Offshore

Prior to submitting a planning application, we undertook detailed studies at the Triton Knoll Offshore Wind Farm site location. These look at the possible impacts the wind farm could have on wildlife (including birds and marine life), habitats and users of the sea such as shipping and fishing activities. The studies formed part of an Environmental Impact Assessment (EIA) the results of which have been written up into an Environmental Statement (ES).

The ES, which has been submitted with the wind farm planning application, describes the proposed wind farm, summarizes any potential environmental impacts and explains the measures we propose to mitigate any significant negative effects.
Should planning consent be awarded for the offshore wind farm, it is important that the consent is sufficiently flexible. This is because it is not yet possible to be specific about the exact details of the wind farm at this early stage for the following reasons:

• Turbine designs (including size and capacity) are changing rapidly as technology moves on. As the wind farm will not be built for a number of years, it is important that the best options (environmentally and economically) are considered when the time comes to purchase the wind turbines.
• It is only possible to gather a limited amount of information about the sub-sea ground conditions at this stage. As a result, the turbine foundation design cannot be decided until after consent is awarded and further design work is undertaken.
• The ongoing work for the electrical system will further influence the design of the offshore wind farm.

The planning application will therefore be based on a broadly defined 'envelope' which includes a range of options (such as the number and size of turbines). The potential 'realistic worst case' is the version of the wind farm being tested in the assessments we are carrying out, ensuring that whatever is installed in the future will have been deemed to have been acceptable by the consenting authorities.

The offshore components

The offshore wind farm components will include:

• a maximum of 288 wind turbines.
• foundation structures for each turbine (and the offshore substations), selected from a range of design options. Scour protection materials may be placed around foundations, to mitigate the effect of sediments being washed away from the bases of the foundations.
• up to five meteorological monitoring masts (to collect wind data)
• up to eight offshore substations
• buried, sub-sea interconnecting electricity cables between the wind turbines and the offshore substations
• a mobile facility which has not yet been defined, such as a vessel, jack up barge or other option located within, or adjacent to, the turbine site for operation and maintenance staff and equipment.

The wind turbines we are currently considering could have a:

• a maximum blade tip height (above lowest astronomical tide, LAT) of 220 metres (m)
• a maximum rotor diameter of 180 m
• a maximum tower diameter of 8 m
• the lowest blade tip height will not be less than 27.4 m above LAT.

Up to nine buried sub-sea export cables that run from the offshore substations to the coastal landfall will also be required. However, these are being considered under the electrical system component of the project within package 2.

The foundation options

The foundation options we are currently considering are:

• Monopiles: either the commonly used steel monopile or potentially concrete monopiles (which would have a diameter of up to 8.5m). These are positioned into the seabed to support the turbine, often to depths of several tens of metres, by either piling (with a pile hammer) directly into the seabed or drilling a hole into which they are lowered
• Multiplies: structures that are secured to the seabed by more than one pile (typically three or four) and may be lattice jackets. The piles are substantially smaller than monopiles (1 to 3 m)
• Gravity bases: a heavy, wide (up to around 45m diameter) base that sits on the seabed to bear the loads of the turbine without needing to be pinned to the seabed. These can have flat or conical bases or consist of more than one (typically circular) base
• Suction caisson: These are akin to upturned buckets. The edge of the “bucket” pushes into the seabed to a depth of perhaps 10 or 15m. As with gravity bases these can consist of either a single bucket (of a diameter similar to the gravity base) or several (replacing the pin piles on multipile structures).