Power system reserves

There are five types of reserve products in the power system, each serving different purposes. These reserve products are designed to work together to meet various needs of the power system, and therefore, they have different technical requirements and are activated in different ways. 

The reserve products maintained by Fingrid are categorized into three groups based on their purposes: 

1. Frequency Containment Reserves (for Normal operation and Disturbances) are used for continuous automatic frequency control. 

1. Frequency Restoration Reserves aim to restore the frequency to the normal range (49.9–50.1 Hz) and release the activated Frequency Containment Reserves back to readiness. These reserves are also used for predictive balancing of electricity production and consumption based on forecasts. 

1. Fast Frequency Reserve is used for frequency control in low inertia situations, in addition to Frequency Containment Reserves. 

Purposes of different reserve products: 

The operating principles of different reserve products vary to serve their intended purposes specifically. Reserves can be classified into different categories based on their activation speeds, activation methods, and control directions. 

The activation speed can vary depending on the reserve product, ranging from about a second to fifteen minutes. 

The activation of the reserve can be based on frequency measurement, activation signal, or activation request. The method of performing the activation can also be classified as either automatic or manual. 

The control direction of the reserve product can be either up or down. Upward regulation refers to a situation where a power plant increases its production and/or a power consumption site decreases its consumption. Conversely, in downward regulation, the power plant decreases its production and/or the power consumption site increases its consumption. In the case of energy storage, charging the storage can be compared to power consumption, and discharging it to power production. 

Additionally, a reserve product can be either symmetric or asymmetric. In a symmetric product, the reserve resource/unit/entity must be able to regulate its power in both directions. In an asymmetric product, regulation is procured only in one direction. 

Activation and control direction of reserve products: 

*For more detailed technical requirements and the prequalification tests performed to verify them, please refer to the page on Reserve Products and Market Participation. 

Principles and overall operation of reserve products: 

The operating principles of different reserve products are illustrated in the above image in a scenario where a large power plant suddenly disconnects from the power system at 0 seconds. 

FFR activates the fastest to ensure rapid power support in situations where the under-frequency disturbance is significant and there is little inertia in the power system to slow down the frequency change. The activation duration is short-term, 5–30 seconds. 

FCR-D is also a quickly activating reserve that activates when the frequency deviates from the normal range of 49.9–50.1 Hz. The activation duration is typically short-term, but if necessary, the activation must be able to continue uninterrupted for at least 20 minutes. 

FCR-N must be fully activated within approximately 3 minutes, and the activation should be able to continue uninterrupted for the entire market period. 

aFRR is a slower reserve product that is activated to release faster reserves for the possible next frequency disturbance. The activation should be able to continue uninterrupted for the entire market period. 

mFRR is the slowest of the products and is used to balance deviations and also to release faster reserves. The activation should be able to continue uninterrupted for the entire market period. 

The reserve markets operate on a technology-neutral basis. Any type of technology that can meet the technical requirements is eligible to participate in the reserve markets. Since reserves are needed to maintain the reliability of the power system and the demand for reserves is increasing, Fingrid encourages every party in the power system – including production, consumption, and energy storage – to do their part in maintaining the power balance of the system. 

The technical requirements for reserves can sometimes pose challenges for certain types of technology. Each site must be individually assessed against the technical requirements of each reserve product, and participation in the reserve markets requires the performance of product-specific prequalification tests (excluding mFRR) at the site. 

The reserve capacities verified through prequalification tests for different types of technology for various reserve products are presented on the Reserve Market Information page alongside the product-specific information. 

The reserve maintenance obligations in the Nordic interconnected system (Finland, Sweden, Norway, and Eastern Denmark) are agreed upon in the Nordic System Operation Agreement (Nordic SOA) between the system operators of the Nordic power system. 

FCR-N is always maintained at a total of 600 MW for normal state frequency control. FCR-D, which is procured for disturbance situations, is maintained in such quantities that the permanent frequency deviation caused by a single fault in the power system does not exceed 0.5 Hz. The need for reserves in the Nordic power system is determined by the largest single fault and is dimensioned separately for under-frequency and over-frequency disturbances. An under-frequency disturbance can be caused, for example, by the disconnection of a large power plant or a transmission connection bringing electricity to the Nordic power system. Conversely, an over-frequency disturbance can be caused by the disconnection of a large electricity consumption site or a transmission connection exporting electricity from the Nordic power system. Up to 1450 MW of upward regulation is needed for under-frequency disturbances and 1400 MW of downward regulation for over-frequency disturbances. The jointly maintained FCR-N and FCR-D are distributed annually among the Nordic transmission system operators based on the annual energy consumption and production of each country. 

FFR is procured for managing situations with low inertia. Since the need for FFR depends on the inertia of the power system, it is procured only for certain hours, and the amount procured varies. The estimated procurement amount in the Nordic power system is up to approximately 300 MW. 

It has been agreed that aFRR will be maintained at 400 MW in the Nordic power system. Detailed information about the agreed maintenance amounts is provided separately on Fingrid's website, and the announcements are listed on the aFRR product page. 

Additionally, each Nordic transmission system operator must maintain mFRR to cover the dimensioning fault in their area and the typical longer-term balance deviations of balance responsible parties. Fingrid ensures sufficient capacity for the mFRR energy market alongside the mFRR capacity market with its own standby power plants and those acquired through usage agreements. 

Fingrid primarily fulfills its reserve obligations on a market basis, meaning that reserves are purchased from reserve providers. Additionally, Fingrid can procure reserves from the transmission system operators of neighboring countries, including Estonia and other Nordic countries (Sweden, Norway, and Eastern Denmark). In normal situations, up to one-third of the FCR reserve obligation can be procured from other Nordic countries. More information about the market-based procurement of reserves is provided in the Reserve Markets section. 

Fingrid's national reserve obligations and procurement sources in 2025: