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Ancillary Services

Ancillary Services

Ancillary Services are products, other than energy, that are required to ensure the secure operation of the transmission system.  Under the European Directive 96/92/EC (Article 7), the Transmission System Operator (TSO) is charged with "...ensuring a secure, reliable and efficient electricity system and, in that context, for ensuring the availability of all necessary ancillary services".

In our capacity as TSO, we have developed a set of definitions for Ancillary Services in Ireland, as well as a set of payment arrangements for each Ancillary Service.  These arrangements are described in detail in EirGrid's papers on Ancillary Services Payment Derivation and Ancillary Services Agreements.

The main ancillary services required and defined in Ireland are:

  • Operating Reserve: In the event of a loss of output from a generation unit or an unexpected change in system demand, it is essential to be in a position to make up the shortfall, either from generation units or other sources.  Arranging for customers to reduce their demand requirements can also provide reserve.  To cater for different situations that may arise on the transmission system, reserve is contracted over a variety of time scales.
  • Reactive Power: This is required to maintain voltage balance on the transmission system on a regional basis.  Both static and dynamic provision of reactive power is required.
  • Black Start: This is the ability of a generating set to start up and provide electricity to the transmission system without an external power supply.
  • Automatic Generation Control: This is a means of regulating frequency by controlling the output of selected generation units, through a centrally based closed loop control system.  While it is not routinely used in Ireland at this time, it may be introduced in the future. 
  • System Support Services: The term 'System Support' is used in Ireland to describe services or arrangements provided to the TSO that are of a specific nature, and are generally required in particular local areas.  Unlike Ancillary Services, they do not lend themselves to "system-wide" definitions or procurement.  Arrangements that might come under the general heading of System Support, include the ability of the TSO to exert additional control over the running or outage programme of a key generating station that is located in an area where it provides essential support to the transmission system. 

Ancillary Services are currently being harmonised between Northern Ireland and the Republic of Ireland. The TSOs have been tasked with developing proposals for the Harmonised All-Island arrangements.  The Ancillary Services Harmonisation project has been established to develop and implement arrangements in consultation with the industry and the regulatory authorities. Details of the project and of the current proposals can be found in the Ancillary Services - All-Island Harmonisation Project section.