About the Single Electricity Market (SEM)

The SEM is the wholesale electricity market for the island of Ireland. The SEM is designed to provide least cost electricity generation to meet customer demand across the island.

The SEM formed in 2007, when Ireland and Northern Ireland started trading electricity on an all-island basis. It is a joint venture between the transmission system operators in Ireland (EirGrid) and Northern Ireland (SONI).

The SEM is operated by the Single Electricity Market Operator (SEMO).


The SEM Committee is the decision-making body which governs the market. It is jointly regulated by the regulatory authorities in Ireland (CRU) and Northern Ireland (Utility Regulator).

The committee consists of:

  • three CRU representatives
  • three Utility Regulator representatives
  • one independent and a deputy independent member


The SEM was redesigned in 2018 to harmonise the all-island and European wholesale electricity markets. Since Brexit, there has been no direct physical connection between the SEM and the European electricity market, but the markets will become connected again once the Celtic Interconnector between Ireland and France is operational. The harmonisation of the two markets allows for free trade across borders without discrimination between internal and cross-border transactions.

The key benefits of SEM include:

  • a more competitive market
  • the promotion of security of supply
  • better investment signals for investors
  • maximising the use of renewables
  • making efficient use of existing infrastructure

SEM includes six markets or auctions.

  1. The day ahead market
  2. The intraday market
  3. The balancing market
  4. The capacity market
  5. The system services market
  6. A forwards market