A Joint Evaluation of the Wind and Wave Energy Resources Close to the Greek Islands

sustainability

Article A Joint Evaluation of the Wind and Wave Energy Resources Close to the Greek Islands

Daniel Ganea, Valentin Amortila *, Elena Mereuta and Eugen Rusu

Department of Mechanical Engineering, Faculty of Engineering, “Dunărea de Jos” University of Galati, 47 Domneasca Street, Galati 800008, Romania; [email protected] (D.G.); [email protected] (E.M.); [email protected] (E.R.) * Correspondence: [email protected]; Tel.: +40-741-772-778

Received: 28 April 2017; Accepted: 7 June 2017; Published: 15 June 2017

Abstract: The objective of this work is to analyze the wind and wave energy potential in the proximity of the Greek islands. Thus, by evaluating the synergy between wind and waves, a more comprehensive picture of the renewable energy resources in the target area is provided. In this study, two different data sources are considered. The ﬁrst data set is provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) through the ERA-Interim project and covers an 11-year period, while the second data set is Archiving, Validation and Interpretation of Satellite Oceanographic data (AVISO) and covers six years of information. Using these data, parameters such as wind speed, signiﬁcant wave height (SWH) and mean wave period (MWP) are analyzed. The following marine areas are targeted: Ionian Sea, Aegean Sea, Sea of Crete, Libyan Sea and Levantine Sea, near the coastal environment of the Greek islands. Initially, 26 reference points were considered. For a more detailed analysis, the number of reference points was narrowed down to 10 that were considered more relevant. Since in the island environments the resources are in general rather limited, the proposed work provides some outcomes concerning the wind and wave energy potential and the synergy between these two natural resources in the vicinity of the Greek islands. From the analysis performed, it can be noticed that the most energetic wind conditions are encountered west of Cios Island, followed by the regions east of Tinos and northeast of Crete. In these locations, the annual average values of the wind power density (Pwind) are in the range of 286–298.6 W/m2. Regarding the wave power density (Pwave), the most energetic locations can be found in the vicinity of Crete, north, south and southeast of the island. There, the wave energy potential is in the range of 2.88–2.99 kW/m.

Keywords: wind and wave power; Greek islands; coastal environment; renewable energy; synergy

1. Introduction The objective of this paper is to present a more comprehensive picture of the wind and wave energy potential close to the Greek islands. These are located in the Mediterranean Sea, more speciﬁc in the Ionian Sea, Aegean Sea, Sea of Crete, Libyan Sea and Levantine Sea (Figure1). The Ionian Sea basin is located south of the Adriatic Sea, between Greece (east) and Italy (west) and Libya Sea (south). It has a maximum depth that exceeds 5121 m and a volume of 10.8 × 104 km3 [1]. The surface of the Ionian Sea is 173,493 km2 [2]. The Aegean Sea basin has a maximum depth of 2568 m, a surface area of 192,026 km2 [2] and a volume of 7.4 × 104 km3 [1]. The Aegean Sea is located between Turkey (east) and Greece (west).

Sustainability 2017, 9, 1025; doi:10.3390/su9061025 www.mdpi.com/journal/sustainability Sustainability 2017, 9, 1025 2 of 22 Sustainability 2017, 9, 1025 2 of 22

Figure 1. The geographical positions of the 26 reference points: (A) Ionian Sea; (B) Aegean Sea; (C) Figure 1. The geographical positions of the 26 reference points: (A) Ionian Sea; (B) Aegean Sea; (C)Sea Seaof Crete; of Crete; (D) (D)Levantine Levantine Sea; Sea; and and (E) (E)Libyan Libyan Sea Sea(figure (ﬁgure processed processed from from Google Google Earth Earth (2017)). (2017)).

The Sea of Crete has a maximum depth of 3294 m [3] and it is part of the southern Aegean Sea. The seaThe is Sea located of Crete north has of a Crete, maximum being depth stretched of 3294 from m the [3] andMyrtoan it is part Sea ofin the southernnortheast, Aegean the islands Sea. Theof Kythera sea is located and Antikythera north of Crete, in the being east, stretched and west from of the the islands Myrtoan of Rhodes, Sea in the Karpathos northeast, and the Kassos. islands of Kythera and Antikythera in the east, and west of the islands of Rhodes, Karpathos and Kassos. The surface of the Levantine Sea is over 320,000 km2, reaching a depth of 4384 m [4]. This basin 2 is borderedThe surface in the of thenorthwest Levantine by Sea the is Aegean over 320,000 Sea, kmin the, reaching north aby depth Turkey, of 4384 at mthe [4 east]. This by basin Syria, is borderedLebanon, inIsrael the and northwest the Gaza by Strip the Aegean and at the Sea, south in the by north Egypt by and Turkey, Libya. at the east by Syria, Lebanon, IsraelFinally, and the the Gaza Libyan Strip Sea and is at located the south south by of Egypt Crete, and west Libya. of the Levantine Sea and north of Libya. Finally,The Greek the climate Libyan is Sea predominantly is located south Mediterranea of Crete, westn and of theinfluenced Levantine by Seathe andEtesian north winds. of Libya. These are strongThe Greek winds climate that blow is predominantly from May to Mediterranean October with and a high influenced frequency by the in EtesianJuly and winds. August. These A aresignificant strong winds weather that influence blow from is May notable to October in the with basins a high of the frequency Aegean in and July andIonian August. seas. AThe significant Etesian weatherwinds are influence stronger is in notable the afternoon in the basins and blow of the from Aegean the and northeast Ionian to seas. theThe north Etesian in the winds northern are strongerAegean inbasin, the afternoonwhile in the and central blow part from of the the northeast basin blow to thefrom north the north in the [5]. northern Aegean basin, while in the centralIn part2014, of the the Greek basin electricity blow from production the north [5 was]. 48 TWh, while the consumption was of 53 TWh. The Inmain 2014, energy the Greek sources electricity are produced production from was fossil 48 TWh,fuels 70.4% while the(out consumption of total installed was ofcapacity), 53 TWh. Thehydroelectric main energy plants sources 11.4% areand produced 15.1% coming from fossilfrom renewable fuels 70.4% sources (out of (RES). total installedOn a global capacity), scale, hydroelectriccomparing the plants level of 11.4% the produced and 15.1% energy coming from from RES, renewable Greece is sources ranked (RES).at number On a20. global Denmark, scale, comparingGermany and the Nicaragua level of the occupy produced the first energy three from positions RES, in Greece 2012. is ranked at number 20. Denmark, GermanyNevertheless, and Nicaragua due to occupyits geographical the first three positioning positions and in 2012.characteristics, 17,400 km of coast length and aNevertheless, maritime surface due to of its 114,507 geographical km2, the positioning Greek marine and characteristics,environment represents 17,400 km a of very coast suitable length 2 andframe a maritimefor an intense surface RES of exploitation. 114,507 km , the Greek marine environment represents a very suitable frame for anAccording intense RES to the exploitation. National Renewable Energy Action Plan, developed according to the directive 2009/28/EC,According the toGreek the National Ministry Renewable of Environment, Energy ActionEnergy Plan, & Climate developed Change according [6] has to theestimated directive a 2009/28/EC,balance between the Greekthe conventional Ministry of Environment,methods (lignite, Energy petroleum, & Climate natural Change gas, [6] hasetc.) estimated and RES a balance(geothermal, between photovoltaic, the conventional wind and methods hydro, (lignite, etc.) fo petroleum,r electricity natural generation. gas, etc.) It andis estimated RES (geothermal, that, in photovoltaic,2017, the energy wind production and hydro, capacity etc.) for will electricity be close generation. to 62 TWh, It is69% estimated of the energy that, in 2017,being theproduced energy productionusing conventional capacity methods will be close and to31% 62 using TWh, RES 69% (11 of the TWh energy wind being and 5.5 produced TWh hydro, using etc.). conventional In 2018, methodsGreek executives and 31% estimate using RES an increase (11 TWh of windthe energy and 5.5 production TWh hydro, capacity etc.). by In 3.1%. 2018, A Greekdecrease executives by 2.3% estimateof the conventional an increase ofenergy the energy production production and capacityan increase by 3.1%.of the A RES decrease energy by 2.3%production of the conventional capacity by energy13.6% is production desired. In and 2019, an increasethe energy of theproduction RES energy capacity production is estimated capacity to by grow 13.6% by is 3%. desired. RES Inenergy 2019, thegeneration energy productionwill increase capacity by 11.3%, is estimated while the to co grownventional by 3%. RESmethods energy will generation produce willwith increase 2.4% less by 11.3%,energy. while Furthermore, the conventional according methods to the will current produce estimates, with 2.4% the less year energy. 2020 Furthermore, comes with accordinga dramatic to thechange current of picture. estimates, Thus, the an year RES 2020 energy comes production with a dramatic representing change 41.7% of picture.of the total Thus, installed an RES capacity energy (68 TWh) is desired. According to these statistics, a drastic decrease of the conventional electricity production is previewed in the favor of the RES. At this point, Greece’s proposed plan for a Sustainability 2017, 9, 1025 3 of 22 production representing 41.7% of the total installed capacity (68 TWh) is desired. According to these statistics, a drastic decrease of the conventional electricity production is previewed in the favor of the RES. At this point, Greece’s proposed plan for a sustainable development emphasis on wind energy production growth (more than 64% compared to 2017) also has to be highlighted. The topic of energy is an extremely important one. Researchers all over the world are trying to find the best technologies to distribute electricity more effectively, economically, and securely even to remote located areas. Combined distributed energy resources (DER) form microgrids (MG) that are usually used to counteract these problems [7–9]. Distributed energy resources typically use renewable energy sources, and increasingly play an important role in the electric power distribution system. Real-time energy management systems, based on complex algorithms, are implemented for increasing MG efficiency, avoiding instability in the power generated by the imbalance between the generated power and the load demand [9–13]. The marine areas represent the most sustainable environments from the point of view of the renewable energy extraction [14] while islands can be considered the perfect locations for MG implementation. Economically speaking, marine areas have a significant influence on the global financial mechanism. Besides ship transportation and conventional resource exploitation, these areas are very competitive regarding RES exploitation. From this perspective, an actual trend is represented by the joint research studies on wind and waves. Previous studies focused on evaluating the wave or the wind conditions of the ocean coastal environments of Atlantic, Pacific and Indian [15–22] in order to find the best areas for WEC or wind turbine implementation. By analyzing the resulted capacity factor of a Wave Dragon device, it can be observed that the most promising location for wave energy exploration are south of South America, Africa, Australia and Greenland. The capacity factor was in the range 37.8–57.5%. In these studies, the data were provided by numerical models, or based on measurements. Enclosed and semi-enclosed seas are also vital energy sources. Although their energy potential is not as high as an ocean, there is an upward trend in evaluating them [15,23–28]. Previous studies, developed on altimeter data, reanalysis data or in situ measurements, showed that enclosed seas as the Black Sea, Caspian Sea and also Mediterranean Sea can be reliable energy sources for the proximal territories. By analyzing the performances of a Vesta V90.3 wind turbine within the Mediterranean Sea, it can be observed that the capacity factor has optimal values. Depending on the studied area, this factor varies in the best cases in the range 40% to 70%. A single marine location can be used for capturing various RES (wind, wave, thermal energy, etc.) using hybrid farms [29–31], or by collocating wave energy converters in the vicinity of the wind turbines. Marine energy exploration also has its risks and rewards. Besides producing green energy, wind turbines, wave energy converters and hybrid farms are expensive and pose a large risk in development [32]. Even so, according to a recent study [33], there is an actual trend in sustainable electricity generation not only among G20 countries but all over the word. Since 2005 to 2014, even if the conversion to energy of RES does not always have a positive relationship with sustainability, RES exploitation has gained ground to the detriment of conventional resources. A solution of this problem in order to decrease the LCOE (levelized the cost of electricity) and diminish the risk/reward factor is to use for the exploitation of multiple RES one common system [34–36]. This solution can have crucial benefits. The most important one is the low cost of the electric grid infrastructure. Using a common grid infrastructure, the most significant cost of an offshore project (a third of the project) can be diminished. In addition, a shared location can reduce the operational and the maintenance costs. Furthermore, the marine farms can also have environmental benefits [37,38] by decelerating the erosion processes. Studies show that, in some cases, the down wave climate and especially the nearshore circulation patterns that control the beach dynamics can be significantly influenced by the presence of a marine energy park. To this point, it can be mentioned that joint evaluations of the wind and wave energy in the vicinity of the Greek islands, highlighting the synergy between the two renewable resources, were not performed up to now. In general, most of the existing studies are focused only on one renewable Sustainability 2017, 9, 1025 4 of 22 resource. From this perspective, the objective of the present work is to provide a more comprehensive picture of the potential in terms of renewable energy of the coastal environment located in the vicinity of the Greek islands. Taking into account the fact that the island environments are in general poor in conventional sources of energy, the fact that they might have a good potential in terms of marine resources represents an issue of enhanced importance for a sustainable development of these areas. From this perspective, the objective of the present work is to evaluate the potential of the main renewable resources (wind and waves) in the island environment of Greece. Furthermore, the novelty of this article lies in the fact that, for now, the synergy between the wind and wave energy close to the Greek islands has not yet been evaluated in detail. In this study, two sets of data were analyzed. The first covers the 11-year period between 1 January 2005 to 31 December 2015, while the second the six-year period 1 January 2010 to 31 December 2015.

2. Materials and Methods

2.1. The Target Areas The geographical space of the target areas is located in the ranges: 33.0◦N to 42.0◦N, latitude and 18.0◦E to 30.0◦E, longitude. Thus, 26 reference points have been considered in the nearshore of the main Greek islands. When planning this study, three important aspects have been taken into account. The first is represented by the distance to the shore that should not exceed 4 km. The second is the sea depth that should not exceed the limit of 100 m, and finally, the third is that the selected points should be located in the proximity of an island. Regarding the distance to the shore, in this study, only 29.3% of the selected points do not match the first condition. Five of the points studied exceed the limit of 4 km, mainly because they were selected to serve more than one island. Figure1 illustrates the geographical positions of the reference points selected. The study area was divided into five zones, denoted as A, B, C, D and E. Zone A consists of 5 points (A1 to A5), corresponding to the Ionian Sea basin. These points are located at a minimum distance to the shore of about 1.8 km and a maximum distance of 2.92 km, while the sea depths vary from 62 m to 86 m (Table1). Zone B contains 8 points (B1 to B8). These points are located in the Aegean Sea at a distance ranging from 1.6 km to 14 km and with sea depths between 60 m and 98 m.

Table 1. The geographical locations and the main characteristics of the points considered in the Ionian and Aegean seas.

Distance to Shore Sea Point Latitude Longitude Depth (m) Proximity Island (km) A.1 39.63 19.71 62 Kerkyra 2.50 A.2 38.46 20.52 79 Kefallonia 2.20 Ionian A.3 38.06 20.53 62 Kefallonia 3.74 A.4 37.68 20.76 86 Zakynthos 1.80 A.5 36.28 22.89 77 Kythira 1.92 B.1 39.88 25.46 60 Limnos 8.00 B.2 38.99 26.27 67 Lesvos 1.67 B.3 38.49 25.84 73 Cios 2.41 B.4 37.66 25.21 71 Tinos 2.70 Aegean B.5 37.28 24.87 98 Syros 8.80 B.6 37.44 26.57 90 Patmos 5.47 B.7 36.89 25.25 82 Naxos 14.00 B.8 36.84 26.94 88 Kos 7.00

The geographical locations and the main characteristics of the last 13 points considered are presented in Table2. Thus, zone C consists of 8 points (C1 to C8), all of them located in the Sea of Sustainability 2017, 9, 1025 5 of 22

Crete. It has to be mentioned that all of the points selected in zone C match the three initial conditions outlined. The distance to shore varies from 1.34 km to 3.55 km while the sea depth from 63 m to 96 m.

Table 2. The geographical locations and the main characteristics of the points considered in the Crete, Levantine and Libyan seas.

Distance to Shore Sea Point Latitude Longitude Depth (m) Proximity Island (km) C.1 36.17 23.09 92 Kythira 3.56 C.2 36.66 24.29 63 Milos 3.22 C.3 36.49 26.37 96 Astypalaia 2.39 C.4 36.13 27.68 89 Rhodes 1.93 Crete C.5 35.57 27.06 73 Karpathos 1.49 C.6 35.34 26.31 87 Crete 2.27 C.7 35.48 25.22 89 Dia 1.34 C.8 35.71 23.73 95 Crete 2.00 D.1 36.00 27.95 98 Rhodes 2.98 Levantine D.2 35.35 26.95 92 Kasos 2.14 E.1 35.01 25.95 96 Crete 2.20 Libyan E.2 34.91 24.77 95 Crete 1.60 E.3 35.18 24.03 71 Crete 1.50

Zone D consists only of 2 points D1 and D2 located in the Levantine Sea. The ﬁrst point is in the proximity of the Rhodes Island (2.98 km), while the second is close to Kasos Island (2.14 km). Both points are located at a maximum sea depth of approximately 90 m. The Libyan Sea basin corresponds to zone E, and the 3 reference points considered are E1 to E3. These points are located south of Crete at an average distance to shore about 1.8 km and a sea depth average value of 87 m.

2.2. The ECMWF Data Set ECMWF (European Centre for Medium-Range Weather Forecasts) creates global data sets that describe the atmosphere and oceans in recent history. In order to reanalyze the archived observations, it uses forecast models and data assimilation techniques. The system developed includes a 4D analysis that has 12 h analysis windows. ERA-Interim is an ongoing ECMWF project (1979–present) that contains quality data sets with a various number of marine environmental parameters. For the presented study, the ERA-Interim dataset was processed. A spatial resolution of 0.75◦ × 0.75◦ was considered. The time interval represents 11 years of data, 1 January 2005 to 31 December 2015, for two streams. The ﬁrst stream is the atmospheric model. This dataset contains parameters as 10-m U and 10-m V wind components. These parameters can be used to determine the wind speed at 10-m height (U10) and also the wind direction. The second stream is represented by the wave model. This stream contains parameters as the signiﬁcant wave height of combined wind-waves and swell, mean wave direction and mean wave period for four hourly intervals (corresponding to 00:00:00, 06:00:00, 12:00:00, 18:00:00) of each day. Both ECMWF models can be used to determine the power generated by wind and waves corresponding to a certain location.

2.3. The Aviso Date Set Archiving, validation and interpretation of satellite oceanographic data (AVISO) is an important source of satellite measurements regarding the wind and wave parameters. As a principle, it measures the time taken by a pulse to travel back and forth from a satellite antenna to its receiver and also the Sustainability 2017, 9, 1025 6 of 22 shape and intensity. Altimeter data are used also to compute the wind velocity and the signiﬁcant wave height (SWH). For processing altimeter data from diverse missions (Saral, Cryosat-2, Jason-1&2, T/P, Envisat, GFO, ERS-1&2 and even Geosat), the Ssalto/Duacs system processes are used. In this study, the used satellite data consists of one measurement per day covering the period 1 January 2010 to 31 December 2015. A spatial resolution of 1◦ × 1◦ was considered on a local scale.

2.4. Wind Power Potential Using the power density index, the wind energy potential in a chosen location can be computed as:

1 P = ρ × U3 , (1) wind 2 10

3 where U10 represents the wind speed at 10 m (in m/s), and ρ is the air density (1.22 kg/m ). Because most offshore wind turbines function at 80 m height, the initial data set can be adjusted to match this proﬁle using a logarithmic law [39]:

ln z80 z0 U80 = U × , (2) 10 ln z10 z0 where z0 is the sea surface roughness (0.0002 m), while z10 and z80 represents the heights at 10 m and 80 m, respectively. Thus, the wind energy potential at 80 m height can be determined using the following power density index: 1 P = ρ × U3 , (3) wind 2 80 The output energy [kW] generated by a certain wind turbine can be determined by the follow formula: Pwtgenerated = Pwind × A × Cp, (4) where A is the swept area of the wind turbine while Cp is the efﬁcient coefﬁcient based on Betz law. For simulating a real case scenario, a Siemens SWT-3.6-120 wind turbine [40] has been considered, and its characteristics are provided in Table3.

Table 3. Operational data and rotor information of Siemens SWT 3.6-120 wind turbine.

Siemens SWT 3.6-120 Operational Data Rotor Rated power (MW) 3.6 No. of blades 3 Cut-in wind speed (m/s) 3 Blade length (m) 58.5 Rated wind speed (m/s) 12.5 Rotor diameter (m) 120 Cut-out wind speed (m/s) 25 Swept area (m2) 11,300

2.5. Wave Power Potential The wave power potential or the energy ﬂux (kW/m) in deep waters can be determined using the following equation: ρ × g2 P = × T × H2, (5) wave 64 × π m s 3 where ρ is the sea water density (1025 kg/m ), g is the acceleration generated by gravity, Tm is the wave periodicity, while Hs represents the signiﬁcant wave height. Sustainability 2017, 9, 1025 7 of 22

3. Results

3.1. Analysis of the Wind Intensity Distribution A detailed investigation of the wind intensity distribution in the nearshore of the Greek islands is presented in this subsection. The analysis focuses on the wind conditions in terms of the wind speed at 80 m height and the wind direction. Figure2 presents the wind conditions of the entire area studied corresponding to the 11-year period considered (2005–2015). Figure2a illustrates the annual average, diurnal/nocturnal and maximum/mean values. In this study, the diurnal period is considered the interval from 6 to 18, while the nocturnal period from 18 to 6. ECMWF provided this data set. Following the analysis of the results, it can be noticed that the wind speed is rather constantly distributed in the Greek nearshore. By analyzing the wind conditions in the Ionian Sea, it can be mentioned that the wind tends to be more intense during the diurnal period, except for the reference point A5. The maximum mean value recorded in this region was 19.95 m/s (corresponding to the reference point A4 with an annual average of 6.13 m/s) while the minimum is 16.88 m/s (for the reference point A1). In addition, in the reference point A5, the energy potential has a quite balanced distribution, concerning the diurnal and nocturnal wind intensities. Regarding zone B (Aegean Sea), a rather different situation can be noticed. In this area, the points studied have a higher energy potential. The maximum value recorded was 22.05 m/s in the point B3, while the minimum corresponds to the point B8 (20.74 m/s). The annual average value recorded in the reference point B3 is 7.88 m/s. By analyzing the conditions in area B, it is noticed that the wind is more intense, globally speaking. Regarding now the diurnal and nocturnal distributions, it can also be noticed that the wind is more intense during the nocturnal period for 77.7% of the reference points considered. Zone C is the area associated with the Sea of Crete. By analyzing the data set, it cannot be identiﬁed a clear distribution between the diurnal and nocturnal wind intensities. Regarding the highest speed wind recorded in this area, this was 21.47 m/s in the reference point C2, characterized by an annual average value of 7.28 m/s. Areas D and E show a high energy potential. In the reference points considered for these two areas, the nocturnal period seems to be more energetic. The maximum wind speed recorded in zone D is 20.67 m/s (point D2), while, in zone E, it is 20.62 m/s (point E1). As regards the annual average value, this is in the point D2 7.63 m/s and 7.66 m/s for the reference point E1. Figure2b illustrate the wind conditions at 80 m height for all of the 26 reference points according to the AVISO data set corresponding to the six-year interval (2010–2015). By analyzing the results presented in Figure2, it can be noticed that, in terms of the wind intensity, there is a considerable difference regarding the results corresponding to the two different data sets. Thus, by comparing Figure2a,b, it can be mentioned that the AVISO data set had a more ﬂattened distribution based on the annual average and the maximum mean values. The different distributions illustrated in Figure2 when considering the two data sets (ECMWF and AVISO) has as possible explanations the facts that ECMWF data is related to an 11-year time interval, while the AVISO data is only six years. At the same time, the resolutions in both space and time of the data are also quite different. Thus, for AVISO, the spatial resolution is 1◦ and the temporal resolution 24 h, while, for the ECMWF data, the spatial resolution is 0.75◦ and the temporal resolution 6 h. Sustainability 2017, 9, 1025 8 of 22 Sustainability 2017, 9, 1025 8 of 22

(a)

(b)

Figure 2.2. WindWind speed speed at at 80 80 m m height, height, evaluation evaluation corresponding corresponding to all to 26-referenceall 26-reference points. points. ECMWF ECMWF data weredata were processed processed (a) for (a the) for 11-year the 11-year period period (2005–2015), (2005–2015), and AVISO and AVISO data set data (b) forset the(b) 6-yearfor the period6-year (2010–2015).period (2010–2015).

The ECMWF data set was taken into account to continue the study due to the fact that this data The ECMWF data set was taken into account to continue the study due to the fact that this data set is more complex in terms of the parameters available and covers a longer time period. For set is more complex in terms of the parameters available and covers a longer time period. For example, example, ECMWF data contain information about wind, U and V components that are suitable in ECMWF data contain information about wind, U and V components that are suitable in determining determining the wind direction. Moreover, the ECMWF data provides also a higher time resolution. the wind direction. Moreover, the ECMWF data provides also a higher time resolution. In choosing the most representative points for each of the five areas considered, the annual In choosing the most representative points for each of the ﬁve areas considered, the annual average values of the parameter U80 and also the maximum mean values were taken into account. average values of the parameter U and also the maximum mean values were taken into account. Thus, by analyzing the ECMWF data80 set (Figure 2a), it can be noticed that, regarding the parameter Thus, by analyzing the ECMWF data set (Figure2a), it can be noticed that, regarding the parameter U80, both the highest maximum mean and the annual average correspond to the reference points U , both the highest maximum mean and the annual average correspond to the reference points selected,80 which are A4 and A5 for zone A, B3 and B4 for zone B, C6 and C7 for zone C, D1 and D2 for selected, which are A4 and A5 for zone A, B3 and B4 for zone B, C6 and C7 for zone C, D1 and D2 for zone D and E1 and E3 for zone E. zone D and E1 and E3 for zone E. The time intervals considered are: spring diurnal (SP-D), spring nocturnal (SP-N), summer The time intervals considered are: spring diurnal (SP-D), spring nocturnal (SP-N), summer diurnal diurnal (SM-D), summer nocturnal (SM-N), autumn diurnal (A-D), autumn nocturnal (A-N), winter (SM-D), summer nocturnal (SM-N), autumn diurnal (A-D), autumn nocturnal (A-N), winter diurnal diurnal (W-D), and winter nocturnal (W-N). (W-D), and winter nocturnal (W-N). Figure 3 illustrates the wind conditions at 80 m heights for the two points located in zone A. The Figure3 illustrates the wind conditions at 80 m heights for the two points located in zone A. distribution by classes indicates that the wind intensity is mainly less than 10 m/s. By analyzing the The distribution by classes indicates that the wind intensity is mainly less than 10 m/s. By analyzing the results corresponding to the reference point A4, it can be noticed that the wind blows mainly from results corresponding to the reference point A4, it can be noticed that the wind blows mainly from the the SE (Figure 3c), while, for the reference point A5 from the SW, E and ESE (Figure 3d). The SE (Figure3c), while, for the reference point A5 from the SW, E and ESE (Figure3d). The distribution distribution by intervals (seasons and day periods) is presented in Figure 3b. It can be observed that by intervals (seasons and day periods) is presented in Figure3b. It can be observed that the wind the wind is more intense during the winter period. During the wintertime, the mean values are in is more intense during the winter period. During the wintertime, the mean values are in the range the range 7.34–7.75 m/s, while, for the other periods, in the range of 4.59–6.35 m/s. Regarding now 7.34–7.75 m/s, while, for the other periods, in the range of 4.59–6.35 m/s. Regarding now the diurnal the diurnal and nocturnal periods, it can be noticed that, for the point A4, the wind is more intense and nocturnal periods, it can be noticed that, for the point A4, the wind is more intense during the during the diurnal period, while, for the point A5, it tends to be more active during the nocturnal diurnal period, while, for the point A5, it tends to be more active during the nocturnal period. period.

Sustainability 2017, 9, 1025 9 of 22 Sustainability 2017, 9, 1025 9 of 22

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(a)

(b) (c) (d)

Figure 3. Zone A wind speed evaluation at 80 m height; (a) wind speed intervals associated with the Figure 3. Zone A wind speed evaluation at 80 m height; (a) wind speed intervals associated with wind rose charts; (b)( bwind) speed mean values for different in(tervalsc) of the period studied (1 (Januaryd) the wind rose charts; (b) wind speed mean values for different intervals of the period studied 2005Figure to 313. ZoneDecember A wind 2015.); speed (c )evaluation wind roses at corresponding 80 m height; ( ato) windpoint speed A4; (d intervals) wind roses associated corresponding with the (1 January 2005 to 31 December 2015.); (c) wind roses corresponding to point A4; (d) wind roses towind point rose A5. charts; (b) wind speed mean values for different intervals of the period studied (1 January corresponding to point A5. 2005 to 31 December 2015.); (c) wind roses corresponding to point A4; (d) wind roses corresponding Forto point the zoneA5. B, the wind conditions are presented in Figure 4. It can be noticed that the wind energyFor the potential zone B, during the wind the conditionsdiurnal and are nocturna presentedl periods in Figure is well4 .balanc It caned. be The noticed most thatenergetic the wind energyperiod potentialFor for the both duringzone points B, the (B3 wind diurnal and conditions B4) and was nocturnal winter are presented diurnal periods (Figurein isFigure well 4b), balanced.4. Itwhile can bethe The noticed less most energetic that energetic the one wind is period spring nocturnal. The mean values for the winter period are in the range 8.81–9.01 m/s, while, for for bothenergy points potential (B3 andduring B4) the was diurnal winter and diurnal nocturna (Figurel periods4b), is while well thebalanc lessed. energetic The most oneenergetic is spring spring,period forsummer both pointsand autumn, (B3 and in B4) the was range winter 6.95–7.71 diurnal m/s. (Figure By analyzing 4b), while Figure the less 4b, energetic it can be one also is nocturnal. The mean values for the winter period are in the range 8.81–9.01 m/s, while, for spring, noticedspring nocturnal.that the wind The intensitymean values had foran almostthe winter linear period ascending are in trend. the range The 8.81–9.01wind conditions m/s, while, for thefor summerreferencespring, and summer autumn,points B3and inand autumn, the B4 range were in similar6.95–7.71 the range (Figure m/s.6.95–7.71 4b,c). By analyzing Them/s. wind By analyzing speed Figure was4 b,Figure mainly it can 4b, beless it also thancannoticed be15 m/salso that the windandnoticed its intensity direction that the had waswind an from intensity almost the SW. linear had an ascending almost lin trend.ear ascending The wind trend. conditions The wind for conditions the reference for the points B3 andreference B4 were points similar B3 and (Figure B4 were4b,c). similar The wind(Figure speed 4b,c). wasThe mainlywind speed less was than mainly 15 m/s less and than its 15 direction m/s was fromand its the direction SW. was from the SW.

(a)

(b) (c) (d)

Figure 4. Zone B wind speed evaluation at 80 m height; (a) wind speed intervals associated with the (d) wind rose charts; (b)) wind speed mean values for different( cin) tervals of the period studied (1 January 2005Figure to 314. ZoneDecember B wind 2015.); speed (c evaluation) wind roses at corresponding80 m height; (a to) wind point speed B3; (d intervals) wind roses associated corresponding with the Figure 4. Zone B wind speed evaluation at 80 m height; (a) wind speed intervals associated with towind point rose B4. charts; (b) wind speed mean values for different intervals of the period studied (1 January the wind rose charts; (b) wind speed mean values for different intervals of the period studied 2005 to 31 December 2015.); (c) wind roses corresponding to point B3; (d) wind roses corresponding (1 January 2005 to 31 December 2015.); (c) wind roses corresponding to point B3; (d) wind roses Figureto point 5 B4. shows the wind conditions at 80 m height corresponding to zone C. The distribution by classescorresponding indicates to that point the B4. wind speed was mainly less than 15 m/s (Figure 5c,d). Figure 5c,d also showFigure that, in 5 theshows reference the wind point conditions C6, the main at 80 windm height direction corresponding is from S-SE to zone and C.SE Thewhile distribution for point C7 by fromFigureclasses S and5indicates shows S-SE. theAccordingthat wind the wind conditionsto the speed ECMWF was at 80 mainlydata, m heightin le zoness than correspondingC, the 15 windm/s (Figure was to more zone5c,d). intense C.Figure The during 5c,d distribution alsothe by classeswintershow that, indicatesperiod. in the The thatreference mean the values wind point speedareC6, inthe the was main range mainly wind 8.73–8.77 direction less than m/s, is 15fromwhile m/s S-SE for (Figure andthe otherSE5 c,d).while intervals Figurefor point in5 c,dthe C7 also rangefrom S6.31–7.44 and S-SE. m/s. According By analyzing to the theECMWF diurnal data, and in no zonecturnal C, the wind wind distributions, was more intense it can beduring noticed the show that, in the reference point C6, the main wind direction is from S-SE and SE while for point C7 thatwinter this period. varies forThe point mean C6. values Regarding are in the referencerange 8.73–8.77 point C7,m/s, the while wind for was the slightly other intervals active during in the from S and S-SE. According to the ECMWF data, in zone C, the wind was more intense during the therange nocturnal 6.31–7.44 period. m/s. InBy addition, analyzing Figure the diurnal 5b indicates and no thatcturnal the refe windrence distributions, point C6 stands it can out be because noticed winteritthat shows period. this avaries high The energyfor mean point potential values C6. Regarding are even in during the the range reference summer. 8.73–8.77 point C7, m/s, the while wind was for theslightly other active intervals during in the rangethe 6.31–7.44 nocturnal m/s. period. By analyzingIn addition, the Figure diurnal 5b indicates and nocturnal that the windreference distributions, point C6 stands it can out be because noticed that this variesit shows for a high point energy C6. Regarding potential even the during reference summer. point C7, the wind was slightly active during the nocturnal period. In addition, Figure5b indicates that the reference point C6 stands out because it shows a high energy potential even during summer. Sustainability 2017, 9, 1025 10 of 22 Sustainability 2017, 9, 1025 10 of 22

Sustainability 2017, 9, 1025 10 of 22 (a)

(a)

(b) (c) (d)

Figure 5. Zone C wind speed evaluation at 80 m height; (a) wind speed intervals associated with the Figure 5. Zone C wind speed evaluation at 80 m height; (a) wind speed intervals associated with the wind rose charts; ((b) wind speed mean values for different(c in) tervals of the period studied( d(1) January wind rose charts; (b) wind speed mean values for different intervals of the period studied (1 January 2005 to 31 December 2015.); (c) wind roses corresponding to point C6; (d) wind roses corresponding 2005Figure to 31 December 5. Zone C wind 2015.); speed (c) wind evalua rosestion at corresponding 80 m height; (a to) wind point speed C6; (intervalsd) wind associated roses corresponding with the to to point C7. pointwind C7. rose charts; (b) wind speed mean values for different intervals of the period studied (1 January 2005 to 31 December 2015.); (c) wind roses corresponding to point C6; (d) wind roses corresponding The ECMWF data shows that, for the reference point D1, the wind was more intense during the to point C7. diurnalThe ECMWF period (Figure data shows 6b). Regarding that, for thethe reference point point D2, D1, the the wind wind was was slightly more active intense during during the the diurnalnocturnal periodThe ECMWF period. (Figure dataFigure6b). shows Regarding 6b alsothat, showsfor the the reference thatreference the pointwind point wasD2,D1, the more wind wind energetic was was more slightly during intense activesummer during during and the the winter. During the summer, the mean values were in the range 6.87–8.11 m/s, while during the nocturnaldiurnal period. period Figure(Figure6 6b).b also Regarding shows thatthe reference the wind point was D2, more the energeticwind was slightly during active summer during and the winter. winter, the mean wind speed values are in the range 7.40–8.29 m/s. Regarding spring and autumn, Duringnocturnal the summer, period. theFigure mean 6b valuesalso shows were that in thethe rangewind 6.87–8.11was more m/s,energetic while during during summer the winter, and the these were in the range 6.10–7.16 m/s. By analyzing the intensity, it can be noticed that, for both meanwinter. wind speedDuring values the summer, are in thethe rangemean 7.40–8.29values were m/s. in the Regarding range 6.87–8.11 spring andm/s,autumn, while during these the were in referencewinter, the points, mean thewind wind speed speed values was are mainly in the less range than 7.40–8.29 15 m/s (Figurem/s. Regarding 6c,d). Figure spring 6c,d and also autumn, show the range 6.10–7.16 m/s. By analyzing the intensity, it can be noticed that, for both reference points, that,these in were points in D1the andrange D2, 6.10–7.16 the wind m/s. direction By analyzin is mainlyg the from intensity, the SE. it can be noticed that, for both the windreference speed points, was the mainly wind less speed than was 15 mainly m/s (Figure less than6c,d). 15 m/s Figure (Figure6c,d 6c,d). also Figure show 6c,d that, also inpoints show D1 and D2,that, the in points wind D1 direction and D2, is the mainly wind direction from the is SE. mainly from the SE. (a)

(a)

(b) (c) (d)

Figure 6. Zone D wind speed evaluation at 80 m height; (a) wind speed intervals associated with the wind rose charts; ((b) wind speed mean values for different(c in) tervals of the period studied( d(1) January 2005 to 31 December 2015.); (c) wind roses corresponding to point D1; (d) point D2. FigureFigure 6. Zone 6. Zone D D wind wind speed speed evaluationevaluation at at 80 80 m mheight; height; (a) wind (a) wind speed speed intervals intervals associated associated with the with wind rose charts; (b) wind speed mean values for different intervals of the period studied (1 January the windFigure rose 7 illustrates charts; ( bthe) wind distributi speedon meanof wind values conditions for different for zone intervals E in correspondence of the period with studied the 2005 to 31 December 2015.); (c) wind roses corresponding to point D1; (d) point D2. (1U80 January parameter. 2005 toThe 31 distribution December 2015.); (mean (c )values) wind roses indicates corresponding that, in this to pointregion, D1; the (d )wind point was D2. more activeFigure during 7 illustratesthe winter. the Thus, distributi the windon of speed wind mean conditions values forduring zone winter E in correspondence were in the range with 8.54– the 8.93 m/s, while during spring, summer and autumn in the range 7.03–7.96 m/s. UFigure80 parameter.7 illustrates The thedistribution distribution (mean of values) wind conditions indicates that, for zone in this E inregion, correspondence the wind was with more the U80 Figure 7c,d shows that the wind speeds are mainly less than 15 m/s. Regarding now zone E, the parameter.active during The distribution the winter. Thus, (mean the values) wind speed indicates mean that,values in during this region, winter were the wind in the was range more 8.54– active wind direction was mainly from S-SE in point E1 and S-SW and E-SE in point E3. during8.93 the m/s, winter. while Thus,during thespring, wind summer speed an meand autumn values in duringthe range winter 7.03–7.96 were m/s. in the range 8.54–8.93 m/s, Figure 7c,d shows that the wind speeds are mainly less than 15 m/s. Regarding now zone E, the while during spring, summer and autumn in the range 7.03–7.96 m/s. wind direction was mainly from S-SE in point E1 and S-SW and E-SE in point E3. Figure7c,d shows that the wind speeds are mainly less than 15 m/s. Regarding now zone E, the wind direction was mainly from S-SE in point E1 and S-SW and E-SE in point E3. Sustainability 2017, 9, 1025 11 of 22 Sustainability 2017, 9, 1025 11 of 22 Sustainability 2017, 9, 1025 11 of 22

(a) (a)

(b) (c) (d) (b) (c) (d) Figure 7. Zone E wind speed evaluation at 80 m height; (a) wind speed intervals associated with the FigurewindFigure rose 7. 7. Zone Zonecharts; E Ewind ( windb) wind speed speed speed evaluation evaluation mean values at at80 80m for mheight; different height; (a) (windina)tervals wind speed speedof theintervals period intervals associated studied associated (1 with January with the wind2005the wind torose 31 charts; roseDecember charts; (b) wind2015.); (b) speed wind (c) wind mean speed roses values mean corresponding for values different for to differentin tervalspoint E1; of intervals (thed) windperiod of roses thestudied periodcorresponding (1 January studied 2005to(1 Januarypoint to 31 E3. December 2005 to 31 2015.); December (c) wind 2015.); roses (c )corresponding wind roses corresponding to point E1; (d to) wind point roses E1; (correspondingd) wind roses tocorresponding point E3. to point E3. 3.2. Analysis of Wave Intensity Distribution 3.2.3.2. Analysis Analysis of of Wave Wave Intensity Intensity Distribution Distribution Figure 7 shows a detailed picture of the wave conditions close to the Greek islands by Figure 7 shows a detailed picture of the wave conditions close to the Greek islands by evaluatingFigure 7the shows parameters a detailed Hs pictureand Tm offor the all wavethe 26 conditions reference closepoints. to theAs Greekdefined islands in Equation by evaluating (5), the evaluating the parameters Hs and Tm for all the 26 reference points. As defined in Equation (5), the wavethe parameters power is Has combinationand Tm for all between the 26 reference the square points. of the As definedsignificant in Equation wave height (5), the and wave the powerwave waveperiod.is a combination power For this is astudy, betweencombination the theECMWF squarebetween data of thethe set significantsquarewas take ofn thewaveinto significant consideration height and wave the due waveheight to the period. and fact the that For wave this period.datastudy, set theFor is ECMWFmorethis study, complex. data the set TheECMWF was ECMWF taken data into dataset considerationwas also take containn into dueinformation consideration to the fact about thatdue the thisto wavethe data fact period set that is more thisand datadirectioncomplex. set is and Themore also ECMWF complex. covers data a The longer also ECMWF contain time period. data information also The contain most about representative information the wave period about points andthe in terms directionwave ofperiod the and wave and also direction and also covers a longer time period. The most representative points in terms of the wave energycovers apotential longer timewere period. selected The having most as representative a basis the mean points values in termsof the ofparameters the wave H energys and Tm. potential Thus, energy potential were selected having as a basis the mean values of the parameters Hs and Tm. Thus, 10were reference selected points having have as a basisbeen theselected mean valuesfor a deta of theiled parameters analysis, Htwos and forT meach. Thus, of the 10 referencefive zones. points By 10analyzinghave reference been the selected points ECMWF forhave adata detailedbeen set selected (Figure analysis, 8),for twoita candeta for beiled each concluded analysis, of the five thattwo zones. the for mosteach By analyzing appropriateof the five the zones.points ECMWF Byfor analyzingthedata analysis set (Figure the of ECMWF 8the), it wave can data be intensity concludedset (Figure distribution that 8), it the can most beare concluded appropriate the same thatas points thethe referencemost for the appropriate analysis points of previouslypoints the wave for theconsideredintensity analysis distribution for of the the wind wave are analysis the intensity same (A4 as distribution theand reference A5 for zoneare points theA, B3 previouslysame and B4as forthe considered zonereference B, C6 for andpoints the C7 wind previouslyfor analysiszone C, consideredD1(A4 and and D2 A5 for for thezone zone wind D A, and analysis B3 E1 and and B4(A4 E3 for andfor zone zoneA5 B,for E). C6 zone From and A, C7this B3 for andperspective, zone B4 for C, zone D1 in and this B, C6 D2subsection, and for zoneC7 for there D zone and will C, E1 D1beand evaluatedand E3 D2 for for zone the zone E).parameters D From and thisE1 significant and perspective, E3 for wavezone in thisE).height From subsection, (Hs this) and perspective, therethe wave will period bein this evaluated subsection,(Tm) in the terms parameters there of theirwill be evaluated the parameters significant wave height (Hs) and the wave period (Tm) in terms of their meansignificant values wave for the height diurnal (Hs) and thenocturnal wave periodintervals. (Tm In) in addition, terms of the their evolution mean values of these for parameters the diurnal meanwasand nocturnalstudied values forwith intervals. the respect diurnal In to addition, and the nocturnalfour the seasons evolution intervals. each of thesedivided In addition, parameters into thetwo wasevolution intervals. studied of Thus, withthese respectthe parameters intervals to the wasstudiedfour studied seasons are: with eachspring respect divided diurnal to into the(SP-D), two four intervals. springseasons nocturnal Thus,each divided the intervals(SP-N), into summer studiedtwo intervals. are:diurnal spring Thus, (SM-D), diurnal the intervalssummer (SP-D), studiednocturnalspring nocturnalare: (SM-N), spring (SP-N), autumndiurnal summer diurnal(SP-D), diurnal (A-D),spring (SM-D), autumnnocturnal summer nocturnal (SP-N), nocturnal summer(A-N), (SM-N), winter diurnal autumn diurnal (SM-D), diurnal (W-D) summer (A-D), and nocturnalwinterautumn nocturnal nocturnal (SM-N), (W-N). (A-N),autumn winter diurnal diurnal (A-D), (W-D) autumn and winter nocturnal nocturnal (A-N), (W-N). winter diurnal (W-D) and winter nocturnal (W-N).

(a) (a) Figure 8. Cont. Sustainability 2017, 9, 1025 12 of 22 Sustainability 2017, 9, 1025 12 of 22

Sustainability 2017, 9, 1025 12 of 22

(b)

Figure 8. Main wave parameters, evaluation corresponding to all 26-reference points. ECMWF data Figure 8. Main wave parameters, evaluation corresponding to all 26-reference points. ECMWF data were processed (a) significant wave height (m); (b) wave period. were processed (a) significant wave height (m);( (bb)) wave period. FigureThe wave8. Main analysis, wave parameters, corresponding evaluation to the correspon points A4ding and to all A5, 26-reference is presented points. in Figure ECMWF 8. Regardingdata Thethe wereparameter wave processed analysis, significant (a) significant corresponding wave wave height, height toit can the(m); be points(b )noticed wave A4 period. that and it A5, is an is almost presented imperceptible in Figure difference8. Regarding the parameterof intensity significant between the wave diurnal height, and nocturnal it can be noticedintervals that(Figure it is 9a,c). an almost The analysis imperceptible corresponding difference to of The wave analysis, corresponding to the points A4 and A5, is presented in Figure 8. Regarding intensityeach betweenseason can the be diurnal seen in andFigure nocturnal 9b,d. By intervals analyzing (Figure these figures,9a,c). The it can analysis be concluded corresponding that, in the to each the parameter significant wave height, it can be noticed that it is an almost imperceptible difference Ionian Sea basin in terms of significant wave height, the waves were more intense during the winter seasonof intensity can be between seen in Figurethe diurnal9b,d. and By nocturnal analyzing intervals these figures,(Figure 9a,c). it can The be analysis concluded corresponding that, in the to Ionian period and less intense during the summer. Seaeach basin season in terms can be of significantseen in Figure wave 9b,d. height, By analyzing the waves these were figures, more it can intense be concluded during the that, winter in the period Regarding the wave period, it can be noticed that the reference point A4 was characterized by andIonian less intense Sea basin during in terms the of summer. significant wave height, the waves were more intense during the winter lower values, on average by 14%. period and less intense during the summer. RegardingThe histograms the wave presented period, in it canFigure be 10a,c noticed presen thatt the the evolution reference of point the wave A4 wasconditions characterized in the by Regarding the wave period, it can be noticed that the reference point A4 was characterized by lowerpoints values, from on the average Aegean by Sea. 14%. By analyzing the significant wave heights, diurnal against nocturnal, it lower values, on average by 14%. Thecan be histograms noticed that presented there is practically in Figure no 10 differena,c presentce of theintensity. evolution The seasonal of the wave distribution conditions shows in the The histograms presented in Figure 10a,c present the evolution of the wave conditions in the pointsthat from both the points Aegean have Sea. rather By analyzingsimilar characteristics the significant in terms wave of heights, significant diurnal wave against height. nocturnal, The points from the Aegean Sea. By analyzing the significant wave heights, diurnal against nocturnal, it it canmaximum be noticed mean that value there is isequal practically to 1.24 m no during difference winter of nocturnal intensity. (point The B3) seasonal while the distribution minimum is shows can be noticed that there is practically no difference of intensity. The seasonal distribution shows that both0.75 m points during have summer rather nocturnal similar (point characteristics B4) (Figure in 10b). terms According of significant to period, wave the height.waves in The the maximumpoint that both points have rather similar characteristics in terms of significant wave height. The B4 have slightly higher periods (Figure 10c,d). meanmaximum value is mean equal value to 1.24 is equal m during to 1.24 winter m during nocturnal winter (pointnocturnal B3) (point while B3) the while minimum the minimum is 0.75 m is during summer0.75 m nocturnal during summer (point nocturnal B4) (Figure (point 10b). B4) According (Figure 10b). to According period, the to wavesperiod, in the the waves point in B4 the have point slightly higherB4 have periods slightly (Figure higher 10 periodsc,d). (Figure 10c,d).

(a) (b)

Figure 9. Zone A, evaluation of the wave conditions considering the ECMWF data for the 11-year

interval 2005–2015; ((ca)) Hs mean values comparison of diurnal against nocturnal(d) for total time; (b) Hs mean values comparison of diurnal against nocturnal for each season; (c) Tm mean values Figure 9. Zone A, evaluation of the wave conditions considering the ECMWF data for the 11-year Figurecomparison 9. Zone A,of diurnal evaluation agains oft thenocturnal wave for conditions total time; considering (d) Tm mean the values ECMWF comparison data forof diurnal the 11-year interval 2005–2015; (a) Hs mean values comparison of diurnal against nocturnal for total time; (b) Hs intervalagainst 2005–2015; nocturnal (fora) eachHs meanseason. values comparison of diurnal against nocturnal for total time; mean values comparison of diurnal against nocturnal for each season; (c) Tm mean values (b) Hs mean values comparison of diurnal against nocturnal for each season; (c) Tm mean values comparison of diurnal against nocturnal for total time; (d) Tm mean values comparison of diurnal comparisonagainst nocturnal of diurnal for each against season. nocturnal for total time; (d) Tm mean values comparison of diurnal against nocturnal for each season. Sustainability 2017, 9, 1025 13 of 22 Sustainability 2017, 9, 1025 13 of 22

Sustainability 2017, 9, 1025 13 of 22

(a) (b)

Figure 10. Zone B, evaluation of the wave conditions considering the ECMWF data for the 11-year Figure 10. Zone B, evaluation of the wave conditions considering the ECMWF data for the 11-year interval 2005–2015; (a() cH) s mean values comparison of diurnal against nocturnal(d for) total time; (b) Hs interval 2005–2015; (a) H mean values comparison of diurnal against nocturnal for total time; mean values comparisons of diurnal against nocturnal for each season; (c) Tm mean values Figure 10. Zone B, evaluation of the wave conditions considering the ECMWF data for the 11-year (b) Hscomparisonmean values of diurnalcomparison against ofnocturnal diurnal for against total time; nocturnal (d) Tm mean for values each comparison season; (c )ofT diurnalm mean values interval 2005–2015; (a) Hs mean values comparison of diurnal against nocturnal for total time; (b) Hs comparisonagainst nocturnal of diurnal for againsteach season. nocturnal for total time; (d) Tm mean values comparison of diurnal mean values comparison of diurnal against nocturnal for each season; (c) Tm mean values against nocturnal for each season. Figurecomparison 11 presents of diurnal the againsanalysist nocturnal of the significant for total time; wave (d) height Tm mean and values of the comparison mean wave of diurnalperiod for the pointsagainst belonging nocturnal to for the each Sea season. of Crete, corresponding to the time interval January 2005–December Figure2015. Regarding 11 presents the theparameter analysis significant of the signiﬁcant wave height, wave no noticeable height anddifferences of the can mean be observed wave period by for the Figure 11 presents the analysis of the significant wave height and of the mean wave period for pointscomparing belonging the to diurnal the Sea and of nocturnal Crete, corresponding periods (Figure to11a). the By time analyzing interval the Januarydistribution 2005–December by seasons, 2015. the points belonging to the Sea of Crete, corresponding to the time interval January 2005–December Regardingit can be the noticed parameter that both signiﬁcant points had wavethe same height, evolution. no The noticeable highest values differences were recorded can be during observed by 2015. Regarding the parameter significant wave height, no noticeable differences can be observed by winter diurnal nocturnal. comparingcomparing the diurnal the diurnal and and nocturnal nocturnal periods periods (Figure 11a). 11a). By By analyzing analyzing the distribution the distribution by seasons, by seasons, it can beit can noticed be noticed that boththat both points points had had the the same same evolution.evolution. The The highest highest values values were wererecorded recorded during during winter diurnalwinter diurnal nocturnal. nocturnal.

(a) (b)

Figure 11. Zone C, evaluation of the wave conditions considering the ECMWF data for the 11-year interval 2005–2015; (a)( cH)s mean values comparison of diurnal against nocturnal(d )for total time; (b) Hs mean values comparison of diurnal against nocturnal for each season; (c) Tm mean values Figure 11. Zone C, evaluation of the wave conditions considering the ECMWF data for the 11-year Figure 11. Zone C, evaluation of the wave conditions considering the ECMWF data for the 11-year interval 2005–2015; (a) Hs mean values comparison of diurnal against nocturnal for total time; (b) Hs interval 2005–2015; (a) H mean values comparison of diurnal against nocturnal for total time; mean values comparisons of diurnal against nocturnal for each season; (c) Tm mean values (b) Hs mean values comparison of diurnal against nocturnal for each season; (c) Tm mean values comparison of diurnal against nocturnal for total time; (d) Tm mean values comparison of diurnal against nocturnal for each season. Sustainability 2017, 9, 1025 14 of 22

m comparison of diurnal against nocturnal for total time; (d) Tm mean values comparison of diurnal Sustainabilityagainst 2017nocturnal, 9, 1025 for each season. 14 of 22

A detailed investigation of wave conditions for the zone D is presented in Figure 12. Thus, the histogramsA detailed given investigationin this figure show of wave that conditions point D2 has for on the average zone D waves is presented higher with in Figure 21.7% 12 in. terms Thus, ofthe significant histograms wave given height in this and figure with show7.2% in that terms point of D2the has mean on wave average period. waves As higher previously with 21.7%shown, in winterterms is of characterized significant wave by higher height signific and withant 7.2%wave inheights terms and of the periods mean (Figure wave period.12c,d). As previously shown,The wintersignificant is characterized wave height by and higher mean significant period of wave the heightsLibyan andSea periodspoints, corresponding (Figure 12c,d). to the time intervalThe significant January wave 2005–December height and mean 2015period is presen of theted Libyanin Figure Sea 13. points, As it corresponding can be seen, tothe the wave time intensityinterval Januaryis sensibly 2005–December equal in both 2015points. is presented By analyzing in Figure Figure 13 13b,c,. As it it can can be be seen, noticed the wavethat, during intensity the is winter,sensibly the equal waves in bothwere points. higher Byby analyzing50% compared Figure to 13 theb,c, summer. it can be Regarding noticed that, wave during period, the winter, the same the evolutionwaves were is noticed higher byin 50%both compared locations. toAs the in summer.the previous Regarding cases, wavethe highest period, values the same were evolution recorded is duringnoticed the in bothwinter. locations. As in the previous cases, the highest values were recorded during the winter.

(a) (b)

FigureFigure 12. 12. ZoneZone D, D, evaluation evaluation of of the the wave wave conditions conditions considering considering the the ECMWF ECMWF data data for for the the 11-year 11-year interval 2005–2015; (a) Hs mean values comparison of diurnal against nocturnal for total time; (b) Hs intervalinterval 2005–2015; 2005–2015; (a) ( aH) s Hmeans mean values values comparison comparison of diurnal of diurnal against against nocturnal nocturnal for total for time; total (b time;) Hs mean values comparison of diurnal against nocturnal for each season; (c) Tm mean values mean(b) H s valuesmean valuescomparisoncomparison of diurnal of diurnal against against nocturnal nocturnal for foreach each season; season; (c) ( c)TmT mmeanmean values values comparison of diurnal against nocturnal for total time; (d) Tm mean values comparison of diurnal comparisoncomparison of of diurnal diurnal agains againstt nocturnal nocturnal for for total total time; time; ( (dd)) TTmm meanmean values values comparison comparison of of diurnal diurnal againstagainst nocturnal nocturnal for for each each season. season.

(a) (b)

Figure 13. Cont. Sustainability 2017, 9, 1025 15 of 22

Sustainability 2017, 9, 1025 15 of 22 Sustainability 2017, 9, 1025 15 of 22

Figure 13. Zone E, evaluation of the wave conditions considering the ECMWF data for the 11-year

interval 2005–2015; (a) Hs mean values comparison of diurnal against nocturnal for total time; (b) Hs (c) (d) mean values comparison of diurnal against nocturnal for each season; (c) Tm mean values Figure 13. Zone E, evaluation of the wave conditions considering the ECMWF data for the 11-year comparisonFigure of 13.diurnalZone E, agains evaluationt nocturnal of the wave for conditions total time; considering (d) Tm mean the ECMWF values data comparison for the 11-year of diurnal interval 2005–2015; (a) Hs Hmean values comparison of diurnal against nocturnal for total time; (b) Hs against nocturnalinterval 2005–2015; for each (season.a) s mean values comparison of diurnal against nocturnal for total time; mean values comparison of diurnal against nocturnal for each season; (c) Tm mean values (b) Hs mean values comparison of diurnal against nocturnal for each season; (c) Tm mean values m comparisoncomparison of of diurnal diurnal agains againstt nocturnal nocturnal for for total total time; time; ( (dd)) TTm meanmean values values comparison comparison of of diurnal diurnal 4. Discussionagainstagainst nocturnal nocturnal for for each each season. season. The wind power density (Pwind) is presented in Figure 14. By analyzing this parameter, it can 4.4. Discussion Discussion be noticed that the points located in the proximity of Zakynthos island (A4) and Kythira Island (A5) TheThe wind wind power power density density (Pwind) (Pwind) is is presented presented in in Fi Figuregure 14. 14 .By By analyzing analyzing this this parameter, parameter, it it can can have the lowest energy potential. Thus, the annual average value for the point A4 is 140.44 W/m2, bebe noticed noticed that that the the points points located located in in the the proximity proximity of of Zakynthos Zakynthos island island (A4) (A4) and and Kythira Kythira Island Island (A5) (A5) 2 2 while thehavehave maximum the the lowest lowest meanenergy energy valuepotential. potential. is Thus,4.84 Thus, kW/mthe the annual annual. Regarding average average value value the for forpoint the the pointpoint A5, A4 A4the is annual140.44 W/m average,2 , was 2 147.37 W/mwhilewhile2 andthe the maximum maximumthe maximum mean mean value valuemean is is of4.84 4.84 4.83 kW/m kW/m.2 .Regarding Regarding2. Another the the point point A5, with A5, the the low annual annual energy average average potential was was is D1. 2 2 Thus, the147.37147.37 point W/m W/m D1 and 2hasand the the the maximum maximumannual averagemean mean of of 4.83 4.83of 198.25kW/m kW/m. 2AnotherW/m. Another2 and point point a maximumwith with low low energy energy mean potential potential of 4.73 is is D1.KW/m D1. 2. Thus, the point D1 has the annual average of 198.25 W/m2 and2 a maximum mean of 4.73 KW/m2. 2 ThreeThus, of thethe point most D1 energetic has the annual locations average with of 198.25 resp W/mect toand the a maximumwind power mean density of 4.73 KW/m were . B3 (in the ThreeThree of of the the most most energetic energetic locations locations with with resp respectect to to the the wind wind power power density density were were B3 B3 (in (in the the proximity of Cios Island, 2.41 km to shore), B4 (in the proximity of Tinos Island, 2.7 km to shore) and proximityproximity of of Cios Cios Island, Island, 2.41 2.41 km km to to shore), shore), B4 B4 (in (in the the proximity proximity of of Tinos Tinos Island, Island, 2.7 2.7 km km to to shore) shore) and and C6 (in theC6C6 proximity(in (in the the proximity proximity of Crete, of of Crete, Crete, 2.27 2.27 2.27 km km km to to toshore) shore) shore)... RegardingRegarding Regarding these these these points, points, points, the the maximum maximumthe maximum value value was was value in in was in 2 2 the rangethethe 6.03–6.57 range range 6.03–6.57 6.03–6.57 kW/m kW/m kW/m2, while, 2while, while the the theannual annual annual averageaverage average is isin inin the the the range range range 286–298.96 286–298.96 286–298.96 W/m W/m. W/m2. 2. In addition,InIn addition, addition, for the forfor theremainingthe remaining remaining points, points, the thethe annual annuannu averagealal average average value value is value in theis in range isthe in range198.25–275.03 the 198.25–275.03range W/m198.25–275.032 W/m2 while the maximum mean in the range 4.77–5.96 kW/m2 2. W/m2 whilewhile the the maximum maximum mean mean in thein the range range 4.77–5.96 4.77–5.96 kW/m kW/m. 2.

Figure 14. Wind power density, annual average, diurnal mean, nocturnal mean and maximum mean for the 10 reference points considered. Figure 14. Wind power density, annual average, diurnal mean, nocturnal mean and maximum mean Figure 14.Furtherfor Wind the 10 on, referencepower the Siemens density, points SWT considered. annual 3.6-120 average, wind turbine diurnal is mean,considered nocturnal to evaluate mean the and wind maximum potential. mean for Thethe 10wind reference turbine points performance considered. curve is represented in Figure 15 [40]. Considering the power variationFurther with on, respect the Siemens to the wind SWT speed, 3.6-120 a more wind detailed turbine isinvestigation considered toof evaluatethe wind theconditions wind potential. can be FurthercarriedThe wind on, out. the turbine This Siemens includes performance SWTparame curve3.6-120ters issuch represented wind as: operating turbine in Figure capacityis considered 15[ 40 (OC%),]. Considering torated evaluate capacity the power the (RC%) variationwind and potential. capacity factor (Cf%). The windwith turbine respect toperformance the wind speed, curve a more is detailed represen investigationted in Figure of the wind15 [40]. conditions Considering can be carried the power variationout. with This respect includes to parameters the wind suchspeed, as: operatinga more detailed capacity (OC%),investigation rated capacity of the (RC%) wind and conditions capacity can be factor (Cf%). carried out. This includes parameters such as: operating capacity (OC%), rated capacity (RC%) and capacity factor (Cf%). Sustainability 2017,, 99,, 10251025 16 of 22 Sustainability 2017, 9, 1025 16 of 22

Figure 15. Siemens SWT 3.6-120 wind turbine power curve. FigureFigure 15. 15. SiemensSiemens SWT SWT 3.6-120 3.6-120 wind wind turbine turbine power power curve. The capacity factor (Figure 16a) represents the ratio between the electric power produced by the turbine,TheThe Pwtgenerated,capacity capacity factor factor in(Fig (Figure a urespecif 16a)16ica) representslocation represents and the the ratio maximum between outpthe electric electricut, Prated, power power of aproduced produced single Siemens by the the turbine,turbine,SWT 3.6-120 Pwtgenerated, Pwtgenerated, system (6): in in a a specif speciﬁcic location location and and the the maximum maximum outp output,ut, Prated, Prated, of of a single Siemens SWTSWT 3.6-120 system (6): Pwt generate Pwtgenerate CC f == Pwt generate ×100100,, (6) C f = P 100, (6) f ratedrated (6) Prated The operatingoperating time time percentage percentage of aof wind a wind turbine turb is indicatedine is indicated by the operating by the operating capacity parameter capacity (FigureparameterThe 16 operatingb). (Figure This parameter16b). time This percentage parameter can be determinedof cana wind be det basedturberminedine on is thebased indicated cut-in on the wind by cut-in the speed windoperating (3 m/s)speed capacity and(3 m/s) the parametercut-outand the windcut-out (Figure speed wind 16b). (25 speed m/s). This (25 Theparameter m/s). maximum The can maximum performancebe determined performance of abased wind of on turbine a windthe cut-in is turbine highlighted wind is highlightedspeed by the (3 ratedm/s) by andcapacitythe ratedthe cut-out (Figurecapacity wind 15 (Figurec). speed This 15c). parameter(25 m/s).This parameterThe can maximum be computed can be pe computedrformance based on basedof the a ratedwind on the speedturbine rated (12.5 is speed highlighted m/s) (12.5 and m/s) theby thecut-outand rated the value.cut-out capacity value. (Figure 15c). This parameter can be computed based on the rated speed (12.5 m/s) and theBy cut-outanalyzing value. the the reference reference points points considered considered in in the the Io Ioniannian Sea, Sea, it itcan can be be noti noticedced that that this this area area is isthe the leastBy least analyzing suitable suitable for the for a reference wind a wind turbine turbinepoints implementation considered implementation. in .the The Io The capacitynian capacity Sea, factor it can factor corresponding be noti correspondingced that to this these to area these two is thetwopoints least points has suitable a has mean a for mean value a wind value of turbine32.6%. of 32.6%. The implementation Theoperating operating ca.pacity The capacity capacity factor factor for factor these for corresponding these two twopoints points was to these washigh high two(A4 points(92.99%A4 92.99% has and a and meanA5 A592.95%), value 92.95% ofwhile), 32.6%. while the theThe rated ratedoperating capacity capacity ca pacityis israther rather factor small. small. for Thisthese This means two means points that that wasa a turbine high (A4 can 92.99%operate and with A5 maximum 92.95%), efﬁciencyefficiency while the forfor rated 8.34%8.34% capacity ofof thethe timetime is rather inin thethe pointsmall.point A4 A4This andand means 8.79%8.79% that inin A5.A5. a turbine can operateAccording with maximum to this study, efficiency thethe bestbest for 8.34% suitablesuitable of areasareathe times for in a windthe point turbine A4 and implementation 8.79% in A5. are the areas correspondingAccording toto thethis Aegeanstudy, the Sea, best Sea suitable of Crete area ands for LibyanLibyan a wind Sea.Sea. turbine Figure implementation 16 illustrates that are the the zone areas B correspondingpoints have a totaltotalto the meanmean Aegean CCff value Sea, Sea of 50.22%50.22%of Crete forfor and B3B3 Libyan andand 49.35%49.35% Sea. Figure forfor B4.B4. 16 By illustrates analyzing that the the operating zone B pointscapacity, have itit was wasa total noticed noticed mean that thatCf itvalue isit quiteis ofquite 50.22% high, high, 94.32% for 94.32% B3 for and point for 49.35% point B3 and for B393.83% B4. and By 93.83% foranalyzing B4. Thefor B4. ratedthe operatingThe capacity rated capacity,forcapacity this zone forit wasthis indicates zonenoticed indicates that that a wind it that is turbinequite a wind high, has turbine to94.32% function has tofor onfunction point average B3 on and 23.03%average 93.83% of 23.03% the for time B4.of forthe The pointtime rated for B3 capacityandpoint 22.36% B3 for and this for 22.36% B4.zone Regarding indicates for B4. Regardingthat the a seasonal wind the turbine distribution,seasonal has todistribution, function it can be on noticed itaverage can be that 23.03% noticed the of RC thatthe parameter timethe forRC pointincreasesparameter B3 and during increases 22.36% the during winter. for B4. the The Regarding wint nexter. best The the area next seasonal for best a wind area distribution, turbinefor a wind implementation it turbine can be implementation noticed is the that Libyan the is Sea.RCthe parameterTheLibyan mean Sea. valueincreases The of mean the during capacity value the of factor wint the er.capacity of bothThe zonenext factor best E points of area both is for 47.64%.zone a wind E Regardingpoints turbine is 47.64%.implementation the operating Regarding capacity, is thethe Libyanitoperating can be Sea. noticed capacity, The thatmean it thiscan value hasbe noticed of the the values capacitythat 96.98% this factorhas in th point eof values both E1 and zone96.98% 98.26% E pointsin point in E2.is E1 47.64%. By and analyzing 98.26% Regarding thein E2. rated the By operatingcapacity,analyzing zone capacity,the Erated has it acapacity, can mean be ofnoticed zone 16.49%. E that has The thisa Seamean has of Cretethofe 16.49%. values energy 96.98%The potential Sea in of point Crete in the E1 energy points and 98.26% studiedpotential in is E2. ratherin theBy analyzingsimilarpoints studied to thatthe rated fromis rather areacapacity, E.similar The zone pointto Ethat has C6 from isa characterizedmean area of E. 16.49%. The by point aTheCf C6valueSea is of characterized ofCrete 49%, energy OC of by 96.88potential a C andf value in RC the of f points17.51%,49%, OC studied while of 96.88 pointis ratherand C7 RC by similar of a C17.51%,f of to 48.33%, that while from OC point area of 96.99C7 E. by The and a C point RCf of 48.33%, of C6 17.43%. is characterizedOC of 96.99 and by RC a C of value 17.43%. of 49%, OC of 96.88 and RC of 17.51%, while point C7 by a Cf of 48.33%, OC of 96.99 and RC of 17.43%.

(a) (a) Figure 16. Cont. Sustainability 2017, 9, 1025 1717 of of 22 22 Sustainability 2017, 9, 1025 17 of 22

(b) (b)

(c) (c) Figure 16. Assessment of the Siemens SWT 3.6-120 wind turbine performances. The results are based Figure 16. Assessment of the Siemens SWT 3.6-120 wind turbine performances. The results are based onFigure the ECMWF 16. Assessment data (2005–2015) of the Siemens and they SWT are 3.6-120 presented wind in turbine terms performances.of the mean values The results for: (a) are capacity based on the ECMWF data (2005–2015) and they are presented in terms of the mean values for: (a) capacity factoron the (%); ECMWF (b) operating data (2005–2015) capacity (%); and they(c) rated are presentedcapacity (%). interms of the mean values for: (a) capacity factor (%); (b) operating capacity (%); (c) rated capacitycapacity (%).(%). The wave power represents the energy flux in kilowatts per meter of the wave crest (kW/m). The wave power represents the energy flux in kilowatts per meter of the wave crest (kW/m). The waveThe wave power power corresponding represents theto the energy 11-year ﬂux ininterval, kilowatts from per January meter of 2005 the waveto December crest (kW/m). 2015, The wave power corresponding to the 11-year interval, from January 2005 to December 2015, structuredThe wave power on annual corresponding average, diurnal to the 11-year mean, interval, nocturnal from mean January and 2005maximum to December mean, 2015,is presented structured in structured on annual average, diurnal mean, nocturnal mean and maximum mean, is presented in Figureon annual 17. average, diurnal mean, nocturnal mean and maximum mean, is presented in Figure 17. Figure 17.

Figure 17.17. WaveWave power power density, density, Pwave, Pwave, annual annual average, average, diurnal diurnal mean, nocturnalmean, nocturnal mean and mean maximum and Figure 17. Wave power density, Pwave, annual average, diurnal mean, nocturnal mean and maximummean, for themean, 10 referencefor the 10 points reference considered. points considered. maximum mean, for the 10 reference points considered. The wave power distribution presented in Figure 17 for the 10 reference points shows the The wave power distribution presented in Figure 17 for the 10 reference points shows the differences between the zones studied. By analyzing the wave power density, it can be noticed that differences between between the the zones zones studied. studied. By By analyzing analyzing the the wave wave power power density, density, it can it canbe noticed be noticed that the points C6, C7 and E1 have the highest energy potential in terms of the wave power. For these thethat points the points C6, C6,C7 and C7 and E1 have E1 have the the highest highest energy energy potential potential in in terms terms of of the the wave wave power. power. For For these points, the annual average wave power is in the range 2.88–2.99 kW/m. In addition, the points A4 points, thethe annualannual average average wave wave power power is is in in the the range range 2.88–2.99 2.88–2.99 kW/m. kW/m. In addition,In addition, the pointsthe points A4 andA4 and D1 have the lowest energy potential. The annual average value for the point A4 is 1.7 kW/m, andD1 have D1 have the lowest the lowest energy energy potential. potential. The annual The annu averageal average value for value the point for the A4 point is 1.7 kW/m,A4 is 1.7 while kW/m, for while for the point D1 is 1.76 kW/m. The Aegean Sea points, B3 and B4, also recorded a low energy whilethe point for D1the ispoint 1.76 D1 kW/m. is 1.76 The kW/m. Aegean The Sea Aegean points, Sea B3 points, and B4, B3 also and recorded B4, also arecorded low energy a low potential. energy potential. The wave power values are in the range 1.95 kW/m to 2.02 kW/m. Thepotential. wave The power wave values power are values in the rangeare in 1.95the range kW/m 1.95 to 2.02kW/m kW/m. to 2.02 kW/m. The maximum mean value recorded for the 11-year interval in the point E3 is 92.45 kW/m. The maximum mean value recorded for the 11-year11-year intervalinterval inin thethe pointpoint E3E3 isis 92.4592.45 kW/m.kW/m. Looking now at Figures 14 and 17 altogether, some similarities and differences in terms of the Looking now at Figures 14 and 17 altogether, some similarities and differences in terms of the wind and wave energy in some locations can be noticed. The most significant difference is that, wind andand wavewave energy energy in in some some locations locations can can be noticed.be noticed. The The most most significant significant difference difference is that, is whilethat, while the maximum values of the wind power correspond to the locations from the Aegean Sea, in whilethe maximum the maximum values values of the windof the power wind correspondpower correspond to the locations to the locations from the from Aegean the Sea,Aegean in terms Sea, in of terms of wave power, the highest potential occurs in the Sea of Crete. Actually, in this area, the wind waveterms power,of wave the power, highest the potentialhighest po occurstential in occurs the Sea in ofthe Crete. Sea of Actually, Crete. Actually, in this area,in this the area, wind the power wind power can also be considered relevant. Thus, according to the data presented in the two figures, in power can also be considered relevant. Thus, according to the data presented in the two figures, in Sustainability 2017, 9, 1025 18 of 22 Sustainability 2017, 9, 1025 18 of 22 canterms also of bewave considered power, the relevant. coastal Thus, environment according of to Cr theete data is 45.73% presented higher in thethan two in figures,the Aegean in terms Sea, ofwhile, wave in power,terms of the wind coastal power, environment it is only 2.91% of Crete sma isller. 45.73% At this higher point, than the in specific the Aegean patterns Sea, of while,wave ingeneration terms of windand propagation power, it is onlyin the 2.91% areas smaller. targeted At should this point, also the be specific considered, patterns which of wave are extensively generation anddiscussed propagation in Makris in the et al. areas [24]. targeted From this should perspectiv also bee, considered, in the area whichof the areGreek extensively islands, the discussed strongest in Makriswaves are et al.not [24 always]. From co thisrrelated perspective, with the in highest the area wind of the conditions. Greek islands, the strongest waves are not alwaysThe correlated bivariate withdistributions the highest for windthe wave conditions. parameters (Hs and Tm) corresponding to five reference pointsThe are bivariate illustrated distributions in Figure 18 for. These the wave diagrams parameters present (H stheand distribuTm) correspondingtion of the sea to states five reference for each pointszone, being are illustrated defined by in the Figure parame 18ters. These significant diagrams wave present height the(Hs) distribution and mean wave of the period sea states(Tm), and for eachthey zone,were designed being defined for the by 11-year the parameters interval significantfrom 1 January wave 2005 height to (31H sDecember) and mean 2015. wave Furthermore, period (Tm), andthe wave they were power designed isolines for are the represented 11-year interval for fromfour 1different January 2005energy to31 levels December (5 kW/m, 2015. 25 Furthermore, kW/m, 50 thekW/m, wave 100 power kW/m). isolines are represented for four different energy levels (5 kW/m, 25 kW/m, 50 kW/m, 100 kW/m).Figure 18a corresponds to the point A5 and shows that the bulk of occurrences is located aroundFigure the 18isolinea corresponds of 5 kW/m. to theFigure point 18b A5 corresponds and shows that to the bulkB3 point, of occurrences and it can is be located noticed around that, thealthough isoline most of 5 of kW/m. the occurrences Figure 18b are corresponds also close to the isoline B3 point, of 5 and kW/m, it can the be energy noticed isthat, more although focused mostthan ofin theall occurrencesother cases. areMoreover, also close relevant to theisoline occurre ofnces 5 kW/m, can also the energybe noticed is more near focused the isoline than of in all25 otherkW/m. cases. Moreover, relevant occurrences can also be noticed near the isoline of 25 kW/m. Regarding nownow thethe points points C6, C6, D2 D2 and and E3, E3, it can it can be noticed be noticed that thethat energy the energy is more is widelymore widely spread andspread the and bulk the of bulk occurrences of occurrences are found are closer found to closer the isoline to the ofisoline 25 kW/m. of 25 kW/m.

(a) (b)

Figure 18. Cont. Sustainability 2017, 9, 1025 19 of 22 Sustainability 2017, 9, 1025 19 of 22

(e)

Figure 18. Bivariate distributions corresponding to ﬁvefive reference points. ECMWF data processed for ((a)) pointpoint A5;A5; ((b)) pointpoint B3;B3; ((cc)) pointpoint C6;C6; ((dd)) pointpoint D2;D2; ((ee)) pointpoint E3.E3.

5. Conclusions In the presentpresent work,work, bothboth datadata sourcessources consideredconsidered cover the entire marine environment of the Greek coastal environment. The differencedifference between the two data sets consists mainly in the fact that the firstfirst one one having having a higher a higher temporal temporal and spatial and spatial resolution, resolution, while the while second the can second provide can information provide withoutinformation the without restriction the of restriction the geographical of the geographical characteristics. characteristics. On the other On hand,the other ECMWF hand, providesECMWF informationprovides information about wind, about including wind, the including U and V components, the U and that V arecomponents, suitable in determiningthat are suitable the wind in directiondetermining and the also wind information direction about and also wave information period and about direction. wave Furthermore, period and direction. ECMWF Furthermore, also covers a longerECMWF time also period. covers a longer time period. Analyzing thethe wind wind and and wave wave dynamics dynamics in the in targetthe target areas, itareas, can beit concludedcan be concluded that the nearshore that the nearshore and offshore areas close to the Greek islands have a significant energy potential. and offshore areas close to the Greek islands have a significant energy potential. By analyzing the Greek National Renewable Energy Action Plan, developed in the scope of the By analyzing the Greek National Renewable Energy Action Plan, developed in the scope of the directive 2009/28/EC, the Greek Ministry of Environment, Energy & Climate Change estimates a directive 2009/28/EC, the Greek Ministry of Environment, Energy & Climate Change estimates a balancing between the conventional and RES exploitation methods. Thus, until 2020, an RES energy balancing between the conventional and RES exploitation methods. Thus, until 2020, an RES energy production of 41.7% from the total installed capacity (68 TWh) is desired. Given this context, it can production of 41.7% from the total installed capacity (68 TWh) is desired. Given this context, it can be be concluded that the wind and wave conditions in the coastal areas studied may represent a concluded that the wind and wave conditions in the coastal areas studied may represent a suitable suitable alternative for reducing the gap between RES and the conventional methods. The synergy alternative for reducing the gap between RES and the conventional methods. The synergy between the between the RES studied (wind and waves) can thus induce a sustainable development in the Greek RES studied (wind and waves) can thus induce a sustainable development in the Greek economy. economy. At this point, it has to be highlighted that Greece geographical positioning and characteristics, At this point, it has to be highlighted that Greece geographical positioning and characteristics, being a peninsular and insular country with a 17,400 km of coast length and a maritime surface being a peninsular and insular country with a 17,400 km of coast length and a maritime surface of of 114,507 km2, has an important potential in RES exploitation. 114,507 km2, has an important potential in RES exploitation. The objective of this work is to present a more comprehensive picture of the wind and wave The objective of this work is to present a more comprehensive picture of the wind and wave energy potential close to the Greek islands due to the fact that in this area the synergy between these energy potential close to the Greek islands due to the fact that in this area the synergy between these two RES has not been extensively evaluated in the past. In this study, two different datasets have been two RES has not been extensively evaluated in the past. In this study, two different datasets have analyzed. The first covers the 11-year time interval between 1 January 2005 to 31 December 2015 and been analyzed. The first covers the 11-year time interval between 1 January 2005 to 31 December was provided by ECMWF, while the second one is provided by AVISO and covers the six-year interval 2015 and was provided by ECMWF, while the second one is provided by AVISO and covers the 1 January 2010 to 31 December 2015. six-year interval 1 January 2010 to 31 December 2015. The targeted area of the study is located in the Mediterranean Sea. More precisely, there were The targeted area of the study is located in the Mediterranean Sea. More precisely, there were analyzed locations found in the perimeter of the Ionian (A), Aegean (B), Crete (C), Levantine (D) and analyzed locations found in the perimeter of the Ionian (A), Aegean (B), Crete (C), Levantine (D) and Libyan (E) seas. When initially analyzed, 26 reference points were considered. For a more detailed Libyan (E) seas. When initially analyzed, 26 reference points were considered. For a more detailed investigation, the analysis was further focused on the 10 most representative points in terms of energy investigation, the analysis was further focused on the 10 most representative points in terms of potential. Thus, for each of the five areas considered, two locations were selected. The aim of the energy potential. Thus, for each of the five areas considered, two locations were selected. The aim of study was to identify the most energetic locations, from the perspective of future wind turbines and the study was to identify the most energetic locations, from the perspective of future wind turbines WEC implementation. Thus, parameters such as U80, Hs and Tm were assessed. By processing and and WEC implementation. Thus, parameters such as U80, Hs and Tm were assessed. By processing Sustainability 2017, 9, 1025 20 of 22 analyzing the dynamics of these parameters, it was possible to determine the energy potential of the Greek islands as well as the synergy between the two resources. Regarding the wind energy potential, it can be noticed that a higher potential is in the proximity of Cios and Tinos islands (Aegean Sea), Crete and Dia islands (Sea of Crete), Kasos Island (Levantine Sea) and south of Crete (Libyan Sea). In these areas, the U80 mean annual values are in the range 7.63–7.88 m/s, while the annual average wind power is in the range 270.94–298.96 W/m2. By analyzing the wave power density, it can be observed that the points C6, C7 and E1 have the highest energy potential. For these points, the annual average wave power was in the range 2.9–3 kW/m. Furthermore, a Siemens SWT 3.6-120-wind turbine power variation in respect to the wind speed was considered to evaluate the energy potential. A detailed investigation was conducted. This includes the analysis of the following parameters: operating capacity (OC%), rated capacity (RC%) and capacity factor (Cf%). The resulted data indicate the fact that the capacity factor is in the range of 32.02–50.23%, the minimum mean value being recorded south of Zakynthos Island, while the maximum was recorded west of Cios Island. The maximum performance of a wind turbine is highlighted by the rated capacity parameter (RC%). The results indicate that this parameter is in the range 8.32% (south of Zakynthos Island) to 23.03% (west of Cios Island). The operating time percentage of a wind turbine is indicated by the operating capacity parameter (OC %). By analyzing the data, it can be noticed that a Siemens SWT 3.6-120 wind turbine had a mean operating capacity of 95.31%. The bivariate distributions of the wave parameters, north and south of Crete and south of Kasos Island, illustrate that the energy potential is more spread and the bulk of occurrences are found closer to the 25 kW/m isoline. Regarding the areas west of Kythira and Cios islands, the bulk of occurrences are located around the isoline of 5 kW/m. Future works will be focused on the identification of the most relevant hot spots in the Greek island environment by performing high resolution simulations with phase averaged spectral wave models. Subsequently, another issue is related to evaluations of the performances of various devices for wind and wave energy conversion in the hot spots identified above. Finally, it can be concluded that the Greek marine environment has relevant wind energy resources as well as a good potential for hybrid wind-waves energy exploitation, especially from the perspective of the development of the WEC devices especially designed for the small amplitude waves.

Acknowledgments: This work was carried out in the framework of the project proposal REMARC, submitted under the number PN-III-P4-IDPCE-2016-0017 to the Romanian Executive Agency for Higher Education, Research, Development and Innovation Funding, UEFISCDI. The authors would like also to express their gratitude to the reviewers for their constructive suggestions and observations that helped in improving the present work. Author Contributions: Daniel Ganea and Valentin Amortila has gathered, processed and analyzed the data. Elena Mereuta has done the literature review and drawn the main conclusions. Eugen Rusu has guided this research and discussed the data. All of the authors have participated in the writing of the paper. The final manuscript has been approved by all authors. Conflicts of Interest: The authors declare no conflict of interest.

Nomenclature

AVISO archiving, validation and interpretation of satellite oceanographic Cf capacity factor DER distributed energy resources ECMWF European Centre for Medium-Range Weather Forecasts Hs wave height LCOE levelized the cost of electricity MG microgrid MWP mean wave period OC operating capacity Sustainability 2017, 9, 1025 21 of 22

Pwave wave power density index Pwtgenerated the output energy generated by a wind turbine Pwind wind power density index RC rated capacity RES renewable energy resources SWH signiﬁcant height of combined wind-waves and swell Tm wave periodicity U10 wind speed at 10 m U80 wind speed at 80 m WEC wave energy convertor

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