1. Introduction
Green cities are defined as cities characterized as having clean air and water, running a low risk of major infectious disease outbreaks, being resilient to natural disasters, encouraging green behavior, and having a relatively small ecological impact [
1]. Therefore, green cities are related to, among other things, renewable energy sources (RES), the use of which is environmentally friendly, minimizes ecological influence and increases the quality of air in the city. The relationship between green cities and renewable energy sources can be found in a report prepared by the European Green City Index, in which 30 European capitals were evaluated in terms of their current environmental performance [
2]. The ranking takes the following factors into consideration: air cleanliness, CO
2 emission, a strategy of CO
2 reduction or the percentage of renewable energy in the total energy production [
3]. Similarly, Albino and Dangelico [
4] noticed that the RES use is closely related to the philosophy of green cities and is an essential practical aspect.
Another element of green cities is environmentally friendly transport [
3,
5]. It is about, among other things, supporting bicycle mobility, as is being done by municipal authorities of Polish cities, such as in the city of Szczecin, by building bicycle paths and urban bicycle stations. Nevertheless, a larger ecological potential for cities is the application of solutions used by a higher number of citizens rather than the expansion of bicycle infrastructure. It is obvious that far more city dwellers use their own cars and public means of transport. Consequently, better results in terms of reducing pollution emissions can be obtained by solutions such as electric or hybrid cars [
6] as well as public transport powered by electricity, i.e., trams and electric buses [
7]. However, it should be noted that the use of electric vehicles in the city causes increased demand for electric energy related to the necessity of charging vehicle batteries. As a result, such a demand brings about the increase in energy production from conventional sources, mostly from coal, even in cities where the power industry is to a great extent based on RES [
8]. Therefore, air pollution reduction resulting from the use of electric vehicles is lower than is assumed [
9]. The problem is even bigger, since almost all energy for the city is produced by coal power plants. It may turn out that air pollution emission generated by a coal power plant (resulting from the necessity of energy production for charging electric vehicles) is larger than the air pollution emission when conventional vehicles are used instead of electrically powered vehicles [
10]. Therefore, one cannot talk about a green city as long as it mostly relies on coal energy. Instead, energy production technologies based on RES should be introduced more frequently.
The use of RES as pro-environmental action is one of the main aims of the energy policy [
11]. Renewable energy sources are the basic element of a low-carbon economy [
12], and their percentage in the total energy production is continuously increasing and will continue to increase in both the European Union [
13] and Poland [
14,
15]. On the other hand, the highest portion of energy production in Europe [
13] and Poland is supplied by wind turbines [
15,
16,
17]. The Polish wind potential is comparable to that of the “world wind giant” Germany and other countries in which a significant share of energy is obtained from wind, such as Denmark or Sweden [
18]. An inland wind turbine is distinguished by lower capital spending and maintenance costs among RES, as seen in
Table 1.
The data show that wind is the most optimal renewable energy source. What is more, the highest economic and market potential for wind energy in Poland (by 2020) is in West Pomeranian Province, as depicted in
Table 2. The economic potential was determined by considering arable lands in a given province with appropriate wind conditions on which wind farms can be constructed. From the potential investment areas, all areas subject to protection were excluded. These areas are national parks, landscape parks, nature reserves, the Natura 2000 protected areas, areas of protected landscapes and protected area buffer zones. The market potential (part of the economic potential that can be used within a definite period of time) was calculated by means of a Modular Energy System Analysis and Planning Environment (MESAP) model, as part of an Energy [R]evolution project, on the basis of current market and political factors [
20].
The city of Szczecin plays an important role in the West Pomeranian region. The analysis of the present energy policy of the city confirms that it is primarily based on a conventional source of energy; that is, coal [
21]. There are two coal power plants, “Pomorzany” and “Szczecin”, located in the city. They significantly support the electric power grid during rush hours and therefore generate harmful emissions in the city. The situation with regard to potential wind conditions and ecological limitations seems to be unfavorable and is reflected in the Regional Innovation Strategy which emphasizes the need for a continuous increase of the RES share in energy production, as presented by Urząd Marszałkowski Województwa Zachodniopomorskiego [
22]. An analysis of other economic and social factors of the city also conveys substantial RES investment possibilities such as the use of technological and social potentials of the city and the region as well as the availability of investment grounds; for instance, neighboring districts that have low economic value but are also “good” locations for wind farms, e.g., an area between the town of Goleniów and the northwest part of DąbieLake [
23].
The complex analysis of an RES investment location also requires a detailed analysis of the technological potential of the city and the region. In Szczecin, and in the vicinity of the city, there are many production companies related to wind energy. In Goleniów, LM Wind Power is manufacturing rotor blades for wind turbines. In total, about PLN (Polish złoty) 600 million will be invested, which is going to generate about 1400 jobs (currently 600) [
24]. LM Wind Power also has a service center in Szczecin, where approximately 140 workers are employed [
25]. There is also KK Wind Solutions, located in Szczecin, which produces wind turbine control systems. The company employs about 570 workers in the area of Szczecin [
26,
27]. As for the ability of investment to diversify an economically unstable shipbuilding sector within the city, Bilfinger MARS Offshore serves as a prime example. This company manufactures foundations for offshore wind farms, and over PLN 500 million were invested to build the factory, which will employ about 500 workers [
28].
Apart from manufacturers of wind farm elements, an important part of a potential investment process is planning and the realization of wind farm projects. Here, EPA-Wind, a Szczecin-based company, should be mentioned. This company, which employs over 40 workers [
29], deals with data analysis, measurements, preparation and realization of wind energy projects. A Polish division of the RP Global concern also has its registered office in Szczecin. RP Global Poland deals with the design, implementation and maintenance of wind farms [
30]. There are many business entities that act as subcontractors and are responsible for constructing wind turbines. The detailed analysis of a broader social context of investment makes us consider the social potential of the city. Wind energy investment in the vicinity of Szczecin would also positively increase the number of workplaces related to wind energy when investment preparation is concerned, as well as the management, maintenance and repair of wind turbines. Estimates concerning the number of positions created by the wind energy sector are presented in
Table 3.
Furthermore, according to research for the European Commission, people employed in the RES sector often come from other sectors where they had lost their jobs, such as the shipbuilding or steel industries [
32]. This observation is of utmost importance in the context of Szczecin, where the most significant social problem has been the bankruptcy of one of the biggest employers, i.e., Szczecin Shipyard, in 2002 [
33].
On the basis of the arguments presented above, one can state that the construction of wind farms in the vicinity of Szczecin is very important, both for perceiving the city as a “green city” and for social and economic reasons. Therefore, the aim of this paper is to identify conditions that should take place so that a potential investor would chose the Szczecin region as a construction area of wind farms. The aim is achieved by means of a kind of a decision game, which assumes that the investor, who has several good locations for constructing wind farms, makes a decision with the use of a multiple-criteria decision analysis (MCDA) method. Methodologically, the article presents an attempt to build guidelines for using MCDA methods as a tool for identifying and constructing the decision-maker’s preference model by maximizing the utility of a given decision variant. Such an approach is a complement to possible plains of application of MCDA methodology in areas different than classical problems of choice, ranking and sorting.
2. State of the Art
Decisions related to RES ought to be seen as multiple criteria decision making problems with correlating criteria and alternatives [
34]. As far as RES decision problems are concerned, many criteria, which are usually mutually conflicting, should be considered [
35]. Often, a decision made in this field is related to the necessity of taking into account different and contradictory interest groups [
36,
37]. This is because of complex relationships between technological, economic, environmental, ecological, social and political conditions and aspects of the application of RES. Therefore, a natural tool for supporting such decisions are MCDA methods [
38]. This stems from the fact that MCDA methods can provide a technical–scientific decision-making support tool that is able to justify choices clearly and consistently, especially in the renewable energy sector [
39,
40].
In the literature, one can find many examples of MCDA applications in the field of RES. These methods are employed in order to: choose an energy production technology, analyze different scenarios of RES development, optimize energy production, and evaluate RES-based power plants on the environment or to select location for this kind of power plants. RES-related problems and MCDA methods applied to solve the problems have been variously reviewed [
34,
36,
41]. Research also deals with the application of MCDA methods to wind energy; for example, Kaya and Kahraman [
42] first selected an energy production technology (wind energy received the highest mark), and then faced the problem of finding a location for an on-shore wind farm working in the chosen technology. Lee, Chen and Kang [
43] presented the problem of location selection of an on-shore power plant and Wątróbski, Ziemba and Wolski [
44] for an off-shore power plant. Moreover, Latinopoulos and Kechagia [
45] as well as Al-Yahyai et al. [
46] based frameworks for location evaluation of on-shore wind farms on GIS (Geographical Information System); Aydin, Kentel and Duzgun [
47] presented a similar framework for location evaluation of hybrid power plants, which use wind energy and solar-PV energy. Yeh and Huang [
48] determined criteria and their weights for the problematic of selection of a wind farm location. Aras, Erdogmus and Koc solved another problem concerning the location selection of a wind observation station [
49]. Chang [
50] considered a more complex problem presented in the selection of specific energy production technologies and their locations. As for other decision problems, Cavallaro and Ciraolo [
40] carried out an evaluation of wind power plants designs. The designs were different in quantity and power of wind turbines and were evaluated in terms of their suitability to one specific location. Lozano-Minguez, Kolios and Brennan [
51] evaluated foundations (truss) for off-shore wind installations. Individual articles, along with their criteria and MCDA method are presented in
Table 4. Here, the criteria were divided into seven categories:
technical aspects of the wind farm and its devices;
spatial location of the farm with reference to surrounding area;
economic issues especially ones related to the planned investment costs;
social factors related to building and operating the wind farm;
issues concerned with ecological aspects of the investment;
environmental factors of the vicinity in which the farm is to operate; and
legal articles and aspects related to the internal policy in terms of constructing wind farms.
In
Table 4, one can find out that the location evaluation of wind farms is often influenced by spatial criteria, such as a distance from the road network and the power grid. Another frequent technical criterion is the amount of generated energy. In the context of generated energy, the environmental aspect is essential; i.e., wind speed, as it directly influences the amount of generated energy. Among the economic criteria, the most crucial ones seem to be investment, operation and maintenance costs. Social factors are also of importance; above all, the social acceptance of constructing a wind farm and of changes to the surroundings. A basic ecological factor that is often mentioned among the criteria is an estimated emission intensity reduction related to withdrawals from fossil fuels. The volume level of wind turbines, the influence on protected area and distance from such areas are often listed among the ecological factors.
Lately, a dynamic development of MCDA methods has been observed. Both new methods are created and well-known techniques are further developed. They are widely used in decision problems related to, for instance, sustainable development, ecology or wind energy. In this area, both European and American school decision-making methods are applied [
52]. When analyzing the literature, one can notice in order to solve decision problems related to wind energy, the analytic hierarchy process (AHP) method is most often used. A generalization of the AHP method, in the form of analytic network process (ANP), is also employed. The reasons for this are relatively simple: computational algorithms for these methods and the possibility of hierarchical structurization of a decision problem [
43]. However, AHP/ANP methods are based on qualitative evaluations, therefore, they do not make it possible to precisely present quantitative data. In decision problems related to wind power engineering, other methods of the American decision-making school are also applied, such as Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), Vlsekriterijumska Optimizacija I KOmpromisno Resenje (VIKOR), simple additive weighting (SAW) or ordered weighted averaging aggregator (OWA) and their developments using fuzzy number arithmetic [
42]. As far as the European decision-making school methods are concerned, ELimination Et Choix Traduisant la REalité (ELECTRE) methods as well as the preference ranking organization method for enrichment evaluation (PROMETHEE) method are often used [
44]. These methods are especially used when a quantitative data approach is applied. Independently, e.g., Latinopoulos and Kechagia [
45], Al-Yahyai et al. [
46] as well as Yeh and Huang [
48] attempted, successfully, to combine several methodological approaches. The AHP (or also ANP) method is frequently used to determine a priority vector, whereas other techniques (e.g., Decision Making Trial and Evaluation Laboratory (DEMATEL), OWA, and SAW) are often employed in the aggregation process of final decision variants.
4. Research Results
Preference modeling in the PROMETHEE method consists of defining a preference direction for each criterion (max, min), indicating preference functions used for individual criteria (usual criterion, quasi-criterion, criterion with linear preference, level-criterion, a criterion with linear preference and indifference area or Gaussian criterion) and determining potential thresholds and providing their weights of criteria. These preferences are depicted in
Table 9.
Next, performance aggregation of alternatives based on the PROMETHEE procedure was conducted. The obtained positive, negative and net values of preference flows are presented in
Table 10.
The analysis of the obtained ranking (
Table 10) indicates that the location of Szczecin is not an alternative that should be selected. Therefore, which actions should be taken in the active decision model so that alternative A1 would win the first place in the ranking should be considered. There are two kinds of action that can be taken:
persuading the investor to change their criteria preferences and support Szczecin as better than Alternatives A2 and A3; or
taking action in order to increase the values of alternative A1 to improve the criteria that currently the location of Szczecin is considered worse than alternatives A2 and A3.
The research, conducted with the use of a sensitivity analysis into an investor’s criteria preference changes was carried out in such a way it could influence the improvement of the Szczecin location. Location A1 outperforms the best alternatives with regard to criteria C1, C3, C5 and C10. Therefore, it can be in first place in the case of increasing weights of only these criteria. The sensitivity analysis for the weights of the above-mentioned criteria is presented in
Figure 4.
The sensitivity analysis points out that for any increase in the weights of the criteria C3 and C5, alternative A1 will never be first in the ranking. The effect can be achieved only by increasing the weights of the criteria C1 and C10 and proportionally decreasing the other criteria. For C1, the limit weight when alternative A1 is first in the ranking is 35%. With reference to the initial weight of 12%, it would be a considerable change in the decision-maker’s preference. However, for criterion C10 it is 23%, which is only 3% higher than the initial weight of this criterion. The values of
net and rankings obtained for the indicated weights of the criteria C1 and C10 are depicted in
Table 11.
It is doubtful that the decision-maker changes their criteria preferences, so one needs to consider how alternative A1 could become more attractive than A2 and A3. Considering criteria, one should eliminate those which would be difficult to influence. These include mean wind speed, the amount of generated energy, the distance from the road network and being situated in the Natura 2000 protected area. Similarly, one cannot significantly influence the estimated investment costs and profits because they are based on approximate data. One can take into account the connection of the potential wind farm to a 400 kV power grid, which would improve the evaluations of alternative A1 with reference to the “power grid voltage” criterion. However, such action results in a significant increase in the distance to the connection and moves the location of Szczecin into the second position in the ranking, just behind alternative A2. Justified action would be to increase acceptance for the potential investment in the local community (social acceptance). Indeed, an analysis of the value of this criterion for alternative A1 without introducing any modifications to other criteria indicates that when social acceptance for locating a wind farm in the vicinity of Szczecin is at the level of 59%, alternative A1 is ranked first. The analysis is presented in
Figure 5.
It should be noted that when the value of social acceptance for alternative A1 is at the level of ca. 40%, there is a change in the sequence of alternatives A2 and A3 in the ranking, although these alternatives have not been modified in any way. Nevertheless, such a phenomenon is possible in the case of methods based on an outranking relation, and PROMETHEE method belongs to this family.
In the case of the AHP method, preference modeling is carried out by pairwise comparisons of criteria. The weights of the criteria are very close to those used in the PROMETHEE method. A pairwise comparison matrix of the criteria is depicted in
Table 12.
The performance aggregation of the alternatives was conducted by pairwise comparison of the alternatives with regard to subsequent criteria. Aggregated preference vectors for individual criteria as well as the final preference vector, synthesized to a single criterion, are presented in
Table 13.
When comparing
Table 10 and
Table 13, it can be easily noticed that due to the application of the AHP method, alternatives A2 and A4 changed their positions in the ranking. The change is drastic, since the positions were not neighboring ones, but the first and the second positions in the ranking. Moreover, alternative A1, as in the PROMETHEE ranking, comes third.
In the case of the AHP ranking, an increase in weight of selected criteria cannot put alternative A1 first in the ranking. This statement results from the analysis of
Table 12, where it can be noticed that there is no criterion with regard to which alternative A1 would outperform alternatives A3 and A4, which take the leading positions in the ranking. This is why, in this case, the sensitivity analysis was omitted.
In the next step of the research, when the preference vector of variants was calculated, similar to the ranking obtained by means of the PROMETHEE method, whether leveling evaluations of A1 and A4 with regard to criterion C7 (social acceptance) would allow alternative A1 to be the best in the ranking was tested. However, it turned out that it was unsuccessful, since after this, alternative A1 came second, just behind A4. Only a considerable increase in the value A1 for criterion C7 allowed it to move to the first position and become a preferred alternative. Pairwise comparison matrices and preference vectors for social acceptance and the final ranking of alternatives, obtained with a given pairwise comparison matrix, are presented in
Table 14,
Table 15 and
Table 16.
5. Summary
Conditions and environmental, economic and social factors determine the complexity of issues related to green cities. They reflect a close relationship between green technology and transport as well as green RES. Local economic and social conditions can simultaneously be a way to redirect goals and priorities set in the given decision problem of a RES location.
The article makes a successful attempt to model the problem of evaluating the usefulness of a wind farm location for the needs of the green city of Szczecin. Therefore, the article has carried out a multiple-criteria evaluation of the potential of the wind farm location in the region of the city of Szczecin against the background of reference (regarding the best wind conditions) location alternatives in Poland. Consequently, the detailed analysis of the economic and social factors of the city resulted in including them in the prepared decision model. The research was conducted in the form of a decision game with the use of carefully-selected MCDA methods (AHP and PROMETHEE) and the research depicted the gravity of criteria determining social acceptance of an RES investment in a given region. The necessity of using complementary approaches was dictated, on the one hand, by the possibility of an intuitive dialog with the decision-maker and the simplicity of structuring and expanding the model (the AHP method), and, on the other hand, the possibility of taking into account several different types of data (forms of preference information) in one model, which was the domain of the model prepared with the use of the PROMETHEE method.
While this paper was focused on the problem of identifying conditions that should take place so that a potential investor could chose the Szczecin region as a construction area of wind farms, the selected approach can be generalized towards other areas in the field of decision making. In the situations when it is possible to adjust parameters during the search for compromise solutions, the use of the proposed approach extends typical areas of MCDA models applications beyond the classic Roy problematics [
52] and can be used as a generalized framework.
In the course of the research, it has been found that there are possibilities of developing and completing the prepared model. Undoubtedly, taking into consideration real interest groups and adapting the decision model to these conditions seem to be an interesting direction. The use of the Novel Approach to Imprecise Assessment and Decision Environments (NAIADE) or group development of the PROMETHEE method can be a suggested direction.