6.4. Summary

82. Table 6.4   Open ▸ summarises the calculated operation and maintenance phase emissions associated with the Array, which totals between 607,989 tCO2e and -141,591,681 tCO2e, depending on the avoided emissions scenario used. Note that negative values represent avoided emissions, i.e. emissions that would have occurred without the Array.

Table 6.4: Operation and Maintenance Phase Emissions Summary

7. Decomissioning

83. The majority of emissions during the decommissioning phase relate to the use of plant/equipment for the Array’s decommissioning, disassembly, transportation to a waste site, and ultimate disposal and/or recycling of the equipment and other site materials.
84. At this stage, the approach to decommissioning the Array is still to be determined. However, it is anticipated that all floating structures, mooring lines, OSP topsides and foundations to the seabed level will be completely removed. Associated infrastructure, such as cables, scour protection and anchors and piles below the seabed may either be left in situ or removed, in accordance with the decommissioning plan. It may be decided, closer to the time of decommissioning, that removal will result in greater environmental impacts than leaving components in situ.
85. The components of the wind turbines are considered to be highly recyclable. When disposing of wind turbines, recycling is the preferred solution. This not only prevents the materials from being sent to landfills, but also reduces the need for the extraction of primary materials. Material which cannot be recycled might be used for incineration or energy from waste. It is considered the same approach can be applied to all mooring lines, OSP topsides and foundations and cables retrieved during decommissioning.
86. Cables and other infrastructure, such as anchoring systems, may be left in situ during decommissioning. This will not result in additional emissions during this phase. As such, emissions associated with the disposal of materials at the end of their lifetime is considered to be immaterial and may even result in future avoided emissions. This impact is not assessed further.
87. In the absence of detailed information regarding offshore transport movements during the decommissioning phase, it has been assumed that such emissions equal those associated with the construction phase, totalling 385,615 tCO2e. Given carbon emissions associated with use of plant and fuel is expected to have achieved good levels of decarbonisation at the decommissioning phase of the Array, this is likely to present a conservative MDS.
88. Given the negligible rates of sediment accumulation and associated carbon sequestration in the Array area, there is not anticipated to be any material change to the blue carbon stocks over the Array’s operational lifetime (as detailed in paragraph 32 and 59). As such, any disturbance to the seabed and blue carbon habitats that may result from infrastructure removal at the decommissioning phase is not likely to result in the release of additional emissions not captured by the range of likely emissions presented in the assessment of construction effects. Therefore, this impact is not assessed further.

8. Cumulative Assessment

89. It is important to note that the Array cannot deliver the avoided emissions detailed in section 6.2 without associated transmission infrastructure to enable connection of the Array to the Grid. This transmission infrastructure has associated emissions for its construction, operation and maintenance and decommissioning phases that must be considered within the cumulative assessment for climatic effects.
90. However, detailed design parameters for the transmission infrastructure are not available at the time of writing. As such, the calculations presented below represent a high level estimate of total emissions with a high degree of uncertainty. Such emissions estimates have been informed by assumptions based on indicative parameters provided by the project team for the Array alongside available design information for the Proposed offshore export cable corridor(s) and Proposed onshore transmission infrastructure. As the future transmission projects and applications are brought forward in relation to the transmission infrastructure, the assessment presented below will be enhanced and refined. These updated assessments will be detailed within future climatic effects chapters.
91. Major elements of the transmission infrastructure are likely to comprise:

• offshore export cables and cable protection;
• onshore export cables;
• onshore converter stations; and
• cables from the converter stations to National Grid substations.

92. Throughout this assessment, it has been assumed that the total operational lifetime for the transmission infrastructure is the same as the Array (35 years).
93. The total length of the Proposed offshore export cable corridor(s) between the Array and the Proposed landfall location(s) is indicatively circa 400 km, and up to four offshore export cables may be required. The construction and operation and maintenance phase emissions for the offshore export cables associated with the Proposed offshore export cable corridor(s) have been calculated based on the methodology in paragraphs 50 and 80. Total emissions during the construction and operation and maintenance phases are shown in Table 8.1   Open ▸ .
94. It has been assumed that the Proposed offshore export cable corridor(s) will have the same cable protection requirements as the inter-array and interconnector cables per kilometre. Total emissions during the construction phase are shown in Table 8.1   Open ▸ .
95. Two onshore export cable corridors are planned for the Proposed onshore transmission infrastructure, one of which is approximately 15 km in length, and the other is approximately 60 km in length. Six cables are anticipated to be required for the each of the 15 km and 60 km onshore export cables. The construction and operation and maintenance phase emissions for the onshore export cables have been calculated based on the methodology in paragraphs 50 and 80 above. Total emissions during the construction and operation and maintenance phases are shown in Table 8.1   Open ▸ .
96. Four converter stations are planned for the Proposed onshore transmission infrastructure, with an indicative power of 1 GW per converter station. Electrical equipment, such as transformers, busbars, etc are anticipated to comprise the majority of embodied emissions for the converter stations. As such, the emissions for the electrical equipment required for the converter stations have been calculated based on the methodology in paragraph 53. Total emissions during the construction phase are shown in Table 8.1   Open ▸ . Maintenance schedules for these are not available at this stage, however it is anticipated that emissions associated with operation and maintenance of the converter stations would be captured within transport emissions, detailed in paragraph 101.
97. Grid connection cables are also anticipated to be required from the converter stations to the National Grid substations. Six cables are anticipated to be required per converter station, with an indicative length of 5 km. The construction and operation and maintenance phase emissions for the cables have been calculated based on the methodology in paragraphs 50 and 80 above. Total emissions during the construction and operation and maintenance phases are shown in Table 8.1   Open ▸ .
98. Emissions resulting from disturbance to blue carbon habitats have been calculated based on the total length of offshore export cable for the Proposed offshore export cable corridor(s). In the absence of detailed information regarding the extent of disturbance during construction of the Proposed offshore export cable corridor(s), it is assumed that the offshore export cable(s) will have the same area of disturbance per kilometre as the inter-array and interconnector cables of the Array. Site-specific benthic surveys have not yet been undertaken for the Proposed offshore export cable corridor(s), and as such a site-specific blue carbon emissions factor is not possible. Instead, the Array blue carbon emissions factor of 5.00 tC/ha has been used (see paragraph 43). Future applications will include detailed benthic surveys, which will enable a more refined calculation of the blue carbon stocks present within the Proposed offshore export cable corridor(s).
99. Total construction phase emissions resulting from disturbance to blue carbon habitats have been calculated following the methodology in paragraphs 41 to 45. Emissions shown in Table 8.1   Open ▸ .
100. As stated in paragraph 88, there is not anticipated to be any material change in the blue carbon stocks over the operational lifetime of the Array. This is also assumed for the Proposed offshore export cable(s) in the absence of further detailed information. As such, it is not anticipated that there will be additional disturbance (and associated emissions) to blue carbon habitats for the Proposed offshore export cable corridor(s) during the operation and maintenance, and decommissioning phases, as activities are not likely to disturb blue carbon habitats additional to those accounted for during the construction phase.
101. Transport emissions have been calculated to make up 4% of total construction emissions, and 54% of total operation and maintenance emissions (excluding avoided emissions), for the Array. Corresponding uplifts have therefore been made to the total construction and operation and maintenance emissions of the transmission infrastructure respectively, in the absence of detailed transport information. Uplifts are presented in Table 8.1   Open ▸ . As detailed in paragraph 87, decommissioning emissions are assumed to be equal to construction transport emissions for the Array, and this assumption has also been applied to the transmission infrastructure for the purposes of the cumulative assessment.
102. Table 8.1   Open ▸ summarises the calculated emissions associated with the transmission infrastructure, which totals 3,076,000 tCO2e.

Table 8.1: Cumulative Assessment Emissions Summary – Proposed Offshore Export Cable Corridor(s) and Proposed Onshore Transmission Infrastructure