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Glossary · Energy industry & energy transition

FCR, Frequency Containment Reserve

FCR Frequency Containment Reserve balancing reserve frequency maintenance grid frequency ancillary service

FCR stands for Frequency Containment Reserve (in German: Frequenzhaltungsreserve). In Germany it was formerly called primary control power (Primärregelleistung, PRL). It is the fastest type of balancing reserve: it intervenes automatically as soon as the grid frequency deviates from its set point. After a sudden disturbance, such as the outage of a large power plant unit, FCR is meant to prevent the frequency from continuing to fall or rise. It holds the deviation at a new, stable value. However, it does not bring the frequency back to 50 hertz, nor does it eliminate the cause of the disturbance.

The grid frequency in the Continental European synchronous grid is nominally 50.0 hertz. It continuously indicates whether feed-in and withdrawal are in balance. If power is lacking because more is consumed than generated, the frequency falls. In the case of a surplus, it rises. In the case of a deficit, positive FCR is therefore needed, i.e. more feed-in or less consumption. In the case of a surplus, negative FCR is needed, i.e. less feed-in or more consumption.

How FCR works technically

There is no central call-off system for FCR. Each technical unit with an awarded contract measures the grid frequency itself on site and regulates its output with a local proportional controller (P controller). The change in output follows the deviation from 50.0 hertz linearly. Between 49.99 and 50.01 hertz there is a dead band: within it, providers do not have to deliver any FCR. This avoids constant switching between positive and negative delivery. At a deviation of ±200 millihertz, the entire contractually committed FCR must be available after 30 seconds at the latest. This power must then be sustained for up to 15 minutes.

A simplified example: a plant has committed 10 MW of FCR and the frequency falls to 49.90 hertz. That is a deviation of 100 millihertz, i.e. about half of the deviation at which full power is due. The plant then delivers roughly 5 MW additionally, either through more feed-in or through less consumption. The exact shape of the characteristic curve is governed by the prequalification conditions of the transmission system operators. European law also stipulates that activation must not be artificially delayed and must begin as soon as possible after a frequency deviation.

Activation is based on solidarity. All FCR units in Continental Europe respond to the same frequency, regardless of which transmission system operator caused the imbalance. Because the many P controllers only stabilise the deviation, a balance deviation remains. The causing system operator must offset this with automatic frequency restoration reserve (aFRR) and manual frequency restoration reserve (mFRR). Only then does the frequency normalise, and the FCR is available again for the next disturbance.

Legal framework and dimensioning

The legal framework in the EU is set by Regulation (EU) 2017/1485 on electricity transmission system operation, often called SO GL. Article 153 governs how much FCR must be held available. In the Continental Europe synchronous area, FCR must cover at least the reference incident. This is set at 3000 MW in the positive direction and 3000 MW in the negative direction. That corresponds roughly to the simultaneous outage of two large power plant units. The transmission system operators may additionally use a probabilistic method. It takes load, generation and inertia into account and is intended to limit the risk of insufficient FCR to at most once in 20 years. The size of each system operator's share depends on its share of net generation and consumption in the synchronous area over one year. The requirement is redetermined at least annually.

Article 154 contains the minimum technical requirements. These include full provision after 30 seconds at the latest at a deviation of at least 200 millihertz, and undelayed activation. In addition, FCR providers must supply the system operator with information, for example a time-stamped status indicating whether FCR is currently activated. Whether a plant meets these requirements is verified in prequalification. Only then may it take part in tenders. A plant that appears flexible in normal operation is therefore not automatically suitable for FCR.

Procurement in Germany and Europe

The four German transmission system operators procure FCR via the joint platform regelleistung.net. They do so within the cross-border FCR cooperation with system operators from several neighbouring countries. Since 1 July 2020 there have been daily day-ahead auctions with 4-hour products. A day therefore has six time slices, from 0 to 4 a.m. through to 8 p.m. to midnight. Bids are possible until 8 a.m. on the day before delivery.

Unlike aFRR and mFRR, FCR is a symmetric product. Anyone offering 1 MW must be able to deliver both 1 MW of positive and 1 MW of negative FCR. Separate positive and negative offers do not exist for FCR. Remuneration follows the uniform-price method (pay-as-cleared): all providers awarded a contract receive the highest accepted capacity price. For FCR, only this capacity price is paid. There is no separate remuneration for the energy delivered, such as the energy price (Regelarbeitspreis) that exists for aFRR and mFRR.

It follows that the costs arise mainly from reliable capacity provision, not only upon deployment. A power plant must keep headroom available both upwards and downwards. A battery storage system must manage its state of charge so that it can respond in both directions. An industrial consumer must set up its processes for short-term changes in power. These restrictions are opportunity costs that providers factor into their bids.

Power, energy and distinctions

FCR is stated in megawatts. What is meant is power held available, not a quantity of energy. How much energy actually flows depends on how large the frequency deviations are and how long they last. For context: 1 MW of FCR that is fully activated for 15 minutes corresponds to 0.25 MWh. In normal operation the frequency usually fluctuates only slightly around 50 hertz. The energy quantities are then small and often change direction.

  • FCR and inertial response: Inertial response comes mainly from the rotating masses of synchronously coupled machines. When the frequency falls, these release kinetic energy immediately, physically and without any measurement. FCR, by contrast, is a measured and controlled power adjustment in the range of seconds. Grid-forming inverters can take over frequency-supporting functions, but do not automatically replace all properties of synchronous machines.

  • FCR and frequency restoration: aFRR must be fully activated within 5 minutes and mFRR within 15 minutes. Both are called up specifically for a control area and take over from FCR. FCR is not a replacement power plant and not a solution for lasting imbalances.

  • FCR and grid congestion: A frequency deviation affects the entire synchronous area, whereas a line bottleneck is a spatial transport problem. Other instruments such as redispatch exist for that. FCR can change load flows, but it serves frequency containment, not congestion management.

Significance in the changing power system

With more wind and solar power, the source of the power changes. The physical need for balance, however, remains the same. At the same time, new providers have entered, above all battery storage systems. They can change their power very quickly and in both directions. Their energy content is, however, limited, so they require careful state-of-charge management. For such units with limited energy storage, special requirements apply regarding how long they must sustain an activation. Controllable consumers such as cooling processes, pumps or electrolysers are also fundamentally eligible. Whether they actually participate depends on prequalification, process risks, metering and control technology, and capacity prices.

The existence of FCR proves neither that a power system is secure nor that it is insecure. Every large interconnected system must expect disturbances and therefore needs such a reserve. What is meaningful is whether the FCR is adequately sized, reliably available and properly coordinated with the downstream reserves. Frequency containment is one building block of security of supply, but not the same thing. Security of supply also includes sufficient generation and storage capacity, high-performance grids, fuel availability and crisis processes. In the event of a disturbance, FCR buys the crucial first seconds to minutes until other balancing and market processes restore equilibrium.

Sources

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Edited by eCMS on 11.11.2026 19:47

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