Offshore wind energy - draft sectoral marine plan: sustainability appraisal

The sustainability appraisal considers the potential environmental, social and economic effects of the sectoral marine plan, including potential development scenarios and alternatives to them, drawing on information contained in the SEA, HRA and SEIA.

3 Approach to the Sustainability Appraisal

3.1 Introduction

3.1.1 The following sections set out a brief overview of the processes used in the SEA and SEIA. Full details are provided in the SEA ER[76] and SEIA.[77]

3.1.2 In addition to the SEA and SEIA processes described below, a Habitats Regulation Assessment has been undertaken, to establish the potential likely significant effects of development under the plan on Natura 2000 designated sites. The approach applied for the HRA is presented in detail in Appendix B of the HRA report.

3.2 Development of Alternatives / Scenarios

3.2.1 The DPOs for offshore wind identify potential broad locations within which future arrays might be located. However, in order to provide a sufficient basis to carry out assessment, it is necessary to make assumptions about the potential scale (potential installed capacity), nature (the types of technologies) and timing of possible development within these DPOs. Possible socio-economic impacts associated with array export cables, also need to be taken into account where practicable.

3.2.2 Given the inherent uncertainty in seeking to predict the scale and timing of development, a number of scenarios were developed, primarily relating to different possible scales of development within the DPOs, so that these uncertainties could be explored. The impacts of these scenarios were then compared against the 'do nothing' option in seeking to estimate the potential positive and negative impacts associated with offshore wind development within the DPOs.

Developing Scenarios relating to the Potential Scale of Future Development

3.2.3 At a UK level, at the start of 2019 there were 7.9 gigawatts (GW) installed offshore wind capacity and around 23.9 GW of additional offshore wind with formal rights (at various stages of planning, consenting or construction).

3.2.4 Scotland currently has five operational offshore wind sites with a total capacity of over 900 MW: the Beatrice offshore wind farm (588MW) (from mid-2019), the Hywind Scotland Pilot Park project (30 MW capacity), Robin Rigg (174 MW capacity), Levenmouth Demonstration Turbine (one 7 MW turbine) and, the European Offshore Wind Deployment Centre deployed 11 turbines, with a total capacity of 93 MW.

3.2.5 Within Scottish Territorial Waters there are currently plans to install up to a further 1.2 GW capacity of offshore wind in two further short-term option sites Inch Cape and Neart na Gaoithe), together with up to 4.8 GW capacity within two Round 3 sites in offshore waters - Moray Firth (1.9 GW) and Firth of Forth (2.9 GW).

3.2.6 There are currently few long-term projections for potential future offshore wind development for the period covered by the Draft Plan (up to 2050).

3.2.7 Key indications of potential future UK offshore wind capacity requirements include:

  • Offshore Wind Industry Council Sector Deal[78]: aiming for 30 GW UK installed capacity by 2030.
  • Committee on Climate Change 2018 Progress Report to Parliament[79]: considered scenarios of 28-34 GW UK offshore wind installed capacity by 2030.
  • National Grid Future Energy Scenarios[80]: estimated between 26-53 GW UK offshore wind installed capacity by 2050 in four different energy scenarios. These scenarios seek to take account of factors such as the electrification of transport and the potential role of interconnectors and electricity storage capacity.
  • The UK passed legislation in June 2019 committing it to net zero greenhouse gas emissions by 2050[81], and the Scottish Parliament passed the Climate Change (Emissions Reductions Target) Act on 31 October 2019, committing Scotland to becoming a net-zero society by 2045;
  • In August 2019, The Crown Estate announced further leasing for 2017 project extension applications totalling 2.85 GW.[82]
  • In October 2019, The Crown Estate initiated Round 4 leasing with a proposed installed capacity of at least 7 GW in English and Welsh waters.[83]
  • European Wind Energy Association[84]: indicated that UK installed capacity could be as high as 55 GW by 2030 under a high scenario, assuming 98 GW of offshore wind in the North Sea. Discussions in the North Sea Energy Forum have also indicated interest in exploring options for up to 200 GW installed capacity in the North Sea by 2050, although this would be dependent on the establishment of a North Sea grid.

3.2.8 By 2035, National Grid scenarios suggest a total Scottish generating capacity of between 13 and 25 GW, primarily from renewables. This potentially leads to increasingly dynamic Scottish network behaviour depending on factors such as weather condition and price of electricity. With demand in Scotland not expected to exceed 5.7 GW by 2040, which is much less than the Scottish generation capacity, Scotland will be expected to export power into England. At times of low renewable output, however, Scotland may need to import power from England.[85]

3.2.9 The future requirement for and contribution of offshore wind to UK supply will depend inter alia on cost competitiveness of offshore wind, UK Government policy in relation to other forms of electricity generation such as nuclear new build and community renewables, the development and cost-effectiveness of electricity storage capacity for intermittent sources of generation and the pace of electrification of transport.

3.2.10 In terms of progress towards national targets, The Committee on Climate Change[86] noted that Scotland is performing well in reducing greenhouse gas emissions compared to the rest of the UK, and met its annual legislated target for 2016. Overall, Scottish emissions are now 49% below 1990 levels, and Scotland is on course to outperform the interim emissions reduction target for at least a 56% reduction in actual emissions by 2020. The Scottish Government introduced the Climate Change (Emissions Reduction Targets) (Scotland) Bill to the Scottish Parliament in May 2018 following advice from the Committee on the definition and levels of the new targets. The Bill was passed in October 2019, committing Scotland to becoming a net-zero society by 2045.

3.2.11 In view of the significant planned expansion of renewables and the scope to further develop renewables opportunities, which would make Scotland a significant net exporter of renewable energy, the Committee on Climate Change[87] notes that the main challenges to Scotland achieving its long-term emission reduction targets relate to tackling emissions from agriculture and transport.

3.2.12 Investment in electricity infrastructure is crucial to realising Scotland's renewable energy potential, allowing power to flow from remote areas of high resource, where grid connections are often weak, to major centres of demand. This is particularly the case for the Highlands and Islands, where connection to the mainland grid network can be challenging.

3.2.13 Overall, the above evidence could indicate a clear potential requirement for new leasing of OWF at UK level of between 10-20 GW installed capacity by 2050 with a possibility of greater demand depending on progress with a North Sea grid. Some of this requirement will be met from further leasing offered by The Crown Estate for England, Wales and Northern Ireland waters, but there is also an opportunity for Scotland to contribute to meeting this demand.

3.2.14 Based on the above, three scenarios (termed 'Low Case', 'Medium Case' and 'High Case') have been developed for the purposes of this study relating to different scales of possible future offshore wind development within the DPOs at national level in the period 2020 to 2050 as follows (in terms of additional capacity beyond existing lease agreements):

  • Low Case: 3 GW installed capacity;
  • Medium Case: 5 GW installed capacity;
  • High Case: 10 GW installed capacity;

3.2.15 A recent review of the density of offshore wind turbine layouts for European offshore wind projects[88] indicated that densities were largely within the range 4.3-6.5 MW per km². This density is governed by the need to maximise harnessing of the wind resource without affecting the performance of adjacent turbines within an array. Assuming an average density of 5 MW per km² for future projects under the Plan and based on the combined area of the DPOs, the DPOs have a combined potential to accommodate over 70 GW installed capacity. This capacity is an order of magnitude greater than the likely demand under the Plan.

3.2.16 In order to carry out a realistic assessment of the potential environmental and social and economic impact of possible development under the Plan, consideration has been given both to possible scales of development within each DPO and possible scales of development at regional and national levels. These assumptions are set out in Table 2.

3.2.17 The assessment of the potential impacts of development within individual DPOs has assumed that development occurs at a 'maximum realistic level' (column 5 of Table 2) having regard to the overall capacity of the DPO and the anticipated overall scale of likely development under the Plan at regional and national levels.

3.2.18 At regional scale, it is unlikely that development will occur in every DPO in a region and some locations will be taken forward in preference to others. Table 2 therefore also includes assumed realistic regional scales of development under the scenarios. To quantify impacts at regional level the sum of the project-level impacts has been scaled back pro rata to the regional scenario totals. To quantify impacts at national level, further scaling back of the regional totals has been undertaken in line with the overall scale of likely development under the Plan at national level under each scenario.

3.2.19 For individual DPOs, in line with the broad parameters for the Plan, it has been assumed that the minimum scale of development within any DPO is 100 MW.

Table 2 Indicative Capacity and Occupancy of Draft Option Plan Areas

Region DPO Area
Potential installed capacity
Realistic maximum development scenario for DPO
Regional Low Scenario
Regional Medium Scenario
Regional High Scenario
East E1 3816 19.1 3
E2 1287 6.4 2
E3 474 2.4 1
Sub-total 5577 27.9 6 1 2 3
North East NE1 776 3.9 2
NE2 464 2.3 1
NE3 339 1.7 1
NE4 440 2.2 1
NE5 496 2.5 1
NE6 699 3.5 2
NE7 1027 5.1 3
NE8 401 2.0 1
Sub-total 4641 23.2 12 1.5 3 4.5
North N1 1163 5.8 2
N2 560 2.8 2
N3 1106 5.5 2
N4 200 1.0 1
Sub-total 3030 15.1 7 1 2 3
West W1 1107 5.5 2
Sub-total 1107 5.5 2 0.5 1 2
South West SW1 292 1.5 1
Sub-total 292 1.5 1 0.3 0.6 1
Total 14646 73.2 28 4.3 8.6 13.5
Scaled back in national scenario to: 3 5 10

Developing an Indicative Programme

3.2.20 The timing of possible development within individual DPOs is particularly uncertain. The assumption has been that the Draft Plan will look to enable development within the period 2030 to 2050. Assuming Plan adoption in 2020, it is possible that consenting could be completed in some DPOs within 4 years with construction in these areas starting as early as the late 2020s, and for those schemes to become operational by the early 2030s. Whilst it is not possible to predict precisely when and where development may come forward, for the purposes of this assessment differing assumptions have been made at individual DPO, regional and national levels.

3.2.21 For the purposes of assessing the individual DPOs within the SEIA it has been assumed (as a worst-case assumption, and to allow different DPOs to be compared on the same terms) that construction will begin in 2028 with construction completing and operation starting in 2030.

3.2.22 The assumptions on the temporal sequencing of development at regional and national scales are summarised in Table 3 and Table 4. In these scenarios, the latest developments enter operation in 2042 in order that some element of operational cost is included in the assessment. The mitigation requirements in relation to DPOs NE2-6 and E1-3 (to address concerns regarding potential ornithological impacts) may result in development within these DPOs and regions being delayed. This delay has not been incorporated into the temporal assumptions, as this would have the effect of reducing the apparent negative economic impacts of those DPOs/regions over the assessment period. The potential delay in progression may move the impacts for some DPOs slightly later, but there is uncertainty around how long the mitigation will be in place.

Table 3 Temporal assumptions used in regional assessments

Region Scenario Total development in region
Development Size
Year entering operation
East Low 1 1 2030
Medium 2 1 2030
1 2035
High 3 1 2030
1 2035
1 2040
North East Low 1.5 1 2030
0.5 2035
Medium 3 1 2030
1 2035
1 2040
High 4.5 1.5 2030
1.5 2035
1.5 2040
North Low 1 0.5 2030
0.5 2035
Medium 2 1 2030
1 2035
High 3 1 2030
1 2035
1 2040
West Low 0.5 0.5 2030
Medium 1 1 2030
High 2 1 2030
1 2035
South West Low 0.3 0.3 2030
Medium 0.6 0.3 2030
0.3 2035
High 1 0.5 2030
0.5 2035

Table 4 Temporal assumptions used in national assessments

Region Scenario Total development in region
Development Size
Year entering operation
National Low 3 1 2030
1 2035
1 2040
Medium 5 1 2030
1 2033
1 2036
1 2039
1 2042
High 10 2 2030
2 2033
2 2036
2 2039
2 2042

3.3 SEA Approach

3.3.1 A considerable amount of work has already been undertaken to explore the potential wider environmental effects of activities associated with offshore wind development. Of particular relevance are the SEAs that were previously undertaken for the 2011[89] and 2013[90] Sectoral Marine Plans for Offshore Wind. The SEA builds upon the assessment methodology, information and findings of the respective Environmental Reports that were produced as part of these assessments. This is to help ensure consistency in the strategic assessment of offshore wind energy development in Scotland.

3.3.2 The latest evidence regarding environmental effects of offshore wind farm development and mitigation of effects from available research and monitoring results has also informed this assessment. These include outputs from the ScotMER (formerly SpORRAn) process and other research programmes, such as ORJIP and the DECC/BEIS Offshore Energy SEA.[91]

3.3.3 Other relevant sources of information include the SEAs that have been prepared to assess the designation and management of four MPAs[92], the designation of marine pSPAs[93], proposed fisheries management measures in MPAs and SACs[94], and Wild Seaweed Harvesting[95], as well as the ongoing SEA of the plan to improve protection given to Priority Marine Features (PMFs) outside the MPA network[96] and the SEA of the plan to designate a deep sea marine reserve in Scottish waters.[97]

3.3.4 The 'Sectoral Marine Plan for Offshore Wind Energy (Regional Locational Guidance (RLG))[98], provides a national baseline for each relevant marine sector included in the assessment in Section 2 of that report with Region specific information in Sections 3 to 7.

3.3.5 The SEA builds upon the baseline from the RLG and presents a high level and qualitative account of the type and potential magnitude of environmental effects that might be expected to arise from development under the Sectoral Marine Plan. The SEA also assessed the potential effects that could arise from the development scenarios that were developed as reasonable alternatives.

3.3.6 A summary of the scope of the assessment and associated potential effects is presented in Table 5.

Table 5 SEA topics scoped into the assessment

SEA Topic

Potential Effects

Biodiversity, Flora, and Fauna

  • Loss of and/or damage to marine and coastal habitats, including benthic and intertidal habitats (for example, due to smothering of benthic habitats and substratum loss);

  • Effects on key receptors and prey species, including disturbance, noise effects, EMF exposure, collision risk, habitat exclusion, and barriers to wildlife movement;

  • Positive effects arising from habitat enhancement, such as the creation of artificial reefs, new roosting structures and exclusion of habitat damaging activity;

  • Effects of pollution releases on both species and habitats; and

  • Effects from introduction and spread of Invasive Non-Native Species (INNS).

Population and Human Health

  • Effects arising from noise, vibration, light, dust and shadow flicker effects from all phases of development;

  • Effects on residential amenity stemming from construction/installation/operational activities;

  • Issues of navigational and aviation safety and collision risk; and

  • Effects on marine and coastal recreation and access

Soil (Marine Geology and Coastal Processes)

  • Effects on subsea geology, sediments, and coastal processes arising from changes in hydrodynamics and the existing wave regime.

Water Quality

  • Effects on ecological status;

  • Effects on water quality (for example, due to increases in suspended sediment loads and turbidity as well as an increase in pollution incidents); and

  • Effects of the presence of structures on local currents, wave regimes, and water column mixing, as well as secondary effects on sedimentation and erosion beyond the sites.

Climatic Factors

  • Contribution to supporting a diverse and decarbonised energy sector; and

  • Coastal facilities may be at risk from climate change.

Cultural Heritage

  • Loss of and/or damage to historic environment features and their settings, including coastal and marine archaeology and historic MPAs.


  • Both temporary and longer term effects on landscape and coastal character and visual receptors arising from the presence of structures including any ancillary infrastructure.

Reasonable alternatives

3.3.7 The development of the Draft Plan has been an iterative process that has been informed throughout by relevant environmental information and has given regular consideration to reasonable alternatives. These alternatives are confined to the consideration of alternative offshore wind opportunities, in line with the focus of the Draft Plan.

3.3.8 The initial Areas of Search scoping work identified prospective Areas of Search, in line with the objective of the plan to identify locations for potential future offshore wind development in the period up to 2050 in Scottish waters, through a consideration of multiple constraints that would restrict potential for sustainable offshore wind development or where offshore wind development would be likely to adversely affect the environment, other sectors or users of the sea. These initial AoS have been refined following consideration of feedback received through the initial consultation on the AoS, extended engagement with key stakeholders, preparation of the RLG, cross-sectoral steering group feedback and updated analysis resulting in the identification of 17 DPO areas in which offshore wind energy could potentially be sustainably pursued. Section 1.2 above describes how these areas were identified and where others were removed from the process.

3.3.9 An assessment of reasonable alternatives has been undertaken at each of the assessment stages described in detail in Section 3.6. The first stage of the assessment has involved setting out the potential environmental effects associated with a range of alternative offshore wind technologies that could be implemented in Scottish marine waters.

3.3.10 The second stage has been to apply the potential environmental effects identified in the first stage to spatial and locational constraints identified in the baseline data for each of the DPOs. The DPOs (see Figure 4) themselves constitute reasonable alternatives as they represent different options for fulfilling the objectives of the Draft Plan, based on varying levels of constraint and opportunity as described above.

3.3.11 The third stage in the assessment has been to determine the potential cumulative environmental effects associated with development in multiple DPOs at a regional and national scale. For the assessment of cumulative effects at regional and national scales, three scenarios, described above in Section 3.2, relating to different realistic scales of possible future offshore wind development within the DPOs, have been considered. These three scenarios give indicative low, medium and high development scenarios of installed capacity within the DPOs at regional and subsequently national scale. The SEA and SEIA use these scenarios to inform the assessment of a broad range of impact scenarios.

3.4 SEIA Approach

3.4.1 The methodology for the assessment of social and economic impacts has built on similar previous studies[99],[100],[101] and previous EIAs for offshore developments. It follows wider guidance on impact assessment including Scottish Government guidance on Business and Regulatory Impact Assessment[102] and HM Treasury's Green Book methodology.[103]

3.4.2 The methodology is set out in detail within the SEIA and covers:

  • Scenarios relating to future offshore wind development;
  • Defining relevant marine activities for inclusion in the assessment;
  • Establishing a baseline;
  • Scoping;
  • Detailed assessment methodology;
  • Assessing negative economic impacts to marine activities;
  • Assessing positive economic impacts to marine activities;
  • Assessing social impacts on individuals, communities and society;
  • Assessment of positive economic impacts; and
  • Approach to assessing combined impacts.

Collation and preparation of baseline information

3.4.3 To assess the potential social and economic impacts of potential offshore wind development on relevant marine activities, it is necessary to establish a baseline (counterfactual) for each sector affected, against which the potential impacts of the Plan can be assessed.

3.4.4 Baseline information is therefore required for each relevant marine activity including:

  • The current location, intensity and economic value of activity; and
  • How the location, intensity and economic value might change over time in the absence of the Plan.

3.4.5 The 'Sectoral Marine Plan for Offshore Wind Energy (Regional Locational Guidance (RLG))[104], provides a national baseline for each relevant marine sector included in the assessment in Section 2 of that report with Region specific information in Sections 3 to 7.

Quantification of Potential Impacts (Negative and Positive)

Assessing Negative Economic Impacts to Marine Activities

3.4.6 The assessment of negative economic impacts has been conducted for individual DPOs and at regional and national levels. Detailed methods for each sector are provided in Appendix E of the SEIA.

3.4.7 Analysis of interactions between offshore wind development and other marine activities is generally based on spatial analysis using geographical information system (GIS) tools to provide a quantitative estimate of the interaction.

3.4.8 Estimates of economic impacts are then made following different approaches, all based on the likely effect of key economic indicators of performance:

  • Where an interaction would result in a material reduction in the level of output from an activity, the economic impact is assessed in terms of a reduction in Gross Value Added (GVA) and employment;
  • Where an interaction would result in an increase in that activity's operating costs but would not result in a reduction in economic output from that activity, the impacts are expressed in terms of monetary impacts; and
  • Where an interaction might create investment uncertainty for an activity, such uncertainties are noted in the analysis but not quantified.

3.4.9 Where an interaction has the potential to affect economic output, resulting in impacts to GVA and employment, in line with Scottish Business and Regulatory Impact Assessment (BRIA) guidance[105], a distributional analysis of the economic impact has also been carried out. The outputs from this distributional analysis have been used to inform the assessment of social impacts. Further details on the methods used to assess impacts to GVA and employment and for the distributional analysis are provided in Appendix E of the SEIA.

3.4.10 The economic assessment has been undertaken for a time period of 40 years, starting in 2020 and finishing in 2059 to capture the main period of potential impacts and excluding repowering and decommissioning which could start to occur in the very final years. This ensures that the assessment covers the likely period of construction of deep water wind projects (expected from the late 2020s), with operation assumed in the scenarios to commence in the period 2030 to 2042).

3.4.11 In line with latest HM Treasury guidance, the standard 3.5% declining discount rate has been used for positive and negative impacts over the 40-year time period. The impacts of the offshore wind plan could extend to cover long-term, intergenerational effects so the reduced discount rate was applied as a sensitivity (this excludes the pure social time preference). The reduced rate starts at 3% for years 0-30, compared with 3.5% for the standard discount rate. This then declines to 2.57% (years 31-75) compared with 3.0% for the standard discount rate.

Assessing Positive Economic Impacts to Marine Activities

3.4.12 Positive impacts for the Scottish economy are calculated at both national and local authority level. The percentage local retention rates included in the scenarios are used as the basis for identifying what level of spend is retained in Scotland and what level would lead to impacts being felt elsewhere (outside Scotland). Since these percentages are reported on a regional scale, multipliers are applied to enable knock-on jobs and GVA to be estimated.

3.4.13 In addition, leakage from one region to another is an important consideration in the regional assessment, as well as leakage outside of Scotland for the national assessment. A sensitivity test has been undertaken to assess what the additional impacts might be if there is leakage from the West region to the North and North East regions, rather than if all leaked spend is invested outside of Scotland (e.g. England or Ireland). Consideration is also given to the impacts of substitution effects, where growth in the supply chain in response to investment in offshore wind could substitute for activity in other industry sectors due to capacity limitations (displacement from other sectors would count as a negative impact for the affected sector). This is reported based on the capacity of the supply chain to deliver the expected level of spend in each region individually and across Scotland as a whole.

3.4.14 BVG Associates (2019)[106] gives a breakdown of undiscounted capital and operational costs for a typical offshore wind farm, based on a 1 GW wind farm using 100 10 MW turbines located 60 km from shore in 20 m water depth. Development and project management is assumed to begin in 2022. This is used as the basis for estimating total spent along the supply chain. The total spend per activity are applied with the percentages assumed for local retention as the basis for estimating the GVA and jobs that could be generated associated with the scale and programme of future development. The levels of spend retained locally are combined with multipliers to give an estimate of the positive impacts in terms of GVA and jobs that could result from the level of spend (where this is assumed to give a measure of the change in output). However, the impacts will be derived for the Scottish economy as a whole on the basis of national multipliers.

3.4.15 National multipliers are available for Scotland. National multipliers detail the relationship between producers and consumers and the interdependencies of industries for a given year. They offer a picture of the flows of goods and services (products) in Scotland but they are only available for the onshore economy.[107]

3.4.16 Multipliers are assigned to the most relevant SIC codes for each of the activities given in the BVG (2019) report:

  • Development and project management: multipliers used for 71 (architectural services, etc.: includes other engineering activities such as 'design activities for the construction of civil engineering works');
  • Wind turbine supply: multipliers used for 28 (machinery and equipment);
  • Balance of plant: multipliers used for 41-43 (construction);
  • Installation and commissioning: multipliers used for 41-43 (construction); and
  • Operation, maintenance and service: multipliers used for 33 (repair and maintenance).

3.4.17 There are two types of multipliers available depending on the level and round of effects being calculated. Direct and indirect impacts are captured by Type I multipliers. Direct impacts relate to the specific sector, whereas indirect impacts relate to the businesses that supply that sector. Type II multipliers also include induced effects (the effect attributable to the ensuing change in compensation of employees which may cause further spending and hence further changes in final demand).

3.4.18 Multipliers are available for GVA and employment effects from the Scottish Government.[108] Multipliers for GVA effect reflect the direct and indirect (and induced if Type II multipliers are used) GVA changes to the direct output change, due to a unit increase in final use. Employment effect multipliers apply to changes in output, or GVA. Applying the GVA effect to the change in output (estimated as locally-retained spend) for each activity (development and project management, wind turbine supply, balance of plant, installation and commissioning, and operation, maintenance and service) is used to calculate the change in GVA for the economy as a whole. Similarly, applying the employment effect to the change in output (as £ million) enables an estimate to be made of the number of jobs affected (as full-time equivalents). The multipliers used in this study are given in Appendix C of the SEIA).

3.4.19 For further detail on the SEIA methodology see the full SEIA report.[109]



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