May 14, 2024

Frequency Containment Reserve

By using Frequency Containment Reserve, unexpected shifts in power generation can be quickly corrected, such as power plant outages, sudden wind changes or cloudy weather. It's important to keep the stable balance between supply and demand that the power grid needs to function properly.

What is Frequency Containment Reserve?

Balancing services level out frequency deviations in the electricity grid to ensure that electricity consumption and production are constantly matched. In the event of frequency deviations, such as an outage at a power plant, reserve power is used to restore the balance between supply and demand within seconds.

“Operating Reserve”, which is used to maintain frequency, is categorized into primary reserve, secondary reserve and tertiary reserve. These categorizations are based on their activation times and the duration of activation. 

  1. Frequency Containment Reserve (FCR) is the primary control reserve that responds to sudden deviations in less than 10 seconds. It provides a short-term burst of power for usually up to 15 minutes.
  2. Automatic Frequency Restoration Reserve (aFFR) is the secondary frequency control mechanism activated automatically within 30 seconds to provide short-term power for up to 12.5 minutes.
  3. Manual Frequency Restoration Reserve (mFRR), or tertiary frequency control, restores primary and secondary frequency control reserves to manage bottlenecks in the transmission grid. It is activated by grid operators and therefore has a longer activation time and can provide power for up to several hours.
Time of availability for the balancing services

Types of FCR

Frequency Containment Reserve is designed to automatically respond to any changes in grid frequency within short amounts of time. The optimal grid frequency in Europe is 50 Hertz (Hz) and compliance to this setpoint is crucial to maintain a stable grid. 

There are two main types of FCR: 

  • The Frequency Containment Reserve for Normal Operation (FCR-N) aims to maintain the grid’s frequency within the range of 49.9 Hz to 50.1 Hz. Therefore, the FCR-N must be capable of increasing or decreasing power production. 
  • The Frequency Containment Reserve for Disturbances (FCR-D) is a special variant only in the Nordics that reacts when the frequency is outside of the standard 49.5 Hz to 50.5 Hz range. The FCR-D is divided into separate parts for up- and down regulating. It is also divided into dynamic and static products. The dynamic FCR-D can be continuously regulated and detects reserves quickly when the deviation decreases. The static FCR-D requires more time after activation and can’t be regulated continuously.

Why is FCR needed?

Power grids rely on inertia. While most people associate inertia with the physical concept of “an object in motion stays in motion,” this is equally true for the power grid as its inertia is 

based on thousands of synchronized generators, rotating with 50Hz. An imbalance between production and consumption speeds up or slows down the rotating mass, therefore causing a slight deviation to the grid frequency. 

Together with other grid balancing services, FCR works as a safety mechanism to maintain the grid frequency by counteracting short-term imbalances between energy consumption and generation. The maintenance of this target point is crucial to ensure grid safety. While fossil-fuel power stations are more consistent and predictable with their power supply, renewable energy sources are more variable and intermittent. Sudden deviations in production can then lead to changes in frequency, which must be counterbalanced. 

For example: if the wind suddenly drops and wind turbines across a large area start generating less electricity, then the amount of electricity being fed into the grid is less than what is being consumed, and the frequency in the grid will decrease. These fluctuations can lead to instability if they are not quickly compensated. This is where the frequency containment reserves come into effect, especially the fast reserves. These could be in the form of battery storage, hydraulic storage power plants or as a derivative in conventional power plants.

Leveraging small-scale flexibility for FCR

While traditionally, frequency containment reserves were provided by large-scale power plants, the shift to renewable energy means that leveraging the flexibility of small-scale assets is increasingly important and efficient. Aggregating the flexibility of residential battery energy storage systems, for example, helps to create a dispatchable unit of power that can quickly compensate for frequency deviations. The major benefit here is that residential batteries are increasing exponentially due to the many benefits they provide households, meaning this simply utilizes the flexibility of assets that are already available.

Key steps here are aggregation and disaggregation. Aggregation involves pooling together and activating the potential power capacity of over 1,000 storage units into a single dispatchable unit. Disaggregation means splitting up the activated flexibility into actual control signals for the individual assets so that it can be used for local purposes, such as self-sufficiency optimization.

Players: Aggregators, FRPs, TSOs and BSPs

The role of an aggregator (or flexibility service provider) is to accumulate flexibility from active customers/prosumers and their flexible assets and sell it to Flexibility Requesting Parties (FRPs), the Transmission System Operator (TSO), via the Balancing Service Provider (BSP). The FCR capacity is procured ahead of time (usually on day-ahead markets). Remuneration between the aggregator and FRP is based on availability and, optionally, on the activated energy.

FCR regulations

Regulations for FCR come from the interaction between the TSO, the European Network of Transmission System Operators (ENTSO-E) and the responsible government authorities. ENTSO-E developed the System Operation Guidelines (SOGL) and the Electricity Balancing Guidelines (EB-GL), which provide a framework to keep the grid in balance. As a general rule, the TSOs suggest market design requirements for FCR procurement and their conditions to the government authorities, who must approve the proposals before they come into force. The ENTSO-E area defines the necessary FCR procurement requirements. Regulation must change, however, to account for the changing market and roles of players, as aggregated small-scale flexibility plays a more significant role in balancing services.

Regulation also plays a crucial role in encouraging or slowing the adoption of new aggregated FCR services. For example, regulation has helped FCR-D become widespread in Sweden, and is increasingly prominent in Denmark, but its adoption is still limited as it does not exist in central Europe due to the larger grid.

How is FCR activated?

The frequency containment reserve must be available within 30 seconds and has to cover a period of 15 minutes, as per ENSO-E regulations. Participants of the FCR cooperation must provide a tendered quantity if the frequency deviation is not within the limit between 49.99 Hz and 50.01 Hz. The FCR is activated automatically. After half a minute, the TSO activates automatic frequency restoration reserve (aFRR) to replace FCR. In some cases, aFRR activation can be avoided via imbalance netting through International Grid Control Cooperation (IGCC). The IGCC enables European TSOs to prevent simultaneous activation of aFRRs in opposing directions in neighboring grid zones. To provide grid stability within the continental Europe synchronization area, a volume of 3000 megawatt (MW) positive and negative control reserve is constantly ready for activation.

FCR activation and balancing process

Volume of FCR

The volume of procurement for the FCR is determined by the ENTSO-E and is settled within the European synchronous area every year. The volume is adjusted to the power input of the previous year. As mentioned, the same volume of positive and negative primary reserve must be procured. Within the European synchronous area there is a core share of 30% of the FCR demand that describes the minimal demand that is to be procured inside a country. The 30% rule also applies within the FCR Cooperation but must be at least 100 MW – except for western Denmark due to IT limitations.

Share and demand of country in the regional FCR market 2021 via ENTSO-E

gridX’s role in the flexibility value chain for explicit flexibility

As an aggregator, gridX pools the flexibility of distributed energy resources (DERs) to maintain grid stability. gridX already covers the step of integration and control of small-scale energy assets and aims to also cover the step of aggregation and disaggregation, as well as optimizing, stacking and forecasting. gridX’s advanced energy management system places it in a unique position of being able to optimize both locally, such as within a house, and at a system level.