One of the characteristics of electrical energy is that it cannot be stored in large quantities. This means that, for the correct functioning of the electricity system, the amount of energy generated by the power stations must be exactly the same as that being consumed at the exact moment it is being demanded. In other words, a constant balance between generation and real-time demand must be maintained to avoid unbalances which could represent frequency deviations with regard to the nominal value of 50 Hz.
The role of Red Eléctrica, as system operator, consists on ensuring this balance in the Spanish electricity system.To this end, it produces the electricity demand forecasts, oversees the operation of the generation facilities and manages the transmission facilities in real-time, constantly ensuring that scheduled generation in power stations matches consumer demand. Should a difference arise between the two, it sends the appropriate instructions to the power stations to increase or reduce their electricity production is such a way that it ensures the safety margins necessary to face possible unexpected losses in generation or changes in scheduled consumption.
In the peninsular system, Red Eléctrica is also responsible for managing what is known as the ancillary services markets; markets which allow the generation schedules freely established by balance responsible parties in the day-ahead market and bilateral contracts, and subsequently in the intraday markets to be adjusted to the quality, reliability and security requirements of the electricity system. Ancillary services or the adjustment markets are understood as the means available for the resolution of technical constraints of the system, the allocation of ancillary services and the management of deviations.
In order to ensure the constant balance between generation and demand in real time in the non-peninsular systems of the Canary Islands, the Balearic Islands, Ceuta and Melilla, Red Eléctrica carries out an economic dispatch of the generation units.
Red Eléctrica prepares the annual power demand evolution forecasts, together with the relevant coverage, for the medium and long term. These forecasts are essential in order to draw up the transmission grid development plans for the upcoming years, which approved by the Ministry of Industry, Tourism and Trade.
As set out in current regulations, system operation ancillary services are defined as:
Solución de restricciones técnicas
Ancillary service whose aim is to resolve technical constraints of the system, by limiting and modifying, as deemed necessary, the production schedules of generation units and of pumped storage generation so that technical constraints identified can be resolved with the lowest cost for the system.
Balancing Services managed and remunerated through market mechanisms:
- Secondary control. An optional ancillary service whose purpose is to maintain the generation-demand balance, automatically correcting deviations with respect to the anticipated power exchange schedule of the ‘Spain’ Control Block and those frequency deviations that may occur in the system. Its temporary action horizon ranges from 20 seconds to 15 minutes. This service is remunerated through market mechanisms via two concepts: availability (control band) and net usage (energy). Secondary control energy is equivalent to the use of the European standard product known as automatic Frequency Restoration Reserves (aFRR).
- Tertiary control. An optional ancillary service that, if subscribed to, is binding in nature and is accompanied by the generators obligation to bid the active power capacity it can increase or decrease, taking into consideration the availability of the primary source of energy. This service is managed and remunerated through market mechanisms. Its purpose is to adjust control deviations between generation and consumption as well as restore the secondary control band reserve used. The tertiary control band reserve is defined as the maximum variation of active power generation that a production unit can perform within a maximum of 15 minutes. Tertiary control energy is equivalent to the use of the European standard product known as manual Frequency Restoration Reserves (mFRR).
- Balancing energy from Replacement Reserves (RR). Service that aims to address system imbalances between generation and consumption, and to restore or support the required level of frequency restoration reserve (secondary and tertiary control energy). It is a service of a voluntary nature, which requires manual activation in a maximum time of 30 minutes, and is remunerated through market mechanisms.
In accordance with the provisions of Commission Regulation (EU) 2017/2195 of 23 November 2017 establishing a guideline on electricity balancing and in order to contribute to the development of the European internal energy market, the management of balancing energy of type RR (European project TERRE) and the process for automatic imbalance netting between systems (European project IGCC) are already being carried out. It is foreseen that tertiary control (mFRR) and secondary control (aFRR) services are to be managed in the coming years through the new European balancing platforms planned for each of these services (European projects MARI and PICASSO), in accordance with the timetable set out in said Regulation.
Participation in balancing services requires prior authorization and certification by Red Eléctrica as system operator, a certification process that requires, among other things, having successfully passed the certification tests specifically established for this purpose.