In October 2011, Argyll Tidal Limited (ATL) received an Agreement for Lease (AfL) with the Crown Estate under Section 3 of the Crown Estate Act 1961. This agreement initiated the investigation of the potential for development of a demonstration tidal energy array of up to 3 MW in the North Channel off the western coast of the Mull of Kintyre, Argyll and Bute, Scotland. ATL worked with Nautricity Limited (NL), a Scottish tidal energy technology developer.
It was originally proposed that up to 6 of these devices would be deployed at the development site subject to the appropriate consents and licenses being granted.
During the feasibility and design stages of the development, ATL sought a grid connection offer from the local distribution network operator (DNO) Scottish Hydro Electric Power Distribution (SHEPD). Due to Transmission Network constraints in the wider Argyll and Bute region and the limited capacity of the Local Distribution Network, for technical reasons it became clear that without construction of extensive and costly new grid infrastructure it would not be possible to connect more than a single CoRMaT device to the existing electricity network. ATL therefore abandoned plans for a multi-device array and refocused the development to a single 500kW demonstration device. As the capacity of the development was now less than 1MW, Marine Scotland Licencing Operations Team (MS-LOT) confirmed that the Development would only require a Marine License only. MS-LOT also confirmed that consent application would require robust supporting environmental information but not a formal Environmental Statement (ES) under the Environmental Impact Assessment (EIA) Regulations.
As the development would also include onshore elements to facilitate the connection of the device to the existing grid connection, an onshore planning application to the local planning authority (Argyll and Bute Council) was also required.
From a technology suitability perspective, the Development Site near Kintyre was chosen for its water depths and resource levels which were well matched to the moored Nautricity device and less compatible with fixed bottom solutions. Additional factors contributing to the suitability of the Argyll Tidal Demonstration Project Development Site included an absence of environmental designations on the site or in the immediate vicinity and the proximity of the site to the demand centre in Scotland (central belt). It was planned for the device to operate on site for up to 7 years.
North Channel off the western coast of the Mull of Kintyre, Argyll and Bute, Scotland.
The development had a capacity below 1MW therefore the Development did not require consent under Section 36 of the Electricity Act. A Marine License was granted under the Marine (Scotland) Act 2010 by Marine Scotland (the licensing authority) on 9 May 2014, which can be viewed here.
An Environmental Appraisal was prepared by the Developer and a marine license granted in May 2014. At the time of writing in September 2021 the project remains on hold, with no further developments made in this time.
In February 2015, Nautricity secured a grid connected test berth at EMEC’s Falls of Warness tidal test site and deployed the CoRMaT device in April 2017. Further information on this project can be accessed here.
Key Environmental Issues
Several potential impacts were identified, however only the following was considered to be potentially significant:
- Risk to navigational safety from failing of the device/ mooring
In dealing with risk of device/mooring failure, the following measures are proposed
- The mooring system will be approved by an appropriate classification society; this is also a requirement of the Applicant’s Agreement for Lease with The Crown Estate.
- Telemetry measures will be installed to continually monitor the device enabling the device to be switched off immediately in an emergency event.
- Regular inspections of the mooring system as part of the device operation and maintenance plan should be undertaken.
- The operator will develop appropriate contingency plans and emergency response procedures in the form of ‘The Emergency Response Cooperation Plan (ERCoP)’ in agreement with the relevant stakeholders.
The CoRMaT device comprised a neutrally buoyant cylindrical nacelle with contra-rotating rotors (upstream – 3 blades, downstream – 4 blades) in close proximity around a common axis of rotation. This arrangement encouraged stability during operation and eliminated the requirement for a rigid support structure to transmit operational loads to the seabed. CoRMaT generated at variable speed via a submersible, contra-rotating permanent magnet generator with the rotor and stator driven directly by the upstream and downstream rotors respectively. For the planned demonstration deployment at the Mull of Kintyre, a minimum clearance of 10m below chart datum was intended to be maintained above the hydrobuoy to allow safe passage of vessels and to distance the buoy from wave action, the loading from which is most severe close to the surface. The lower tips of the rotors would be at least 7m from the seabed in order to operate above the highly sheared, lower resource region of the turbulent bottom boundary layer. A rigid ‘stinger’ with float surround would connect the nacelle to the yaw limiter. The nacelle was approximately 2.5m in diameter and 9.5m in length. Initially, 10m diameter rotor blades would have been fitted with scope for future upgrade to a maximum of 14m diameter. The overall system design would allow the nacelle to self-align with the predominant flow direction following periods of slack water. Power generation would be governed by site-specific flow conditions.
The device had a cut-in speed of 1 m/s, a rated output in flows greater than 2.5m/s and a maximum rotational speed (for each rotor) of 12 rpm.
The device and mooring system would be attached to 3 cylindrical can foundations anchored to the seabed via drilled and grouted pins. The can dimensions were not expected to exceed 1.4m in height and 0.8m in diameter. The spread and relative orientation of the foundation locations to the tidal flow would be determined by a number of design factors including deployment depth, the morphology and bathymetry at the deployment location and local resource variations. Drilling depths were not expected to be greater than 12m and the diameter of holes would likely to have been in the 140 – 250mm range. Cuttings - rock fragments - would be flushed away. The anchors would be solid cylindrical steel pins of diameter in the range 75-150mm. A non-shrink, high strength grout would secure the anchor pins. All grouting operations would be sealed to prevent loss of grout to the environment.
The mooring system would be comprised of a ‘platform’ of 3 steel wire lines. A single line would be connected to each of the foundation cans and these would meet approximately mid-water column and connect to the yaw limiter. The ‘platform’ mooring line inclinations would be dependent on design factors including deployment depth, foundation specification and local resource level. Operational tilt resulting from thrust and drag loading would be up to 30 degrees from the upright position. The mechanical yaw limiter acted as the connection point for the CoRMaT system via a rigid ‘stinger’. Its operational function was 2-fold:
• To allow alignment with prevailing tidal flow direction; and
• To prevent coiling of the electrical and control cable passing through its centre.
The hydro buoy would be foam-filled, constructed from steel with suitable corrosion and anti-fouling protection and be tethered to the upper plate of the yaw limiter using steel mooring lines. To avoid disturbance to the flow upstream of the rotor swept area, the lower surface of the hydro buoy would be located above rotor tip height in the water column. The hydrofoil profile has been selected to offer stable performance through a wide range of angles of attack. It was expected that the maximum dimensions of the hydro buoy would be a 6.5m chord length and an 8m span. As with the final specification of the mooring system and foundations, the design of this element would be determined in light of detailed information on the local flow environment.
Power would be delivered to shore via an electrical export cable (3 phase, 3.3kV) protected in a single 4” to 6” diameter drill pipe run. Also enclosed within the drill pipe would be a 230V electrical supply cable and fibre bundle for the CoRMaT control and braking systems. The connection for electrical export, electrical supply and communications cabling would most likely be dry-mate. Detailed design activity may have concluded that additional means of securing the pipeline to the seabed would be required at exposed sections of the route e.g. use of subsea cable mattress.
The subsea export cable landing j-tube would bound the offshore and onshore elements of the project. Landward of this point, a short tail of the subsea cable-in-pipe (approximately 25-50m in length) would protrude from the wider diameter j-tube following a winched installation. It was anticipated that conduits would be buried in a trench of up to 1m depth along this section. An isolator / earth switch would interface the onshore electrical equipment within the container compound from the generator. It was expected that the isolator would be containerised and located within the compound. The container compound would house both project and Distribution Network Operator (Scottish Hydro Electric Power Distribution) equipment. Project-side equipment would include:
• An isolator / earth switch bridging onshore electrical equipment and the generator
• Converters, transformers and switchgear housed in a number (provisionally 3) of compact containers
The DNO equipment comprised switchgear on a concrete plinth housed within a GRP enclosure.
|2x Multicat||Installation (Pipeline)||Used to tow and position pipeline|
|Rigid hull inshore craft||Installation (Pipeline)||To monitor float out of pipeline|
|Guard vessel||Installation (Pipeline)||To ensure safe transit of the pipeline|
|Barge||Installation (Mooring)||Approximately 30m in length with drilling rig. Install mooring pins and device mooring.|
|Workboat||Installation (Mooring and device)||Approximately 20m in length. Aid in the instalment of mooring pins and mooring. Also used to tow device to site.|
Baseline Assessment: Argyll Tidal Demonstrator Project
|Receptor||Study Description||Design and Methods||Results||Status|
|Marine Mammals||Vantage point surveys of marine mammals by MacArthur Green.||Visual survey of marine mammals.||Site used by only a small number of grey seals. Harbour porpoise and Common dolphin observed, no other cetacean species or basking sharks recorded.||Completed|
|Birds||Vantage point surveys of birds by MacArthur Green.||Visual vantage point survey of birds.||Multiple species were observed in the area. No Common or Arctic turns were recorded which may have been expected to occur. Some non-seabird species (peregrine, oystercatcher, curlew, swift, hooded crow and raven) were recorded but not considered in analysis because they do not enter the water, hence will not be vulnerable to effects of the development.||Completed|
|Invertebrates||Habitat and species identification of invertebrates by Precision Marine Survey Ltd.||Drop down video survey.||The area is characterised by variable, tide swept rocky substrata interspersed with, or influenced by, coarse mixed sediments.||Completed|
|Physical Environment||Geological and bathymetric survey.||A multi-beam survey of the development site region inshore of the 20m contour.||NA||Completed|
|Ecosystem Processes||Flow model conducted by RES Offshore.||Regional numerical flow model of the North Channel area.||The south-eastern corner of the Development Site is the region of highest tidal resource with much of the northern and western areas being too benign for development. Maximum flow speeds are approaching 4 m/s in the highest resource areas with |
corresponding mean speeds of 1.8 m/s.