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.
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:
|Direction||Time Period||Firm capacity available||Additional capacity potentially available from National Grid||Maximum capacity actually available due to SONI constraint|
|Northern Ireland to Scotland||Up to 30th November 2020|| 80 MW||420 MW||400 MW|
|1st December 2020 to 31st October 2021||250 MW||250 MW||400 MW|
|1st November 2021 to 31st March 2022||160 MW||340 MW||400 MW|
|1st April 2022 onwards||500 MW*||0 MW||400 MW|
|Scotland to Northern Ireland||1st April – 31st October||450 MW|
(May be reduced to 410 MW under certain system outage conditions)
|1st November – 31st March||450 MW||N/A||N/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.