Offshore Wind Farm in the Southeast Aegean Sea and Energy Security

Abstract

This paper deals with the creation, in realistic terms, of an offshore wind farm between the Greek islands of Karpathos and Kassos in the Dodecanese complex. In this context, the terms and conditions for the possible existence of an offshore wind park in Greece are analyzed; the technical components of such a project are described; the offshore wind farm, which was designed by the authors, is presented in detail; and the location selected for its installation is assessed. Moreover, the benefits for the islands of Karpathos and Kassos and for the Greek State, as well as financial data adapted to this specific offshore wind farm and SWOT analysis for the two phases of the project, are presented. The authors conclude that an investment in this project would be viable in economic terms and feasible, despite it being a small-scale project.

1. Introduction

The transition to a sustainable society constitutes an urgent challenge, since the climate crisis is increasingly threatening humanity’s future, the planet, and prosperity. The contribution of Renewable Energy Sources (RES) in this transition is crucial and their importance is indissolubly connected with containing the increase in temperature to 1.5 °C, in comparison with 1990 levels. In addition, the expansion of RES in the European Union (EU) is consistent with the European Green Deal. Specifically, this is the plan via which the EU aims to reduce net greenhouse gas emissions by at least 55% by 2030 (the “Fit for 55” package), compared to 1990 levels, and through which the EU aims to achieve zero-net emissions of greenhouse gases by 2050 [1]. This will make it the first climate-neutral continent by the middle of the century. Moreover, the European Climate Law, which came into force on 29 July 2021 [2], incorporates the goals defined in the European Green Deal into law. The framework of the European Green Deal is supplemented with some extra initiatives and strategies, such as the EU Climate Pact and the EU Climate Adaptation Strategy.

The widespread focus on renewables and the growing attention on them has also been seen in Greece, with the governments promoting the use of RES. Specifically, in Greece, RES should have completely substituted electric generation from lignite by 2028 (in collaboration with other forms of energy), although the new lignite power plant “Ptolemaida V”, according to Greek officials, will remain in operation as a strategic reserve unit beyond that date [3]. In any case, it is cheaper to build wind or solar infrastructure than to operate the existing lignite assets [4,5]. However, natural gas will be used in the European Union as a transitional fuel during the gradual integration of RES and under the strict conditions posed by the “EU Taxonomy” [6].

In general, the penetration of RES is encouraged by many states through various regulatory measures, incentives, and subsidies [7], since renewables are “at the core of the transition to a sustainable energy future” [8]. Global energy demand is rising due to economic and population growth [9]. Therefore, the world needs new reserves and renewables represent an endless source.

Aside from the fact that our planet is in danger and that RES offer endless energy, another reason for promoting the expansion of RES is energy security. The war in Ukraine, which started on 24 February 2022, as a result of Russian troops invading Ukrainian territory, exposed the need to diversify energy sources and to reduce EU dependence on Russian fossil fuels (according to the European Commission [10], ‘’In 2021, the EU imported more than 40% of its total gas consumption, 27% of oil imports and 46% of coal imports from Russia. Energy represented 62% of EU total imports from Russia”). The REPowerEU plan, published on 8 March 2022 [11], was designed to help the EU to move away from Russian fossil fuels, through energy saving, the diversification of energy supplies—to reduce the risk of interruptions in the supply of natural gas and other fossil fuels—and by promoting the penetration of RES and strengthening economic growth, security, and climate action.

Therefore, promoting renewables and reinforcing energy security constitute the core of the EU’s efforts in the field of energy. In the case of this paper, the authors selected to develop an offshore wind park and not an onshore, since the majority of the offshore projects demonstrate a higher energy performance and higher capacity factors than onshore wind parks, due to the better wind conditions in the sea [12] and also due to the absence of possible physical obstacles (such as mountains and hills). One of the key differences between offshore and onshore wind power generation is consistency. OWFs generate electricity at a steadier rate. Moreover, OWPs could be placed to a greater extent in the sea. Additionally, difficulties related to available space, such as land acquisitions, may arise complications regarding a possible installation of an onshore wind farm. Furthermore, OWFs have, in general terms, lower risk of social opposition [13].

Given all of the above, in this article, we aim to describe a wind farm in Greek territorial waters. This project was designed by the authors as a pilot. In this manner, we can improve our knowledge about the development of offshore wind parks in Greece, which does not currently have an offshore wind farm. Such a project can provide multiple benefits for the country as a whole.

2. Materials and Methods

In the Supplementary Material document, the authors of this paper present an extremely thorough economic analysis conducted for the purpose of this scientific study. In the financial analysis, which was adapted to the potential offshore wind park (OWP) between the Greek islands of Karpathos and Kassos, the authors calculated the total costs of the project considering many parameters.

In particular, the Capital Expenditure (CapEx), the Operational Expenditure (OpEx), a special fee, the value-added tax (VAT), the inflation, the discount rate, the residual value, the Net Present Value (NPV), the Internal Rate of Return (IRR), and the Levelized Cost of Energy (LCOE) were taken into account.

In order to make the calculations, the authors finalized the numbers that they used in the financial analysis via a detailed search and by communicating with executives from the energy market and with firms in the energy sector. Both provided useful data, which were vital for the financial analysis in this project.

2.1. Description of the Plan

The objective of this paper was twofold; thus, two phases were developed. Specifically, the first goal (the first phase: January 2023–December 2027) was a plan of the construction of an OWP that covered the energy needs of the two islands at an extremely high rate. At present (June 2023), these two islands, Karpathos and Kassos, are not interconnected with the mainland system and Kassos is energy-dependent on Karpathos.

The second goal (the second phase: January 2028–December 2052), after the anticipated interconnection (by 2027) of Karpathos and Kassos with the mainland system and, therefore, with the Hellenic Electricity Transmission System (HETS), was to assess the contribution of an offshore wind farm (OWF) to the national energy mix. The transition from the first to the second phase is presented in this paper. In any case, both islands were selected to participate in the project. However, some differences regarding the parameters (e.g., in the first phase, the two islands were not interconnected with the mainland system, while in the second, they were and in addition the number of wind turbines differed between the two phases of the project) were observed between the two phases.

In Greece, until the time of the delivery of this paper (June 2023), no OWF has been installed. The characteristics of some areas of the country are considered to be favorable for the construction of such a wind park. For that reason, this technology can be developed, gradually, in Greece.

2.2. The Possibility of the Installation of an Offshore Wind Farm in Greece

A previous study claims that, in the Aegean Sea, there is wind potential of 7–10 GW [14]. In addition, according to the estimations of European Wind Energy Association (EWEA), by 2030, Greece (the country had participation from RES in its production mix in 2021 41.48% [15]) could have a 500 MW installed capacity of offshore wind power, in an optimistic scenario [16]. Nevertheless, according to Greek officials, the country’s aim regarding offshore wind energy will be reviewed via the new National Energy and Climate Plan. In addition, in the new National Energy and Climate Plan, the target for RES participation in overall Greek electricity generation is expected to be increased from 61% (National Energy and Climate Plan of 2019) to 80% [17], i.e., to 2.7 GW, by 2030 and includes a pilot project (the aim is 17.3 GW of offshore wind power by 2050 [17]). According to estimations [18], the offshore wind energy targets in Greece will mobilize 6 billion private investments (EUR 28 billion by 2050) and will create more than 8000 new direct and indirect jobs by 2030.

In 2010, the Ministry of the Environment and Energy of Greece distinguished marine areas across the country that were appropriate for the installation of OWFs. The criteria set were as follows [19]:

• Exclusion of areas where the development of OWFs is incompatible with other uses, within a zone of six nautical miles (nm).
• Exclusion of areas with depths greater than 50 m.
• Avoidance of places with significant effects on the environment.
• Minimization of visual disturbance.

In addition, areas that are bounded by the Greek armed forces were excluded.

Twelve areas were finally chosen. These are located in Saint Efstratios, Alexandroupoli, Karpathos, Othonoi, Thassos, Kymi, Lemnos (north and south), Lefkada, Petalious, Samothrace, and Fanari, and represent a total capacity of 1.2 GW. However, locations for floating OWPs were not examined. Instead, only bottom-fixed technology was assessed [20].

According to the draft of the National Offshore Wind Farm Development Program (2023), Crete, Dodecanese, northern Aegean, Cyclades, and the Alexandroupolis marine area will be included in the first phase of area concessions for the development of offshore wind farms in Greece [21].

Nevertheless, from 2010 to the present (June 2023), the plans have not been activated. The current (June 2023) timetable stipulates that the construction of the first offshore wind parks will begin at the end of 2028 [22].

Of note, there is a wind farm in Saint Georgios (Greece), in the Saronic islands complex, which has offshore characteristics (for example, submarine cables), but it is an onshore wind park and is connected with the mainland system.

2.3. Legislative Framework in Greece

With law 3468/2006, for the first time, Greece permitted the installation of OWFs.

Two years later (December 2008), with Article 5 of the joint ministerial decision (n. 49828) for the approval of the “Special spatial planning framework for renewable energy sources”, the national area was divided into categories, including offshore marine areas.

Further regulations were institutionalized with the enactment of law 3851/2010. Moreover, there are also general references to OWPs in laws 4414/2016, 4546/2018, and 4685/2020.

The decision to install an OWF must be in agreement with the “Special framework for spatial planning and sustainable development for renewable energy sources”. In this document (49828/2008, Article 10), 11 special criteria are defined for the spatial planning of OWFs.

In November 2019, the Ministry of the Environment and Energy of Greece published its National Energy and Climate Plan. However, as was previously mentioned, this plan is under revision mainly due to the EU’s attempt to gradually reduce dependence on Russian fossil fuels. Moreover, in the Greek National Energy and Climate Plan of 2019, the importance of OWPs’ possible future contributions to the energy mix was underlined [23].

Although progress was noted on 30 July 2022 due to law 4964/2022 with the title “Provisions for the simplification of environmental licensing, environmental inspections and environmental protection, urgent forestry, zoning and urban planning provisions, establishing a framework for the development of OWFs, confrontation of the energy crisis and circular economy issues”, the issue of the positioning of OWFs, which is extremely important, has not yet (June 2023) been regulated. There is no marine spatial plan, even though, according to announcements, it is being prepared.

In March 2023, a bill (titled “Renaming the Energy Regulatory Authority to Waste Regulatory Authority, of Energy and Water and expanding its scope with responsibilities over water services and urban waste management, strengthening of water policy—Modernization of the legislation on the use and production of electricity energy from renewable sources through the incorporation of EU directives 2018/2001 and 2019/944—More specific provisions for renewable energy sources and environmental protection”) from the Ministry of the Environment and Energy of Greece was submitted to the national parliament for discussion and voting. In this bill, there is a reference (Article 164 of law 5037/2023—titled “Promotion of the implementation of pilot projects of offshore wind farms”) to offshore wind farms. Specifically, according to Article 164 of law 5037/2023, “The marine area that extends south of the coastline of the Evros Regional Unit and north-northeast of Samothraki, is defined as an OWP pilot project development area, for OWPs projects up to a total capacity of 600 MW. Part of the area is demarcated as an Area of Organized Development OWPs, while with the same procedure, part of the area is demarcated as a First Choice Area (i.e., in line with the European directions for the “go-to-areas”, for the rapid deployment of new installations for the production of energy from renewable sources [24]) of RES”. In addition, “the maximum estimated power of OWPs Projects that can be installed in each OWF installation area cannot be less than 200 MW”.

3. Results

3.1. Monopile vs. Floating Units in Greece and the Reasons behind Our Selection

The Mediterranean region, including Greece, has deep waters, even at a very short distance from the coast [25]. This facilitates the creation of OWFs with floating foundations. Even at a distance of 5 km from the shore, the water depth can be 150–300 m, and, in most cases, more than 30 m [26], which is the limit for monopile foundations. On the contrary, these water depths do not occur in the North Sea, which is generally shallow.

In order to limit the visual impact (and, theoretically, people’s reactions), to increase profits and the participation of the OWF in the energy mix, and to harness more wind potential, the installation of a floating OWP is favored by some experts. On the other side, a floating OWF could also trigger social reactions due to the possible visual impact, since a wind turbine is visible at a distance of approximately 40 km.

The authors of this article selected a monopile foundation for the project analyzed for the following reasons: the lower costs [25], it is a common technique in shallow waters, the relative simplicity of installation, and the technology’s maturity (from the 5566 offshore wind turbines in EU and UK waters at the end of 2021, 4780 were installed using monopile foundations [27]). In addition, because Greece does not yet have an OWF and needs to gain experience, a smaller OWF, with lower costs, simpler procedures, and less of a visual impact, such as that described in this article (between Karpathos and Kassos), may more easily interest investors. Moreover, the authors believe that such a park could create a basis for bigger projects in the future, when offshore wind power technology is more familiar in Greece.

Furthermore, despite not having been constructed, the two projects already licensed in Greece by Regulatory Authority for Energy (RAE) in Alexandroupoli (the area for the pilot project involving the development of an offshore wind farm) and in Lemnos were designed at a distance of 10–15 km (at water depths 30–45 m) from the shore, with bottom-fixed technology, so the visual impact would be inevitable and there may be social opposition.

In addition, even an investment for a small-scale project with similar characteristics to that in this article could be viable in economic terms and feasible, as is demonstrated in the authors’ economic analysis. Moreover, this project could contribute to the energy mix of the country even to a small degree.

3.2. The Selection of the Location

One of the twelve zones selected for the installation of an OWF in Greece belongs to the marine area of Karpathos and Kassos (Figure 1), which are in the southeastern part of the country and specifically in the Dodecanese complex. A company called “Minoika Thalassia Aiolika Parka A.E.” made an undivided application for six locations in the Karpathos and Kassos areas. As shown in the picture below in yellow, four are in Kassos (north) and two in Karpathos (southwest). The total capacity was designed to be 350 MW.

However, we decided not to locate the OWF in the proposed areas, but in a location to the southwest of Karpathos (Figure 2), which also falls under the jurisdiction of the Ministry of the Environment and Energy of Greece. Our selection is explored below.

We based our decision on the criteria posed by experts in order to select one of the best locations in Greece for such a project.

3.3. The Assessment of the Criteria for the Selection of the Area

3.3.1. Wind Potential

Firstly, the wind potential in the selected area is extremely powerful. According to an analysis [28] that took into account wind data from 1995 to 2009, the characteristics around Kassos are ideal for the development of an OWF (the mean annual wind speed of the island was measured at 8.03 m/s). However, according to the transition energy plan for Kassos [29], the mean annual wind speed was calculated at 11.61 m/s (i.e., the calculation period did not refer to the relative analysis, but was from 2011 and later).

In addition, in the context of the first analysis, it was observed that the highest average wind speed value in the Karpathian Sea was during summer, at approximately 9 m/s. Thus [30], the area of interest for this project is not only favorable, but ideal (Figure 3).

In 2019, the most frequent wind direction in the selected area was southeasterly.

3.3.2. Water Depth

The water depth in the southern zone of the selected area, near the wider part of Karpathos, fluctuates between 10 and 50 m. Specifically, the water depth is 10–32 m in the southern part of the selected area, 20–50 in the central part, and 27–44 in the northern part. The monopile-type foundation for offshore wind turbines (OWTs) cannot be installed in water depths greater than 30 m.

The authors decided that the most suitable location for the installation of an OWF in this area was that selected by the Ministry in 2010, i.e., to the southwest of Karpathos, in a location with an average water depth of 32 m (the average water depth for OWF installations in Europe was 33 m at the end of 2019 [31]) and a depth of 10 m at certain points. This location is opposite the Saints Thedoroi area. The exact site for this OWF project is marked by red dots in Figure 4.

3.3.3. Visual Impact Assessment

An evaluation of the visual impact is one of the first steps in the installation of an OWF and is often a cause of conflict [32]. An OWF can be visible in different ways, i.e., from different angles and at different distances; thus, the aesthetic factor is subjective due to the different observation points.

In the selected location, the visual impact of an OWF in water depths of approximately 10–32 m is inevitable. In this project, the authors made a tremendous effort to limit any visual impact and demonstrated full respect for the local people, who do not want any visual disturbance; however, limiting the impact to zero was impossible.

Nevertheless, as was already mentioned, the authors chose to locate the OWF to the southwest of Karpathos (Figure 4). Saints Theodoroi beach is opposite this site; however, the OWF is not visible from the beach as the authors “hided” the OWP behind a hill on the right side of the beach. If, hypothetically, the OWP were to be installed at the point described, the OWF would be visible from the hill, where there is a tavern. Furthermore, it is impossible to hide the OWF from Araki beach, which is on the right side of the bay, or from Araki resort (Figure 5).

If the OWF was located higher on the map, it would be a short distance from the commercial and touristic locations of Karpathos, Finiki, and Arcesine, which would entail a serious risk and the effect would be much greater (e.g., loss of tourism revenue).

Therefore, the authors tried to minimize any visual impact by locating it in the least touristy area, as compared with the popular areas of Finiki and Arcesine, in Saints Theodoroi. However, in any case, as it is highlighted above, some visual disturbance is inevitable.

3.3.4. Environmental Protection and “Natura 2000”

Environmental protection constitutes one of the main concerns when assessing the criteria for an OWF installation. Human development should work in harmony with nature. Thus, the negative impact of human activities should be minimized.

“Natura 2000” sites should be protected and respected, because they house flora and fauna of importance, which are threatened with extinction, are vulnerable, are rare, or are locally prevalent. The sites within “Natura 2000” are designated under the Birds and the Habitats Directives [33,34]. Furthermore, in Greece, “the “Natura 2000” network includes a total of 446 areas occupying terrestrial zones of more than 27% of the Greek territory and marine areas of more than 19% [35].

In Figure 6, the red areas are some of the most significant places for birds in Greece. The whole of Kassos and of the northern part of Karpathos are highlighted. These sites are of vital importance for the maintenance of vulnerable birds and those threatened with extinction. In addition, in Figure 7, the yellow areas denote wildlife refuges (seven in number), and Figure 8 shows “Natura 2000” sites in green, in Kassos and Karpathos.

Consequently, the area examined for the installation of an OWF is sensitive and a focus on environmental responsibility is required in order for nature to be protected. Of course, the reason for the authors not selecting a location in the wider area of Kassos is obvious, i.e., the whole Kassos area is integrated in “Natura 2000”, which is prohibitive for the implementation of such a project.

3.3.5. Distance from Settlements and Distance from Ship Routes

Restrictions exist in relation to the distance from traditional and non-traditional settlements and the distance from ship routes.

Firstly, the minimum distances from residential networks are different for traditional and non-traditional settlements. The minimum distance between an OWF and a residential network is 1 km, whereas it is 1.5 km from an OWF and a traditional settlement [36]. In the examined area, there is no real concern, as the distance from the closest settlement on south Karpathos is 6.18 km (i.e., in this area, there are only old settlements, with a small number of probably uninhabited homes, which are used mainly for the activities of stock-farmers and rural objectives). The distance from Arcesine is 5.55 km, the distance from Finiki is 6.48 km, and the distance from Poli in the east of Kassos is 11.17 km.

Moreover, only one shipping route passes through the examined area, as is shown in Figure 7 and Figure 8 with the dotted line. The fewer existing shipping routes, the higher the area ranks. Therefore, the area examined in this project has an excellent rank. In general, when an OWF is designed, there is a possibility of conflict with the shipping sector, because there is a risk that the available space for navigation will be reduced by the OWF and this affects the safety and the efficiency of shipping movements. Moreover, a distance between an OWF and a shipping connection of 0.5–3.5 nm (0.8–5.6 km) is tolerable [37] when planning the installation of an OWF. The relevant distance in our case is 0.8 km. Therefore, the distance is sufficient and the possibility of conflict with the shipping sector is reduced, which is one more advantage [37].

3.3.6. Distance from the Shore

There is no definition of a sufficient distance from the shore, not even in Article 10 of the “Special framework for spatial planning and sustainable development for renewable energy sources”, in which appropriate distances are taken into account. Among these distances, the distance from beaches or significant shores from every perspective is outlined. This distance, which is not exactly a “distance from a shore” given that it does not include every shore, is 1.5 km. Of course, the larger the distance from a shore, the lower the visual disturbance.

In general, distances from a shore could be classified as small, medium, and large [38]. This project was assessed to be a short distance from the shore. Moreover, distance from a shore is a factor that plays a critical role in the cost. Therefore, concerns about the distance from a shore not only relate to social and engineering issues, but also economic aspects [39].

3.3.7. Seabed Conditions in the Examined Zone

The assessment of the seabed conditions in the selected area between Karpathos and Kassos for the installation of an OWP constitutes an essential procedure for the purposes of this project. The seabed should be evaluated in every such project, since the installation of OWTs requires stable seabed conditions, as there are significant geo-hazards, which can cause the collapse of an OWT.

The Greek area is divided into three zones [40] of seismic risk. In addition, it is known that an earthquake can lead to ground acceleration [41], fact that is an important parameter during the design of seismic resistant structures, such as an offshore wind farm. In the first zone, the ground acceleration is 0.16 g; in the second zone, it is 0.24 g; and in the third zone, it is 0.36 g. The areas belonging to the islands of Karpathos and Kassos are classified in the second zone (0.24 g) [42]. In Greece, only the areas that belong to the third seismic hazard zone (0.36 g) are excluded from becoming OWF installations; thus, the location selected between Karpathos and Kassos is appropriate for the installation of an OWF (Figure 9), in terms of possible seismic activity.

3.4. The Presentation of the Authors’ OWF

3.4.1. OWTs’ selection

The OWF in this project has the shape of a polygon (the total area is 1.787 km²). This is shown in Figure 10.

In this polygon, the authors decided to locate a total of nine OWTs in two phases.

Three OWTs were constructed in January 2023, providing that the previous steps (e.g., the environmental impact assessment) in project development were completed. Six OWTs will be added in January 2028, after the expected energy interconnection (by 2027) of Karpathos and Kassos with the mainland.

The nine OWTs are manufactured by the German firm Siemens Gamesa.

Specifically, the authors decided to select the model “SWT-3.6-107” (2005). This wind turbine has a nominal power of 3.6 MW and the diameter of its rotor is 107 m. Furthermore, it has three blades and its swept area is 8992 m². A monopile-type foundation was chosen by the authors for the wind turbines, mainly due to the water depth (approximately 10 and 32 m), but also for the reasons analyzed above.

3.4.2. Design and Capacity of the OWF

The total capacity of the OWF in this project will move through three stages. The capacity of the wind farm during its first 5 years (January 2023–December 2027) of operation will be 10.8 MW (three wind turbines × 3.6 MW). In the period of January 2028–December 2048, and after the interconnection of Karpathos and Kassos with the mainland, it will operate with nine OWTs and have a total capacity of 32.4 MW (nine wind turbines × 3.6 MW). In the period of January 2049–December 2052, the OWF will operate with six OWTs with a total capacity of 21.6 MW (six wind turbines × 3.6 MW), since the first three OWTs need to be dismantled, because their lifespan is 25 years.

According to a previous study [43] in which 27 European OWFs were analyzed, the average downwind and crosswind spacing of such a project is 7.5 D and 5.9 D, respectively (i.e., D symbolizes the diameter of the rotor). When the layout of wind turbines is designed, experts across the world take into account the diameter of the rotor. Consequently, the authors took into consideration these particular downwind and crosswind spacings. Τhe units in the area covered by the OWF between Karpathos and Kassos were designed for the needs of the particular project and upon relevant request of the authors by the firm “Hellenic Cables S.A”, with whom we communicated in December 2020.

In the area selected by the authors, the installation of a total of nine OWTs is realistic, because the wind turbines were designed to be at an adequate distance from each other, according to the previously mentioned requirements. In addition, the larger the rotor’s diameter, the larger the power in MW. Therefore, increasing the MW would entail a larger rotor diameter, which, at the same time, would require more space or fewer wind turbines.

Furthermore, the wind turbines were placed vertically to the direction of the wind (southeasterly) in order to maximize efficiency.

However, it is essential to underline the fact that wind turbines do not operate at a maximum level. They ‘’produce at or above their average rate around 40% of the time. Conversely, they produce little or no power around 60% of the time’’ [44].

3.4.3. Cables for the OWF

Regarding the interconnection of the OWF, the authors selected cables from the Greek firm “Hellenic Cables” (

Table 1. The proposal of the firm “Hellenic Cables” regarding the sizing of the cables for the OWF described in this project.

For the Sizing of the Cables, the Following Points Were Considered:
Number of wind turbines	9
Power of each wind turbine	3.6 MW
Voltage level for the transfer of energy from the offshore wind farm to the onshore substation	33 kV
Voltage level for the interconnection of the wind turbines	33 kV
Power factor cosφ	1
Electricity per wind turbine	67 A
Power requirement for 9 wind turbines and cable-carrying capacity	603 A

Source: edited by the authors.

and

Table 2. The proposal of the firm “Hellenic Cables” regarding the length of the cables for the OWF described in this project.

The Cable Lengths
Total length of inter-array cables	5392.8 m
Length of submarine cable from the last wind turbine to the grounding	1000 m
Total length of the submarine cables	6392.8 m
Distance from the grounding to the onshore substation (monopolar cable)	3000 m
Total length of onshore cables (three monopolar cables)	9000 m

Source: edited by the authors.

). On 28 December 2020, the company, which has a great deal of experience in offshore wind projects around the world, submitted a written proposal to the authors regarding the installations of the cables for the OWP between Karpathos and Kassos.

The proposal from “Hellenic Cables”, which was adopted for this project, is presented below (the prices are from 2019).

Moreover, “Hellenic Cables” provided the authors with options (aluminum and copper) for the submarine cables and their costs (

Table 3. The proposal of the firm “Hellenic Cables” regarding the options for the submarine cables for the OWF described in this project.

Options for the Submarine Cables (a Total Length of 6392.8 m)
Material of the Conductor	Cross Section of the Conductor (mm2)	Cable Cost per Meter (EUR/Meter)
Aluminum	630	165
Copper	400	220

Source: edited by the authors.

). For the OWF between Karpathos and Kassos, the authors selected aluminum for the submarine cables, not only because it is cheaper, but also because it is used in most countries in Europe in similar projects. On the other hand, copper is mainly used in Greece and is more expensive.

Concerning the onshore cables, “Hellenic Cables” proposed (

Table 4. The proposal of the firm “Hellenic Cables” regarding the onshore cables for the OWF described in this project.

For the Onshore Cables
Conductor Material	Cross Section of the Conductor (mm2)	Cable Cost per Meter (EUR/Meter)
Copper	400	220

Source: edited by the authors.

) using copper because much more power can be transferred in comparison with aluminum. In addition, copper is used in the majority of onshore wind projects in Greece, but we did not exclude the possibility of using aluminum.

As was already mentioned, three OWTs were constructed in January 2023, before the interconnection of the islands of Karpathos and Kassos with the mainland. These OWTs were installed on the lower side shown in Figure 11 on the right. Consequently, the first OWT is at a distance of 1000 m from the shore, the second is at a distance of 802.5 m from the first, and the third is at a distance of 631.3 m from the second. In addition, as it was stated above, six OWTs will be constructed in January 2028, after the interconnection. However, the first three OWTs need to be dismantled before the other six. This will not cause any malfunction to the OWF provided that the cables located before and after the OWTs that will be removed are connected to each other. This is not a difficult task and it entails negligible additional costs that were not included in the economic analysis.

3.4.4. Onshore Substation and Transition to the High-Voltage Network Plan

OWFs can have both an offshore substation and an onshore substation for their operation. However, they can only operate with an onshore substation when the OWP is near the shore. In this case, the offshore substation is not needed and its installation could significantly increase the cost, without it actually being useful for the operation of the OWF.

As a consequence of the above and given the fact that the OWP (

Table 5. A summary table of the characteristics of the OWF between Karpathos and Kassos (Greece) designed by the authors for this project.

Summary Characteristics of the OWF in This Project between Karpathos and Kassos
Total number of wind turbines		9
Wind turbine	Manufacturer	Siemens Gamesa
	Model	SWT-3.6-107
	Nominal power	3.6 MW
	Diameter of the rotor	107 m
	Swept area	8992 m2
Total area		1787 km2
Type of foundation		Monopile
Water depth		10–32 m
Substation		Onshore
Cables	Offshore	Aluminum, 6392.8 m
	Onshore	Copper, 9000 m

Source: Edited by the authors.

) is near to the shore, the authors decided not to include an offshore substation, which would be unnecessary. Therefore, an onshore substation will be installed in Karpathos approximately 3 km from the OWF, near to roads and in a flat area without mountains. It should be noted that there are no limitations about the distance from coasts regarding the potential installation of an onshore substation.

This onshore substation, which will be connected via cables with the OWF, will be approximately 1 acre in size and will be built in harmony with the local environment. The substation will include, among other things, two measurement medium-voltage panels, protection and control panels, and the SCADA system, and there will be access to the internet. The cables from the onshore substation will meet with the first pillar of the existing local medium-voltage distribution network. If one does not exist near the onshore substation, it will be constructed after the relevant agreement between parties. From the moment the OWF is connected with the first pillar of the existing local medium-voltage distribution network, the cost will cease to burden the energy producer (i.e., the firm that assumes the project). The cables and the medium-voltage substation infrastructure will feed the medium-voltage grid of Karpathos with the produced energy and, in this way, the OWF will be connected to the low- and medium-voltage network of the island and, of course, to the energy-dependent Kassos.

Karpathos and Kassos are currently (June 2023) non-interconnected islands; however, by 2027, they are scheduled to be connected to the HETS. This fact will entail Karpathos and Kassos being connected via a 150 kV substation to the mainland transmission grid through submarine cables. In this future scenario, the onshore substation described above will not serve the purposes of the project. The grid will not be low- or medium-voltage, but a high-voltage grid. For that reason, at the same point, a new six acre onshore substation with even more equipment will be created, because the voltage coming from the OWF will need to be transformed in the onshore substation at 150 kV after the transition to the high-voltage network. The cost for this onshore substation will be around EUR 3 million, i.e., EUR 2.3 million more than the first (EUR 700,000) onshore substation. Nevertheless, the first onshore substation could be used as an intermediate measuring station.

3.4.5. Examination of Ports and Final Selection

Despite the fact that Kassos is small, it has one of the biggest ports on any Greek island. It has been operating since 2005, and it replaced the old port of the island, being bigger than the two of Karpathos (Pigadia and Diafani). Moreover, the OWF is a distance of approximately 13.5 km from the port of Kassos, while the port of Pigadia (Karpathos) is a distance of approximately 33.15 km from the OWF and the port of Diafani (Karpathos) 62 km from the OWF. For all the above-mentioned reasons, the authors selected the port of Kassos, so that the special vessels are transported faster, as well as lower energy consumption, the necessary equipment, and the specialized crew, for the needs of the installation of the OWF.

3.4.6. The Lithium-Ion Batteries Used for the OWF in This Project

For both phases of the project (the first phase with non-interconnected islands and the second phase when Karpathos and Kassos are interconnected), the authors selected to use lithium-ion batteries. The purpose of the use of batteries is the storage of energy produced by RES, in order to be used, mainly, under conditions of peak demand and low production from RES.

For the energy purposes of Karpathos and Kassos, there are eight generators with a total nominal power of approximately 16.6 MW [29]. All of them use mazut or diesel, leading to a total cost of energy production for the Karpathos–Kassos grid of 222.13 EUR/MWh (i.e., the total cost for the operation and maintenance of the autonomous production station of Karpathos was 92.69 EUR/MWh in 2019) [29]. By installing the OWF and the lithium-ion batteries (the new National Energy and Climate Plan revises the target of energy storage in batteries from 1.2 GW to 5.6 GW [17]), the major proportion of these generators can be withdrawn. In the second phase (interconnected islands), the autonomous production station of the Public Power Corporation (PPC) of Karpathos will remain in reserve in the case of emergency, since the energy, which will be channelized by the HETS (the OWF in this project will participate in the HETS), will cover the needs of the two islands.

The lithium-ion batteries used for the project, once installed in the onshore substation, will last for 10 years on average. Thus, after their installation, they will need to be substituted twice over the length of the project. In addition, it is noted that a lithium-ion battery can maintain the stored energy for up to 6 months, but there are losses of around 5% for each month. Every MWh from lithium-ion batteries costs EUR 500,000–600,000 and, for the project in this paper, 2 MWh each (6 MWh, in total, for the complete life of the OWF; the batteries should be substituted every 10 years, so the authors put them in year 0, year 10 and year 20 of the project) were selected by the authors. A cost of EUR 550,000 for each MWh was calculated; thus, the overall cost is EUR 3,300,000 (EUR 550,000 × 6 MWh).

To collect information concerning the lithium-ion batteries, the author conducted an interview (11 January 2020) with the Electrical Engineer, Mr. Simos Parcharidis, who, at the time of the interview, was working for the Greek firm “Sunlight”, which specializes in energy storage and lithium-ion batteries.

3.5. Benefits for Karpathos and Kassos and for the Greek State

Public acceptance of the installation of an OWF between Karpathos and Kassos could be affected by the local community’s unfamiliarity with RES and by how the benefits for the municipalities and the residents of these two islands are presented.

Despite not all being achieved, the benefits proposed for the two islands in this project are related to their participation in the development of the project and to the fact that, during the first phase (January 2023–December 2027), an interconnection with the mainland will not be activated. Therefore, the proposed benefits are recorded as follows: (1) jobs for local people (the exploitation of human resources); (2) compensatory projects of any form could be taken into consideration, depending on the needs of the two islands [45]; (3) the promotion of the two islands due to such a project could bring positive results, for example, it could increase tourism; (4) the roads on the two islands could be lit with “smart” lamps, which will draw energy by the OWF; (5) the installation of charging stations for electric vehicles (the municipalities can replace some of their vehicles with electric vehicles), which will be charged with energy coming from the OWF; (6) the municipalities could receive an annual amount of money, as compensation, from the company (or companies) that would undertake the project; (7) through the development of Energy Communities, residents could participate in the shared capital; and (8) the operation of the OWF will almost completely eliminate the production of energy from fossil fuels on these two islands.

After the energy interconnection of Karpathos and Kassos with the mainland, there will be many benefits for the local communities and for the Greek State in general: (1) The limitation of blackouts, mainly due to damage to the old submarine cables that connect Karpathos and Kassos or damage to the autonomous production station of the PPC of Karpathos. This is essential for entrepreneurs on the two islands, because power cuts provoke significant losses (i.e., electrical devices are “burned” and products stored in refrigerators spoil). (2) The limitation of blackouts could decrease the risk for those who make use of oxygen supply devices on the two islands (people who use oxygen devices in their homes or at treatment rooms and hospitals; Kassos does not have a hospital, but Karpathos has). In the past, people’s lives were endangered due to power outages and because there was no emergency generator. (3) The OWF will contribute to the increase in the share of RES to the Greek energy mix and consequently to achieving national green targets. (4) The increase in the contribution of RES will entail lower electricity prices for all the residents of Greece. (5) The pace of climate change can be significantly reduced through RES; thus, environmental protection can be achieved.

3.6. Economic Analysis

The economic analysis in this paper was based on elements and data as of the first quarter of 2021. This analysis consisted of the Capital Expenditure (CapEx) and Operational Expenditure (OpEx) [46] calculations, and the Net Present Value (NPV) and the Internal Rate of Return (IRR).

The total lifespan of the project (including both phases) was considered to be 30 years. Moreover, the relevant residual value [47] was also taken into consideration. The NPV of this investment was calculated to be equal to EUR 820,037.29, which is positive and well above zero. The IRR was calculated to be equal to 7.83%, which is more than the discount rate (7.5%) and was taken into account in the economic analysis. Therefore, the results from the IRR method were in agreement with the results of the NPV method.

The result of the financial analysis for the specific OWP demonstrates that an investment in this project is viable in economic terms and feasible.

The detailed data and calculations of the economic analysis are available in the Supplementary Material document of this paper.

3.7. SWOT Analysis

A SWOT analysis, for the first phase examined in this project, is presented below (

Table 6. First phase: the offshore wind farm is installed, while the islands of Karpathos and Kassos are not interconnected in energy terms with the mainland.

Strengths	Weaknesses
Favorable location, high wind resource. Protection of the environment and low impact, in general, to the everyday life (respect to the local daily life). Many benefits for the two local communities. Provision for the future energy interconnection of the two islands (transition).	The selection of the port of Kassos may raise questions about its appropriateness. However, the choice of this port occurred after the examination and was based on the reasons that have been analyzed in detail.
Opportunities	Threats
“Turn” to the clean energy. Achieving goals with low cost, mature technology (monopile foundation), and a few wind turbines. Use of batteries (storage). Exploitation of the Greek ports, shipyards, industry of cables, and industry of concrete.	Absence of such a project in Greece → no experience. Lack of specific legislative framework and methodology by the Greek State. Strong bureaucracy: unknown required times and lack of time accuracy. Lack of infrastructure (e.g., appropriate ports). Possible social reactions.

Source: Edited by the authors.

). Regarding the second phase of the project, when the offshore wind farm will already be operating and the islands of Karpathos and Kassos will be interconnected in energy terms with the mainland, the difference will be that benefits will favor not only the local communities, but also the Greek State:

4. Discussion

In this project, an OWF between the non-interconnected islands of Karpathos and Kassos (the latter is energy-dependent on the first at the time of writing) in Greece (in the Dodecanese complex) was designed by the authors, in realistic terms, to operate in two different phases.

In the first phase (January 2023–December 2027), the two islands were not considered to be energy-interconnected with the mainland system, something that is expected to take place by 2027, according to the plan of the Independent Power Transmission Operator (IPTO).

In the second phase (January 2028–December 2052), the authors considered Karpathos and Kassos to be energy-interconnected with the mainland system and, for that reason, some elements were modified in comparison with the first phase. The transition from the first to the second phase for the same offshore wind project was predicted.

The authors described all of their decisions about the selection of the location of the installation, the foundation type, the OWTs, the cables, the onshore substation, and the port. Furthermore, they analyzed why the area of interest is one of the best in Greece for such a project, presenting, step by step, all the criteria that should be examined. In addition, energy-storage technology, via the use of lithium-ion batteries, was exploited for the purposes of the particular OWF.

In addition, the price of sale (76 EUR/MWh) of the produced energy was also calculated. According to a study of the European Union [48], the average selling price of the energy produced by offshore wind should be 54–65 EUR/MWh to be reasonable for the consumers and competitive for the producers. However, the price for this technology (i.e., specifically, this price is defined for the floating offshore wind), in Greece, is estimated to be achieved in 2030 at 76 EUR/MWh and in 2050 at 46 EUR/MWh [25].

The benefits for the two islands, if they were to decide to participate in the development of the project, and the benefits for the Greek State via this OWF were outlined. At the same time, social reactions are possible. The authors also analyzed the strengths, weaknesses, opportunities, and challenges, through the SWOT method for the two phases of the project.

Our financial analysis, adapted to the specific OWP, demonstrated that an investment in this project would be viable in economic terms and feasible, despite it being a small-scale project. Nevertheless, even a small-scale project of this kind could have a positive economic effect, as offshore wind power technology has many advantages.

It should also be noted that, for the needs of this project, the authors communicated with a number of people who provided useful information.

In conclusion, the OWF created by the authors for this project was designed not to significantly disrupt the everyday lives of the local people and to respect the environment. For that reason, a small number of OWTs was selected, and a less inhabited area that is less touristy and generally less developed than other areas was decided upon. Moreover, our aim was to show that there are solutions with gains for all parties (the state, companies, and local communities) and with the smallest possible disruption to the environment.

At the European Union level, this particular OWF could play a role in the overall strategy of the EU, which aims to increase its offshore wind capacity to at least 111 GW by 2030 and to 317 GW by 2050 [49] in order to strengthen its energy security, diversify its energy sources, and achieve its climate targets [50]. At the global level, according to the International Energy Agency (IEA), “global annual offshore wind installations are expected to increase 50% to over 30 GW in 2027” [51]; thus, every contribution to “green” energy is desirable.

The Greek State has no experience in offshore wind power, but promotes the development of the first OWF (an OWF could be characterized as a project of strategic importance [52], due to its contribution to the enhancement of the national or local economy and of the competitiveness) in its marine area. Greece is considered by experts to be an ideal place for such an installation due to its big ports, its shipyards, and its cable and concrete industries, which will all benefit from offshore wind projects. To begin with, a small-scale project such as the one described in this paper may be a good option.

Furthermore, Greece has many challenges to face and there are many areas in which progress can be made (e.g., the legislative framework, bureaucracy, and power grids). Moreover, there are many challenges related to offshore wind power, which is a promising technology, but has yet to become widespread due to its high costs.

Further research on this issue in relation to possible opportunities in Greece, and the strengths and weaknesses of offshore wind power projects in the country, will be of great benefit.