Abstract
As part of their ongoing development programme, Marine Current Turbines Ltd (referred to hereafter in this report as MCT) proposes the installation of an array of tidal turbines for the commercial production of electricity in Kyle Rhea, a narrow strait between the Isle of Skye and mainland Scotland. Kylerhea, also discussed in this report is a village to the south west of the Kyle Rhea. The combined generation capacity of the array will be up to 5MW, comprising of four of SeaGen tidal turbine devices, with the capacity of each device of 1.2MW. The development of this array represents a natural progression in development, following the successful installation and operation of a single SeaGen device in Strangford Lough, Northern Ireland, the world’s first commercial tidal turbine.
This environmental scoping report provides initial background information and determination of the environmental constraints and benefits associated with the construction and installation of an array of tidal turbines in Kyle Rhea. As such, this report represents the first key stage in the Environmental Impact Assessment (EIA) process and has been produced to facilitate the identification and assessment of the potential environmental impacts associated with the project. The report will also ensure that all consultees are fully aware and informed of the scheme.
An initial site selection exercise was conducted by MCT, supported by Royal Haskoning, and included early consultation with Scottish Natural Heritage (SNH) and Marine Scotland (MS), as well as the Energy Consents Unit of Scottish Government. Royal Haskoning was commissioned to write an environmental scoping of the Kyle Rhea site in preparation for the submission of a full Environmental Statement (ES) to accompany applications for consent for installation of the array (see Section 2, Policy and Legislation).
The objectives of this report are to:
- Outline the technology to be installed on site;
- Briefly describe the techniques proposed for installation and highlight options still under consideration;
- Identify and summarise the known baseline conditions on site;
- Identify environmental constraints and benefits of the site;
- Consider and suggest possible environmental impact which may arise from the development;
- Identify any studies required for assessment of the project; and
- Identify the most appropriate approach to studies and subsequent impact evaluation.
Project Description - Technology
The technology which is proposed for the Kyle Rhea tidal array is based upon the SeaGen device installed and successfully operated in Strangford Lough, with some minor improvements or alterations to the design. The SeaGen turbine in Strangford Lough is one of the most studied, tested and reliable designs in the world.
Tidal turbines are, in principle, similar to submerged windmills driven by high tidal current velocities, deriving energy from huge volumes of flowing water. However, as water is 800 times denser than air, tidal turbines can be smaller in scale than wind turbines and devices within arrays can be positioned closer together because tidal streams generally provide bi-directional movements rather than the multidirectional movements of wind.
The basic requirement for cost-effective power generation from tidal streams is a mean spring peak velocity exceeding about 2.5 metres per second (m/s). Such flows have the major advantage of being an energy resource as predictable as the tides which cause them, unlike wind or wave energy which respond to the less predictable dynamics of weather systems.
The SeaGen turbine developed by MCT consists of axial flow rotors, of 16 - 20m in diameter, which drive a generator via a gearbox, much like a hydro-electric turbine or a wind turbine. The rotors turn at a maximum of 14.3rpm with a tip speed of each rotor is a maximum of 12m/s. Twin rotors are mounted on a wing-like cross beam, extending either side of a tubular tower, which itself protrudes approximately 10m above the water surface (during Mean Sea Level). The cross beam can be raised above the water surface on hydraulic rams to allow efficient maintenance and repair as required. Subsurface, each SeaGen turbine is likely to be mounted on a quadropile drilled and pinned into the seabed providing high stability with a minimal direct seabed footprint of approximately 3.1m2. The minimum depth of the rotor tips will be 3m to allow smaller vessels to pass close to the tower and during most states of the tide the depth will be considerably more.
Project Description - Site Selection
A site selection process was carried out to identify and assess potentially suitable sites for the small array in the UK. An evaluation of alternative sites using weighted comparative criteria was undertaken by the MCT project team to assess and justify site selection. Determination of site suitability comprises a number of components, characterised by the following main criteria:
- Weather exposure;
- Proximity to grid connection;
- Environmental sensitivities;
- Tidal flow regime energy;
- Bathymetry (22-35m depth);
- Site accessibility from local and national perspective; and
- Logistics and proximity to marine operations support.
Whilst it is recognised that each site considered is unique, the multiple criteria approach outlined above justified the selection of Kyle Rhea as the optimum site for the establishment of a temporary evaluation system of the marine current turbine.
Key factors that identified Kyle Rhea as an ideal site to locate the proposed tidal array included:
- The high current velocities likely to be encountered, predominantly in well-defined bi-directional flows, providing a complete spectrum of velocities for the prototype technology to be trialled under;
- The wave sheltered environment of the Kyle presents a number of advantages, including ease of maintenance and access and increased safety even during winter months.
In addition to the key points above, the ‘in principle’ support from the relevant authorities and stakeholders in Scotland was an important factor in the choosing of Kyle Rhea.
It is therefore considered that siting a small array of tidal turbines in Kyle Rhea could significantly accelerate the development of a clean renewable energy technology in the UK in a way not possible at other sites.
Project Description - The Site
The site boundary for this scoping study is shown in Figure 1.1, and encompasses the majority of Kyle Rhea, an area of approximately 2km2.
Onshore infrastructure is likely to include construction of a substation on the shore adjacent to the array (this could be either side of Kyle Rhea) and directional drilling between the substation and the array. The substation will connect to the national grid via existing infrastructure.
A detailed layout and position of the array will be finalised after collection of key data and identification of key constraints, for example, seabed characteristics and ecology.
The site is accessible from both the mainland, via the Old Military Road to Gleneig off the A87 south of Loch Duich, and from the Isle of Skye, via a minor road from the A87 at Ashaig to the settlement of Kylerhea. Immediately south of the proposed site, a small ferry crosses the Kyle between Gleneilg and Kylerhea during the summer. A minor airport is present on the Isle of Skye, with the nearest large airport at Inverness, approximately 1 hour away.
It is anticipated that the majority of material and equipment for construction and installation will be transported by sea. However, detailed logistical plans would be finalised at a later stage.