1. Introduction
The global context generated by the rapid population growth and by the development of new technologies implies an increase in the energy needs. By combining this aspect with the actual energy producing capability, which uses mainly conventional methods (natural gas, lignite, petroleum, etc.) and has a negative impact to the environment, it results that it is urgently required to find effective methods of counteraction. From this perspective, the topic of energy remains an extremely important one [
1]. Globally, many policies aiming to put into practice, on medium and long-term, methods for the energy sector development were adopted. In this way, the energy sector will become more efficient and sustainable. Developing and implementing energy policies is also an important condition in order to achieve strategic goals, which will propagate further in the economic development.
Various studies show that the feed-in tariff policy mechanism is really effective in fostering the sustainability transition of the energy sector and also to promote the investments in renewable energy [
2,
3]. Thus, the growth of renewable resource extraction (wind, wave, geothermal, photovoltaic, and hydro, etc.) for generating electricity is pursued in the detriment of the conventional methods. For example, the European Union sets very specific targets for 2020 and 2030, as part of its long-term energy strategy, which covers the improved energy efficiency, emission reductions, and an increased share of renewables. An energy roadmap for the year 2050 has been also devolved. This aims to reduce the greenhouse gas emissions by 80–95% until 2050 when compared to the 1990 level. Through these energy policies, the European Union desires to ensure its citizens that they can access secure, affordable and sustainable energy supplies [
4,
5].
An example of good practice is followed by the Romanian Ministry of Energy, thought the energy policies. The Romanians energy strategy, according to the Ministry of Energy [
6], covers a 15-year interval (2016–2030), with an outlook to 2050. According to this document, the energy policy covers the strategic goals, principles, main areas of state intervention and new directions for development. This trend is followed not only by the members of the European Union as Bulgaria [
7] but also by countries like Georgia, Russia, Tukey, Ukraine, etc. The principles that all countries consider are: energy security, competitive market, consumer interests of first priority, transparency, smart grids and energy storage, smart buildings with energy self-sustainability and the most important is represented by the clean energy [
8,
9,
10,
11,
12].
One of the most permanent and sustainable renewable resources is the wind energy. According to the European Wind Energy Association (EWEA), the wind energy potential extraction has gained more and more ground. By analyzing the EWEA annual reports it can be observed a substantial growth of the energy volume extracted. Since 2014, when the installed wind power capacity was 142 GW (about 92.2% onshore and only 7.8% offshore), to 2017 the onshore and offshore cumulative wind power installation grew by 18.8% (about 16.8% onshore and only 43.6% offshore). According to this statistic, Germany (56.1 GW), Spain (23.2 GW) and the United Kingdom (18.9 GW) together represent 58% of all the cumulative installed capacity of the European Union. In the middle of the rank are countries as: Romania (3 GW), Belgium (2.8 GW), Austria (2.8 GW), Greece (2.7 GW), Finland (2.1 GW) and Bulgaria (0.7 GW) [
13].
However, a deep discrepancy between the EU countries can be observed, and this also regards the onshore versus offshore capabilities. In order to grow the offshore, wind energy exploitation it is required that researchers should find first the best new locations to exploit this green energy. The amount of land still available for the wind energy exploitation is becoming limited and there are also significant environmental issues. On the other hand, the offshore locations present some advantages, especially brought by the existence of large marine areas suitable for the wind farm development. The increase in wind speed with the distance from the coastline, together with the existence of less turbulence, allow for the turbines more energy extraction than the similar operating onshore [
14,
15].
The results of various previous researches indicate the fact that the Black Sea wind power potential cannot be neglected, especially for the countries located in the proximity of the sea [
16]. From this perspective, the objective of this paper is to present a more complete picture of the wind energy potential of the Black Sea during the present and near future periods, by using two different data sources. The novelty of the present study also arises from the fact that such a detailed analysis has not yet been carried out for this area. A significant amount of researchers studied the green energy potential of the enclosed and semi-enclosed seas by using various techniques as reanalysis data, satellite data and climate models [
14,
17,
18,
19,
20,
21,
22].
Davy et al. [
23] carried out an analysis of the climate change impacts on wind energy potential in the European domain. The study was focused on the Black Sea and conducted by using a single-model-ensemble. The authors show that in the near future the wind intensity pattern in the Black Sea basin will not suffer relevant negative impact due to climate change. This feature would make the offshore wind-farms in the Black Sea to be a viable source of energy for the neighboring countries. Another important work that illustrates the wind power potential over the Mediterranean and the Black seas is performed by Koletsis et al. [
24]. The authors analyzed by exploring six regional climate model simulations for the present period and two for the future periods. These models were produced in the framework of the ENSEMBLES project. The results for the Black Sea show that this basin is a suitable environment for the green energy extraction (average wind power being estimated in the range 500–900 W/m
2, with a deviation of ±50 W/m
2 during the future periods).
Onat et al. [
25] conducted an analysis of the wind climate and of the wind energy potential for several regions in Turkey. The authors analyzed also a small region of the Black Sea, located in the west (Amasra) by using a five-layer Sugeno-type ANFIS model developed with MATLAB-Simulink software. The relationship between the wind speed and other climate variables was also determined and the resulted data confirm that the Amasra region is a location with a good potential for the wind energy extraction. According to this study, the average power density at 10 m height is 232 W/m
2 (nearly good), at 50 m height is 603 W/m
2 (good) and at 80 m height is 1300 W/m
2 (very good).
The wind pattern of the Black Sea was also evaluated by Onea and Rusu [
17], considering 12 years of data from the U.S. National Centers for Environmental Prediction (NCEP). In that study, the authors analyzed the wind power distribution taking into account the diurnal versus nocturnal variations. According to the above mentioned study, the northwestern and northeastern sectors of the Black Sea are the most suitable for wind energy extraction. The northwestern sector of the Black Sea was also analyzed by Lin-Ye et al. [
26]. Their approach considered a hybrid methodology involving the Simulating WAve Nearshore (SWAN) spectral wave-model to produce wave-climate projections. The wave model was forced with wind-fields corresponding to the two climate change scenarios.
From this perspective, the present study aims to characterize the offshore wind power potential of the Black Sea during the present and the near future, by analyzing four databases. Following this objective, the structure of the proposed work includes first a presentation of the materials and methods considered, focused on the description of the target area and of the databases taken into account. The next section presents the results providing in some reference points the wind speed and also the wind power. These relate both the 30-year period considered from the past (1981–2010) and that estimated for the near future period analyzed (2021–2050). Finally, a discussion of the results was also carried out. Thus, the novelty of this paper can be summarized as follows:
A detailed description of the wind conditions over the Black Sea basin from two major sources (Era-Interim and Euro-Cordex) covering the recent past (1981–2010).
An estimation of the expected wind climate in the near future (2021–2050) under two different RCP scenarios (RCP4.5 and RCP8.5).
Evaluation of the climate change impacts on the wind speed and wind energy potential by performing comparisons between the past and the future projections.
4. Conclusions
From the comparative analysis of the wind speed at 10 m over the sea level simulated by RCM from EURO-CORDEX, the RCA4 model respectively, against the data existent in ERA-Interim database, a good correlation was noticed between these two datasets in the Black Sea area. On the other hand, probably due to the fact that the spatial resolution of the RCM model is higher than that from ERA-Interim, the wind speeds provided by RCA4 in the reference points considered in the Black Sea basin are slightly higher than those indicated by ERA-Interim.
The analysis of the wind speed annual averages shows that the wind speeds at 10 m height have a different evolution in the areas considered in the Black Sea. In general, for the present period, it was observed that the Evaluation wind speed averages are higher than those from ERA-Interim with values ranging from 0.06 to 0.25 m/s. Through the linear trend, it was observed that in 75% of the cases both data have the same trend (upward trend—the maximum value is 0.144 m/s per decade).
The daily averages of the wind speeds provided by both databases present a very good correlation. The Pearson correlation coefficient varies in the range 0.51 to 0.92. More precisely 71% of the data are in the interval of very high correlation, 25% are in the interval of high correlation and only 4% have a reasonable correlation. The differences between the daily values were assessed by the analysis of the root mean square error and Bias. The results of the analysis show that RMSE is in the range 0.25 to 0.50 m/s, while the bias values, in all points they are negative (ranging from −0.25 to −0.06 m/s). Thus, the low RMSE and Bias values together with the higher values of the correlation indexes show that there is a good agreement between the data provided by ERA-Interim and those from the RCM model (Evaluation data).
As the results of the present work show, in most of the cases there are no relevant differences in the average wind speeds (smaller than 0.4 m/s) simulated under both scenarios. This is probably due to the fact that until the mid-century the differences between the two RCPs considered are not very high. According to the near future data, both scenarios present approximately the same values in terms of annual averages. Regarding the linear tendency for the period 2021–2050, the RCP4.5 scenario shows that the wind speed will have a low decrease in 92% of the points (values ranging from −0.044 to −0.009 m/s per decade) while the RCP8.5 a small increase in 83% of the cases (values ranging from 0.008 to 0.044 m/s per decade).
As regards the average wind power potential in winter season, for 51% of the reference points a significant increase was observed for the near future (both scenarios) compared with the present values, while for 41% only a slight growth. For both scenarios, a small decrease was noticed only in the point B.n.1. The most energetic zones of the Black Sea are the western part of the basin (northwest and southwest areas) and also in the east and south of the Crimea Peninsula. More precisely, in these points, the total wind power averages for the 30-year time interval are higher than 500 W/m2. As expected, in the winter time the higher wind speeds and wind powers are encountered, while the lower values are found in the summer.
The fact that it was noticed an increase of the mean values of the wind resources in 95.6% of the reference points considered in the Black Sea, either under the RCP4.5 or RCP8.5 scenarios, can be considered beneficial from the perspective of the wind projects and this can give momentum to the installation of the wind farms in the areas already identified as having a good potential, as for example the western side of the basin. From this perspective, it is well known that some European areas are affected by a decrease of the wind resources (see for example [
35,
47,
48]).