The proposed array will consist of four SeaGen S devices, giving a combined capacity of up to 8 megawatts (MW). Infrastructure including intra-array and export cables, ancillary onshore works and works in the inter-tidal zone will be required to connect the array to the electricity distribution network. The infrastructure needed to produce grid compliant electricity is contained within the SeaGen system itself, requiring no external power conditioning. Initial studies indicate that the grid connection point would likely be on the Isle of Skye. The aim of the project is to serve as a test case for the development of the technology, with this particular array operating for up to 25 years .
The SeaGen S system, developed by Marine Current Turbines (MCT), consists of twin power trains mounted on a crossbeam which is supported by a monopole. The cross beam can be raised above the water by winching it up the monopole support structure. Rotor blades are positioned in the top third of the water column and can be pitched through 180 degrees, allowing them to operate in bi-directional flows. Previous trials have shown that the SeaGen S is capable of achieving more than 48% efficiency over a broad range of current velocities. SeaGen S can be deployed in water depths up to 38 metres and achieves rated power in tidal currents of greater than 2.4m/s. The developers have recently updated the design, giving each machine an operational capacity of 2MW and increasing the rotor diameter from 16 to 20m .
Each device will have either a tripod or quadropod foundation structure with each ‘foot’ terminating in a pin-pile (up to 2m diameter), drilled and grouted into a rock socket in the seabed. A quadropod structure is considered in the impact assessments throughout the Environmental Statement as a worst case scenario. Each rock socket may be up to 11m deep and up to 2.2m in diameter, providing a worst case seabed footprint of up to 15.2m2 for each quadropod. The foundations will also support access ladders, J-tubes (to prevent export cable damage), corrosion protection equipment and a boat landing platform. The decision on final foundation design will be subject to data derived from geotechnical and geophysical surveys, metocean conditions, barge availability, installation and operations methodology, and life-cycle cost.
The array will be joined in a daisy chain formation using intra-array cabling. The intra-array cables will be 33kV, typically 3-core copper conductors with insulation/conductor screening and steel wire armouring. A single AC subsea export cable rated at 33kV is required to bring generated electricity from the array to the project substation. The export cable will be directionally drilled from the substation location to a ‘break out’ point as close as possible to the array. The cable will have a polypropylene outer sleeve with an external diameter of approximately 140mm and will include internal fibre optic communication links for control purposes. The total length of the export cable is up to 500m.
An assessment of the grid infrastructure in the vicinity of the project has indicated that the connection options suitable for the project are all on Skye rather than on Scottish Mainland. The grid network in the vicinity of the project is currently at full capacity; however there is a planned upgrade to the transmission network with a new high voltage direct current (HVDC) link to the Western Isles which will free-up sufficient capacity on Skye in 2015 which ties in the commissioning phase for the project (see Chapter 5, Project Description). A small substation containing electrical switchgear (around 6m x 3m footprint by 3m high) will be required for the project. A prefabricated container will be used to house the substation. Each SeaGen device contains a separate transformer within its structure, so that the onshore substation size can be kept to a minimum.
The installation method has not yet been finalised. It is therefore not possible at this time to specify exactly what vessels will be used. However three installation scenarios are currently being considered:
|Aspect of installation scenario||Jack up barge scenario||Moored barge scenario||Dynamic positioning scenario|
|Size of vessel||150m x 45m||100m x 30m||155m x 30m|
|Footprint of mooring system||4 triangular lattice legs with circa 40m2 foot area||4 to 8 100 tonne gravity blocks (5m x 5m) or drag anchors (3m x 5m) with some anchor chain catenary, estimated at 80m length on seabed at 1m diameter||Dynamic positioning holding a footprint of +/- 5m|
|Number of tugs required||Jackup vessel is typically self-propelled, but possible single tug required for initial positioning (30x22m)||Possible that barge will have DP for assisting with initial positioning while laying anchors, however possible X2 tugs (30m x 22m)||N/A|
|Anchor handling vessel||N/A||Multicat (c.25m LOA) or small AHV to install
gravity blocks and handle moorings
|Flat top barge (to bring out large items)||N/A||N/A||N/A|
Kyle Rhea, between the Isle of Skye and the west coast of Scotland.
|Section 36 (Electricity Act) Consent||Scottish Ministers||TBC|
|Marine Licence (Marine (Scotland) Act) Consent||Marine Scotland||TBC|
|Licence to Disturb Marine Species||Marine Scotland||TBC|
|Licence to Disturb Basking Shark||Marine Scotland||TBC|
|Town and County Planning Permission||District of Skye and Lochalsh – Highland Council||TBC|
Atlantis Resources purchased MCT’s/Siemens’ portfolio of tidal sites, including Kyle Rhea, in early 2015. However, in March 2016, it was announced that Atlantis would relinquish the Agreements for Lease that it held at two of these sites, Kyle Rhea and Anglesey Skerries. Ownership of these sites has now been 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.
Sea Generation (Kyle Rhea) Ltd had spent 2 years carrying out surveys and studies to inform the feasibility and design of the project and the Environmental Impact Assessment (EIA). The EIA was complete and an application for a Marine Licence was submitted to Marine Scotland. An Environmental Statement detailing the findings of the EIA was submitted in support of the application. Marine Scotland conducted a formal consultation process where bodies such as SNH, MCA, Northern Lighthouse Board and RSPB were consulted on the project. The consultation process ran from the 22nd of February 2013 to the 5th of April 2013. Marine Scotland aimed to make a recommendation with regard to the consenting of projects within approximately 9 months .
The following potential impacts were deemed to be potentially significant during the EIA process:
- The introduction of marine non-native species during construction;
- Destruction, obstruction or damage to otter breeding sites, places of rest or shelter and disturbance or reckless injury and killing;
- Collision risk between marine mammals and the device during operation;
- Mortality or physical injury to fish and shell fish as a result of pollution from routine and accidental discharges during construction and operation.
- Adverse effects on local commercial fisheries due to restricted access to fishing grounds on either side of the array.
- Adverse effects on the local seascape and the costal character of the area.
- Collisions between vessels operating in the area and vessel collision with the array .
Mitigation measures: The following key mitigation and best practice measures to be applied are outlined in the Environmental Statement:
- Development of an Environmental Management Plan (EMP) to be agreed with the Highland Council, SEPA, SNH and Marine Scotland, following submission of this ES. The EMP will be a working document detailing the environmental actions highlighted in the ES, all activities to be carried out on site, responsibilities for those activities, environmental risks and the management protocols to be put in place to control these, as well as identification of personnel responsible for each element of the EMP;
- An Environmental Monitoring and Adaptive Management Plan (EMAMP), to be agreed with Marine Scotland (MS) and Scottish Natural Heritage (SNH);
- A detailed Construction Method Statement (CMS) and a Pollution Control and Spillage Response Plan to be prepared and agreed with SEPA, SNH and MS-LOT prior to commencement of construction;
- All work will be undertaken to an overarching Health, Safety and Environmental Management System (HSEMS), which will include the CMS, the PIRP and the Environmental Management Plan. The project will be supervised in accordance with the Construction Design and Management Regulations (2007);
- Pollution Control and Spillage Response Plans to be developed and included in the EMP;
- A Construction Traffic Management Plan (CTMP) will be developed in consultation with the Highland Council which will include details of the construction vehicles proposed (size; weight; number of axles); construction programme; swept path analysis, preferred route to access the project site; details of any deflectograph surveys required pre and post-construction, temporary signal control during construction, and protocols for Abnormal Indivisible Loads (AILs);
- Site Waste Management Plan to be developed and agreed with SEPA and Marine Scotland
- Horizontal Directional Drilling (HDD) utilised to reduce or remove the pathway for impacts to many receptors.
- Area of disturbance associated with all works will be kept to a minimum.
- Substation and drilling rig footprints will be sited outside of the SAC and SSSI boundary to reduce impacts on sensitive features; and
- An Environmental Clerk of Works (ECoW) will be appointed, to be present on site and oversee the construction phase. The clerk of works will have responsibility for overseeing the implementation of ecological mitigation measures agreed with the key regulators, SEPA, SNH and Marine Scotland .
Environmental webpage: http://www.seageneration.co.uk/environmentalaspects.php