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 services are defined as:
Resolution of system technical constraints
Adjustment service whose aim is to resolve the technical constraints of the system, by limiting and modifying, as deemed necessary, the production schedules of the power stations o pumped storage generation that allow technical constraints identified to be resolved with the lowest cost for the system, and the subsequent rebalancing of generation and demand to offset schedule modifications incorporated to resolve the identified system technical constraints.
Balancing Services managed by markets mechanisms:
- Secondary regulation. An optional ancillary service whose purpose is to maintain the generation-demand balance, correcting automatically deviations with respect to the anticipated power exchange schedule of the ‘Spain’ Control Block, and the system frequency deviations. Its temporary action horizon ranges from 20 seconds to 15 minutes. This service is remunerated by means of market mechanisms via two concepts: availability (control band) and usage (energy). It is equivalent to the European product known as aFRR - automatic Frequency Restoration Reserves.
- Tertiary regulation. An optional ancillary service that, if subscribed to, is accompanied by the obligation to bid, and is managed and remunerated by means of market mechanisms. Its purpose is to resolve the deviations between generation and consumption and the restoration of the secondary control band reserve used. The tertiary control band reserve is defined as the maximum variation of power generation that a generation unit can perform within a maximum of 15 minutes, and which can be maintained for at least 2 hours. It is equivalent to the European product known as mFRR - manual Frequency Restoration Reserves.
- Deviation management. An optional service managed and remunerated by market mechanisms. The objective is to resolve the deviations between generation and demand which could appear in the period between the end of one intraday market and the beginning of the next intraday market horizon. It is equivalent to the European product known as RR - Replacement Reserves.
According to 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 internal electricity market, ancillary services’ management, currently confined to national level, will be managed by European platforms for each service in the coming years, according to the roadmap established in the Regulation.
The participation of facilities in the ancillary services market requires prior authorization by Red Eléctrica as System Operator, which in turn, requires the successful fulfilment of specially established tests for these purposes.
The test protocols are available on the balance responsible parties section on the e-sios website: https://www.esios.ree.es/en/balance-responsible-parties> Documentation> Help guides and documents> Technical notes.