How the Market and Grid Interact

Explore the relationship between the electricity grid and the market.

The Electricity Grid and Market

All of us power our lives with electricity. EirGrid is responsible for the electricity grid and market in Ireland. The grid is an intricate system of cables that transports electricity from where it is generated to where it is used.

The electricity market is where generators and suppliers trade electricity. A lot of work happens behind the scenes to balance supply and demand. Market trading ensures that we have a safe and reliable electricity supply.

The Integrated Single Electricity Market (I-SEM)

Since 2018, the I-SEM is the wholesale electricity market for Ireland and Northern Ireland. It brings together these two markets into an all-island arrangement. The wholesale electricity market is where electricity is bought and sold before being delivered to consumers. Its two main participants are generators and suppliers.

It aims to deliver:

  • Security of supply across the island.
  • A competitive process for setting prices, including the use of capacity auctions.
  • Use the interconnectors more efficiently.
  • Maximise the use of renewable sources of electricity.

SEMO and SEMOpx make up parts of the electricity market. They are overseen by the SEM Committee, consisting of the Commission for the Regulation of Utilities (CRU) in Dublin, the Utility Regulator (UR) in Belfast, plus an independent member and a deputy independent member.

Role of SEMO

The Single Electricity Market Operator (SEMO) operates and administrates the Single Electricity Market. The Single Electricity Market consists of:

  • Two ex-ante energy markets: where market participants submit their bids and offers before the market closes.
  • A balancing market: balances real-time supply and demand for electricity.
  • Two markets for financial instruments: where participants can hedge against price fluctuations months or years before the energy is delivered.
  • A market for capacity remuneration: for generators and interconnectors who deliver energy into the grid.

These markets operate independently and on different timelines. See the SEMO website for more details on how each of these markets operate.

Role of SEMOpx

Single Electricity Market Operations (SEMOpx) operate the day-ahead and intraday electricity markets for Ireland and Northern Ireland. These are the two ex-ante markets for trading energy.

The day-ahead market is a daily auction. It closes the day before the energy is delivered. The intraday market is closer to real time, with three auctions every day.


Interconnectors with other countries also help our power system to run effectively. In the past, our geographical location was a challenge. It meant that electricity prices tended to be higher in the all-island market than in Great Britain.

We now have 2 interconnections in place with Great Britain. This allows us to share power across our networks. Electricity flowing more efficiently should help to lower prices. Energy flows between:

  • Ireland and Wales with the East West Interconnector.
  • Northern Ireland and Scotland with the Moyle Interconnector.

Interconnectors also allow us to support more renewable generation. Our Shaping Our Electricity Future section shows more about how we plan to leverage renewable energy. 

Future Interconnectors

The Moyle interconnector went into commercial operation in 2002, while EWIC was 2012.

We are currently working to deliver the Celtic Interconnector between France and Ireland. It is expected to be completed in 2026.

Work is also underway to build Greenlink, an subsea interconnector between Great Britain and Ireland which will allow power to flow in either direction. This is due to be completed in 2024. 

See our Interconnection page for more details.