OSP arrangements

  1. The arrangement of OSPs has been reviewed to cover a variety of scenarios which reflects the ongoing uncertainty around the grid connection location and required transmission technology. Optionality in the final OSP and transmission technology is required to facilitate faster deployment to achieve UK and Scottish Government decarbonisation and climate change targets as set out in the project objectives ( Table 4.1   Open ▸ ).
  2. As noted in Table 4.4   Open ▸ , the PDE for the Array EIA Report presents two options for OSPs: either up to six large OSPs, or up to three large OSPs and up to 12 small OSPs. It was also confirmed that these would be installed with fixed jacket foundations. It should be noted that the second option within the EIA PDE, up to three large OSPs and up to 12 small OSPs, represents an increase in the number of platforms from the PDE set out within the Array EIA Scoping Report. Whilst there will be more individual structures, it is considered that these remain within the PDE presented within the Array EIA Scoping Report as the overall collective footprint, size, volume and number of piles remain the same and would not increase the predicted likely significant effects that are assessed within the Array EIA Report. This arrangement has the potential to increase the efficiency of the Array by reducing transmission losses within the inter-array and offshore export cable infrastructure.
  3. To accommodate the larger OSPs and account for uncertainty in the ground conditions across the site, the hammer energy associated with pile driving at the OSP locations has been increased from 3,000 kJ at scoping to 4,400 kJ. This aims to mitigate against any challenging geological conditions that may restrict pile installation once final layouts are developed and following completion of further geotechnical surveys planned prior to construction. The advice received in the Ossian Array Scoping Opinion (MD-LOT, 2023) has been considered in light of the revised maximum hammer energy and has been applied to the assessments presented within this Array EIA report. Potential impacts in relation to subsea noise from piling were scoped in via the Array EIA Scoping Report, therefore it is considered that the advice outlined in the Ossian Array Scoping Opinion is relevant and has been considered and applied within the subsea noise modelling (see volume 3, appendix 10.1 and volume 2, chapter 10).

                        Floating Foundation Design

  1. Due to the ongoing development of floating foundation concepts and commercial constraints, such as supply chain restrictions, the Applicant have aimed to maintain optionality in final floating foundation design. This strategy aims to take advantage of innovative solutions that have the potential to overcome technical and commercial challenges and mitigate environmental effects. Floating foundation concepts with top connections high above the water column with wide anchor spreads and taut mooring lines were considered for inclusion within the PDE. However, mooring line connections above the water line can result in excessive corrosion of chain within the splash zone. There are also operational challenges in having mooring lines in close proximity to the water surface, potentially within vessel underkeel clearance values that can restrict navigation. Therefore, within the PDE, the upper limit of mooring line connection was confirmed as 5 m below the sea surface with a maximum mooring line angle of 82 degrees from vertical to reduce the risk of subsurface vessel allision and corrosion on mooring line infrastructure.

4.5. Export Cable Corridor and Grid Connection

  1. In 2020, the Offshore Transmission Network Review (OTNR) was launched by the UK Government and is currently ongoing, with the purpose to ensure that the network connections for offshore wind generation are delivered efficiently and consider environment, cost to consumers, local communities and deliverability (HM Government, 2022a; National Grid, 2022a). The UK Government released the British Energy Security Strategy policy paper in April 2022 which sets out the ambition to deliver up to 50 GW of offshore wind by 2030, including up to 5 GW of floating offshore wind (HM Government, 2022b). It is necessary that there is a coordinated approach in place with regard to the offshore grid network and landfall points in order to achieve this ambitious target. As part of the OTNR, National Grid have developed the Pathway to 2030 Holistic Network Design (HND) to set out a coordinated approach for connecting 23 GW of offshore wind (National Grid, 2022a). The findings of the HND have fed into a Detailed Network Design (DND) which will be taken forward by the organisation(s) responsible for developing that part of the network, and the HNDFUE is currently being undertaken by National Grid (National Grid, 2022b). In June 2023, National Grid reported that they were working on the Final Strategic Options Appraisal after which they will publish the recommended design (National Grid, 2023).
  2. In March 2024, as part of the ongoing HNDFUE, National Grid Electricity System Operator (ESO) published their Transitional Centralised Strategic Network Plan (TCSNP) in the ‘Beyond 2030’ report (National Grid, 2024). Beyond 2030 sets out National Grid ESO’s recommendations to achieve a decarbonised electricity network. The proposed grid design aims to facilitate transmission of a number of offshore wind farm projects. Within this publication it was confirmed that Ossian will be offered two grid connection locations in Lincolnshire, one at Weston Marsh and one at the Lincolnshire Connection Node. Onshore and offshore route optioneering work has now been commenced by the Applicant to determine the Proposed offshore and onshore export cable corridor(s), and location(s) for the Proposed onshore convertor station(s).
  3. Due to the ongoing nature of the HNDFUE, and the uncertainty associated with landfall locations, and grid connection dates, the Applicant is currently progressing separate consenting applications for the Proposed offshore export cable corridor(s) and Proposed onshore transmission infrastructure.
  4. This approach was presented within the Array EIA Scoping Report (Ossian OWFL, 2023) and agreed with MD-LOT via the Ossian Array Scoping Opinion (MD-LOT, 2023).

4.6. Conclusion

  1. The EIA Regulations require “A description of the reasonable alternatives (for example in terms of project design, technology, location, size and scale) studied by the applicant, which are relevant to the proposed project, the regulated activity and their specific characteristics, and an indication of the main reasons for selecting the chosen option including a comparison of the environmental effects…”. The Applicant has provided a description in this chapter of the reasonable alternatives considered for the Array, including location, project technology and project design, size and scale, and the process for selecting the proposed development for the Array as presented in this Array EIA Report.
  2. The main reasons for selecting the Array are as follows:
  • Geotechnical conditions indicated that the full site area was suited to the deployment of a variety of anchoring solutions that could reduce impacts of supply chain constraints (see paragraphs 62 and 63, and paragraph 76 to 80).
  • The area of the Array was appropriate for deployment of floating wind turbine technology across the full area, but could not support a commercial scale fixed bottom or hybrid site due to the limited areas with water depths less than 70 m. The shallow areas of the Array were deemed suitable for fixed bottom OSPs which could reduce technical challenges associated with large numbers of dynamic cables converging at floating platforms (see paragraphs 62 and 63, and paragraph 76 to 80).
  • The Array was selected to reduce environmental effects following detailed constraints analysis. Table 4.5   Open ▸ presents key environmental comparisons taken in to account pre- and post- award of the CES Option to Lease Agreement that has fed into site boundary identification and design evolution.
  1. The Applicant is utilising a PDE approach which considers a realistic range of project design parameters, as described in volume 1, chapter 3. Any impacts resulting from the Array have been assessed in this Array EIA Report using the Maximum Design Scenario (MDS) approach.
  2. Although the final design of project components to be used for the Array are yet to be selected, the PDE approach presented in the Array EIA Report and the constraints set in the Section 36 consent will ensure that the constructed project complies with the assessment set out in the application.

 

Table 4.5:
Summary of Key Environmental Comparisons

Table 4.5: Summary of Key Environmental Comparisons


4.7. References

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Brown and May Marine Ltd. (2021). ScotWind Constraints Mapping: Commercial Fisheries. Technical Report. Document reference: 201900174-CF.

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IPCC (2023). Summary for Policymakers. In: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC, Geneva, Switzerland.

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[1] CES leased 25 GW during the ScotWind leasing round, at the time of writing the Sectoral Marine Plan is currently being updated to take account of the full 25 GW leased.

[2] As defined within the SMP (Scottish Government, 2020a).

[3] Subsequent site-specific FLiDAR measurements have recorded mean wind speeds exceeding the IEC Class I value.