West Islay Tidal Energy is a joint venture between DP Marine Energy Ltd. (DPME) a renewable energy developer part of the DP Group of companies and DEME Blue Energy (DBE) part of the DEME Group. DP Marine Energy has been working towards developing a tidal energy site off the West Coast of Islay since 2008, and aims to install a 30 MW array in the near future. The development site lies approximately 6km off the Rinns of Islay, and covers approximately 2km2 of seabed. The long term goal is to expand the array, eventually producing a project providing up to 400 MW. In 2009, DP Marine Energy commenced a two year marine mammal and bird survey campaign in the area. Upon the completion of these surveys in 2011, an Agreement for Lease for the development area was granted by the Crown Estate (1).
The site development proposals are based on a technology neutral approach in an attempt to minimise development risk by deferring final device selection until technology is more proven whilst still ensuring that the project progresses to reach the point of construction as quickly as possible in order to contribute to government renewable energy targets. It is not possible to adopt a completely neutral approach given the physical constraints and resources at the site; therefore a design envelope has been developed based on generic design philosophy. The design envelope includes seabed mounted devices that are either surface piercing or nonsurface piercing with horizontal axis turbines. The design envelope considers two device types, the first being a twin rotor system with blades capable of 180 degree rotation to optimise on flood and ebb tidal streams. The rotor diameter would be typically up to 20m. The second system is a bi-directional ducted tidal turbine with direct drive to a permanent magnet generator. Such devices currently in production are the SeaGen S developed by Marine Current Turbines and Alstom’s TGL device (2).
Mooring and foundations:
There are many different possible methodologies for securing the turbine in position, these include a gravity base, piled or pin-piled fixed base. The MCT/Siemens device incorporates two turbine units attached to a lifting cross arm mounted on a steel tower anchored in the seabed (the Seagen S). Alstom’s turbine is mounted on a tripod support structure pinned to the seabed. Hammerfest propose a similar tripod foundation but with ballast used to keep the structure in place (4). Alternative floating support structure systems have also been considered as part of the EIA using the Bluewater BlueTEC floating platform as reference for the design envelope (3).
The inter-array cabling will be marshalled and exported to shore via up to three 33kV subsea export cables, landing at Islay. A number of routes were considered with potential landing points identified near Portnahaven, Bowmore and Kintra. The preferred option and the one which is described within the Environmental Statement (ES) is to route the export cable east from the tidal park to a landfall location at Kintra on Islay. This route has been selected in preference to the other two as it is the most direct route and so the most cost effective. Additionally it passes through areas of limited ecological sensitivity and provides the minimum onshore route length and therefore reduces potential visibility issues (4).
Following landfall at Kintra the cable route continues overland to a substation located west of Port Ellen before leaving Islay via another landfall in Kilnaughton Bay. From here the cable then continues sub-sea for approximately 35km to landfall on the Kintyre peninsula prior to continuing overland to the main substation at Carradale. Given the long connection distance, it is probable that the voltage will require to be stepped up from 33kV to around 132kV to avoid excessive line losses. This will require a 33/132kV substation to be constructed on Islay. It is expected that the sub-station will be located in the vicinity of Kilnaughton Bay to enable the sub-sea section of cable to transmit at higher voltages to reduce losses and the potential for fault levels. From the landfall at Carradale the 132kV subsea cable will continue underground until connected into a termination module prior to onward routing either overhead on wooden poles or underground. This decision will depend on several factors including environmental, technical and cost considerations. It will be necessary to locate a small control/metering building adjacent to the Carradale substation prior to connection into the substation. This building will house protection and metering equipment to enable the appropriate electrical protection to be provided for the system and to meter the generated electricity prior to connection.
The main installation vessel will remain on site carrying out installation activities while a transport barge will be tasked with sailing between the installation site and the base port for loading of the components. The number of vessel movements and type of vessels used will depend on the selected turbine technology (4). This information will be provided in the Construction Method Statement once the final design has been completed; however the installation works is most likely to be carried out by either jack up vessels, dynamic positioning vessels or heavy lift vessels. The vessels that are likely to be used are outline in the following table.
|Type of installation vessel||Option 1: Large size Jack up barge as installation vessel||Option 2: Medium size Jack up barge as installation vessel||Option 3: Dynamic positioning scenario|
|Size of vessel||150m x 45m||68m x 38m||155m x 30m|
|Footprint of mooring system||4 triangular lattice spuds with circa 140m2 spud area||4 circular spuds ca. 10m² spud area (possibly extended with spud cans)||Dynamic positioning holding a footprint of +/- 5m|
|No. tugs required||Jack up vessel is typically self-propelled||Jack up vessel is typically self-propelled, but possible single tug required for initial positioning (30x22m)||N/A|
|Anchor handling vessel||N/A||N/A||N/A|
|Flat top barge (to bring out large items)||N/A||N/A||N/A|
|Crew change support vessel (vessel length)||Up to 26m||N/A||Up to 26m|
|Install vessel||100m x 50m||N/A||100m x 50m|
|SeaGen unit installed by||Same vessel||JUP vessel in case SeaGen S unit split up into multiple sections or by HLV (Heavy Lifting Vessel)||DP2 vessel in case SeaGen S unit split up into multiple sections or by HLV 4|
6km South West of the Rinns of Islay, South West Scotland.
An application for consent was submitted in 2013. Marine Scotland has consulted on the application and will make recommendations in due course.
|Marine Licence (Marine (Scotland) Act)||Marine Scotland||TBC|
|Section 36 (Electricity Act) Consent||Scottish Ministers||TBC|
|Licence to Disturb Basking Shark||Marine Scotland||TBC|
|European Protected Species Licence||Marine Scotland||TBC|
In October 2011 The Crown Estate granted DPME an Agreement for Lease. A suite of environmental baseline characterization surveys to inform EIA commenced in 2011. The Environmental Statement was published in 2013 in support of an application for statutory consents. Following consent it is expected that drilling and foundation installation will begin in 2015 and the project is expected to launch in 2019.
Several potential impacts were identified during the Environmental Impact Assessment, however only the following were deemed to be potentially significant:
- Mortality or death of marine mammals as a result of collisions with operating turbines; and
- Temporary loss of fishing grounds due to the construction of the development (4).
Environmental webpage: http://www.dpenergy.com/projects/tidal/west-islay-tidal-energy-
Environmental Statement can be downloaded from here: http://www.gov.scot/Topics/marine/Licensing/marine/scoping/DPMarineEnergy
A number of key mitigation and best practice measures have been proposed throughout the ES. These are as follows:
- Development of an Environmental Management Plan (EMaP) to be agreed with SNH and Marine Scotland, following submission of this ES. The EMaP 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 EMaP;
- An Environmental Monitoring Programme (EMP), 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 EMaP. The project will be supervised in accordance with the Construction Design and Management Regulations (2007); and
- Pollution Control and Spillage Response Plans to be developed and included in the EMaP (4).