alternatives compatible with EIA principles were determined. The results of the analysis were analyzed compared with the F29 map section of the 1/100,000 scale of environmental plan of the Zonguldak-Bartın-Karabük planning region, and it was investigated whether there were any legal contradictions (Directorate General of Spatial Planning 2022). Additionally, it has been investigated whether the optimal areas determined within the scope of the study are areas that need to be protected by considering the sensitive areas in Annex 5 of the EIA Regulation.
(i) "National Parks," "Nature Parks," "Nature Monuments," and "Nature Conservation Areas" defined in Article 2 of the National Parks Law No. 2873 and designated in accordance with Article 3 of this Law, (ii) "Wildlife Protection Areas, Wildlife Development Areas, and Wild Animal Settlement Areas" determined in accordance with the Land Hunting Law No. 4915.
(iii) In the 1st, 2nd, 3rd, and 5th subparagraphs of the fırst paragraph titled "Definitions" of Article 3 of the Law No. 2863 on the Protection of Cultural and Natural Assets, the areas defined as "Cultural Assets," "Natural Assets," "Sites," "Protected Areas," and the areas identified and registered in accordance with the relevant articles of the same Law and the Law dated 17/6/1987 and numbered

(on the Amendment of Certain Articles of the Law No. 2863 on the Protection of Cultural and Natural Assets and the Addition of Certain Articles to this Law).
Within the scope of the literature review and institutional interviews conducted for Safranbolu district, the coordinate information of the areas with special status defined as "cultural assets," "natural assets," "protected areas," and "protected areas" identified within the borders of the district were determined, and these areas were accepted as restricted areas, although these areas have been determined as optimal areas. Within the scope of the environmental analysis carried out within the scope of the study, different legal bases were examined. The determined optimal areas are evaluated in terms of international conventions as below: It is seen that there are no plant species in the IUCN categories among the plant species detected in the determined areas and their immediate surroundings. None of the plant species in the study area are included in the Bern Convention Annex-1 list.

(ii) Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
There is no plant species included in the CITES Convention among the plant species detected in the determined areas and their immediate surroundings. The CITES Convention is a contract that binds the import and export of wild animal and plant species, in short, international trade with certain permits and documents between the contracting countries.
(iii) Convention on the Protection of Wetlands of International Importance, especially as Waterfowl Habitat (RAMSAR Convention).
There are no areas protected by the Ramsar Convention in the class of "Class A Wetlands" according to international criteria in the designated areas and their immediate surroundings.
There is no restrictive situation within the scope of other international conventions to which Türkiye is a party (Espoo Convention, Barcelona Convention, European Landscape Convention, etc.).
Relevant legal limitations in the Turkish legislative system: In this context, on the basis of the "Principle Decision on Solar Power Plant (SPP) in Natural Protected Areas" published and enacted in the Official Gazette No. 29959 dated January 25, 2017, which establishes SPP areas by considering the integrity of the natural system and on the basis of the "Principle Decision numbered 100, amended the Resolution on Solar Power Plants (SPP) in Natural Protected Areas," published and enacted in the Official Gazette No. 31898 dated July 20, 2022. Qualified natural protected areas and sustainable conservation and controlled use areas within the administrative boundaries of Safranbolu District are accepted as restricted areas in the process of determining the optimal area for SPP (SAYS 2022). After determining the location for the SPP facilities planned to be established in Türkiye, in accordance with the EIA Regulation, which is included in the Turkish legislative system (given in the Introduction Section) and entered into force after being

Implementation
It is also necessary to determine a method for selecting criteria to be used in the MCDM method to be used in solving problems in the field of renewable energy (Wang et al. 2009). The general characteristic of decision-making problems is fuzziness, and FAHP allows the preferences of decision-makers to be expressed in adaptable ways (Güler and Yomralıoğlu 2018). Additionally, classical MCDM methods cannot reveal the ambiguity of human thought too much (Ecer 2018). For all these reasons, the FAHP method was used in this study. Firstly, the fuzzy number equivalents of the linguistically expressed criteria determined by the experts were determined, and the binary comparisons of the criteria obtained in line with the expert opinions are shown in the binary comparison matrix in Table 2.
For the extent analysis method that will be used, we must calculate the value of the fuzzy synthetic extent with respect to the i parameter (Chang 1996) shown in Eq. (1), where all the M_(g_i)^j, j = 1, 2, 3 are triangular fuzzy numbers lying in Table 2.
The fuzzy synthetic extent values and normalized weights for the parameters are given in Table 3.
Using the geometric mean method proposed by Buckley (1985), the fuzzy weights and weights for the parameters are given in Table 4.
(1) Because of FAHP weighting with different sorting methods, it was calculated that the solar radiation criterion has the highest weight, followed by distance to substation, slope, aspect, land use, distance to roads, distance to streams, geology, distance to fault lines, and distance to settlement centers. Considering the calculated weights of the parameters, the maps in Fig. 3 were combined and the restricted areas were removed from this map and SPP suitability maps were created for the study area.
In the study, methodologies were compared in temperate climate conditions in Europe. The findings obtained in the study and analysis results could support legal regulations for updating sustainable urban policies. In a study of Omenge et al. (2020), the structures in Kenya-the country has rich renewable energy resources in Africa-in terms of environmental and social impact assessment procedural steps were investigated. They preferred qualitative research methods including a descriptive research design with simple random sampling and the law of statistical regularity for promoting renewable energy resource development in Kenya.
The studies in the literature given above have methodologies with an environmental or technical dimension for sustainable development. In this study, it is presented an inclusive content in which the environmental and technical dimensions are integrated in terms of the research process carried out and the findings and results obtained. This study highlights how we achieve sustainable development by integrating technical and environmental dynamics in decisionmaking, in addition to determining the suitability of the location of the SPP using one of the multi-criteria decisionmaking methods. This study was produced by integrating the fundamental principles of the impact assessment systems into the fuzzy analytical hierarchy process in line with the legal and administrative framework in Türkiye. We focused on both qualitative and quantitative research techniques. In other words, this study, which was carried out based on the scientific, technical, and legal frameworks, has the significant statistics data to present the findings and results according to the methodology.

Conclusion
As a sector, energy is among the main areas that have the greatest impact on sustainable development. Renewable energy use processes should be based on qualitative and quantitative research processes of the studies carried out to support sustainable production in real terms.
Sustainable sectoral activities that support sustainable development aim to conduct natural, cultural, and social environmental components by considering the balance of protection and use. In other words, sustainablebased management of development should be ensured by considering different environmental dynamics and natural resource reserves in this context, and possible negative impacts in the future should be prevented. Thus, efficient and balanced utilization of resources in electricity generation can be ensured. In the generation of electricity using renewable energy resources, the process should be based on scientific research and the legal and administrative limitations of the countries to be truly sustainable. In this direction, it can be stated that the basic principles of impact assessment systems integrated into the technical analysis process in this study aim to realize the generation of electricity from solar energy in a sustainable process.
The technical processes developed on the optimal site selection for renewable energy sources using analytical tools within the scope of multi-criteria decision making and developing concrete proposals where the protectionutilization balance is observed are among the main working areas of impact assessment systems. In other words, the sustainability of the natural, cultural, and social environmental components, which are among the main issues considered by environmental assessment processes, with the balance of protection-use, aims to minimize cultural pressure and environmental risks arising from sectoral activities. GIS and MCDM methods are tools that enable the selection of the best choice among many alternatives in site selection studies. One of the most widely used and preferred methods among MCDM methods is the FAHP method, which enables the expression of decision-makers' preferences in adaptive ways. In this study, an FMCDM model has been developed to determine the areas where SPP can be established in Safranbolu, a touristic district. In the study, 10 different criteria were used, and we observed that the results obtained were directly related to the selected criteria.
In this study, it is shown that FAHP should be preferred to better express the verbal uncertainty in the process of deciding how important one criterion is compared to another criterion by the decision-maker by pairwise comparison. The FAHP method should be preferred, especially in cases where the number of pairwise comparisons is high, the process takes a long time, and fuzziness occurs in the decision-maker. For the mathematical expression of verbal expressions in environmental, social, and economic criteria, sub-criteria integration with the fuzzy relationship is important in obtaining more accurate results.
To meet the energy needs of Safranbolu District, which was included in UNESCO's World Heritage List in 1994 and is a museum city with its architectural, historical, and natural accumulations, utilization of SPP will contribute to cheap, clean, and sustainable energy supply. The obtained SPP suitability map can be used in preliminary evaluations by investors. Accordingly, Safranbolu District has very suitable areas for SPP installation in the central and western parts but also has areas suitable for SPP installation in the northern and southern parts. The results obtained from this study are expected to help decision-makers in future studies on land management in and around the study area. The process of environmental analysis integrated into the process of optimal site selection for solar energy systems in Türkiye, which is rich in natural resources, is recommended to be used as an effective tool in scientific and public studies to support sustainable sectoral land uses. This situation will support the efficient and balanced use of renewable energy resources by preventing, to a great extent, the negative impacts that are likely to occur in the future.
Data availability All data and materials generated or analyzed during this study are included in this published article and its supplementary information. Data will be made available on request.

Declarations
Ethical approval and consent to participate Not applicable.

Competing interests
The authors declare no competing interests.