1. Introduction

  1. This Greenhouse Gas (GHG) Technical Report sets out the methodology and calculations of the GHG emissions for the Ossian Array (hereafter referred to as ‘the Array’). These calculations inform the assessment of climate change impacts in volume 2, chapter 17. This Technical Report should be read in conjunction with the chapter as supporting information.
  2. GHG emissions have been estimated by applying published emissions factors to activities in the baseline and to those required for the Array. The emissions factors relate to a given level of activity, or amount of fuel, energy or materials used, and therefore to the mass of GHGs released as a consequence. This Technical Report presents the technical calculations which relate to the potential magnitude of impact as assessed within volume 2, chapter 17.
  3. The GHGs considered in this Technical Report are those in the ‘Kyoto basket’[1] of global warming gases expressed as their carbon dioxide (CO2)-equivalent (CO2e) Global Warming Potential (GWP). This is denoted by CO2e units in emissions factors and calculation results. The GWPs typically used are the 100-year factors in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (IPCC, 2013) or as otherwise defined for national reporting under the United Nations Framework Convention on Climate Change (UNFCCC).
  4. The scope of this Technical Report relates to the Array during the construction, operation and maintenance and decommissioning phases. Key emissions sources included in the assessment are:
  • land use (seabed) change;
  • embodied carbon emissions in materials for the offshore infrastructure required (the wind turbines, (alongside their floating substructures, and mooring and anchoring systems), the fixed bottom Offshore Substation Platforms (OSPs) and inter-array and interconnector cables);
  • offshore transport emissions during the construction, operation and maintenance, and decommissioning phases; and
  • avoided emissions associated with the abatement of required fossil fuel generators and their associated emissions related with the United Kingdom (UK) electricity grid. Note that avoided emissions presented as part of the Array would be realised at the point of grid connection as part of the Proposed offshore export cable corridor(s) and the Proposed onshore transmission infrastructure, which are subject to separate applications.

2. Study Area

  1. Figure 2.1   Open ▸ illustrates the climatic effects study area for the Array which encompasses the proposed Array area (i.e. the area in which the wind turbines and associated infrastructure will be located) in the context of the domestic and international scope as developed on the basis of established Institute of Environmental Management and Assessment (IEMA) guidance (IEMA, 2022) utilised throughout this chapter. Domestic scope considers the local and national policy and targets concerning GHG and climate resilience.
  2. GHG emissions have a global (international) effect rather than directly affecting any specific local receptor. The impact of GHG emissions occurring due to the Array on the global atmospheric concentration of the relevant GHGs, expressed in CO2-equivalents (CO2e), is therefore considered within this assessment.

Figure 2.1:
Climatic Effects Study Area

Figure 2.1: Climatic Effects Study Area


3. Methodology

3.1. Methodology Overview

  1. Published benchmarks have been used to establish the baseline of current and future grid-average carbon intensity for the UK. Baseline information for this, as well as other relevant activities for the Array have been informed via the following source:
  • Department for Energy Security and Net Zero (DESNZ) (formerly Department for Business, Energy and Industrial Strategy (BEIS) (DESNZ, 2023a) Valuation of Energy Use and Greenhouse Gas: Supplementary guidance to the HM Treasury Green Book.
  1. GHG emissions caused by an activity are often categorised into ‘scope 1’, ‘scope 2’ or ‘scope 3’ emissions, following the guidance of the World Resources Institute (WRI) and the World Business Council for Sustainable Development (WBCSD) Greenhouse Gas Protocol suite of guidance documents (WRI and WBSCD, 2004). These categories are as follows:
  • scope 1 emissions: direct GHG emissions from sources owned or controlled by the company, e.g. from combustion of fuel at an installation;
  • scope 2 emissions: caused indirectly by consumption of purchased energy, e.g. from generating electricity supplied through the national grid to an installation; and
  • scope 3 emissions: all other indirect emissions occurring as a consequence of the activities of the company, e.g. in the upstream extraction, processing and transport of materials consumed or the use of sold products or services. Downstream use of products and services sold to customers would also be captured under scope 3 emissions.
  1. This assessment has sought to include emissions from all three scopes, where this is material[2] and reasonably possible from the information and emissions factors available, to capture the impacts attributable most completely to the Array. These emissions are not separated out by defined scopes (scope 1, 2 or 3) in the assessment.
  2. Due to the nature of the Array (i.e. it results in generated electricity from renewable sources being exported to the grid), its total gross GHG emissions includes displaced emissions that would have occurred as a result of predicted UK grid carbon intensity without the Array, i.e. avoided emissions.
  3. The assessment has considered (a) the GHG emissions arising from the Array (during construction, operation and maintenance, and decommissioning phases), (b) any GHG emissions that it displaces or are avoided, compared to the current or future baseline, and hence (c) the net impact on climate change due to these changes in GHG emissions overall.
  4. Consideration of GHG emissions over the lifetime of the Array is required in order to quantify its net contribution to climate change and as such the magnitude of change owing to the Array.

3.2. Embodied Carbon

  1. A Life Cycle Assessment (LCA) comprises an evaluation of the inputs, outputs and potential environmental impacts that occur throughout the lifecycle of a particular project, in this case the Array, encompassing either a cradle-to-gate or a cradle-to-grave (accounting for construction, operation and maintenance, and decommissioning) approach. This can be further broken down into the following LCA phases of development:
  • materials and construction (A1-A5);
  • operation and maintenance (B1-B5); and
  • decommissioning (C1-C4).
  1. As the Array is currently in its early stages of design, data relating to specific metrics for site-specific design details including chosen design and manufacturer of wind turbines and OSPs are currently unavailable.
  2. Therefore, emissions resulting from the manufacturing and construction of the wind turbines, cabling, OSPs and associated Array infrastructure have been calculated via the application of material or fuel emission factors to approximate material or fuel quantities, and published LCA literature. Key sources relied upon for the assessment are as follows:
  • Environmental Product Declaration Power transformer TrafoStar 500 Megavolt amperes (MVA) (ABB, 2003);
  • Inventory of Carbon and Energy (ICE) database (Jones and Hammond, 2019); and
  • UK Government GHG Conversion Factors for Company Reporting (DESNZ and Department for Environment, Food and Rural Affairs (DEFRA), 2023).
  1. Methodology specific to each element comprising the Array is detailed within section 5.2.

3.3. Blue Carbon

  1. The calculation of climate change effects for the Array considers the impact of temporary and permanent habitat loss and disturbance, affecting ‘blue carbon’ stocks within the baseline. The term ‘blue carbon’ refers to organic carbon that has been captured and stored through biological processes in the coastal and marine environment. Blue carbon can be stored within living biomass, root systems and sediments. Within the coastal and marine environment, there are a variety of habitat types that contribute to the global blue carbon stocks, including sediment habitats, such as those found in the climatic effects study area (Cunningham and Hunt, 2023).
  2. Where habitats are disturbed or lost through impacts from a development, this affects the habitat’s ability to store and sequester blue carbon. For example, when organic sediments are disturbed and enter the water column, stored blue carbon within these organic sediments can be converted to CO2 through a process called remineralisation (Cunningham and Hunt, 2023).
  3. Site-specific benthic survey data (see volume 3, appendix 8.1, annex A) and published emission factors have been used to calculate the extent of blue carbon stocks within the climatic effects study area. The resulting impact of the Array upon the blue carbon stocks has been calculated based on the total area of disturbance by the construction, operation and maintenance, and decommissioning of the Array, alongside published literature values for the overall effects of disturbance. Key sources relied upon for the assessment are as follows:
  • Scottish Blue Carbon – a literature review of the current evidence for Scotland’s blue carbon habitats. NatureScot Research Report 1326 (Cunningham and Hunt, 2023);
  • Re-Evaluating Scotland’s Sedimentary Carbon Stocks. Marine Scotland Science (Smeaton et al., 2020); and
  • Benthic and Subtidal Ecology Technical Report (volume 3, appendix 8.1).