Brims Tidal Array Ltd (Previously named Cantick Head Tidal Development Ltd) is a joint venture between OpenHydro Site Development Ltd (OpenHydro) and SSE Renewables (Holdings) UK Ltd (SSER). The proposed development will be deployed as two phases. Phase I consists of up to 60MW with construction expected to begin in 2019. Phase II will be subject to a separate application process, with planned delivery of the fully commissioned 200MW Project in 2023. This phasing will allow BTAL to gain experience of deploying devices in an array of reasonable scale and then evaluating its performance, both technically and environmentally before completing the full build-out.
The original Area of Search identified for this Project was 11km2 off the south coast of South Walls in Orkney. Following the signing of the AfL, the project team engaged in detailed tidal resource assessment surveys in order to characterise the resource in more detail. Complicated flows and eddies were found to be impacting the amount of energy that could be feasibly extracted from the resource at the site, raising concern over the nature of the tidal regime within the AfL and its potential for development. The surveys suggested that the commercially developable resource lies primarily west of the AfL site, in 60m-100m of water, off South Hoy. This has led to a revised AfL located to the west of the original site and the site is now referred to as Brims Tidal.
BTAL’s preferred option is the installation of non-surface piercing tidal turbines at the site. Our preferred technology for the site is the non-surface piercing OpenHydro Open-Centre Turbine, with an appropriately developed Rochdale Design Envelope to allow consideration of alternative turbine technologies within the Project Description. However, there may be a requirement for some surface piercing elements, in particular for offshore hubs/substations. In addition, BTAL wishes to seek consent for a design envelope sufficiently broad to potentially include surface piercing turbine systems, as an alternative option.
The OpenHydro Open-Centre Turbine (OCT) is a bi-directional (bi-directionality ensures that the turbine can extract energy in both the ebb and flood flow directions) shrouded horizontal axis turbine (HAT), which is illustrated in Figure 4.1 below. It is a simple device comprised of four key components: a direct-drive permanent magnet generator, a hydrodynamic duct, a horizontal axis rotor, and a subsea gravity base type support structure. The turbines designed for this site would have an outer diameter of up to 20m, resulting in a turbine height of up to 27m above the seabed. The size of the subsea base will depend on the site design characteristics but is likely to have a length between each foot in the order of 30m - 50m. Only the feet will be in contact with the seabed and the area of the feet on the seabed will be minimal. Each device will be capable of generating at least 1 M W but actual output will be determined through detailed design and will depend on actual individual site conditions. The location, spread and layout of devices and infrastructure will be determined through detailed planning, informed by the EIA, NRA and stakeholder consultation. The OCT design has no need for a gearbox or other complicated components and is based on a philosophy of zero maintenance between overhauls. The turbine is also seawater-cooled and lubricated by seawater, which means there is no requirement for oils or lubricants.
Alternative technologies that are included within the design envolope are all horizontal axis turbines (HAT). A number of such turbines are currently being developed which may be either shrouded or unshrouded. Devices typically have three or more blades which rotate around a nacelle and may be of fixed or variable pitch. Power take-off and generation configurations vary, from utilising direct-drive solutions with no gearbox, through to marinised wind turbine nacelles. Commercial scale devices in development have rotor diameters of up to around 20m. Some illustrative examples of un-shrouded device types to be included for the purposes of a Scoping Opinion are outlined in Figures 4.6 to 4.10 below, but note this is not a definitive list. As can be seen, some of these devices have a single turbine per foundation/structure and some have multiple turbines per foundation/structure.
The support structure for the OpenHydro OCT is an unpi nned gravity base structure, which is installed along with the turbine as one assembly. A general concept view of the OpenHydro subsea base arrangement is provided in Figure 4.2 below. It is likely to have three to four ‘legs’ terminating in cones to provide resistance to sliding forces imparted on the turbine by the currents. The likely length of each side of the subsea base is 30 – 50m and final dimensions would be determined during a detailed design process.
There are a range of potential support structures/foundation types which may be associated with HAT’s. These include monopile foundations (drilled socket in the seabed), multi-leg / braced structure (with pinned piles) or gravity bases (pinned or unpinned). If an alternative technology is selected for build out on the site, the final choice of support structure would be made post-consent, at a more advanced stage of the detailed design process. This approach is analogous to established practice for other offshore renewable energy developments.
Connection of the offshore arrays to the grid will be through one or more export cables to shore. As part of the site design process, export cable routes from the tidal array to landfall and any grid connection options will be identified based on technical and environmental criteria, as well as through discussions with the electricity network operator, regulatory authorities and stakeholders. The type and routing of the cables will be subject to further detailed electrical design for the Project.
All cables would be armoured to protect against abrasion, and where there is a lack of sediment they would be l aid directly onto the seabed. In some areas pre-cast concrete mattresses or a similar form of protection may also be required on top of the cable. In inshore waters and towards landfall points, where there is sufficient sediment, cables maybe buried.
For Phase I of the Project it is envisaged that there will be a requirement for between 1 to 3 export cables, with one cable leading from each sub-sea hub or offshore (surface piercing) substation back along the seabed towards the most suitable landfall location. It is assumed that mechanical excavation will be required to dig a trench into which piping will be l aid or cable directly placed. Another option may be directional drilling at the landfall site. There are a number of landfalls currently being considered including either side of Aith Hope, the coastline south of the Melsetter Estate and the coastline around Brims Ness. The final selected landfall will be closely linked to the decision of where to site the onshore substation. Broad indicative Onshore Cable Corridor Search Areas are indicated in Figure 3.1 above but this will be confirmed by SHE-T who will be responsible for the development of the onshore substation. Tidal turbines will be inter-connected in arrays subsea. A number of factors, including turbine parameters and available technical solutions will influence the number, length, spacing and configuration of inter-array cables. It is anticipated that the majority of the cables would be laid in line with the prevailing tidal flow directions, although clearly there will be a need to interconnect within the arrays, and some cables may run across the prevailing flow directions.
The design of the offshore electrical infrastructure continues to be developed and as such there may be a requirement to have one or several offshore electrical hubs either mounted on the seabed or on a surface piercing structure. The current technical maturity of such infrastructure is not sufficient to allow a definite description to be made at this point.
A surface piercing structure may be part of a turbine installation or a separate structure altogether. Typically, such a pl atform might be supported by a jacket structure, braced monopile or alternatively it could be a moored surface piercing structure. A surface piercing offshore substation would normally be unmanned with access by helicopter or vessel. In the event such a structure becomes a requirement, these may be considered for use as navigational aids, for example, to provide site marking, if appropriate. Alternatively, it may be possible to group a number of turbines together using subsea hubs, using technology currently in development. This is because, at present, the technology limits the voltages at which devices can be connected subsea, which in turn limits the MW rating of cable which can be installed. An offshore platform would bring multiple lower voltage cables together, with the power then being exported to shore on fewer, high voltage cables. The final proposal will be based on both technical and environmental assessment.
There are two main options for constructing a landfall:
- Directionally drilled from a near-shore location to beyond the surf zone and the offshore cable pulled through the drilled duct to shore; or
- Cable burial up an existing beach in an open trench.
In the scenario where horizontal directional drilling (HDD) is required, ideally, the location of the drilling site would be as close to the onshore substation as possible in order to minimise the distance of any onshore electrical cabling. The exact location for cable landfall has not yet been determined but Figure 3.1 above illustrates the AoS.
This is currently outside the scope of the Project. It is expected that SHE-T will be responsible for the onshore substation. However, it is an important part of the development and a typical description is therefore provided below for completeness. It is currently anticipated that the following infrastructure could be included:
- Compound to house a grid transformer and connection terminations;
- A control building compound for housing switchgear, SCADA etc.; and
- An operational/personnel/office compound area.
The exact locations for the onshore infrastructure have not been defined at this stage of the design process and will be determined by SHE-T but the likely search area is shown in Figure 3.1 above. It is currently anticipated that a 33/132kV substation is required. The likely development area such a substation would require for an installed capacity of 200MW is of the order of 70m x 50m. It is likely that the area requirement for Phase I will be less than this. The actual footprint of the substation will be determined by a number of factors such as:
- Whether air or gas substation design is chosen. Air insulation requires considerably more space and i s usually used in outdoor substations. Inert gas is more commonly used where more of the infrastructure is housed indoors; and
- Whether the cables are brought vertically or horizontally into the building. The volume of the substation is likely to remain consistent in order to accommodate control and electrical equipment however the footprint of the building will be greater if the building is constrained to a single story or low rise. The footprint may be reduced if the building is of a greater height allowing more equipment to be stacked.
It is expected that SHE-T carry out the required engineering and environmental assessments on the identified location. This substation will form the connection point for the Project to export power into the national grid.
There are a wide range of installation and removal methodologies currently being trialled in the testing of tidal energy converters and support structures ranging from the use of moored and tugged barges, anchored crane barges, through to dynamically positioned (DP) heavy lift construction vessels. It is likely that this deployment will use DP vessels for the installation of the foundations and devices. A specialist cable laying vessel will be required to lay the export cable(s), this may require more than one vessel. Installation of the possible substation and cables could involve the use of heavy lift or DP vessels. Maintenance activities may also use a DP vessel fitted with a crane.
Off the south coast of South Walls, Hoy, Orkney.
|Marine Licence (Marine (Scotland) Act) Consent||Marine Scotland||TBC|
|Section 36 (Electricity Act) Consent||Marine Scotland||TBC|
|Licence to Disturb Marine Species||TBC||TBC|
|Licence to Disturb Basking Shark||TBC||TBC|
|Town and County Planning Permission||TBC||TBC|
In November 2008, The Crown Estate opened up the Pentland Firth and Orkney Waters Leasing Round (PFOW) to marine energy developers by inviting bids for exclusive site development rights. On the 16th March 2010, The Crown Estate awarded an Agreement for Lease (AfL) for a tidal energy array up to 200MW in capacity. In 2013 a revision was made to the boundary of the AfL area, whereby 80% of the original AfL area was relocated to the west, with the remaining 20% overlapping with the original site. As a result of this boundary change and in order to ensure a name relevant to the Project location, the site name has been revised from Cantick Head Tidal Development to Brims Tidal Array, with the joint venture partnership now called Brims Tidal Array Limited (BTAL). A Scoping Report has now been issued to all stakeholders and interested parties. The Scoping Report provides details of the project and identifies the topics that are proposed to be covered within the Environmental Impact Assessment (EIA) and can be downloaded here.
An EIA has now also been submitted and a marine license application was submitted in June 2016. The EIA and other supporting documents can be accessed via: http://www.gov.scot/Topics/marine/Licensing/marine/scoping/BrimsArray
The following potential impacts were identified.
- Collision risk to birds from turbine;
- Displacement of birds from vicinity of turbine;
Disturbance to birds by vessel activity;
- Disturbance to birds from lighting of TECs and other infrastructure;
- Marine seabed habitat loss/change due to turbine foundations and cable armouring;
- Disturbance to birds due to onshore construction works;
Disturbance to marine mammals from underwater noise generated by construction / deployment vessels;
- Disturbance to marine mammals and basking shark from underwater noise generated during potential drilling activities;
- Marine mammal collision with vessels;
- Seal collision risk (corkscrew incidents);
Disturbance to marine mammals from underwater noise generated by the devices;
- Risk of injury to marine mammals and basking shark from collision with devices;
- Disturbance of spawning grounds (herring and sandeel);
- Disturbance of habitat for demersal species;
- Effects of noise and vibration (increased boat traffic and construction, operational and decommissioning activity) on hearing specialists (i.e. herring and sprat);
- Collision of slow moving larger species (e.g. basking sharks) with the devices or strike of migratory fish;
Effects of electro-magnetic fields (EMF) on elasmobranches and salmonids;
- Changes in the existing habitat (due to colonisation of infrastructure);
Substrate / habitat loss / damage from placement of devices and other infrastructure on the seabed, cable laying and eventual removal during decommissioning;
- Scour around devices and other subsea infrastructure (including vessel mooring cables as result of movement with wave and tides);
- Increased suspended sediment and turbidity from installation of subsea infrastructure in inshore waters;
- Decrease in water flow leading to downstream change in benthic habitat;
Introduction of marine nonnatives;
Impact to benthic communities from any thermal load or EMF arising from the cables during operation;
Colonisation of subsea infrastructure, scour protection and support structures;
- Release of material due to installation of foundations/substructures and devices and offshore hub(s);
- Release of material in water column due to installation of inter-array and export cables;
- Effects to physical processes or beach morphology from installation of cable landfall at the shore;
Change to tidal regime due to presence of foundations/substructures and devices and offshore hub(s);
- Effects to bed load sediment transport due to presence of inter-array and export cables;
- Change to physical processes or beach morphology at cable landfall at the shore;
- Change to physical processes or beach morphology at cable landfall at the shore;
- Change to physical processes due to decommissioning of interarray and export cables; and
- Change to physical processes due to decommissioning of cable landfall at the shore.
Mitigation Measures: TBC
|Coastal and Terrestrial Ecology||All Stages|
|Reinstatement of sensitive habitats (UK BAP or LBAP) will be reinstated following best practice guidance. Material removed from the terrestrial/intertidal habitat should be stored and replaced within the same terrestrial/intertidal habitat following the cable installation works|
|A pre-construction survey for otter will be carried out 8-10 weeks prior to works commencing. If any otter shelters are located, further protection measures will be discussed and agreed with SNH/Marine Scotland and implemented, including the possible need for a European Protected Species (EPS) licence if there is potential for disturbance to otter.|
|Mammal exit ramps will be provided for potential hazards such as steep-sided exposed trenches or holes when contractors are off site (i.e. at night time). Temporarily exposed pipe systems will be capped when contractors are off site to prevent otters from gaining access.|
|If works are due to take place during the bird breeding season (April to August inclusive), a pre-construction breeding bird survey will be undertaken by a suitably qualified ECoW to ensure no nests are present on site or adjacent to the site before works commence.|
|If works are likely to be required during the bird breeding season (April to August inclusive) use of appropriate measures (to be agreed with SNH) to deter birds from breeding on site before construction commences should be implemented at the earliest opportunity before nest building begins. Possible deterrent measures include use of reflective tape or ribbons on posts.|
|Any nesting birds will be noted and works will be programmed to avoid disturbance. An exclusion zone or other alternative approaches to avoid damage or destruction to nests will be devised and agreed as appropriate with SNH. Exclusion zones around active nest sites will be clearly demarcated at the earliest opportunity to protect nesting birds from disturbance. Any nests will be monitored on a weekly basis by the ECoW to determine when the nesting bird ceases usage of the nest and therefore when it is safe to commence works in the area.|
|If a cable landfall location is chosen on South Walls, within the Aith Hope AoS, construction activities will be timed to have commenced before the arrival of Greenland barnacle geese in mid-October.|
|Where works are to be undertaken during the bird breeding season (April to August inclusive), the Ecological Clerk of Works will be present until the works are completed or until it is clear that no breeding birds would be adversely affected by the works.|
|Benthic Ecology||All Stages|
|Pre-construction cable route surveys will be conducted prior to determining the final cable route option and will confirm whether any sensitive habitats are present. BTAL will take all necessary actions to avoid any sensitive habitats identified (e.g. alteration of cable routes). Should disturbance of the habitat be unavoidable BTAL shall undertake consultation with key stakeholders, SNH and MSS, to assess the potential impact significance and agree the best practicable options to minimise impacts to the habitat.|
|Marine standard anti-fouling coatings on turbines and associated infrastructure will only be used where necessary.|
|Management measures will be in place to ensure that any rock placement that is required will be kept to a minimum to reduce seabed disturbance.|
|Marine Mammals||All Stages|
|A vessel management plan will be developed in consultation with SNH and Marine Scotland which will aim to develop a standard transit route and range of vessel speeds for traffic to and from the AfL area with the aim of minimising collision risk.|
|Vessels associated with all Project operations will carry on-board oil and chemical spill mop up kits|
|Installation activities will only take place during suitable weather windows.|