Trading Across the Moyle Interconnector

General Information

The Moyle Interconnector is a High Voltage Direct Current (HVDC) connection between Northern Ireland and Scotland. It is made up of two 250MW cables and can operate in either direction, providing a total connection of 500MW between the all-Ireland Single Electricity Market and the GB market.

Since 1st October 2018, with the arrival of the new I-SEM market on the island of Ireland, the SEM and GB markets are coupled, meaning the physical interconnector flows are determined by the relative prices in the two connected markets.

Previously, long-term transmission rights were allocated in the form of Financial Transmission Rights (FTRs) which paid out the positive day-ahead price difference between the SEM and GB markets to holders. These arrangements were underpinned by the UK’s participation in the EU’s Single Day Ahead Coupling (“SDAC”).

Interconnectors to GB, including Moyle, are no longer able to participate in SDAC as of 1st January 2021, and therefore FTRs are not currently offered. Now Moyle interconnector capacity will be made solely available for allocation in two coupled intraday auctions between the SEM and GB. 

Market parties in the SEM may access these auctions via SEMOpx whilst GB market parties can access them via either the EPEX SPOT or Nord Pool power exchanges. More information on these coupled intraday auctions can be found on the SEMOpx website.

Moyle Capacity

While Moyle is technically able to transport 500MW between the two markets, due to constraints on the transmission networks at either end of the interconnector, the commercial capacity of the interconnector is lower than this.

The maximum available capacity in each direction varies throughout the year, and is given in the table below:

DirectionTime PeriodFirm capacity availableAdditional capacity potentially available from National GridMaximum capacity actually available due to SONI constraint
Northern Ireland to ScotlandUp to 30th November 2020
80 MW
420 MW400 MW
1st December 2020 to 30th September 2021250 MW250 MW400 MW
1st October 2021 – 31st March 2022270 MW205 MW400 MW
1st April 2022 to 30th July 2022475 MW0 MW400 MW
1st August 2022 onwards500 MW0 MW400 MW
Scotland to Northern Ireland1st April – 31st October450 MW
(May be reduced to 410 MW under certain system outage conditions)
1st November – 31st March450 MWN/AN/A

* this is ‘Commercially’ firm, physical firmness TBC

National Grid performs a daily capacity calculation which determines how much capacity can be made available in the NI to GB direction in addition to the prevailing firm capacity.

Further documentation detailing the rules underpinning capacity calculation and FTR allocation and compensation can be found on the Moyle Publications Page.

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