3.1 Scottish Boundaries

The onshore transmission network in Scotland is owned by SHE Transmission and SP Transmission. 

The Scottish NETS is divided into 7 boundaries – 

  • B0 – Upper North SHE Transmission
  • B1a – North West SHE Transmission
  • B2 – North to South SHE Transmission
  • B3b – Kintyre and Argyll SHE Transmission
  • B4 – SHE Transmission to SP Transmission boundary (shared by SHE Transmission and SP Transmission)
  • B5 – North to South SP Transmission
  • B6 – SP Transmission to NGET (shared by SP Transmission and National Grid Electricity Transmission)

The figure below shows the general pattern of power flow directions expected to occur most of the time in the years to come up to 2030, i.e. power will generally flow from north to south. 

 

The arrows in the diagram illustrate power flow directions and are approximately scaled relative to the winter peak flows.

Regional drivers 

Scotland is experiencing large growth in renewable generation capacity, often in areas where the electricity network is limited. 

Over the next 10 years, Scotland is going to be experiencing a rapid growth in renewable generation capacity, mainly wind. This is going to increase the network reinforcement needs in some areas.

Across all the scenarios in the FES, the fossil fuel generation capacity in Scotland reaches nearly zero. By 2030, all scenarios show an increase in interconnector and storage capacities. By 2035, the scenarios suggest a total Scottish generating capacity of between 18 and 38GW. 

The reduction in synchronous generation could lead to challenges with reduced short circuit levels and inertia. This potentially leads to increasingly dynamic Scottish network behaviour depending on factors such as weather conditions and price of electricity.

With gross demand in Scotland not expected to exceed 6GW by 2040, which is much less than the Scottish generation capacity, Scotland will be expected to export power into England most of the time. 

At times of low renewable output, Scotland may need to import power from England. In a highly decentralised scenario like Leading the Way, local generation capacity connected at the distribution level in the Scotland region could reach more than 13GW by 2040. 

Of that capacity, the total embedded generation output will average at around 7GW. This will vary depending on factors like wind speeds, and how other local generators decide to participate in the market.

The anticipated increase in renewable generation in Scotland is increasing power transfer across the Scottish boundaries. On a local basis, with the anticipated generation development in the north of Scotland, including generation developments on the Western Isles, Orkney and the Shetland Islands, there may be limitations on power transfer from generation in the remote Scottish NETS locations to the main transmission routes (B0, B1a). 

As generation within these areas increases over time, due to the high volume of new renewable generation seeking connection, boundary transfers across the Scottish NETS boundaries (B0, B1a, B2, B3b, B4 and B5 and B6) increase. 

The need for network reinforcement to address the above-mentioned potential capability issues will be evaluated in the NOA 2020/21 CBA. Following the evaluation, the preferred reinforcements for the Scotland region will be recommended.
 

Boundary Regions

Click on the regions below to expand the boundary and understand its capability and challenges.

If you would like to learn how to interpret the graphs, click the button below.

Interpreting boundary graphs

The graphs show a distribution of power flow for each scenario, in addition to the boundary power transfer capability and NETS SQSS requirements for the next twenty years. 

Each scenario has different generation and demand so produces different boundary power flow expectations. 

From applying the methodology in the NETS SQSS for wider boundary planning requirements (as discussed in section 2), we determine: 

  • the economy criteria - solid coloured line
  • security criteria - dashed coloured line
  • current boundary capability – solid black line

The current boundary capability is expected boundary capability for the coming 2020/21 year’s winter peak study. This will change over time as the network, generation, and demand change, all of which are uncertain and so a straight back line shows the present capability.

The calculations of the annual boundary flow are based on unconstrained market operation, meaning network restrictions are not applied. This way, the minimum cost generation output profile can be found. 
We can see where the expected future growing needs could be by looking at the free market power flows in comparison with boundary capability.

Using the B6 boundary charts as an example below, there are four charts – one for each of the scenarios in the FES.

On each graph, the two shaded areas provide confidence as to what the power flows would be across each boundary:

  • the darker region shows – 50% of the annual power flow or the 75th percentile in the range of power flows
  • the lighter region shows – 90% of the annual power flows or the 95th percentile in the range of power flows

From the regions, we can show how often the power flows expected in the region split by the boundary are within its capability (black line). 

If the capability of the boundary is lower than the two regions over the next 20 years, there might be a need for reinforcements to increase the capability. 

However, if the line is above the shaded regions, it shows that there should be sufficient capability here and that potentially no reinforcements are needed from a free market power flow perspective until the shaded regions exceed the capability (black line).

Close panel
Boundary B0 – Upper North SHE Transmission

 

 

Boundary B0 separates the area north of Beauly, comprising the north of the Highlands, Caithness, Sutherland and Orkney. 

Boundary flows and base capability

The current boundary capability is limited to around 1.0GW due to a thermal constraint

The power transfer through B0 is increasing due to the substantial growth of renewable generation north of the boundary. This generation is primarily centred around both onshore and offshore wind. There is also the prospect of new marine generation resource in the Pentland Firth and Orkney waters in the longer term. 

Boundary B1a – North West SHE Transmission

 

Boundary B1a runs from the Moray coast near Macduff to the west coast near Oban, separating the north west of Scotland from the southern and eastern regions.

Boundary flows and base capability

The boundary capability is currently limited to around 2.5GW due to a thermal constraint

New renewable generation connections north of the boundary are expected to result in a significant increase in export requirements across the boundary. All generation north of boundary B0 also lies behind boundary B1a. 

In all the future energy scenarios, there is an increase in the power transfer through B1a due to the large volume of renewable generation connecting to the north of this boundary. Although this is primarily onshore wind and hydro, there is the prospect of significant additional wind, wave and tidal generation resources being connected in the longer term.

Contracted generation behind boundary B1a includes the renewable generation on the Western Isles, Orkney and the Shetland Isles with a considerable volume of large and small onshore wind developments. 

A large new pump storage generator is also planned in the Fort Augustus area. Some marine generation is also expected to connect in this region during the ETYS period. This is supplemented by existing generation, which comprises around 800MW of hydro and 300MW of pumped storage at Foyers.

 

Boundary B2 – North to South SHE Transmission

 

Boundary B2 cuts across the Scottish mainland from the east coast between Aberdeen and Dundee to near Oban on the west coast. As a result, it crosses all the main north-south transmission routes from the north of Scotland

Boundary flows and base capability

 

The boundary capability is currently limited to around 2.8GW due to a thermal constraint.

The potential future boundary transfers for boundary B2 are increasing at a significant rate because of the high volume of renewable generation to be connected to the north of the boundary.

The increase in the required transfer capability for this boundary across all generation scenarios indicates the strong potential need to reinforce the transmission system.

The generation behind boundary B2 includes both onshore and offshore wind, with the prospect of significant marine generation resource being connected in the longer term.

There is also the potential for additional pumped storage plant to be located in the Fort Augustus area. The thermal generation at Peterhead lies between boundaries B1a and B2, as do several offshore windfarms and the proposed future North Connect interconnector with Norway.

 

Boundary B3b - Kintyre and Argyll SHE Transmission

Boundary B3b encompasses the Argyll and Kintyre peninsula, and boundary assessments are used to show limitations on the generation power flow out of the peninsula

Boundary flows and base capability

The current boundary capability is limited to around 0.43GW due to a thermal constraint

The generation within boundary B3b includes both onshore wind and hydro generation, with the prospect of further wind generation resource and the potential for marine generation being connected in B3b in the future, triggering the requirement for future reinforcement of this network.

B3b is not currently subject to NOA reinforcement options as current contracted enabling works for customer connections will increase the ability to export power from this region, effectively splitting the network in the South West and altering the boundary.

Boundary B4 – SHE Transmission to SP Transmission

Boundary B4 separates the transmission network at the SP Transmission and SHE Transmission interface running from the Firth of Tay in the east to the north of the Isle of Arran in the west.

B4 cuts across two 275kV double circuits, two 132kV double circuits, two 275/132kV auto-transformer circuits, two 220kV subsea cables between Crossaig and Hunterston substations, and a double circuit with one circuit at 400kV and the other at 275kV

Boundary flows and base capability

The current boundary capability is limited to around 3.2GW due to a thermal constraint.

With increasing generation and potential interconnectors in the SHE Transmission area for all scenarios, the required transfer across boundary B4 is expected to increase significantly over the ETYS period. The prospective generation behind boundary B4 includes around 2.7GW from Rounds 1–3 and Scottish territorial waters offshore wind located off the coast of Scotland.

In all scenarios in the FES, the power transfer through boundary B4 increases because of the significant volumes of generation connecting north of the boundary, including all generation above boundaries B0, B1a, B2 and B3b. This is primarily onshore and offshore wind generation, with the prospect of significant further offshore wind and new marine generation resource being connected in the longer term.

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Boundary B5 – North to South SP Transmission

 

Boundary B5 is internal to the SP Transmission system and runs from the Firth of Clyde in the west to the Firth of Forth in the east.

B5 cuts across three 275kV double circuits and a double circuit with one circuit at 400kV and the other at 275kV. The Kintyre–Hunterston subsea link provides two additional circuits crossing B5

Boundary flows and base capability

The current boundary capability is limited to around 3.7GW due to both thermal and voltage constraints.

The generating station at Cruachan, together with the demand groups served from Windyhill, Lambhill, Bonnybridge, Mossmorran and Westfield 275kV substations are located to the north of boundary B5. 

In all the scenarios in the FES, the power transfer through boundary B5 increases because of the significant volumes of generation connecting north of the boundary, including all generation above boundaries B0, B1a, B2 and B4.

This is primarily onshore and offshore wind generation.

 

Boundary B6 – SP Transmission to NGET

Scotland contains significantly more installed generation capacity than demand, increasingly from wind farms. Peak power flow requirements are typically from north to south at times of high renewable generation output.

Boundary flows and base capability

The boundary capability remains at 5.7GW with the limit being the post-fault load rating of transformers at Harker.

Across all FES, there is an increase in the power transfer requirements from Scotland to England due to the connection of additional generation in Scotland, primarily onshore and offshore wind. This generation increase is partially offset by the expected closure of nuclear plants, the timing of which varies in each scenario.

With the FES including many wind farms in Scotland, the spread of boundary power flows is very wide due to the intermittent nature of the wind. With low generation output in Scotland, it is credible to have power flowing from south to north feeding Scottish demand. The magnitude of the south to north power flows is low compared to those in the opposite direction so network capability should be sufficient to support those conditions.

While the south to north transfer capability is enough to meet demand in Scotland, it is still necessary for conventional synchronous generation to remain in service in Scotland to maintain year-round secure system operation.