Ancillary services: mechanisms that allow the balancing of the system

In order to guarantee the reliability and continuity of the electricity supply, the system operator has to start up the mechanisms that allow adjustments to be made to the system when deemed necessary.

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Red Eléctrica de España, in its role as operator of the Spanish electricity system, performs the necessary actions to ensure the security and continuity of the electricity supply and is responsible for the proper coordination of the electricity generation system and the transmission grid, ensuring that energy produced by the generators is transported to the distribution networks maintaining the required quality level set out in the regulations in force, and at the lowest possible cost for the consumer.

Following the result of the day-ahead market and the communication of the daily execution of bilateral contracts with physical delivery, and during the real-time operation as well, the system operator may identify situations when it considers it necessary to modify the generation schedules to ensure the quality and security of the electricity supply, and to maintain a constant balance between generation and demand.

In order to do this, Red Eléctrica de España uses the system’s ancillary services, managed through market mechanisms, which are basically divided into three groups according to the specific objectives they pursue:

  • Ancillary services aimed at helping guarantee the safety, quality and reliability conditions of the transmission grid elements: resolution of technical constraints processes.
  • Ancillary services aimed at ensuring the availability of the power reserves necessary to maintain the balance between generation and demand: Secondary control band allocation services and additional upward power reserve.
  • Ancillary services aimed at helping maintain system frequency and ensuring the permanent balance between generation and demand: Secondary control, tertiary control and deviation management services.

As of 11 February 2016, production from non-conventional renewable energy sources, such as wind power, solar and small hydroelectric plants, among others, as well as cogeneration and waste facilities, can participate in the system’s ancillary services markets on an optional basis. To do this, the facilities must first pass the qualification and suitability tests established for this purpose in the current regulations. One year later, almost 25% of installed wind power in the Spanish peninsular system has already been qualified and authorised to participate in the deviation management and tertiary control markets.

During 2016, a total of 21.4 TWh of electricity, representing 8.6% of the peninsular demand, was managed through the ancillary services markets. This and other information on ancillary services can be found in the ‘Ancillary Services. Preliminary Report 2016’ published by Red Eléctrica.