7. Security of Supply

7.1. Setting the scene

  1. Decarbonisation is just one of the three pillars of UK energy policy. Low carbon generation of all forms – nuclear, wind and solar included – brings with it new challenges. Current and future energy policy and related actions must also ensure that security of supply is maintained, and that electricity is affordable for all.
  2. Security of supply means keeping the lights on and has two main components. These are:
  • Ensuring that there is enough electricity generation capacity available to meet demand (adequacy); and
  • Ensuring that the quality of electricity supplied to customers falls within a narrow ‘quality’ band during all reasonably foreseeable operational circumstances, and is resilient during rare excursions from this band.
  1. Governments needs to ensure that sufficient electricity generating capacity is available to meet maximum peak demand, with a safety margin or spare capacity to accommodate unexpectedly high demand and to mitigate risks such as unexpected plant closures and extreme weather events. The BESS [108] was published by BEIS against this requirement following emerging concerns on the security of international hydrocarbon supplies and increasingly volatile international markets in early 2022. Key points from the BESS were introduced in Section 3-5 of this Statement of Need.
  2. In general, the larger the difference between available capacity and demand, the more resilient the system will be in dealing with unexpected events, and consequently the lower the risk of a supply interruption. A diverse mix of all types of power generation helps to ensure security of supply, however a low-cost, net zero consistent system is likely to be composed predominantly of wind and solar [29].
  3. The NETS is the integrated electricity transmission system for Great Britain. It connects all generators and consumers in Great Britain which means that currently an assessment of security of supply is relevant at the national level, rather than for Scotland as a standalone nation, although of course there are relevant considerations to be had at the local level in relation to how and where the Project will connect to the NETS.
  4. In this section, power systems and aspects of their operation will be briefly introduced. Challenges associated with integrating renewable generators into existing systems will be characterised, and key points on the contribution of offshore wind generation to system adequacy and system operation are presented. Specifically:
  • The Project will contribute significant capacities of low carbon generation to national system adequacy targets;
  • The diversification of the GB’s electricity supplies through the commissioning of offshore wind assets (such as the Project) to the NETS, alongside other low carbon generation technologies, provides benefits in the functioning of the NETS and ensuring power is available to consumers across the country when it is required, due to its requirement to operate within the stringent operability and control requirements of the Grid Code [89];
  • Technical advances in the field of power electronics and other measures are significantly increasing the utility of power generation assets in the provision of services and protections which support grid operation [90]; and
  • A program of grid investment and operational development by NGESO, regulated by Ofgem, is aiming for safe and secure operation of the NETS at zero carbon by 2025 [36] and for a fully decarbonised electricity system by 2035 [91]. The Holistic Network Design workstream, part of National Grid’s Offshore Transmission Network Review, is a critical step in the process National Grid are following to connect large capacities of offshore wind in an economic and efficient manner, the results of which have been incorporated into the 2022 NOA [115] and are discussed in Section 7.8 following.
  1. This section demonstrates how offshore wind has contributed, and will continue to contribute, to security of supply for GB consumers through being a dependable supply of low carbon power. The Project, if consented, would provide a significant and critical contribution to security of supply for the Scotland and for the wider GB. To provide appropriate context and understanding we set out in brief an introduction to a number of high-level concepts of power system operation.

7.2. Power system operation

  1. Power systems connect supply (sources of power, largely generators) to assets which demand power (industrial, commercial or domestic customers). Power systems are complex; yet they must be designed and operated safely, securely and economically.
  2. Governments define policy to ensure that there is sufficient generating capacity available to meet maximum expected demand. This is called adequacy.
  3. Key power quality characteristics (including frequency, voltage and power shape) must be controlled in order to maintain the synchronicity of all assets. NGESO define this topic area as system operability, specifically: "the ability to maintain system stability and all of the asset ratings and operational parameters within pre-defined limits safely, economically and sustainably” [92]. Protecting the safe operation of a power system when an asset operates outside of its normal expected parameters is also important, and individual transmission-connected generators, such as is planned at the Project, must synchronise to the national grid and maintain their own synchronicity with that system when they are operating.
  4. NGESO also ensure that power demand, or load, and power supply, remain balanced at all times. Balancing requires the right generating assets to be connected and disconnected to/from the right power levels, and at the right time. This can sometimes be at short notice, in response to emergent (fault) conditions. NGESO call those services which support NETS stability and operability are called Ancillary Services.
  5. The voltage level on the system is dependent on the type and quantity of generator and demand load connected to the system at the time. Over-volts occur when power demand is low, and load is too light. Voltage collapse occurs when load (particularly from heavy inductive machinery) is too high. Reactive power helps to maintain voltage levels, and its provision by generators is a mandatory service for transmission-connected generators.
  6. System frequency must also be maintained at the UK's operational frequency of 50 Hz. Unless generation is scheduled to match demand, when system load increases, system frequency dips; and when system load is lightened, frequency increases. Because demand fluctuates continuously through the day, frequency must be continuously managed, and generators must therefore provide frequency response (FR) services. Under FR, generator output is raised on receipt of a signal from the system operator of a falling frequency; and reduced on receipt of a signal from the system operator of a rising frequency. Due to the impact of FR on MW output, generators which are able to provide FR will usually determine the price they would accept to provide the service.
  7. If a sudden and unexpected disconnection of either demand or generation occurs, frequency may change rapidly. System inertia, a measure of the kinetic energy stored in rotating machines which are directly connected to the NETS, helps protect the system against rapid frequency changes. A system with high inertia is less likely to experience rapid system changes and will therefore be more stable, reducing the risk of faults escalating into wide-ranging effects on generators and customers [92]. System inertia is a phenomenon uniquely important to the NETS because of its relatively low levels of interconnection to other, larger, electricity systems such as is the case, in particular, across Europe.

7.3. Operating high-RES electricity transmission systems

  1. The integration of RES and their likely effect on GB's electricity transmission system has been studied for over thirty years. In a 1991 paper [93], M.J. Grubb foresaw that “proper management” of renewable generation assets must be carried out in order to maintain a stable electricity system. The electricity industry has progressively implemented new processes and technologies, and stable operation of electricity systems is being achieved with higher shares of renewable generation on an increasingly regular basis. For example, in both 2019 and 2020, Denmark sourced over 50% of its electricity needs from renewable generation [81, 80]. In GB, renewables’ share of electricity generation was 44% during 2020 [13]. These statistics demonstrate that high proportions of renewable generation can be accommodated within national electricity systems.
  2. The activities associated with integrating renewables into the GB electricity system will increase with their penetration [94]. Energy balance must be managed at all times; and as renewable capacity increases, more services will be required to regain supply / demand balance and retain system control, particularly when demand is either very high or very low.
  3. In order to maintain the quality of electricity supplies, it is critical to determine how important each ancillary service will become in a future energy system, and how capable the generation assets connected to that system will be in providing those services.
  4. Importantly, the dynamic behaviour characteristics for a high-RES system are well understood. For example, NGESO’s System Operability Framework (SOF) [92, 95, 96] describe these characteristics in relation to GB's electricity system.
  5. Technological advance, in particular the introduction of power electronics into generating assets, is increasing the ancillary services and system stability services available from users of the electricity system, for example, by improving an asset’s fast response to system frequency changes, and their ability to withstand periods of system instability without disconnecting.
  6. System stability services are already being provided by many existing and new technologies (e.g. batteries) and more recent advances have been made in the conversion of thermal and pumped storage assets into synchronous inertia providers.
  7. The installation of power electronics at low carbon generation assets enable them to provide important system stability services [90]. By reprogramming the digital power inverters attached to wind turbines, they can emulate the behaviour required by the System Operator. Offshore wind farms under development are well placed to incorporate power electronics into their designs, so as to be able to provide important stability services through their operational lives.

7.4. Connecting generators to electricity networks

  1. GB's electricity system operates at two levels: the high-voltage NETS, and the lower-voltage distribution networks. The NETS is mainly made up of 400kV, 275kV and 132kV assets connecting separately owned generators, interconnectors, large demands and distribution systems, and currently consists of approximately 4,500 miles of overhead line, 1,000 miles of underground cable and 350 substations. Applications for connection to the NETS are assessed through the first-come-first-served “Connect and Manage” process. A growing network of offshore transmission cables is also under development to bring the power generated by future offshore wind projects onshore and to consumers.
  2. Connect and Manage offers are given to those customers who request a connection date ahead of when any identified wider transmission reinforcement works can be completed. The connection agreements contain the requirement for derogation against the NETS Security and Quality of Supply Standards which, once approved, allows for a connection to be made ahead of those wider transmission reinforcement works.
  3. Wider transmission reinforcement works may be required to ensure that, once connected, electricity can flow from generators to where it is needed without constraint or hindrance. Generation connections close to demand centres (e.g. large cities or industrial areas) require the bulk transfer of power over shorter distances and therefore attract both capital and operational cost benefits when compared to generation connections far away from where the power is needed. However, with an ever-growing share of renewable generation capacity on the NETS, the bulk transfer of power over long distances remains vitally important, in order to keep lights on across the whole country when renewable generation output is high only in one area.
  4. Recommendations made by NGESO in their annual NOAs are intended, when delivered, to allow them to manage the future capability of the GB transmission network against an uncertain energy landscape over the coming decades In 2022, NGESO recommended £215M of investment across 94 asset-based projects to maintain the option to deliver projects costing almost £21.7bn – a significant increase in the previous NOA’s 25 asset-based projects costing an estimated £13.9bn [98]. Investments in 2022 would allow National Grid to manage the future capability of the GB transmission network against an energy landscape of significant decarbonisation over the coming decades [91, p6]. Investments are required to expand the transmission network to ensure that GB has a power system capable of delivering on its 2030 renewables ambitions and the UK’s broader net zero target. These costs will ultimately be recovered from consumer bills. As such it is in the interests of consumers to maximise the efficiency and effectiveness of existing and new transmission connections, and ensure value for money is secured for any wider reinforcement works which may be required as a result of new locations.
  5. Grid connection is an important aspect of generation project timescales and costs. The selection and utilisation of efficient grid connections in beneficial locations allows projects to come forwards at lower cost of generation and lower overall cost to consumers.

7.5. Centralised and decentralised generation

  1. Generation assets can be centralised (connecting to the NETS) or decentralised (connecting to the distribution networks).
  2. High voltage transmission systems enable the pooling of both generation and demand, by connecting together large-scale geographically diverse electricity generating facilities with widespread consumer locations. This in turn offers a number of economic and other benefits, such as more efficient bulk transfer of power and enabling surplus generation capacity in one area to be used to cover shortfalls elsewhere.
  3. Distribution networks were originally designed predominantly to transmit power from nodes on the NETS to consumers. By virtue of their role, many distribution networks are located in built up and heavily populated areas, and away from areas of large natural resource potential. They were not designed for the connection of significant electricity generation capacity, but the location of local energy solutions close to consumers allows for a tailoring of solutions to local need, and local and community participation in important schemes. The right facility in the right location may provide both economic and security of supply benefits to local communities, however geographical or technical constraints may arise if too much generation capacity connects to local networks. This may manifest in an upward pressure to both the cost of a distribution network connection agreement, and the period of time generators may have to wait until they are permitted to connect. This may materialise as significant cost, timing and complexity considerations for asset developers and may not always be good news for consumers who ultimately pay for the developments and the operation of the complex distribution systems which result.
  4. The Scottish Government's Local Energy Policy Statement [99] describes the greater role anticipated in Scotland for local energy solutions to meet local energy needs, given the shift away from power generated from centrally located fossil fuel plants and towards substantial increases in renewable generation. However the Scottish Government recognises that local energy cannot be delivered in isolation but must integrate and align with other key Scottish Government policies. Decentralised and community energy systems have important roles to play in achieving Net Zero but are unlikely to lead to significant replacement of larger-scale infrastructure.
  5. As decentralised generation grows, the replacement and growth of transmission connected assets is also foreseen. Although decentralised generation will contribute to meeting carbon emissions targets, increasing energy security and will lead to some reduction in demand on the main transmission system, decentralised generation is not foreseen to replace the need for new large-scale electricity infrastructure to meet UK energy objectives. The recent implicit market preference for decentralised generation connections should be understood in the context of GB’s national electricity system, with 74GW of generation currently connected to the transmission network and 34GW to the distribution network [107].
  6. In all 2022 FES scenarios, decentralisation of generation is expected to increase, driven by the growth in smaller scale renewable generators. Currently 31% of all generation capacity is connected to the distribution networks and FES scenarios project that by 2050, the proportion may develop to between 23% and 39% [107].
  7. Analysis of the FES 2022 scenarios [107] also shows that capacity connected to the distribution networks may grow at similar or higher levels than capacity connected to the transmission network (in 2050, between 2.7 and 4.3 times 2021’s decentralised generation capacity may be connected to distribution systems, while the multiplier for transmission-connected assets ranges between 3 and 3.2). However FES scenarios indicate a total of 202 – 239GW capacity installed at the transmission connected level by 2050 for scenarios which are compatible with Net Zero: almost twice the capacity of potential connections at the distribution level in the same timeframe.
  8. Distribution networks operate at a lower voltage than transmission networks, so generators which connect to these systems must have smaller capacities than those which connect to the NETS. As a consequence, in order to connect the same total generation capacity, more connections would be required at the distribution network level (at a potentially greater overall cost to consumers) than would be required directly into the NETS.
  9. National Grid's Embedded Register [85] lists all connected or contracted to connect large decentralised generation projects in Scotland. A total of 168 onshore wind projects are listed, with a total capacity of 2.9GW. 1.7GW is already connected (108 projects) and a further 60 projects totalling 1.2GW is currently contracted to connect. The average generation capacity of decentralised generators listed on the Embedded Register is 20MW. Over 200 decentralised Scottish wind farms would need to be connected to be equivalent to the capacity opportunity presented by the Project - a four-fold increase in the current pipeline of projects listed on the register. This number is a conservative estimate as offshore wind farms have higher load factors than onshore wind farms, therefore significantly more than 200 average decentralised onshore wind farms would be required to generate the same amount of low-carbon electricity each year as the Project.
  10. NGESO has publicly supported the connection of electricity generation technologies which provide a diverse energy mix to ensure that they can continue to manage supply and demand, for example [13, 100]. In conclusion, the need for distribution connected generation is in addition to, not instead of, the need for additional transmission connected generation; and therefore the development of distribution connected generation will not do away with the need for further transmission connected capacities. The UK-wide and Scottish need for large-scale low carbon generation capacity which will be met by the Project, cannot be met by multiple assets connecting to the distribution systems.

7.6. The characteristics of transmission network connections

  1. Large generators connect to transmission systems and smaller generators connect to distribution networks. Some of the most relevant differences between transmission- and distribution- connected generator characteristics are listed in Table 7‑1.
  2. Distribution-connected generators also contribute to meeting national demand, but because of the way they are connected, they effectively self-dispatch when they are available and offset national demand, thereby reducing the transmission demand level which transmission-connected assets must meet.

 

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Table 7‑1: Characteristics of transmission- and distribution-connected generators

[Author analysis]

 

  1. The connection level of an asset impacts the benefits it brings to bill payers. Four major considerations are:
  • Transmission connected assets provide visibility of their expected generation to the national energy market and NGESO as part of their licence to operate. This increases transparency in the market and allows sensible economic decisions to be made by all market players, including NGESO, in both planning and operational timescales to ensure that power demand and system security needs are met with the least possible cost;
  • Transmission connected assets are required to be available for instruction by NGESO. They are required to participate in the Balancing Mechanism, making their flexibility available (at a transparent and cost-reflective price) to ensure that supply and demand remain balanced at all times. By contrast, distribution assets are not required to do this, although voluntary balancing markets are currently under development for smaller assets at the distribution level;
  • While transmission systems have historically been designed to allow for the connection of large generating assets, distribution systems have not. Connecting generation assets of any meaningful size to distribution systems is becoming more difficult and more expensive;
  • The mandatory requirements for a generator to connect to the NETS include minimum requirements for fault protection as well as system ancillary services (e.g. Obligatory Reactive Power Services). Distribution connected assets have different fault protection requirements (which are harder to enforce) however access to system ancillary services is expected to grow into the future. Transmission-connected assets are therefore differentiated in that they are de-facto required to support system operation in many ways as part of their connection agreement.
  1. Decentralisation is not in itself a strategy nor a requirement of a low carbon energy system, but is a measure which will contribute to the delivery of a flexible, low carbon and affordable energy system. The CCC maintain that continued operation of the NETS remains an important policy to maintain inter-regional connectedness and supports the meeting of national demand from geographically disparate sources [5].
  2. Electricity consumers, either directly or indirectly, pick up costs through their energy bills related to market inefficiencies, economic decision making, asset investments, balancing actions and transmission and distribution system enhancements. Making best use of existing infrastructure and avoiding the need for expensive local network upgrades is also in the interests of the bill payer.
  3. The interaction of decentralised generation with the balancing of the transmission network is complex, which is one reason why it is important to maintain diversity of generation assets across technology choice, scale and connection voltage. The Project contributes to that diversity by replacing closing transmission-connected assets, while transparently conforming to Grid Code operability requirements.

7.7. Offshore wind contributes to system adequacy

  1. In 2013, Electricity Market Reform brought changes to the GB electricity market by introducing a CfD scheme, and a Capacity Market. The CfD scheme encourages assets to come forward by firming up the revenue for assets, thus improving its attractiveness for investors. By bringing more assets forward to commercial operation, system adequacy increases.
  2. Outside of the CfD scheme, system adequacy is primarily managed through the Capacity Market. In return for capacity payments, eligible assets agree to generate at or over a minimum commitment (their “de-rated capacity”) whenever NGESO (subject to a prescribed process) determine that additional generation output is required in order to meet demand.
  3. Wind and solar technology are now included within the Capacity Market [101] and onshore wind and solar were reintroduced to the CfD mechanism in time for the most recent Allocation Round 4. While the Capacity Market is not open to assets which already hold CfD contracts, the inclusion of renewable technologies in the Capacity Market underlines the contribution renewables can make to system security: “The system is typically better off with intermittent capacity than without it – wind farms, for example, can make a contribution to overall security of supply” [102]. Renewable assets also already participate in capacity mechanisms in other highly volatile electricity markets, such as Ireland’s Single Electricity Market, and in parts of the US.
  4. The contribution an asset class makes to overall security of supply can be assessed through its capacity utilisation. By measuring the capacity utilisation of a set of generating assets over a month, the variation in delivered generation from month-to-month as a proportion of total installed capacity, can be calculated. Stable and consistent capacity utilisation is important, because it relates to the reliability of, and therefore NGESO’s ability to depend on, forward forecasts of generation outturn.
  5. Figure 7‑1 displays this metric for 15 GB offshore wind farms which operated through two continuous years, aggregated at a monthly level. It shows that each wind farm has its own generation profile. The five wind farms with the greatest variation in monthly capacity utilisation over the two years are plotted with red lines; the five wind farms with the lowest variation are plotted with green lines and the remainder are plotted with amber lines. The aggregated fleet capacity utilisation is plotted in black.
  6. Aggregated fleet utilisation varies less from month to month than all but three of the individual wind farms, i.e. on average, the black line will not go as high, nor as low, as any of the individual yellow or red lines, and all but three of the green lines. A similar analysis can be carried out over daily, or even hourly tenors, arriving at similar results.

 

Figure 7-1:
Monthly UK offshore wind portfolio capacity utilisation.

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Figure 7‑1: Monthly UK offshore wind portfolio capacity utilisation.

[Author analysis]

 

  1. As GB's offshore wind fleet grows, so too will the stability of the capacity utilisation factor of the fleet versus the individual assets.
  2. At the macro level, a more stable capacity utilisation improves forecast accuracy and allows for a more targeted specification for and use of backup plant, improving system security without creating an excess of generation capacity. Although of course sensible margins will still need to be applied to cover uncommon events.
  3. An Imperial College expert economic analysis of whole system costs of renewables agrees: they show that the integration costs of RES fall on an absolute basis, as capacity increases from 10GW up to 50GW [103].
  4. The National Infrastructure Commission also commissioned a whole-system cost analysis, the results of which were published in 2020 [84]. NIC’s analysis complements that of the Imperial College team, suggesting that: "that there is no material cost impact, either over the short or long term, of deploying renewables faster. Renewables are now the cheapest form of electricity generation due to dramatic cost reductions in recent years.”
  5. Developing a generation portfolio with different renewable sources will also contribute to managing the generation dependability of intermittent generators on a national level. Excess generation may require curtailment and incur economic inefficiencies. and integration measures, including electricity storage, hydrogen and interconnection with other markets, are expected to be developed to capture energy during generation peaks and release it during generation troughs.
  6. Integration measures already available today help balance variable electricity generation onto the grid to meet variable demand. Integration measures also ensure that best use is made of low carbon electricity when it is being oversupplied, including developing other assets with complementary seasonal generation profiles; managing shorter-term intermittency through storage or other measures.
  7. In conclusion, offshore wind is an important asset class which is needed to deliver a required level of generation adequacy in low carbon networks. Although individual offshore wind farms are variable generators, the capacity utilisation of the technology class is more stable than the capacity utilisation of the majority of the individual assets, and this helps keep system operating costs in check.
  8. Increasing the capacity and geographical reach of GB offshore wind generation as the fleet expands to new areas of the Scottish, Welsh and English waters, will increasingly stabilise capacity utilisation. Integration measures will help operate the electricity system at times of very high or very low offshore wind output, and these are already being designed and deployed onto the NETS.

7.8. Network development facilitates offshore wind deployment

  1. The Electricity Ten Year Statement (ETYS) sits at the heart of NGESO's network planning process. It uses scenario inputs from NGESO's FES analyses for both demand and supply to identify points on the NETS where investment is required to expand the capability of the network to continue to deliver electricity reliably. NGESO is responsible for the operation of the transmission systems in Scotland, Wales and England, and offshore, and the ETYS therefore covers all relevant transmission networks. NGESO work with all relevant transmission network operators to develop the ETYS.
  2. The ETYS is produced annually, and the annual NOA process then identifies and assesses potential solutions to the network needs which have been identified in the ETYS. In 2022 the NOA was reissued, incorporating the impact of offshore coordination resulting from the Offshore Transmission Network Review’s Holistic Network Design workstream, the major outcomes of which are discussed further below.
  3. The ETYS is an important element in helping NGESO to achieve the UK ambition of being able to operate a zero-carbon electricity system across Great Britain by 2025: a critical milestone on the UK’s journey to Net Zero by 2050. The most recent ETYS was published in late 2021 [36].
  4. The transmission network is designed to provide enough capacity to send power from areas of generation to areas of demand however boundaries, which split areas of the national network into two parts, identify areas of the network which may encounter power flow limitations in the future depending on where, when and how much generation and consumption is anticipated in each area. The ETYS focusses on identifying critical boundaries such that mitigations can be made to improve reliability and cost performance of the national electricity system and for the benefit of all users.
  5. Figure 7‑2 shows areas of the NETS which are relevant to the Project and to which the Project will connect. The blue lines are 400kV transmission wires: the backbone of the NETS and the main network through which bulk power is transferred. Red lines are also important parts of the transmission network, these are 275kV wires which are more suitable in Scotland and in other densely populated areas of the UK. The green dashed lines represent the boundaries NGESO consider through the ETYS analysis.
  6. Four of the most important transmission boundaries in Scotland are B2, B4, B6 and B7, and the capability of these boundaries is the limiting factor (or enabler) for the flow of low carbon Scottish power south to consumers in England, Wales and Europe.
  • Boundary B2 North to South SSEN Transmission. The potential future boundary transfers for boundary B2 are increasing at a significant rate because of the high volume of renewable generation (including both offshore and onshore wind) to be connected above the boundary, driving an increase in flows from north to south to take low carbon electricity to consumption centres. Potential future connections include generation capacities sited in the N- and NE- Plan Option Areas identified in ScotWind Lease Round 1.
  • Boundary B4 SSEN Transmission to SP Transmission. The potential future boundary transfers for boundary B4 will include around 2.7GW from CfD Allocation Rounds 1-3 as well as offshore wind generation capacities proposed in the Scottish territorial waters located off the north, north-east and potentially east coast of Scotland which came forwards under ScotWind (N-, NE- and E- Plan Option Areas).
  • Boundary B6 SP Transmission to NGET divides the Scotland area from the North of England area. The anticipated growth of wind generation in Scotland will drive a wide range in boundary power flows over the B6 boundary. When wind generation is low, it will be credible for power to flow from south to north, feeding Scottish demand. This will become more frequent as Scotland's generation portfolio becomes more intermittent, i.e. after the closure of Torness nuclear power plant (and potentially Peterhead CCGT if CCS is not installed). South to north power will likely be low compared to north to south flows because of the significant wind resource potential in Scottish waters and on Scottish land, so boundary transfer capacity will be sized according to future renewable generation capacity in Scotland.
  1. The ETYS does not show Boundary B7 as constrained due (among other reasons) to the significant localised industrial demand in the Teesside area.
  2. Significant developments relating to the part of the network shown in Figure 7‑2 include the closure of Hunterston B nuclear power station (1.2GW) on the west coast of Scotland north of the B6 boundary in 2021/22; the anticipated closure of Hartlepool nuclear power station (1.2GW) near Teesside, between the B6 and B7 boundaries, in 2024; and the anticipated closure of Torness nuclear power station on the east coast of Scotland north of the B6 boundary in 2028.
  3. Westernlink HVDC (2.3GW) is a sub-sea cable which connects Hunterston to North Wales. Westernlink became fully operational in 2019 and increased B6 boundary transfer capacity by approximately 50% of its previous value.
  4. The 2021 ETYS reinforces two clear messages. Firstly, that growth in north-south power flows continues with high variability.
  5. With proposed renewable generation located primarily in the north, but demand (both UK and internationally through interconnectors) located primarily in the south, the network must be reinforced to be able to transfer without hindrance the significant amount of electricity generated to where it will be consumed. When wind output is low, flows will need to reverse to ensure that security of supply in Scotland is maintained despite low local generation.
  6. Secondly, the needs identified in the ETYS can and will be met through the timely delivery of network reinforcements described in the Network Options Assessment (NOA) [98]. The growth in government ambition for renewable generation has increased future ETYS boundary flow requirements. To reduce network constraints, the NOA recommended a number of options which, if implemented in line with the recommended schedule, will significantly reduce boundary flow constraints under all FES generation scenarios. The UK-wide integrated strategy of harnessing power from the winds above our seas and transmitting it to our homes and commercial and industrial properties, to be used for traditional purposes as well as displacing carbon-intensive fuels, is underway. The Project is entirely consistent with that strategy and if developed would provide a significant help to the UK and Scotland to meet their climate change aims.
  7. The reinforcement of the transmission system in Scotland and between Scotland and England has already begun, and continued strengthening is essential to deliver the targets set for renewable generation in the Scottish Energy Strategy and Scottish Offshore Wind Policy Statement. Transmission system reinforcement will also provide GB-wide benefits including supporting delivery of the Offshore Wind Sector Deal target of 40GW of offshore wind by 2030, and in so doing will facilitate Scotland and the wider UK in reaching their legally binding NDCs.
  8. The HND supports delivery of 2030 offshore wind ambitions and covers onshore and offshore network upgrade options to support the connection of up to 11GW of projects successful in the ScotWind leasing round with capacity located in each of the leasing zones, as well projects successful in TCE Offshore Wind Leasing Round 4.
  9. ScotWind lease areas are located to the east, north-east and north of Scotland, with one site to the west, as shown in Figure 3-5. All northern and north-eastern sites are located north of the B2 boundary, and the other sites are located north of the B4 boundary. Eastern sites, which are located north of the Proposed Development off Aberdeenshire, will connect above the B6 boundary and possibly above the B4 boundary, although precise grid connection points will need to be confirmed for projects when lease winners progress the design of their grid connection agreements with NGESO in due course.
  10. The NOA classifies options which are essential to facilitate the connection of 50GW of offshore wind in the UK by 2030 as “HND essential” options. Some of those options are shown in Figure 7-3 following.
  11. The HND confirms projects such as the Eastern HVDC Link (4GW in total across multiple stages) as key energy developments required to deliver the UK’s 2030 offshore wind target and ambition. All such projects will enable the safe and efficient transfer of electricity from where it is generated to where it is demanded, and will help to strengthen the local transmission networks through which the energy will flow.
  12. It is clear from Figure 7-3 that there is a greater requirement to reinforce onshore networks north of the B6 boundary in order to connect new projects than there is further south, implying that projects which connect further south have less associated enabling work and therefore potentially a lower delivery risk profile than northern projects.

 

Figure 7-2:
The National Electricity Transmission System in Scotland and north England

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Figure 7‑2: The National Electricity Transmission System in Scotland and north England

[36]

Figure 7-3:
Illustrative map of network upgrade options in North Scotland and Central Belt / Anglo Scottish Border areas

Figure 7‑3: Illustrative map of network upgrade options in North Scotland and Central Belt / Anglo Scottish Border areas

[115]

 

7.9. Network topography near the proposed location

  1. Offshore wind developments in Scotland are permitted only in zones which have been identified and allocated to potential developers by CES (historically: TCE). Offshore wind generation schemes can only be developed through the mechanism put in place by CES for leasing areas of the seabed in a structured and timely way.
  2. The proposed array area for the Proposed Development comprises the former Marr Bank Wind Farm and Berwick Bank Wind Farm proposals into one single opportunity.
  3. The Project includes two grid connection points. These are shown by the two teal circles with red borders on the UK east coast in Figure 7‑2.
  4. The first point is at Branxton near Torness in Scotland. The operating nuclear facility at Torness (1.2GW) requires that the grid system surrounding the area is incredibly robust, both in terms of reliability and transmission capacity. Torness nuclear power plant will close in 2028 (current operator forecast [74]) and connecting the Project near to Torness allows for the prolonged utilisation of transmission capacity which will be freed-up when Torness finally closes. It is in the interest of the consumer for new generation assets to connect to existing infrastructure rather than building new, where the existing infrastructure has useful commercial life.
  5. Torness is also the site chosen for the northern landfall of 2GW of the Eastern HVDC Link system. Eastern HVDC Link is proposed to start construction in 2024.
  6. The second connection point is near Blyth in England. As can be seen from Figure 7‑2, Blyth is near Hartlepool - the location of another nuclear power plant which is scheduled to close in 2024, also freeing up transmission network capacity when it does. Blyth also connects the UK to Norway through the North Sea Link, a 1.4GW subsea interconnector which commissioned in 2021. Although generally power flows from Norway to the UK (electricity is currently cheaper in Norway) at times of high wind, the export of power to Norway to be stored in their pumped storage hydro networks is an excellent example of international collaboration and whole-system thinking. The UK has exported power to Norway on frequent occasions during a very dry period for Norway in 2022.
  7. Critically, both the Project’s grid connection points are located south of the B2 and B4 boundaries, and the English grid connection point is also south of the B6 boundary. This reduces the impact that the Project will have on transmission system flows in Scotland, and any associated works required to reinforce the transmission system.
  8. The Project currently holds a Grid Connection Agreement for the Blyth connection which is effective from 2031.  This second connection was covered by the HND process and as such a coordinated solution was found to optimise connection routes and dates to support 2030 aims. ScotWind projects also covered by the HND also hold Grid Connection Agreements with similar effective dates.
  9. However as shown in Figure 7-3, significant onshore network development is required to facilitate offshore wind connections in the north of Scotland, while the onshore works directly required to connect the Project at Blyth are much smaller. Further, some of the enabling works which will facilitate the Project’s Blyth connection will also facilitate some ScotWind connections.
  10. Previous NOA have identified network strengthening needs further south in England, shown as black and purple lines in Figure 7-3. These upgrades will facilitate power flows through England and therefore will enable the connection of many projects around the country – including ScotWind projects and the Project.  The need for these upgrades is not necessarily to facilitate any one specific project alone.
  11. Diversity in grid connection points for the Project supports the operation of the transmission circuits in and around the local areas by providing multiple routes for power generated by the asset to flow to where it is needed. This also reduces costs associated with connecting and reinforcing single connection points to be able to transfer large power flows, and provides security in diversity should a fault cause one piece of transmission circuit to become unavailable. and minimising the possibility of full curtailment of the Project due to a grid constraint during periods of high wind.
  12. Section 6.3 makes the case that an acceleration in the development of feasible projects is needed to meet Scotland’s high Offshore Wind Capacity Target by 2030, covering planning, construction, financing and connection. Considering the topology of the existing transmission network it is likely that the acceleration of any connection works required for ScotWind projects will also enable an acceleration of the Project’s second connection point at Blyth.  This is because works required to deliver ScotWind projects early will also facilitate the early connection of Blyth.
  13. In the worst case therefore, it is likely that the Project would connect no later than the ScotWind projects which have been covered in the HND process. It may be more likely that the Project will deliver ahead of those projects – and other Scottish offshore wind projects – given its advanced stage of project development in comparison to other projects, and with fewer associated enabling connection works. In this regard, the Project presents the lowest risk option for Scotland to meet its 2030 targets and continue the important task of decarbonisation into the 2030s.
  14. Consenting and delivering the Project in full, will be a critical element of delivering offshore wind generation at the capacities needed to meet the Net Zero commitments while ensuring that the costs of the transmission system are managed. The Project will make a significant contribution to meeting the target capacity in the timeframe required and therefore should be considered as both necessary and urgent.

7.10. Conclusions on security of supply

  1. The Project will support UK electricity system adequacy and dependability.
  2. Section 7.7 showed an analysis of the capacity utilisation of offshore wind as a technology class, and Section 7.6 described the measures required of offshore wind to support system operability due to its connection to the NETS.
  3. Growth in offshore wind capacities, and other renewable technologies, is expected to improve the dependability of those assets as a combined portfolio, and this is expected to reduce further any integration costs associated with such growth.
  4. Connection to the transmission system is of significant importance, enabling an unencumbered and efficient transfer of bulk power across the country, in order to supply electricity whenever and wherever it is needed. The Project’s two separate points of connection are also beneficial from both system reinforcement and system operability cost perspectives.
  5. Connection of the second phase of the Project’s is currently scheduled for 2031. It is likely that the Project will in its worst (latest) case be connectable at the same as the leading ScotWind projects and therefore should be progressed as a low or no regret option.
  6. Global expertise in the operation of electricity systems with high proportions of RES is growing. Offshore wind assets are increasingly able to provide important system services themselves, and integration assets (such as batteries) are being deployed to do the same, as well as to manage short-term supply / demand volatility.
  7. Technologies which help the integration of renewable assets to the grid are being developed and are already in operation in GB.
  8. Consenting the Project, would contribute to an adequate and dependable Scottish and GB generation mix, through enabling the generation of more low carbon power from indigenous and renewable resources, and would enable the Project to make a significant contribution to Scottish and wider UK energy security and decarbonisation needs.