Reserves and balancing power

In the joint Nordic system (Finland, Sweden, Norway and East Denmark), the obligations for maintaining reserves have been agreed in System Operation Agreement between the Nordic Transmission System Operators (TSOs).

Total of 600 MW of Frequency Containment Reserve for Normal operation (FCR-N) is constantly maintained for the frequency regulation of the normal state. Frequency Containment Reserve for Disturbances (FCR-D) is maintained to the extent that the steady state frequency deviation caused by any individual fault is not more than 0.5 Hz. The needed volume of the reserve in the Nordic power system depends on the greatest individual fault, and it is dimensioned separately for under- and overfrequency events. An underfrequency event can be caused by e.g. tripping of a large production unit or of a transmission line importing power to the Nordics. Correspondingly, an overfrequency event can be caused by e.g. tripping of a large consumption unit or of a transmission line exporting power from the Nordics. At most the needed volume equals 1450 MW upregulation for underfrequency events and 1400 MW downregulation for overfrequency events. The jointly maintained FCR-N and FCR-D are divided annually between the Nordic TSOs in relation to the total annual consumption and production in each country.

Fast Frequency Reserve (FFR) is procured to handle low inertia situations. Because the need for FFR is dependent on the inertia of the power system, it is only procured for some hours and the amount of reserve varies. The estimated amount of FFR in the Nordics is max. 300 MW.

It has been agreed that 300–400 MW of Automatic Frequency Restoration Reserve (aFRR) is maintained in predefined morning, evening and night hours in the Nordic countries. The predefined procurement hours are announced on Fingrid's website.

Furthermore, each TSO maintains Manual Frequency Restoration Reserve (mFRR) to cover the dimensioning fault in its own area.

The TSO of each country procures its share of reserves as it considers best. In order to meet reserve obligations, trade can be done between countries. Part of reserves must be maintained nationally, so that the frequency can also be maintained in situations of island operation. In normal situation, a maximum of 1/3 of the obligations for frequency containment reserves can be purchased from other Nordic countries.

Fingrid's reserve obligations and procurement sources in 2024: 

* The procurement started in 2022 and volumes will be gradually increased. The maximum need is about 280 MW.

** A temporary increase to 50 MW is possible.

Fingrid covers the maintenance costs of reserves with a grid network tariff and payments collected in balance services. The costs of the balancing power market are covered by imbalance power.

Reserves are divided into three groups based on their purpose:

1. Frequency Containment Reserves (FCR) are used for the constant control of frequency.
2. The purpose of Frequency Restoration Reserves (FRR) is to return the frequency to its normal range (49.9 - 50.1 Hz) and to release activated Frequency Containment Reserves back into use. 
3. Replacement Reserves (RR) release activated Frequency Restoration Reserves back to a state of readiness in case of new disturbances. (Not used in the Nordic power system)

In addition, Fast Frequency Reserve is used in the Nordics since 2020. It contributes to frequency containment in low inertia situations.

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