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.
The Sound of Islay is a 21km passage of water separating the islands of Islay and Jura on Scotland’s west coast. At its narrowest point, where it is just 1.4km wide, current speeds exceed 5 knots, but the site is generally well protected from wave action. It is 50m to 60m deep at its deepest point, which extends south from Port Askaig for approximately 1.5km. Thanks to this environment there is potential for an up to 10MW site, utilising 24m rotor diameter AR2000 turbines, each of which would be manufactured in Scotland. The timing for the delivery of the project is subject to innovative power purchase agreement legislation.
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’ AR2500 which is currently under development and 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. This next generation AR2000 turbine will be capable of accommodating rotor diameters of between 20 – 24 meters, site dependent, with a cut in speed of less than one meter per second and a maximum output of 2.0 MW at 3.05 m/s for a machine with a 20 meter rotor diameter.
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 grid compliant power
It is estimated that the device 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.
Export Cables: 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).
Foundations: 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.
Onshore Infrastructure: 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
Vessel Spread: The following vessels will be required during construction and operation:
Heavy lift vessel
Heavy lift vessels on site to lift and move substructures onto the barges
Anchor handling vessels
Move substructures from the barge onto location for ballast operations and cable pull ins
Will be used to install the nacelles once the site is prepared
Sound of Islay, between the Isle of Jura and mainland Scotland.
Coordinates: Sound Of Islay Demonstrator Tidal Array lies within the following co-ordinates:
- 55° 50.811 N 006° 06.086 W
- 55° 50.824 N 006° 05.892 W
- 55° 50.762 N 006° 05.854 W
- 55° 50.493 N 006° 05.768 W
- 55° 49.971 N 006° 05.691 W
- 55° 49.962 N 006° 05.883 W
- 55° 50.536 N 006° 06.004 W
Marine Licence (Marine (Scotland Act)
Original application granted (Licence Number 04050/11/0, Reference Number: FKB/Z225).
Reapplied for after change in cable route.
Up-to-date licence issued April 2016 (Licence Number 04050/15/01)
Section 36 (Electricity Act) Consent
Granted March 16, 2011, Licence number
Supplementary Licencing Conditions:
A full list of licence conditions can be viewed in Part 3 of the Marine Licence issued in 2016. Conditions relevant to environmental protection are listed below:
3.1.8 Environmental protection
The Licensee must ensure that all reasonable, appropriate and practicable steps are taken at all times to minimise damage to the Scottish marine area caused by the carrying out of the Licensable Marine Activity.
The Licensee must ensure that any debris or waste material placed below MHWS during the construction and operation of the Works is removed from the Site, as soon as is reasonably practicable, for disposal at a location above the MHWS approved by the Scottish Environment Protection Agency (“SEPA”).
The Licensee must ensure that all substances and objects deposited during the execution of the Works are inert (or appropriately coated or protected so as to be rendered 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 must ensure that the risk of transferring marine non-native species to and from the Site is kept to a minimum by ensuring appropriate bio-fouling management practices are implemented during the Works.
The Licensee must ensure that if oil based drilling muds are utilised they must be contained within a zero discharge system. Any drill cuttings associated with the use of water-based drilling muds situated within the outer boundary of the Works need not be removed from the seabed.
While 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.2 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.2 This change saw the proposed location for the on shore substation move from Jura to Islay.
Atlantis purchased the Sound of Islay site from Scottish Power Renewables in 2016. In April 2016, a Marine Licence was issued relating to the deployment of a turbine array with capacity of up to 10 MW, up to 10 gravity base substructures and cabling to the shore. The project has full consent, grid and an agreement for lease from the Crown Estate. Atlantis intended to build out the site in 2018, however at the time of writing there has been no further progress in development of the site. The timing of delivery of the project is subject to innovative power purchase agreement legislation.
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