1. Introduction
With climate change becoming a major concern across Europe, the UK and Ireland are amongst several nations that have pledged to achieve net-zero carbon emissions by 2050. Energy production and its use are now understood to be responsible for 75% of total greenhouse gas emissions in Europe [
1], so naturally, the decarbonisation of this sector is a priority in reaching these ambitious targets. As island nations, with enormous maritime areas, offshore is a logical place to look for answers in both countries. Forming part of the broader Offshore Renewable Energy (ORE) sector, ocean energy devices turn the energy from moving water into electricity which can power society’s energy needs onshore via underwater cables. However, not all offshore areas are suitable for deploying ocean energy devices. Site selection needs to consider several core geospatial criteria to filter out unsuitable sites. Other, less critical criteria may also need consideration before deciding on whether site conditions are optimum for deployment.
A wide range of factors must be considered when planning where to deploy ORE infrastructure. These can be technical, economic, environmental or social acceptance related [
2]. All are predominantly spatial in nature, thus promoting the suitability of GIS for the assessment. GIS has played a hugely significant role in energy exploration in recent decades, increasingly so for renewable energy. Some work has focused exclusively on the exploration of the resources [
3,
4], including offshore options [
5,
6]. Others apply additional criteria to identify suitable sites for both land-based [
7,
8,
9] and offshore [
10,
11] renewable energy infrastructure. Many studies have adopted various criteria and methods to conduct on-site identification for ORE in recent years [
12,
13,
14,
15], including for wave energy [
16,
17,
18] and tidal energy [
19,
20,
21]. However, a thorough multi-criteria site suitability analysis for wave and tidal energy for the region of interest (see
Section 2.1) is lacking. Furthermore, ORE site selection remains an intricate procedure, as the perceived appropriate weighting and number of inputs (along with their associated values and meaning) vary considerably between stakeholders [
22,
23,
24].
A study of GIS criteria for offshore wind energy noted that the number of parameters feeding site selection could vary between 2 and 14, with a mean of 7 [
25]. However, some of these may not necessarily be hard constraints. For example, the environment (i.e., protected areas) may rightly be considered pertinent to the appropriate selection of a site for ORE deployment, this does not mean that such infrastructure cannot be placed within protected areas (such as SACs, SPAs and MCZs). Therefore, it is best not to exclude such areas from development consideration; instead, the user should be made aware that the area is situated within a protected area which will likely have implications at the planning and consenting stage, as per the EU Habitats Directive [
26]. The varying perceptions of appropriate input criteria and their associated meanings promotes the merit of interactive web-based GIS tools for facilitating instantaneous user input and flexibility on consideration of relevant criteria.
The recent growth of such powerful online GIS applications, collectively known as Web-GIS, has enhanced the implementation of GIS worldwide, and many examples of these implementations have been examined in detail [
27]. Web-GIS tools are particularly effective for sharing common information to a global audience. This concept combines the advantages of GIS with those of the internet to enable easier accessibility, flexibility, organisation and use of a multitude of criteria related to a specific sector, which this paper will demonstrate for ocean energy.
Web-GIS tools relating to coastal and marine matters are referred to as Coastal Web Atlases (CWAs) [
28]. Since its foundation in 2008, the International Coastal Atlas Network (ICAN) has encouraged common standards to be applied to CWAs, typically comprising a map area, legends and tools that enable the marine/coastal data to be visualised and queried. Existing CWAs relating to renewable energy have been examined in detail [
29], including the Wales Marine Planning Portal [
30] and Ireland’s Marine Renewable Energy Atlas [
31], which were particularly relevant and helpful to this work. However, the study also revealed the distinct lack of an open-access GIS tool geared to ocean energy applications, particularly site selection and project feasibility analysis.
In this context, the aim of the research was to develop an open-access CWA bespoke to ocean energy applications, incorporating both site selection and project feasibility analysis functionality. The design and development of the CWA would adhere to the standards set out by ICAN. While this article details the elements that are more relevant to site selection, a future article will detail the aspects relating to project feasibility analysis. A wide range of geospatial data/layers are described in this article which relate to ocean energy site identification in Irish and western UK waters. These data have been developed for the CWA and will be made openly accessible via the tool upon its release. Furthermore, analysis and geoprocessing of this data has been performed in a case study to identify potential and optimum sites within the study area for wave and tidal energy project deployment. Where possible, in situ validation of data that are more influential to site selection has been performed, with the accuracy reported here. The CWA, and the data therein, was developed as part of the Selkie project, a cross-border project aiming to boost marine energy in Wales and Ireland by creating a set of multi-use technology, engineering and operation tools, templates, standards and models for use across this growing sector.
4. Discussion
It was expected that the highest wave power in the study area was observed off the west coast of Ireland given its open Atlantic location. The observation, which aligns with previous studies of the resource [
57,
58,
59], further demonstrates the opportunity available for wave energy extraction at this location. Focusing on detail, the highest mean annual values, reaching 70 kW/m off the northwest coast, also match some of the values in previous work [
57]. The seasonal observations of the wave climate also correlate with the values and patterns of former studies, with values in winter (most productive season) easily reaching more than 100 kW/m off the west coast of Ireland; studies also show that autumn is a more productive season than spring [
57,
58]. The much higher resource availability observed in winter compared to summer is also meaningful in that domestic electricity demand is higher in winter; this indicates a positive relationship between demand and supply. However, wave energy devices have operational limits which will need to survive the harshest conditions at sea [
60]. As the new extremes data produced for this study show that 50-year return wave heights exceed 15 m throughout the Atlantic area, meaning that the region is also likely to pose a significant risk to both the survivability of such deployments and their operational frequency, considering that maximum operating H
s values can range between 4 and 10 m, depending on the type of WEC [
61,
62,
63,
64]. Both technology and project developers will need to give this finding due consideration. The highest extreme values being observed off the northwest and southwest coasts are likely to be associated with the greater depths in these regions off the edge of the continental shelf, meaning there is less energy dissipation due to bottom friction, i.e., along the Rockall Trough and Porcupine Seabight.
With widespread coverage of suitability in the Celtic Sea, the Attenuator technology appears to be best suited to this area, followed closely by the Point Absorber. Furthermore, with cable access to shore possible along the Cork coast, as previously confirmed (
Figure 17), the opportunity for deployment here is pronounced given that Cork has a considerable industrial sector with high energy demands. The OWC has limited suitable coverage in the Celtic Sea because of the technology’s higher resource demand (
Table 7). However, the technology does appear to be well suited to Atlantic areas, particularly off the northwest coast of Ireland and the coast of Kerry and Clare. This finding follows a site suitability study which considered an OWC in the same region of interest, though the hypothetical scenario combined the OWC with an offshore wind deployment [
15]. In that study, the Atlantic Ocean, west of Ireland (as well as Scotland and the Faroe Islands), ranked highest for deployment, followed by limited potential in the Celtic Sea. The study also considered a point absorber deployment, albeit focusing more on the offshore wind element than the wave element in the hybrid scenario. In contrast to the results of the site suitability analysis performed for the point absorber in this study, that study suggested that the Celtic Sea was not suitable for deployment of this technology type. However, this is almost certainly due to the consideration of a minimum depth threshold of 150 m as opposed to the 30 m minimum depth threshold given in this study for the Point Absorber scenario (
Table 8). In accordance with the survey responses, the Point Absorber has suitable areas far offshore in the North Atlantic because of its generous depth range (up to 300 m) (
Table 8). However, such areas would have exceedingly high CAPEX and OPEX associated with the considerable distance to port and grid access, and thus would likely be far less feasible for deployment, as shown for offshore wind [
65,
66]. This will be examined for ocean energy by the authors of this article in a future study. There appears to be considerable deployment potential for all technology types off the Clare coast according to the analysis performed here, an important finding considering that Clare has a 400 kV grid connection point for electricity transmission to Ireland’s capital city Dublin [
67].
Annual accessibility values of less than 20% off Ireland’s west coast, using the 1.5 m Hs and 20 m/s wind speed limits, are also likely to pose a significant concern in terms of operations and maintenance, particularly considering UK guidelines for offshore wind, which suggest that anywhere having accessibility values below 20% is economically unviable [
68]. This finding is significant given that much of the previous work on ORE site selection for the region of interest has not included the geospatial variability of accessibility [
15,
69]. The difference between the two accessibility maps reveals that wave height appears to have a greater impact on accessibility than wind speed, with higher values throughout the study area when the Hs threshold was increased (from 1.5 m to 2 m) and the wind speed threshold was decreased (from 20 m/s to 15 m/s). Using this >20% accessibility threshold as the benchmark, when the latter cut-off values are applied (Hs 2 m and wind speed 15 m/s), there is little or no impact to ocean energy deployment potential throughout the study area.
Almost mirroring the spatial distribution of the wave energy resource, the tidal energy resource is most plentiful in the east of the study area, with the higher values found throughout the Bristol Channel, Irish Sea, North Channel and the Inner Seas off the West Coast of Scotland, a finding consistent with previous assessments for both Ireland [
70,
71] and the UK [
72,
73]. This is due to the funnelling effect of the tide as it is forced between land masses and around headlands [
74]. This was evident throughout the study area. Examples include St. Georges Channel in the Irish Sea and the North Channel between Northern Ireland and Scotland, but particularly around headlands and islands, with highest current speeds on mean springs (>1.5 m/s) evident off Ramsey Island (Wales), Holy Island—Anglesey (Wales), Mull of Galloway (Scotland), Mull of Kintyre (Scotland), Isle of Islay (Scotland) and Rathlin Island (Northern Ireland). Three of these areas, Ramsey Island, Anglesy and Islay, have been previously highlighted as being among the most productive areas for tidal energy in the UK [
73]. In that study, the peak values appear to exceed 2 m/s in more locations than those found here. It is difficult to determine why this occurred, but reasons may well be associated with differences in the models used. Although both models had a similar spatial resolution (1.9 km
2 and 1.8 km
2), they have differing underlying algorithms to determine the depth averaged output. In a prior study of the Irish tidal energy resource [
71], the values were more consistent with the results presented here, ranging between 1.2 and 1.5 m/s in the more productive areas of the Irish Sea (east of Wicklow Head and Rosslare), and only exceeding 1.9 m/s in the Inner Seas off the West Coast of Scotland (southeast of Rathlin Island). In that study, other noteworthy areas of potential for tidal energy around the Irish coast included the Shannon Estuary (between Kerry and Clare), Ram Race (northeast of Belfast) Strangford Lough (east of Inishowen) and Gascanane Sound (Cork). The fact that these additional areas of potential were found in that study, and not in the assessment performed here, is almost certainly due to the higher resolution (405 m) of the model used. This promotes the necessity for such higher resolution models in identifying confined areas of potential for tidal energy deployment.
The removal of areas for fixed bottom tidal energy deployment in the optimum site analysis is due to the extensive coverage of protected areas in this region, as previously shown (
Figure 21). Although the extent of the potential tidal energy deployment areas is limited in comparison to wave, those with the highest resources are close to the coast. This is beneficial in the sense that deployment in such areas will have lower CAPEX and OPEX values associated with the lower distance to onshore infrastructure, as previously stated for offshore wind energy. With most of these high resource intensity areas surrounding islands, this also presents an opportunity for these islands to achieve energy independence, a subject which has been of keen interest in renewable energy research and the focus of many previous studies [
75,
76,
77,
78].
In terms of the tool’s capacity to attract potential interest from the four main user groups defined by ICAN, outlined in the introduction, it can be said that the Selkie CWA will surely be useful and attractive for:
The scientific community—to scope out areas (i.e., using the potential site maps) for further and more detailed investigation of localised patterns in the resource,
Policy makers, both in Ireland and the UK—to help identify zones to be designated for ocean energy deployment within their respective marine plan areas,
The general public—to encourage interest in ORE and realise the enormous potential that the marine space offers Ireland and the UK as they aim to reach carbon neutrality, and,
The education sector—enabling students of both engineering and geography to access a freely available database and information source which can help them to learn about ORE resources and the multiple uses of our marine space.
In the accuracy assessment, results from the validation of both wave models correlated strongly with the in situ data, proving the effectiveness of using such freely available data from the Copernicus Marine Service for modelling the wave climate at the region of interest. It should be noted that the wave buoys chosen for the validation were also close to the coast, an area where similar models with a coarser resolution were found to have inaccuracies in a previous study of the region which used a model with no better than 8 km spatial resolution [
57]. The higher spatial resolution of ≤5 km in both of the newer models is likely to be the reason for these more accurate results close to the coast. The bathymetry model had errors of up to 4 m when compared to the in situ data, which is not a major concern. The model can still be regarded as being appropriate for a study similar to this one, which is focused on scoping out potential areas within a broad region of interest as opposed to a site-specific study. Nevertheless, higher resolution models will be warranted for such site-specific assessments at the local/farm scale before deployment. Furthermore, although the seabed character model achieved consistent accuracy when compared to the in situ validation points in each sea area, it is still highly recommended to seek higher resolution, up-to-date surveys of the seabed prior to actual deployments; these should include depth to bedrock and seabed stability assessments [
44]. With the growing interest and development of the ORE sector in the study region, such services are now available for tender on demand [
79].
Limitations
As previously mentioned, it became apparent during this study that the spatial resolution of the model used for the tidal assessment could be improved. This is due to the considerable local variability of the tidal resource, particularly in comparison to the wind and wave climate. The resolution of the available data failed to capture the detail of the tidal resource in some channels where the width was less than the model node spacing. Such narrow channels often possess a considerable tidal resource due to the increased funnelling effect, but they are unlikely to have the capacity necessary for large scale deployments. These areas should be examined using higher resolution models to assess the potential for tidal energy site suitability. The area with no data coverage on the seabed character off the west coast of Galway and Mayo has excluded these areas from consideration for site suitability, yet they are likely to offer good potential for wave energy deployment. This may be revealed when newly available data come online via the ongoing INFOMAR programme [
80].
5. Conclusions
This paper describes various geospatial datasets relating to ocean energy farm site suitability, and a CWA tool that will facilitate both access to, and analysis of these data. An analytical case study of the data has revealed potential and optimum sites using input criteria provided by ocean energy technology developers. Certain areas of the Atlantic Ocean and Celtic Sea have been shown to have huge potential for wave energy deployment. The Irish Sea, North Channel and Inner Seas off the West Coast of Scotland have some potential for tidal energy deployment (particularly fixed), yet minimum resource thresholds are not met according to some survey responses. At the national scale, but remaining specific to the study area, it can be concluded that Ireland offers huge potential for wave energy deployment, with vast areas of its Atlantic and Celtic Sea marine space meeting the requirements of technology developers’ preferred site criteria. Wales offers significant potential for tidal energy deployment particularly off the southwest and northwest headlands. However, gaining permission to deploy in these areas may be complex given the vast amounts of protect areas at these locations. There is some potential for wave energy deployment in Wales (off the southwest coast), and for tidal energy deployment in Ireland (off the east and north coasts). Although the entirety of their territorial waters was not captured in this study, it is also apparent that there is potential for wave energy deployment in England (off Cornwall) and Scotland (off Islay). Scotland also appears to have significant potential for tidal energy deployment (off the southwestern headlands). The CWA tool itself should prove useful for the purposes of ocean energy site selection, particularly given the flexibility of user input offered through the interactive design. From performing an accuracy assessment on some of the more pertinent data used in the CWA and case study, it can be concluded that the newly available wave models from CMS chosen for the study perform accurately within the study area, even close to the coast, which was an issue with previous products. This is likely due to the finer resolution of the newer wave products used in this study in comparison to the previous work. However, the spatial resolution of the model used in this study for the tidal energy resource assessment could certainly be improved upon, particularly for identifying confined areas of potential for tidal energy within narrow channels and sounds. The bathymetry and seabed character models can be regarded as sufficient for scoping out potential deployment sites at the regional scale, but site-specific assessments are still highly recommended at the local/farm scale prior to any commissioning of an ocean energy farm.
Future Work
Although this study has revealed potential areas for wave and tidal energy deployment, project feasibility requires further complexity, much of which is also geospatial in nature. A future study will use the wave data and current speed data described here and apply it to wave energy power matrices and tidal energy power curves for real WEC and TEC devices in order to produce maps of the technical resource availability, i.e., annual energy production (AEP), in MWh. Furthermore, the accessibility layers, described here, can be transformed into availability layers which show what percentage of time a device is available to produce energy. This can be subtracted from the AEP to reveal how much energy is realistically extractable throughout the study area. Other additional maps/layers will include those showing the proximity to the nearest port and grid access point, which has techno economic (TE) implications on the feasibility of potential ocean energy projects, the most common measure of which is the Levelised Cost of Energy (LCOE). These TE layers (AEP, availability, proximity to port and proximity to grid) will ultimately be combined with other TE data (relating to CAPEX, OPEX and DECEX) and fed into a bespoke, geospatially-geared algorithm which will create maps of the LCOE for the various technology types. All of these TE and LCOE maps will then be added to the Selkie CWA as additional layers.