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Glossary · Energy industry & energy transition

Balancing Capacity

Balancing capacity balancing reserve balancing energy balancing power electricity market frequency maintenance Balancing group security of supply flexibility

In the power system, balancing capacity refers to electrical power that is reserved by contract. A transmission system operator can call on it when needed to bring generation and consumption back into balance. The term is precisely defined in European law: a balancing service provider undertakes to keep a certain volume of reserve capacity available. For the duration of the contract, it must also submit bids to the transmission system operator for a corresponding quantity of balancing energy. In German, the term corresponds to balancing capacity, that is, the reserved power of the balancing reserve. It does not mean the quantity of energy actually delivered. It means the ability and obligation to provide or absorb a certain amount of power within defined technical deadlines.

The unit is megawatt (MW). Balancing capacity describes power, that is, the ability to change generation or consumption at a given moment. If this power is called upon and delivered over a period of time, Balancing Energy results, known in German as Regelarbeit. It is measured in megawatt hours (MWh). An example: a provider can be paid to keep 50 MW available, even if those 50 MW are never called upon during a given period. Balancing energy only flows once the power is activated. EU law groups both under the umbrella term balancing services.

Balancing capacity is a state of readiness for the system as a whole. Power plants, battery storage systems, flexible consumers or pooled small installations commit to not using a defined margin for other purposes. This margin must be available when called upon. This is necessary because generation and consumption must be in physical balance at all times. If they diverge, the grid frequency changes. In continental Europe, the target value is 50 hertz. Balancing capacity ensures that technical resources are available to correct such deviations before they become critical.

Capacity, energy and power

Balancing capacity is often confused with balancing energy. This leads to wrong conclusions about costs, benefits and the needs of the system. Capacity is the reserved power. Energy is the work actually called upon over time. Anyone offering balancing capacity therefore does not initially sell electricity, but an option to stabilise the system. The transmission system operator thereby secures the right to deploy this resource when needed.

This is why a provider can receive money without having delivered a single kilowatt hour of balancing energy. It has sold availability. This has economic value because it gives rise to opportunity costs. A power plant cannot sell the capacity it keeps free as positive reserve on the normal electricity market. A battery must manage its state of charge so that it can discharge or absorb electricity when called upon. An industrial company must plan its processes so that a change in load remains possible within the agreed period. Balancing capacity is therefore not a free by-product of existing installations. It is a product with technical and economic obligations.

Positive balancing capacity means that the system receives additional feed-in or consumption falls. It helps when there is too little electricity in the system. Negative balancing capacity means that feed-in falls or additional consumption is switched on. It helps when there is too much electricity in the system. For aFRR and mFRR, positive and negative reserve are held as separate products in Germany. EU law also provides in principle for both directions to be procured separately. FCR, by contrast, is a symmetric product: anyone offering it must be able to respond in both directions. This is particularly evident with battery storage systems. A battery can only offer positive reserve if it can discharge, and negative reserve only if it can charge. For symmetric FCR it needs both at the same time. Its installed power alone therefore says little about how much balancing capacity it can actually offer.

Types of balancing reserve and activation times

Balancing capacity is not a uniform product. European law distinguishes between frequency containment reserve, frequency restoration reserve and replacement reserve. They differ in how quickly they are activated, how they are controlled and what role they play in the system. In Germany there are three types: FCR, aFRR and mFRR. The Frequency Containment Reserve (FCR) corresponds to the former primary control. It must be delivered in full within 30 seconds. For this purpose, the installations measure the frequency themselves and react automatically and in a decentralised manner. FCR is activated jointly across the entire European interconnected grid, regardless of where the imbalance arose. It arrests the change in frequency, but does not on its own bring the frequency back to 50 hertz.

The automatic Frequency Restoration Reserve (aFRR) balances the position of the individual control area and replaces FCR. For this purpose, the transmission system operator issues a setpoint every four seconds. The requested power must be delivered in full within five minutes. The manual Frequency Restoration Reserve (mFRR) must be delivered in full within 12.5 minutes. It replaces aFRR when the latter is heavily used, and serves to balance larger imbalances. In practice, it is needed rather rarely and usually only for a few quarter-hours. Despite its name, it is now called electronically. According to the joint platform of the German transmission system operators, an activation lasts at most 15 minutes for FCR and at most 60 minutes for aFRR and mFRR. Some European systems additionally use Replacement Reserve, a replacement reserve with even longer time windows. According to the transmission system operators' presentation, Germany does not belong to them.

These products cannot be freely substituted for one another. Anyone who can offer mFRR is not automatically suited to FCR. FCR requires every individual technical unit to measure very quickly and regulate independently. For aFRR, what matters is continuously and automatically adjusting power to a setpoint. For mFRR, somewhat slower resources that can sustain output for longer may also be suitable. Balancing capacity therefore always refers to a specific product, not to an abstract reserve without technical requirements.

Why balancing capacity is needed

Electricity markets do not schedule generation and consumption for every single moment, but in fixed time grids. Day-ahead and intraday trading, schedules, forecasts and the management of balancing groups balance the system for the coming quarter-hours. The actual situation in the grid nevertheless constantly deviates from the plan. Consumption forecasts are not exactly right, wind and solar generation fluctuate, power plants or lines fail, and schedules are not followed exactly.

Balancing capacity closes the gap between the planned market outcome and the actual situation in the grid. It replaces neither the electricity market nor the obligation of balance responsible parties to balance their balancing groups. It is the last level of correction during real-time operation. Without reserves held available, the grid operator would first have to search for available resources in the event of a disturbance. For frequency containment, that would be too slow.

The transmission system operators are responsible. They determine how much balancing reserve is necessary, procure balancing capacity on a market basis and activate it in operation according to fixed rules. In Germany, they calculate the need for aFRR and mFRR using a dynamic procedure. How much FCR each zone must provide is redetermined once a year in line with European requirements. Providers must first pass a prequalification. This involves checking metering, controllability, reaction speed, communication links and verification procedures. For pools, there is the added requirement that many small units must be reliably controlled together. An installation therefore only becomes part of the balancing reserve once it meets the product requirements, has been awarded a contract and is bound by contract. Technical capability, market access and actual availability do not automatically coincide.

Procurement and legal framework in the EU and Germany

In the EU, procurement is governed above all by the Guideline on Electricity Balancing (Regulation (EU) 2017/2195) and Article 6 of the Internal Electricity Market Regulation (EU) 2019/943. Accordingly, the transmission system operator procures balancing capacity. Procurement must be market-based and must not disadvantage anyone, including providers participating via aggregation. The price for balancing energy may not be fixed in advance in the contract for the reservation of capacity. In principle, contracts are concluded at most one day before delivery and are valid for at most one day. The regulatory authority can approve exceptions, but only to a limited extent. Since 1 January 2026, contract durations under such exceptions may not exceed six months. These requirements apply to the EU internal electricity market. How products and deadlines look in detail is determined by each Member State itself.

In Germany, the four transmission system operators tender FCR, aFRR and mFRR daily on the joint platform regelleistung.net. According to the status published there: FCR is tendered in four-hour blocks, and bids are possible until 8 a.m. on the previous day. The capacity market for aFRR closes at 9 a.m., and that for mFRR at 10 a.m. FCR is procured jointly with other European grid operators. For aFRR, Germany and Austria cooperate in procurement. Anyone awarded a contract in the capacity market must submit balancing energy bids equal to the awarded capacity. Since November 2020, there has been a separate balancing energy market for aFRR and mFRR. Balancing energy bids are collected there for every quarter-hour, and providers without a capacity award can also participate there.

Remuneration and cost impact

The price of balancing capacity reflects opportunity costs, technical costs, the risk of a failure and competition. Remuneration differs by product. For aFRR and mFRR, there is a capacity price for reservation. In the event of a call, balancing energy is additionally paid via an energy price, whose marginal prices are determined by the European platforms PICASSO and MARI. For FCR, by contrast, a single capacity payment covers both reservation and delivery. There is no separate energy price there. The widespread claim that the reservation payment is always followed by a separate price for balancing energy is therefore not true for every product.

The separation of capacity and energy creates different incentives. High remuneration for reservation can induce providers to keep capacity free even if a call is unlikely. The prices for balancing energy, by contrast, determine what an actual call costs. If too little reserve is held, the risk increases that frequency deviations will not be controlled. If too much is held, this ties up resources and causes costs that someone has to bear.

The costs do not necessarily arise where the physical cause lies. Depending on national regulation, the costs of reservation are passed on, for example via grid fees. The costs of the balancing energy called are mostly reflected in the prices for imbalance energy. Balance responsible parties pay these prices for their deviations, or receive them. This creates a financial incentive to manage balancing groups as accurately as possible. If deviations are too cheap, good forecasting is less worthwhile. If imbalance energy prices are highly volatile, risks arise for market participants.

At this point, balancing capacity links grid operation with market organisation. Frequency containment is a physical task. It is organised, however, through tenders, product definitions, prequalification and cost allocation. A flexible installation may be technically suitable and yet not participate, for example because of minimum bid sizes, metering requirements, rules on pooling installations or uncertain revenues. Conversely, if controls and sanctions are too weak, a product may attract resources that are only of limited availability in practice. In Germany, the transmission system operators therefore check reservation, among other things, with test activations.

Distinction from capacity market, reserves and security of supply

Balancing capacity is not a capacity market. A capacity market remunerates firm capacity so that sufficient generation capacity is available over longer periods and load peaks can be covered. It concerns Resource Adequacy, that is, the question of whether sufficient resources are available even in tight hours. Balancing capacity, by contrast, concerns the short-term balancing of deviations during real-time operation.

It must also be distinguished from strategic reserves and the grid reserve. These are held outside the normal electricity market to safeguard against bottlenecks, decommissioning risks or critical grid situations. They do not serve ongoing frequency containment on the scale of seconds and minutes. An installation may be suitable for several purposes. However, it must not sell the same capacity several times if this leads to its actual availability being overestimated. Multiple marketing is only permissible if products, time windows and call obligations are clearly separated from one another.

Nor does balancing capacity fully indicate the state of security of supply. A system can hold enough balancing reserve and still get into difficulties, for example during a prolonged Dunkelflaute, fuel scarcity, grid bottlenecks or a lack of firm capacity. Conversely, a system with a lot of installed power plant capacity can become unstable if fast balancing resources or coordination in operation are lacking.

Typical misunderstandings

  • “Balancing capacity is unused generation that just sits idle.” This view overlooks negative reserve, flexible loads, storage and pooled small installations. It also overlooks that reservation is an active decision in operation: the power plant, storage unit, industrial process or pool must be run in such a way that the committed capacity is actually available when called upon.

  • “Reserve that is rarely called upon is superfluous.” With a security product, the benefit lies precisely in assured availability for rare but important deviations. Few calls can also mean that forecasts, balancing groups and markets have worked well.

  • “Balancing capacity equals the size of the storage unit.” With batteries, one must distinguish between power in MW and storage capacity in MWh. For balancing capacity, what counts first is how much power can be delivered or absorbed quickly. How long this is possible depends on the available amount of energy. This must match the product, which for aFRR and mFRR means activations of up to 60 minutes.

  • “Balancing reserve replaces grid expansion or good market design.” Balancing reserve does not resolve local grid bottlenecks if the resource is located at the wrong place in the grid. Nor can it permanently offset misaligned incentives in the balancing group system without causing costs. If market participants are systematically imbalanced, the need for balancing energy rises, and possibly also for reserved capacity.

Renewable energies, flexibility and new providers

With more wind and solar power, the need for short-term balancing changes. However, it does not simply grow in the same proportion. Better forecasts, shorter trading deadlines, larger European balancing areas and more flexible demand can limit the need for reserves. At the same time, short-term forecast errors and steep power changes may increase. The need therefore depends on forecast quality, the market's time grids, the grid situation, European cooperation and the available flexibility. The dynamic dimensioning of aFRR and mFRR in Germany is intended to take such changes into account.

New providers are changing the balancing reserve markets. EU law requires that operators of consumption installations, storage, and conventional and renewable generation installations, as well as third parties, can become balancing service providers. Battery storage systems react very quickly and are particularly suited to FCR and aFRR. Electrolysers, heat pumps, cold stores, charging infrastructure and industrial processes can provide reserve if their operations are flexible enough. An aggregator bundles many small installations into a controllable pool. This requires reliable data, secure communication channels, rules for outages and baseline methods. A baseline describes how consumption or feed-in would have developed without the call. If it is inaccurate, flexibility is feigned or genuine flexibility is paid too little.

European dimension

Balancing capacity is increasingly integrated at European level. FCR is delivered jointly in the synchronous area on the solidarity principle. aFRR and mFRR, by contrast, are deployed on the polluter-pays principle in the control area that caused the imbalance. Balancing energy is increasingly called across borders via European platforms, for aFRR via PICASSO and for mFRR via MARI. The Guideline on Electricity Balancing permits the exchange of balancing capacity between grid operators. For this, sufficient cross-border transmission capacity must be available, and special procedures apply to its allocation. A cheap offer in another control area only helps if the necessary line capacity is actually free at the moment of the call. Balancing reserve always acts within a physical interconnected grid whose stability depends on frequency, line loading and voltage control.

What the term achieves and what it does not

The term balancing capacity describes the short-term readiness that the power system needs in order to stabilise itself in real time. It makes visible that security of supply does not consist only of installed capacity or kilowatt hours generated. Resources are needed that are controllable, reachable, prequalified and available in the right period. These resources cost money, even if they are rarely called upon.

On its own, the term says nothing about whether a power system as a whole is adequately designed. It does not answer whether enough firm capacity is available for multi-day scarcities, whether the grids are sufficiently expanded or whether prices set the right investment incentives. Balancing capacity is power, not energy. It is a reserve for operation, not general generation capacity. It arises from technical suitability, contractual commitment and procurement according to fixed rules. Its importance grows the more power systems depend on the weather and the more decentralised and flexible they become.

Sources

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Edited by eCMS on 11.11.2026 14:57

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