1. Introduction
Offshore renewable energy includes both offshore wind and ocean energy and presents a great potential for development. Τhe European offshore wind energy sector has shown rapid development in recent years, and offshore installations grew 101% during 2017 compared to 2016 [
1]. Up to now, most offshore wind farms operating in Europe have been installed in relatively shallow waters with average depths of 27.5 m and at an average distance from the shore of 41.0 km [
2]. Moreover, the deployed support structures mainly correspond to fixed bottom configurations, i.e. monopile, gravity base, tripod and jacket [
2]. However, the technology of floating offshore wind turbines is rapidly advancing during the last years aiming at giving access to more deep waters, where stronger winds exist. Therefore, various concepts of substructures for floating wind turbines have been and are still being developed, including the spar-buoy, the semi-submersible and the Tension Leg Platform (TLP) concepts [
3]. Moreover, in 2017 the first floating offshore wind farm (Hywind Scotland) started its operation [
2]. On the other hand, wave energy technology presents one of the most advanced and rapidly developing ocean energy technologies, anticipated to be commercially available in the short-to-medium term [
4] and, so far, different types of wave energy converters, in terms of energy absorption mechanism, have been designed and developed [
5], such as oscillating water column devices (e.g. [
6,
7,
8]), floating or submerged oscillating bodies (e.g. [
9,
10]), multi-module floating devices (e.g. [
11,
12]) and overtopping devices (e.g. [
13,
14,
15,
16]).
Although offshore renewable energy projects are considered environmentally friendly developments, there are some environmental impacts that should be taken into account and assessed during their life cycle. Consequently, the majority of offshore wind farm projects, as well as of all the marine renewable energy installations require Environmental Impact Assessment (EIA) to ascertain the effects of the above developments on various biological and physical processes and on the environment. Offshore wind farms affect negatively the marine environment through avian collisions [
17,
18], underwater noise [
19,
20,
21,
22] and electromagnetic fields [
22,
23,
24]. However, there are also positive effects on local biodiversity as the offshore wind turbines can act as artificial reefs [
24,
25,
26]. The extent and the nature of the effect is mainly dependent on the nature of the reef created, the location, and the characteristics of the native populations at the time of introducing the artificial reef [
27]. A scientific review of the potential impacts of offshore wind farms on the marine environment identified key environmental issues related to offshore wind power development such as habitat impacts on fish, marine mammals, birds and benthos, and changes in hydrodynamic conditions and water quality [
25]. Kaldelis et al. [
28] summarized in their study the main environmental and social impacts (pre-construction and post-construction) associated with offshore wind energy developments and concluded that the marine environment is very distinct and that each project should be investigated separately, since the impacts vary greatly among different locations and are absolutely site specific.
The primary concern for wave energy applications is the risk of collisions below the sea surface [
29]. Inger et al. [
30] highlighted the potential impacts of wave farm installations, defining the negative impacts such as habitat loss/degradation, risk of collisions, production of underwater noise and production of electromagnetic fields. Woolf [
31] states the urgency that the behavior of marine mammals, diving birds and fish in the vicinity of wave energy devices should be observed as a prerequisite for establishing any inherent risks. In addition, changes in water velocities can influence the sediment transport and might cause coastal erosion. Finally, large scale wave energy arrays lead to wave field changes (i.e. wave height attenuation in the leeward side of the farm), which may affect negatively coastal eco-systems and neighboring sea activities [
32].
Recognizing the significance of minimizing potential negative environmental impacts in offshore renewable energy projects, several studies have included so far various environmental criteria into offshore wind farm siting applications (e.g. [
33,
34,
35,
36]). These criteria represent adequately specific environmental implications; however, they do not account for an explicit assessment of the potential environmental impacts of an offshore wind farm project during its whole life cycle based on an EIA study. Schillings et al. [
33] included in their analysis nature conservation zones defined as the network of protected areas under the Birds Directive (Special Protection Areas (SPA)) and Habitat Directive (Special Areas of Conservation (SAC)). They provided a wildlife preservation map for the North Sea indicating the areas that are most significant in terms of nature values by applying a series of nature value/vulnerability maps for birds, fish and benthos. Vagiona and Karanikolas [
34] excluded from their analysis of evaluating offshore wind farms in Greece, areas that are characterized as protected either by National or European legislation. Moreover, they used distance from protected areas as an evaluation criterion. Mekonnen and Gorsevski [
35] ranked their decision alternatives for offshore wind farm suitability within Lake Erie using three environmental criteria: bird habitat, fish habitat and navigable waterways. Cristoforaki and Tsoutsos [
36] excluded in their study on offshore wind farm siting in Chania (Greece), SPA, as well as marine areas with distance of less than 1.5 km from international importance wetlands, national forests, declared monuments of nature and aesthetic forests, as well as from Sites of Community Importance. On the other hand, the selection of a suitable site for wave energy projects adopts several environmental exclusive factors that amongst others include: SPA, SAC, sites included in the Emerald Network (Areas of Special Conservation Interest), International Wetland Conservation treaty Areas (Ramsar), habitats of endangered species, marine mammal breeding areas and migration routes and areas protected under regional and national planning and zoning directives [
37]. Nobre et al. [
38] identified the best location to deploy a wave energy farm for an area offshore the southwest Portuguese coast using marine protected areas as one of the several selection factors.
The option of simultaneously utilizing offshore wind and wave energy sources, through the deployment of Hybrid Offshore Wind and Wave Energy Systems (HOWiWaES), that combine in one structure an offshore wind turbine with wave energy converters, presents, nowadays, an important advantage in environmental terms, since it leads to: (i) a better exploitation of natural resources and (ii) reduced impacts compared to the impacts from independent installations [
39]. However, the minimization of negative impacts of these applications on marine biodiversity and ecosystems is considered not only an essential precondition for environmental permission of such projects, but also a prerequisite for their social acceptance. In the framework of site selection for HOWiWaES, Cradden et al. [
40] noted that some environmental issues may require additional monitoring during installation or operation of offshore renewable energy platforms, and this must be fully considered in site-selection. Moreover, in that study, the marine areas designated under Natura 2000 were excluded from potential site selection in the North European offshore areas, while the impact of excluding any development within 1 km from the Natura 2000 areas was additionally investigated. In a similar manner, Vasileiou et al. [
41] used the Natura 2000 network in order to define marine protected areas in the Greek marine environment, which were excluded for the deployment of HOWiWaES.
Based on all the above, it is obvious that up to now many researchers have used several environmental criteria in offshore wind and wave energy siting applications for satisfying environmental constraints and accounting for environmental considerations in the relevant decision making process. There has been, however, no study so far incorporating directly the EIA of such projects into the site selection process in terms of using an explicit siting criterion that expresses in quantitatively terms the potential environmental impacts of these projects throughout their whole life cycle.
EIA is nowadays considered a modern tool of developed societies for the achievement of appropriate compromises between development and environment, aiming at the inclusion of environmental concerns in decision-making and ultimately at promoting a more sustainable development [
42,
43]. An EIA enables the assessment of the environmental impacts of a project occurring during the planning phase of its life cycle, and includes impact assessment, as well as mitigation and prevention measures throughout the whole project’s life cycle. The EIA methodologies that have been developed and applied so far are numerous and include, among others, the Rapid Impact Assessment Matrix (RIAM) [
44,
45,
46,
47,
48,
49]. RIAM has been widely used by environmental impact assessment proponents and include, in its simplest form, a grid-like table, where the characteristics of the environment are presented in one axis and the activities of the project under review in the other. Interactions of the activities and the environment are indicated in the corresponding cells and the entries can indicate the type, the importance, the size, the nature, as well as other features of the impact. Pastakia and Jensen [
46] developed in their study the RIAM in an effort to incorporate subjective judgments into the EIA process. RIAM includes four environmental components (Physical/Chemical (PC), Biological/Ecological (BE), Sociological/ Cultural (SC) and Economic/Operational (EO)) and five impact assessment criteria (importance of condition, magnitude of change/effect, permanence, reversibility and cumulative). RIAM was partially modified by Ijäs et al. [
50] adding a sixth impact evaluation criterion (susceptibility of the target environment) to the evaluation framework. Vagiona [
51] created an EIA tool inspired by RIAM that includes five impact evaluation criteria and eighteen environmental components, and attributes an Environmental Performance Value (EPV) to every project.
Motivated by the significant advantages of integrating the EIA aspect within the site selection process of an offshore renewable energy project, in terms of adequately assessing environmental impacts throughout the whole project’s life cycle and, therefore, supporting social acceptance, this paper presents a methodological framework for evaluating marine areas in Greece towards the identification of the most adequate sites for HOWiWaES, with special focus on the HOWiWaES’ environmental impact assessment evaluation. The present paper advances the site selection decision making process in the case of offshore renewable energy projects and fills relevant existing research gaps by introducing, for the first time, EPV as an evaluation criterion. Analytical Hierarchy Process (AHP) is performed to hierarchically rank 12 predefined siting alternatives, which are fully harmonized with utilization restrictions, economic, technical and social constraints. AHP is applied considering eight evaluation criteria related to economic, technical and socio-political factors, additionally to EPV. The pairwise comparisons of the evaluation criteria are obtained from a group of stakeholders/experts through a questionnaire survey. A Geographic Information Systems (GIS) database is used as a metric tool for determining the relative weights of each siting alternative with respect to all evaluation criteria, except of the EPV, which is calculated through the deployment of an innovative EIA tool developed in the present paper. The rest of the paper is organized in three parts. First, a thorough description of EPV is given, and the environmental components, as well as the features of impacts considered in this research, are presented and described. The second part addresses the methodological framework followed for selecting the most adequate site for HOWiWaES in Greece, incorporating EIA. The third part is concerned with the results of the application. The procedure adopted for selecting the most adequate site for HOWiWaES in Greece is described in detail, so that it can be easily repeated and applied on any study area and at any spatial scale.
2. Calculation of EPV
EPV is introduced as an evaluation criterion to assess the environmental performance of a HOWiWaES’ project at each examined site. Its calculation is based on an integrated and uniform methodology for attributing environmental performance values in projects initiated by [
51]. In this paper, an innovative and modified, compared to [
51], tool that evaluates the impact significance through the whole project’s life cycle (construction, operational and decommissioning phase) is proposed and implemented. More specifically, EPV is determined through the implementation of the following four successive steps: (i) Definition of key environmental components (Step 1), (ii) Weight of importance attribute to each environmental component for two different time conditions (existing and potential) (Step 2), (iii) Evaluation of the impact significance of the project in its main life cycle phases (construction, operation and decommissioning) (Step 3) and (iv) Calculation of EPV (Step 4).
In Step 1, all aspects of the abiotic, natural and anthropogenic environment that might be affected by a proposed project or activity should be defined. In the present research, eighteen environmental components are totally considered, defined as follows: climate, bioclimate, morphology, aesthetics-visional features, geology, tectonics, soils, natural environment, land uses, built environment, historical and cultural environment, socio-economic environment, infrastructures, atmospheric environment, acoustic environment-noise, vibrations, electromagnetic fields, surface waters and groundwater. All the above components cover all aspects of the natural and anthropogenic environment that should be considered in an EIA study.
In Step 2, all eighteen environmental components are qualitatively evaluated, using a five-point scale (1: non-important, 2: slightly important, 3: moderately important, 4: very important, 5: extremely important) and those that are the most urgent and critical for ensuring sustainability of the area are identified. The evaluation is performed twice; once for the existing conditions and once for the future conditions, by attributing a qualitative weight, wkj, k = 1 (existing conditions), k = 2 (future conditions), j = 1,…,18, to each j-th environmental component. Existing conditions refer to the present/existing state of the environment of the study area, while future conditions pertain to the state of the environment that will be formed due to other scheduled projects and activities, without considering the effects of the proposed project. The latter time conditions ensure that the potential dynamic changes performed in the environment are considered.
For implementing Step 3, specific environmental impact assessment criteria are taken into account, which are distinguished into: (i) Primary Criteria (PC) that include nature of impact (PC1) and magnitude of impact (PC2), and (ii) Secondary Criteria (SC) that include permanence of impact (SC1), reversibility of impact (SC2) and confrontability of impact (SC3). The scaling of these environmental impact assessment criteria is presented in
Figure 1. Based on the scaling of this figure and inspired by the environmental score provided by [
46], the impact significance of the project,
akij, k = 1, 2,
i = 1,…,3,
j = 1,…,18, is calculated using the following equation:
where,
k = 1, 2 denote existing and future conditions respectively, as described in Step 2,
i = 1,…,3, corresponds to the three basic phases of a project’s life cycle, namely, construction phase (
i = 1), operational phase (
i = 2) and decommissioning phase (
i = 3), while
j = 1,…,18, denotes the
jth environmental component, as described in Step 1. Based on [
46], it is noted that in Equation (1) the values of PC are multiplied in order to ensure that different nature and different magnitude of impact will always lead to different results. On the other hand, the values of SC are summed up to a single number, so that the combined importance of all individual SC can be taken into account. From a physical point of view, positive and negative
akij values denote that the proposed project at the
k-th time conditions and during its
i-th phase has a positive and a negative respectively impact on the
j-th environmental component, while zero values of
akij denote neutral effect (nor negative nor positive impacts) of the project on this component. Larger positive
akij values correspond to more significant positive impacts, while the existence of larger absolute
akij values in the negative range denotes more significant negative impacts.
Finally, in Step 4, EPV of the examined project is derived using the weighted sum model. Six different alternatives are considered during the life time of the project, by combining the existing and the future conditions of the key environmental components (Step 2) with the impact significance for the construction, the operational and the decommissioning phase of the project (Step 3). The total score,
Akij, of each
j-th,
j = 1,…,18, environmental component for given time conditions (
k = 1 or
k = 2) and for each
i-th,
i = 1,…,3, relevant alternative, corresponding to the construction phase (
i = 1), the operational phase (
i = 2) and the decommissioning phase (
i = 3) of the project at these time conditions, is calculated as follows:
In Equation (2), wkj, k = 1, 2, j = 1,…,18, is the qualitative weight of the j-th environmental component in the existing (k = 1) and future (k = 2) conditions, as defined in Step 2, and akij, k = 1, 2, i = 1,…,3, j = 1,…,18, is the impact significance as obtained from Equation (1). From a physical point of view, Equation 2 expresses quantitatively the relevant impact significance of the project on a j-th environmental component compared to the rest seventeen components at given k-th time conditions and for a specific i-th phase of the project. The EPV is, finally, derived by the aggregation (sum) of all the environmental components’ scores for all the six different alternatives described above.
Based on these alternatives and using the scaling of the EIA criteria (
Figure 1), EPV ranges from 54 (extremely positive impacts) to −162 (extremely negative impacts), as shown in
Table 1.
5. Conclusions
Considering the growing demand for energy and the shift to renewables worldwide, sustainable selection of energy investment projects is gaining increasing interest and importance at all policy levels. The overall aim of this study is to identify the most adequate locations for HOWiWaES developments within a study area (Greece) with emphasis on environmental considerations. The renewable energy site selection problem should involve different stakeholders (policy makers, proponents, regulation authority, investors and society) who can state different preferences and priorities relating to the various evaluation criteria. For this reason, relevant stakeholders and experts in the field of renewable energy sources management were involved in the decision making process. Using the pairwise comparisons of evaluation criteria provided by the experts, it has been possible to identify the appropriate and most suitable locations to host these types of infrastructures.
The integration of analytical tools such as GIS and multi-criteria decision analysis contributes to the effective solution of this multidimensional site selection procedure. Considering a set of evaluation criteria related to economic, technical and socio-political factors, and calculating the environmental performance value at an initial stage of planning, the viability of the proposed and applied methodological process was ensured. The selected evaluation criteria apply strict limitations aiming at the cost-effectiveness of HOWiWaES, the maximization of security, as well as the minimization of environmental impacts and local community reactions.
In this study, wind velocity, wave energy potential and environmental performance value presented the three evaluation criteria with the highest relative significance. The hierarchy problem was induced to 12 pre-defined eligible offshore areas for the siting of HOWiWaES in Greece. The marine area, located East of Crete, presents the most adequate area for the siting of HOWiWaES, mainly due to the simultaneous existence of the largest wind and wave energy potential, as well as its low environmental performance value. The high position in the hierarchy of the marine areas located East of Mykonos and North-West of Crete is attributed to important economic factors such as water depth (adequately satisfied in the second option) and proximity to a local electrical grid with high voltage capacity (adequately satisfied in the third option), as well as to slight environmental effects (adequately satisfied in both options).
As stated above, this paper aims to provide an insight for the site selection problem of renewable energy investments of HOWiWaES in Greece. Extending the above process to other areas worldwide and increasing the number of renewable technologies to be implemented could be included in possible future work. It would also be interesting to combine GIS techniques with other multi-criteria decision methods. The proposed approach can address different stakeholders, while it has a flexible design for considering the evaluation criteria and it is applicable to any candidate area for HOWiWaES deployment.