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 its capacity as TSO, EirGrid has developed a set of definitions for Ancillary Services in Ireland, as well as a set of payment arrangements for each Ancillary Service in harmonisation with Northern Ireland. These arrangements are described in detail in the Harmonised AS Agreement (EirGrid Version).

The contracted Ancillary Services in Ireland are:

• 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 demand customers to reduce their electricity 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.

Ancillary Services are closely related to Other System Charges. These complement other commercial arrangement to incentivise optimum generator and power system performance. The arrangements for both are harmonised on an all-island basis.  Further information on Ancillary Services and Other System Charges is available within the AS & Other System Charges subsite.