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Anglesey Skerries Tidal Stream Array

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Project Site Annex IV

Title: Anglesey Skerries Tidal Stream Array
Technology Type:
Info Updated:
May 19, 2016
AR Series Turbine being lifted with a crane.
Project Status: 
Device never deployed
Atlantis AR Series
Project Scale: 
Commercial array
Installed Capacity: 
10 MW

Site selection, feasibility assessments and environmental studies began in 2006 and a newly created development company, SeaGeneration (Wales) Ltd, was set up in 2008 as a joint venture between Marine Current Turbines and RWE npower renewables to develop the project. MCT was subsequently bought over by tidal industry leader Atlantis Resources Ltd in 2015. The location for the proposed array is a 0.56km2 site between the group of rocks and islands known as the Skerries and Carmel Head.  The site is less than 1km from the Anglesey coast and is characterised by water depths of around 20 to 40m.  The proposed array will consist of up to 9 SeaGen devices and will have a total installed capacity of up to 10 MW.  The site’s close proximity to Holyhead provides access to good port facilities, the national grid and transport connections. The array is expected to operate for up to 25 years, where it will serve as a test case for the development of the technology in multi device arrays.


The technology used will be the Atlantis AR Series Turbines. The AR series turbines are commercial scale horizontal axis turbines designed for open ocean deployment in the most energetic marine environments on the planet. The Atlantis AR turbines are currently available in a 1MW fixed pitched configuration (AR1000), with a 1.5MW turbine system (AR1500) under development with Atlantis’ technology partner, Lockheed Martin. AR series turbines are deployed using a patented stab system that facilitates rapid deployment, retrieval and subsea connection to shore.


Key design Features of the AR tidal turbine systems include:

  • A single axial flow rotor that drives a generator via a gearbox - much like a  wind turbine
  • Complex electrical infrastructure such as converters are located on the shore to reduce the amount of electrical equipment contained offshore
  • Stab system enables rapid retrieval without having to recover the foundation structure - for ease of maintenance
  • AR series turbine systems produce fully gird compliant power

Export cable:

A single 33kV export cable will be laid to transport generated power to the shore, however the route which the cable will take has not yet been finalised. Two possible cable corridors 500m in width have been identified and assessed. The first is the shortest route, resulting in the cable coming ashore between Carmel Head and the western boundary of Hen Borth Bay. The second route runs east from the proposed array site and would come ashore within Hen Borth Bay. A final decision on the cable route will follow the grant of main consent and assessments of technical and economic impacts.


There are three available methods for the installation of the export cable. A decision as to which one will be used is yet to be made and will be dependent upon seabed conditions and the route taken.  The first option involves laying the cable directly onto the seabed; this method leaves the cable vulnerable to physical damage from fishing gear and rocks / coarse sediment circulated by the strong currents. The second available option is trenching the cable using a plough.  It is likely that this method would only take place in the intertidal sections of the cable route. The final option is directional drilling.  A directional drill would create a hole in the bedrock from the land to a point approximately 1km from the array. The cable would then either be entrenched or covered with protective mattresses for the remainder of its route.


Onshore Infrastructure:

Ancillary onshore works and works in the intertidal zone will be required to connect the array to the electricity distribution network.  The landfall location for the export cable is yet to be confirmed but will be within the coastline between Carmel Head and Cemlyn Bay.



The engineering team at Atlantis has developed and patented tools and systems to assist in the safe and rapid deployment of tidal turbines offshore. Offshore safety for staff and contractors is of paramount importance, and hence Atlantis are continuing to invest in the development and testing of diver-free deployment systems.  Expanding the safe operational window for deployment and recovery of turbines offshore has a significant impact on overall project economics, so Atlantis are continuing to invest in new technologies that will allow developers globally to install turbine systems faster, more safely and with a wider range of DP2 vessels.


Between Skerries and Carmel Head on mainland Anglesey.

Licensing Information: 

A summary of the licences and consents granted is provided in the following table:



Competent Authority


Section 36 (Electricity Act) Consent



Marine Licence (Marine (Scotland) Act) Consent



Licence to Disturb Marine Species



Licence to Disturb Basking Shark



Town and County Planning Permission



Process Status: 

Consent for the project had been granted and a grid connection for 2015 secured, with onshore work  underway including feasibility studies and assessment of options for an export cable route, landfall point and substation location. However, the project was shelved in September 2014 after MCT/Siemens suspended the Project with no re-start date.


However, in April 2015 it was announced that industry leader Atlantis had reached an agreement to acquire the entire issued share capital of the Bristol based tidal business MCT from Siemens AG in an all share deal. This purchase included a portfolio of six projects including the Skerries scheme.


Despite the purchase of MCT’s/Siemens’ portfolio of sites by Atlantis, it was announced in March 2016, that they would relinquish the Agreements for Lease that it held at two of these sites, one of which was Anglesey Skerries (the other being Kyle Rhea). Ownership of these sites has now returned to The Crown Estate.


Atlantis stated that they wished to prioritise other sites that are currently under construction and closer to reaching financial close.”

Key Environmental Issues: 

The following potential impacts were identified as being potentially significant during the EIA:


  • Erosion or accretion of shoreline at landfall within SSSI
  • Operational noise causing disturbance and barrier effect to marine mammals
  • Collision risk between marine mammals and device
  • Operation of the device causing displacement of fishing activities
  • Device presence disturbing seascape from a number of view points
  • Collision risk of vessels transiting through the area 


Mitigation measures:


The following mitigation measures were outlined in the Environmental Statement:


  • Scour protection will be considered for areas where significant scour is recorded to prevent any further erosion and associated release of potential suspended sediments.
  • Any trenching will be backfilled immediately to reduce impact of suspended sediment on benthos, fish and shellfish during construction.
  • Marine mammal observer will be present during construction to identify disturbance or injury to marine mammals, basking sharks and marine turtles caused by noise or collision with vessels.
  • Deploy and monitor strategy to protect marine mammals from the effects of operational noise, habitat exclusion, collision risk, and barrier effect of the array will be developed.


Environmental webpage:


Anglesey Skerries Tidal Stream Array is located in United Kingdom.

Baseline Assessment: Anglesey Skerries Tidal Stream Array

General Description:

The following field surveys were undertaken (or commissioned by) the developer to inform baseline characterisation

ReceptorStudy Description Design and Methods Results Status
  • Physical Environment

Geophysical survey by EMU Ltd. in 2008.

Seabed surface sediments have been investigated through geophysical and bathymetric surveys. Bathymetry, interpreted seabed surface geology and isopach were included in the survey.

The survey reported that depth variations across the site appeared to correspond not only to exposed bedrock but also fingers of mobile and static sediment within the area.  Coarse sand and bedrock dominated the central and western region of the surveyed area.  Surrounding this area were regions that contained cobbled silt, gravelly pebbly cobbles, sandy gravel and cobbly sand.  Bedforms with a maximum wave height of 2m have been identified in the surveyed area and have their long axis generally orientated NNW-SSE.  Pockets of sediment infilling the surface topography of the bedrock were clearly identified

  • Intertidal Ecology

MACS visual intertidal habitat survey and faunal analysis of sediment cores

A walkover survey of Carmel Head was conducted followed up with a detailed survey of Hen Borth.

The results from the intertidal survey found the coast around Carmel Head (cable route option 1) to be typically steep rock faces supporting dense communities of kelps on the lower shore, fucoid algae on the mid-shore in sheltered embayments and upper shore all along the coast, barnacles and mussels on the mid-shore on exposed headlands and lichen in the splash zone. There are occasional narrow, steep-sided embayments which end on the landward side in shores of fucoid-covered boulder on the lower shore and clean shingle on the upper shore. In addition, there are several points of cave or overhang biotope which may constitute Annex I habitat.

  • Benthos

Site specific benthic survey

Drop down camera at sites pre-determined from geophysical data. Grabs attempted but failed due to hard substratum.

The site-specific benthic survey identified fifteen biotopes (including one subdivision) in four main habitat types, plus one Sabellaria spinulosa biotope at one of the western reference stations and a further four identified from the potential cable route into Cemlyn Bay.

  • Marine Mammals

Surveys commissioned by the Welsh Assembly Government

Vessel based observations and acoustic surveys using static acoustic monitoring devices. Results provided in the report by Gordon et al. 2010.

Several marine mammal species occur in the region. Over twenty species of cetacean can be seen around the Welsh coastline and of these five species are known regularly to occur. These are harbour porpoises (Phocoena phocoena), bottlenose dolphins (Tursiops truncatus), short-beaked common dolphins (Delphinus delphis), Risso’s dolphins (Grampus griseus) and minke whales (Balaenoptera acutorostrata). Two species of seal also occur on the welsh coast, the grey seal (Halichoerus grypus) and harbour (or common) seal (Phoca vitulina). Relatively high densities of harbour porpoise within the area.

  • Birds

SeaGen commissioned vantage point surveys

Each survey consisted of 3 hours of continuous diurnal observations from two vantage points on Carmel Head. Eight surveys per vantage point per month were carried out between April and September 2009.

A total of 20 species of seabird and five species of seaduck were recorded crossing the Project Site in April – September 2009 by the Seabird surveys. The majority of birds recorded were Manx Shearwater, Auk species (Razorbill and/or Guillemot), Gannet and Herring Gull with these five species comprising over 70% of all birds counted. The majority of individual birds (84%) that were observed transiting the Project Site were flying in close proximity to the adjacent coastline.


Post-Installation Monitoring: Anglesey Skerries Tidal Stream Array

General Description:

A Preliminary Environmental Monitoring Plan is currently being prepared for this project.  The following monitoring measures are proposed within the Environmental Statement. 

ReceptorMonitoring Program Description Design and Methods Results Status
  • Physical Environment

Post installation Bathymetric swathe survey.

Survey of the seabed within 100 m of each SeaGen device and along a 100 m corridor centred on all cable routes where surface laid, to be carried out pre and post construction. A further period of surveys may be deemed necessary on agreement with the Regulator if seabed instabilities are identified.

  • Physical Environment

Beach survey.

Beach survey within 50 m of the landfall, to be carried out pre and post construction, if the cable is surface laid. A further period of surveys may be deemed necessary on agreement with the Regulator if ongoing beach change is predicted and deemed to be an issue.

  • Intertidal Ecology

Shore survey.

Walk over survey and a core sample survey analysis of the softer sediments, including repetition of the sites surveyed for this assessment. Surveys will follow JNCC standard biotope methodology. Results will be published and submitted to the statutory authorities.

  • Benthos

Camera or diver surveys.

Camera or diver survey in combination with benthic grabs for areas of soft-sediments of the main site and cable route (inshore sites only where sediment type is feasible for grabs). These surveys will be undertaken as a baseline and repeated during and after construction.

  • Benthos

Chemical sampling of any soft sediment present

To test for contaminants which may be released into the marine system during construction e.g. trenching of the cable at inshore areas.

  • Benthos

Camera or diver surveys.

A survey using camera or divers to record evidence of colonisation of the structure, rock armour and scour protection and also to record any evidence of scour.

  • Fish


Monitoring will be discussed and agreed with the statutory authorities prior to construction.

  • Marine Mammals

Visual monitoring

Visual monitoring of marine mammal activity around the array pre and post installation to look for evidence of changes in use of the area.

  • Marine Mammals

Acoustic monitoring

Passive acoustic monitoring of echo locating species using the area of the development as well as the ‘coastal corridor’ to the south of the proposed array.

  • Marine Mammals

Visual sea surveys

Surveys of local grey seal haul out sites along with pup production surveys.

  • Marine Mammals

Strike detection monitoring.

On-going remote monitoring of SeaGen rotor strike detection system. This will provide an incident alarm if there are any collisions with the rotor, with the ability for remote shutdown should a mammal strike be confirmed.

  • Birds

No monitoring required given the predicted negligible impact and low bird abundance on the site.

  • Fisheries

Regular interviews with commercial fishermen.

To determine: whether the additional vessel traffic associated with the array has an adverse effect on fishing activity; the status of commercial fisheries in the area relative to current conditions to assess any indirect effects of array; and if the array has had an adverse effect on the use of pots in adjacent waters.

  • Vessel Navigation

Review of operation hazards.

Regular review of the operation and hazards will be undertaken and any necessary modification to procedures will be carried out.

  • Visual Landscape

No future monitoring measures are proposed.

Reports and Papers N/A
Research N/A
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