The graphs show a distribution of power flows for each of our Future Energy Scenarios, 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 chapter 2), we determine for each scenario:

• The economy criteria - solid coloured line

• Security criteria - dashed coloured line

• Current boundary capability – solid black line

Due to the NOA being published after the ETYS, the boundary capability line (red line) is prepared from the 2020/21 (previous year’s) NOA optimal path released in January 2021 which uses the 2020/21 FES and ETYS data. This is the best information available at the time of publication and will change annually and over time as the network, generation, demand and more importantly the NOA optimal path changes. More information about the NOA methodology can be found here. The 50%, 90%, Economy RT and Security RT are calculated from the 2021/22 FES and ETYS processes. Where the NOA transfer capability is not available, there is a black line that provides the current ETYS 2021/22 transfer capability​.

Note: Boundary capability line is affected by the generation and demand profiles within each FES background. Therefore, the graphs are provided for indicative purposes only and cannot be directly compared. ​

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 power flows in comparison with boundary capability.​

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 flows

• The lighter region shows 90% of the annual 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 (red 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 (red line).

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

Boundary flows and base capability

The capability line (in red) is based on the recommendations from the NOA 2021/22 optimal path which uses the 2021 FES and ETYS data as inputs. The 50%, 90% Economy RT and Security RT lines are based on FES 2021. The ETYS and NOA methodologies for this boundary are different and can result in different transfer capabilities.

The current boundary capability is limited to 1.15GW due to a thermal constraint on the Beauly - Shin 132kV circuit.

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 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 capability line (in red) is based on the recommendations from the NOA 2021/22 optimal path which uses the 2021 FES and ETYS data as inputs. The 50%, 90% Economy RT and Security RT lines are based on FES 2021. The ETYS and NOA methodologies for this boundary are different and can result in different transfer capabilities.

The current boundary capability is limited to 1.85GW due to a thermal constraint on the Errocthy - Killin 132kV circuit.

New renewable generation connections north of the boundary are expected to result in a significant increase in export requirements across the boundary, especially along the Beauly – Denny circuit. 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.​

Boundary B2 cuts across the Scottish mainland from the east coast between Aberdeen and Dundee to near Oban on the west coast crossing the main north-south routes from the north of Scotland.

Boundary flows and base capability

The capability line (in red) is based on the recommendations from the NOA 2021/22 optimal path which uses the 2021 FES and ETYS data as inputs. The 50%, 90% Economy RT and Security RT lines are based on FES 2021. The ETYS and NOA methodologies for this boundary are different and can result in different transfer capabilities.

The current boundary capability is currently limited to 2.6GW due to a thermal constraint on the Fetteresso - Kincardine 275kV circuit.

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. This increased generation capacity will drive increasing power flows down the east coast 275kV circuits.​

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 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 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 0.45GW due to a thermal constraint on the Inveraray - Sloy 132kV circuit.

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 separates the transmission network at the SP Transmission and SSEN 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

TThe capability line (in red) is based on the recommendations from the NOA 2021/22 optimal path which uses the 2021 FES and ETYS data as inputs. The 50%, 90% Economy RT and Security RT lines are based on FES 2021. The ETYS and NOA methodologies for this boundary are different and can result in different transfer capabilities.

The current boundary capability is limited to 3.2GW due to a thermal constraint on the Westfield - Longannet 275kV circuit.

With increasing generation and potential interconnectors in the SSEN 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.​

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.

Boundary flows and base capability

The capability line (in red) is based on the recommendations from the NOA 2021/22 optimal path which uses the 2021 FES and ETYS data as inputs. The 50%, 90% Economy RT and Security RT lines are based on FES 2021. The ETYS and NOA methodologies for this boundary are different and can result in different transfer capabilities.

The current boundary capability is limited to 3.6GW due to both thermal and voltage constraints on the Kincardine - Tealing 275kV circuit.

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 separates the transmission network at the SP Transmission and National Grid Transmission interface running roughly along the border between Scotland and England.

Boundary flows and base capability

TThe capability line (in red) is based on the recommendations from the NOA 2021/22 optimal path which uses the 2021 FES and ETYS data as inputs. The 50%, 90% Economy RT and Security RT lines are based on FES 2021. The ETYS and NOA methodologies for this boundary are different and can result in different transfer capabilities.

The current boundary capability is limited to 6.1GW due to a thermal constraint on an SGT at Harker substation.

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.​

With the FES including many wind farms in Scotland, the spread of boundary power flows is very wide due to the intermittent nature of wind. With low generation output in Scotland, it is credible to have power flowing from south to north feeding Scottish demand, particularly on closure of the remaining nuclear plants north of the boundary. The magnitude of the south to north power flows is low compared to those in the opposite direction so network capability is 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 plant to remain in service in Scotland to maintain year-round secure system operation.​