All about Control reserve

As in other European countries, transmission system operator Elia monitors the balance of the Belgian grid. It requires each Balancing Responsible Party (BRP) to maintain a balanced portfolio. In concrete terms, this means that the offtake and injection in its portfolio must be balanced every quarter of an hour, taking into account the volumes traded on the electricity markets. In real time, however, BRPs may face imbalances, for example if a customer suddenly consumes more or a production installation produces less than expected. The imbalances of all Belgian BRPs partially cancel each other out, some BRPs have a positive imbalance (a surplus of energy), others a negative imbalance (a shortage of energy). The remaining imbalance is eliminated by the system operator Elia using balancing power, which it purchases in advance in the balancing markets organized for this purpose. In this way, Elia ensures that it has the necessary resources available at all times to maintain the system balance. Market players offering balancing capacity are remunerated on the basis of the price flow in the balancing market.

The responsibility for maintaining the instantaneous balance between generation and consumption of electricity lies with the transmission system operator (TSO). The TSO has to assure that the control area they are responsible for is in balance. In Belgium there is only one control zone that is covering the whole country and is overlooked by Elia. The control area does not necessarily have to cover a whole country. For example, in Germany there are four zones. To assure the balance in the control area is maintained, Elia outsources this responsibility to the so-called Balance Responsible Parties (BRPs, in Belgium also called ARPs for Access Responsible Parties). A BRP is a private legal entity that overlooks the balance of one or multiple access points to the transmission grid. The BRPs portfolio is also called the balancing group. The BRP composes a balanced portfolio by combining injection, off-take, exchange with other BRPs and possibly in- or export to another control area. Each generator and off-taker in the grid is obliged to have a contract with a BRP/ARP. Alternatively, they can be their own balancing responsible party.

When one speaks of flexibility in the electricity sector, one usually means the possibility to adjust the electrical consumption or the electrical production of an installation or process. This could be in response to a price signal, the grid frequency, or an activation signal from the grid operator.