FCR-D (Frequency Containment Reserve) is a type of ancillary service used to regulate and balance the frequency in the electricity grid by acting as a fast reacting load such as a battery storage. FCR-D is used to manage a sudden over or under generation of electricity in the system, which can cause a change in frequency above the allowed range.
To explain how FCR-D works, let’s take an example: if there is an excess production of electricity in the grid due to faster rotation speed of the generators than demanded by the consumers, the frequency will increase above the normal level. To reduce the frequency quickly, a fast-reacting load is needed that can absorb the energy. The same thing happens in reverse if we take more energy out of the grid than we have in production, then the frequency drops. For example, a battery storage system can help by discharging or recharging.
It is important that the FCR-D consumer is ready to react quickly to the signals in order to quickly stabilize the frequency in the grid. This type of ancillary service is used to quickly regulate and balance the frequency to avoid disturbances and problems in the grid and to keep the frequency within the allowed range.