Atlantis Resources is proposing to develop a demonstration tidal array in the Sound of Islay. The proposed tidal array will have an installed capacity of up to 10 MW of renewable power for export to the grid.
Islay is the most southerly of the main Inner Hebrides and is located to the southwest of the island of Jura. The Sound of Islay is a stretch of water that separates the islands of Islay and Jura. The bathymetry of the channel constitutes a relatively flat and deep seabed with water depths of up to 62 metres with very steeply sloped sides. The site is generally sheltered from wave action which impacts on the west coasts of both Islay and Jura. Studies thus far indicate that the maximum tidal flow within the Sound is 3.7 m/s, with a mean of 1.2 m/s. The array will be configured in a ‘figure of eight’ created by a 48 metre contour line on the seabed.
This site offers a lower average flow speed than the MeyGen site, but as it is both deeper and more sheltered from waves it is possible to deploy larger diameter turbines to capture more energy. The consent conditions allow for deployment of turbines with rotor diameters of up to 26m, giving a swept area more than twice as large as the 18m Phase 1A turbines. Atlantis have received a very high level of interest from prospective turbine suppliers wishing to deploy their technology in these favourable conditions.
It is currently unclear which devices will be used for the Sound of Islay project, however it is likely that they will consist of Atlantis Resources’ newly developed AR 1500 which is scheduled for deployment at the Meygen site. 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 awind 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
There is also potential for Hammerfest Strøm’s (HS) 1.5 MW device to be used which is also scheduled for deployment at the Meygen site. The HS device is a fully submerged, bottom mounted, rotor, variable pitch turbine. The nacelle houses the turbine, gearbox, generator and associated components. The pitch of the rotors is variable to present the most efficient angle of incidence to the oncoming flow. On reversal of the tide the rotors alter pitch so that the turbine generates maximum generation from the tidal environment.
Both 1.5 MW devices will have a rotor diameter of 18m.
It is estimated that the devices can be installed over a period of 72 days (not including weather downtime). This has made allowance for spring and neap tides. Offshore cables and pre substructure installation activities will be conducted in advance of the installation of nacelles.
It is currently planned that each substructure will be lifted, transported and set down during a neap slack tide period. Once moved into position additional ballast will be loaded onto the substructure to secure it against overturning loads imposed by the turbine. Once the substructure is secured in position and stabilised, the high voltage cable will be lifted to the substructure, pulled in and then secured ready for final mating. It is anticipated that positioning, ballasting, pinning, and cable pull will take approximately 56 hours. Throughout the installation process it is unlikely that more than one vessel will be used due to navigational constraints.
The final cable design, and ultimately the size of any cables, will be dependent on the electrical system design, cable layout, installation methods and soil characteristics. However, the preferred design is to have one cable per device, thus approximate dimensions can be given.
Cable specification, assuming that each device has its own cable (therefore a total maximum of 10 cables will be installed) is likely to be of the order:
- 3 x 95 sq mm 6.6kV
- 3 x 16 sq mm 3.3kV
- 1 x optical cable - 10 x s/m fibres
- 10 x 3.5km, double armoured
- Cable OD = 83mm (including armouring)
- Weight in air = 16,150kg/km
A cable protection assessment has been undertaken and points to the best solution as being a combination of free lay of the cable while adding a steel casing cable protection system with intermittent mattressing along the cable route. Burial of cable using land-based equipment is likely to only be a solution close to shore (within 500m); however this is compounded by environmental factors that need to be considered (e.g. the adjacent maerl bed).1
The tripod support structure dimensions are 40m (W) x 30m (L). This will be fixed to the seabed using gravity ballast in the legs and will support the nacelle and rotor structure giving a hub height of between 13.5-16 m from the seabed. A rotor diameter of 18m will give the device a total height from the seabed of approximately 26 m.
An onshore substation and control centre will be required for the array. The landfall location selected on Islay is approximately 2.5km south of the turbine array and is close to the point where the Islay/Jura 33kV interconnector comes ashore. Onshore works will include the cabling up the shore and the creation of a transition pit above MHWS. All of these works can be undertaken using land-based excavators. Within the intertidal zone to the low water mark during low water tidal windows, land-based excavators can carry out trenching operations dependent on soils and overburden of sediments. This is to protect the cable to limit any environmental impact and third party interaction within these areas. Once all the cables have been pulled in, tested and terminated, all excavated material will be placed back over the cable for protection and stability.2
The following vessels will be required during construction and operation:
|Heavy Lift Vessel||Heavy lift vessel on site to lift and move substructures onto the barges.|
|Anchor Handling Vessels||Move substructures from he barge onto location for ballast operations and cable pull ins.|
|Lift Vessel||Will be used to install the nacelles once the site is prepared.|
Sound of Islay, between the Isle of Jura and mainland Scotland.
- 55°50.8111'N, 6°6.0861'W
- 55°50.7621'N, 6°5.8541'W
- 55°49.9710'N, 6°5.6908’W
- 55°50.5360'N, 6°6.0037'W
- 55°50.8242'N, 6°5.8918'W
- 55°50.4930'N, 6°5.7680'W
- 55°49.9621'N, 6°5.8825'W
|Marine License (Marine Scotland Act)||Marine Scotland||Original application granted (Licence Number 04050/11/0, Reference Number: FKB/Z225). Reapplied for after change in cable route.|
|Section 36 (Electricity Act) Consent||Marine Scotland||Granted March 16, 2011, Licene number|
Supplementary Licencing Conditions
The following licence conditions were provided with the Marine License issued by Marine Scotland in 2011. This licence expired in October 2013 and the new licence concerning the new cable route has not yet been issued:
- The licensee shall notify the licensing authority of the date of commencement and the date of completion of all operations relating to the licence. Separate notifications are required at the times of commencement and completion.
- The licensee shall ensure that all substances or articles deposited during the execution of the works are inert and do not contain toxic elements which may be harmful to the marine environment, the living resources which it supports or human health.
- The licensee shall ensure that only the substances or articles described in Part 1 of the Schedule shall be deposited under authority of the licence and that any debris or waste materials arising during the course of the works are removed from the site of the works for disposal at an approved location above the tidal level of Mean High Water Springs.
- The substances or articles described in Part 1 of the Schedule (the authorised deposits) shall be deposited in the following authorised deposit area.'Force majeure' may apply when, due to stress of weather or any other cause, it is necessary to deposit the substances or articles at a location other than that specified above because the safety of human life, or a vessel or vehicle, is threatened. If the substances or articles are deposited in an unauthorised area, full details of the circumstances shall be immediately notified to the licensing authority.
- The licensee shall, within 28 days of completion of the works or within 28 days of the date of expiry of the licence, whichever is the sooner, submit a written report to the licensing authority stating the nature and quantity of all substances and articles deposited below Mean High Water Springs under authority of the licence. Where appropriate, nil returns must be provided.
- The licensee shall ensure that copies of the licence are available for inspection by any authorised Enforcement Officer at: the premises of the licensee; the premises of any agent acting on behalf of the licensee; and the site of the works.
- In the event of the licensee becoming aware that any of the information on which the issue of the licence was based has changed, the licensing authority shall be immediately notified of the details.
- In the event that the licensee wishes any of the particulars set down in Part 1 of the Schedule to be altered, the licensing authority shall be immediately notified of the alterations. It should be noted that changes can invalidate a licence, and that an application for a new licence may be necessary.
- The licensee shall ensure that the substances or articles described in Part 1 of the Schedule are located on the sea bed within the authorised deposit area, and shall undertake regular maintenance operations to relocate or remove any deposits that are located out with this area. Any deposits permanently removed from the sea bed shall be disposed of at an appropriate location above the tidal level of Mean High Water Springs.
- The licensee shall ensure that ancillary equipment deployed or deposited during the course of the works, such as buoys, wires, ropes, ballast weights, anchors and lifting bags, etc is removed as soon as it is no longer required to prevent interference with other legitimate uses of the sea.
- The licensee shall ensure that the methodology for installation of up to ten tidal turbines will be signed off by the Licensing Authority prior to commencement of works. a) The licensee shall prepare a detailed works schedule and method statement following licence issue. b) The licensee shall ensure that all the works are carried out in accordance with the works schedule and method statement as agreed with the licensing authority. c) The licensee shall put in place a contingency plan in accordance with the requirements of the Oil Pollution Preparedness, Response and Co-operation (OPRC) Convention to deal with the impact of accidental spills of oil or chemicals in the marine environment. The licensee shall also put in place a contingency plan to deal with the impact of catastrophic events on the marine environment.
- The method of relocation or removal not involving decommissioning shall be; Confirmed when known.
- Names, and operators, of the vessels to be employed to undertake or support the deposit, relocation or removal operations not involving decommissioning; To be confirmed when the licensee shall ensure that all vessels employed to perform the deposit operation under this licence shall be so constructed and equipped as to be capable of the proper performance of these operations.
- The licensee shall, where appropriate, undertake monitoring of the area pre and post installation and post decommissioning of the deposits on the sea bed subject to this licence e.g. deployment of a remotely operated vehicle. The monitoring shall incorporate, if deemed to be necessary by the licensing authority, physical, chemical and biological investigations, to access the status of the authorised deposits and their impact in the receiving environment. The scope, frequency and spatial extent of the investigations shall be approved by the licensing authority.
- The licensee shall submit, where appropriate, written reports to the licensing authority detailing the results of the monitoring. The written reports shall be prepared by the licensee detailing, where appropriate, the status of the authorised deposits and their impact on the receiving environment and their position (latitude and longitude to three decimal places of minutes). The written report should also detail the nature, quantity and fate of all deposits that are relocated and/or replaced on the sea bed during maintenance operations. Previous monitoring reports may be amended by the addition of an appendix detailing new deposits on the sea bed.
- Should the licensing authority consider it necessary or expedient to remove all deposits made under authority of this licence, for the purpose of protecting the marine environment, the living resources it supports and human health, or of preventing interference with legitimate uses of the sea, the licensee shall undertake to remove those deposits in accordance with the requirements of the licensing authority.
Atlantis purchased the Sound of Islay site from Scottish Power Renewables in 2016. The project has full consent, grid and an agreement for lease from the Crown Estate. Atlantis intends to build out the site in 2018.
While still under the ownership of Scottish Power Renewables a scoping exercise was carried out to identify the main issues that needed addressing as part of the EIA. Following this a number of consultations with statutory and non-statutory bodies took place along with a variety of environmental surveys. An Environmental Statement was produced to support the necessary licence applications. In July 2010, SPR submitted an application under Section 36 of the Electricity Act 1989 to construct a demonstration tidal array in the Sound of Islay. Consent was given in March 2011. An application for a Marine License was accepted by Marine Scotland in May 2011. Post-consent of these licenses discussions were held with the regulator and, as a result of these discussions related to the interpretation of planning legislation, a number of amendments were made to the development. The principal change in relation to this Marine License application relates to a new cable route to shore. A document titled “Cable Route Enviromnetal Information” was submitted by SSE to Marine Scotland in support of the new application. This document was created to assist Scottish Ministers in reaching a decision as to whether permission should be granted for the proposed new cable route to shore. This change saw the proposed location for the on shore substation move from Jura to Islay.
A number of potential impacts were identified in the Environmental Statement, however only the following were deemed to be potentially significant:
- Collision between the device in operation and marine mammals;
- A barrier effect of the array to marine mammal transit through the Sound;
- Collision between the device in operation and elasmobranchs; and
- Otter disturbance during construction and decommissioning activities.
Mitigation measures: The following mitigation measures were outlined within the Environmental Statement:
Physical Environment and costal processes: No mitigation required
Benthic Ecology: No mitigation required
Marine Mammals: An overall approach to mitigation, monitoring and management is proposed, which forms part of a wider deploy and monitor strategy. SPR commits to putting in place a programme of post installation monitoring and any mitigation considered necessary by regulators to avoid significant effects, as part of an on-going programme of adaptive management.
Fish and Shellfish: To mitigate against the impact of noise on shellfish and finfish SPR will adhere to best practice outlined in BS5228-2 (2009) British Standards Code of Practice for noise and vibration control on construction and open sites during all construction activities and best practice guidance in CIRIA C584 (2003) Coastal and Marine Environmental Site Guide during all construction activities.
Anadromous fish: No mitigation required; however, contractors will adhere to good construction practice guidance (e.g. CIRIA guidance, SEPA Pollution Prevention Guidelines). Cable design will aim to minimize EMF fields through appropriate shielding to reduce potential impacts with other EMF sensitive species.
Elasmobranchs: The use of vessel and / or shore based visual observers would allow teams undertaking installation works to be alerted to the presence of basking sharks in the Sound. On receiving such an alert, appropriate mitigation would be put in place, potentially including avoidance of areas where sharks are feeding and modification (e.g. slowing of vessels) or cessation of installation activity until the sharks have moved on from the installation area. Appropriate procedures would be agreed with Marine Scotland. SPR accepts that there is some uncertainty about some potential impacts from the Development and is committed to undertaking a post installation monitoring programme in order to determine the nature of those impacts. SPR is committed to putting in place measures considered necessary by the regulator to mitigate impacts.
Ornithology: Any risk to seabirds of accidental release of marine contaminants will be minimised by adopting safe working practices and having contingency plans in place for dealing with incidents.
Good practices will aim to minimise disturbance to seabirds by vessels associated with the proposed development by avoiding, where possible, preferred feeding areas and adopting voluntary speed restrictions. Artificial nest sites for black guillemots located away from the immediate vicinity of the proposed development site should help reduce disturbance effects on the breeding population of this species. Artificial nest sites should take the form of specially designed nest boxes or providing suitable cavities in stone walls or quays next to the sea. It is anticipated that approximately ten such sites should be constructed given the numbers of existing nest sites that may be affected by the proposed development and that not all artificial sites may become occupied.
Commercial fisheries: A Safety Management System (including an Emergency Response Coordination Plan (ERCoP), appropriate to the scale and nature of the risks involved by the demonstration array, should be developed and put in place prior to installation of the array.
To mitigate against impacts on commercial fishing, turbines and cables should be installed during periods of least fishing activity within the Sound (creeling activity is at its lowest in the summer). Close consultation with local fishermen will help to identify potential mitigation measures.
To avoid entanglement resulting in possible capsize of fishing vessel, the array area will be subject to an application in order to designate it a “No Fishing” (Int. Symbol N21) area. Turbines will also be fitted with rope cutters to clear any fishing gear that may become accidentally entangled. Cable protection will be installed where appropriate and care will be taken to avoid bridging during cable installation i.e. cable should be flat on the seabed with no space underneath where fishing gear could become trapped.
Intertidal ecology: Construction work will be undertaken during agreed daylight working hours (07:00-18:00), where practicable. Artificial light will not be used next to the coastline or rivers at night to allow otters to migrate through the area undisturbed. Construction activities will maintain a strict footprint of works for the corridor of the cable trenching, and construction vehicles and equipment will not be active on, or stored by, the coastline for longer than is necessary.
Environmental webpage: http://www.scottishpowerrenewables.com/pages/sound_of_islay.asp