Ancillary services

Grid users can help maintain balance on the Elia grid. How? By providing 'ancillary services'.

24 countries = 1 grid to maintain balanced

The transmission system operators from 24 interconnected countries operate their grids as a single large European electricity network through which energy flows freely. Accordingly, we can source supplies from across Europe in order to, say, take advantage of attractive wholesale prices or cope with the outage of a major production unit. 

Energy is continually injected into the highly interconnected European grid by various facilities, including: 

  • power stations;
  • wind turbines;
  • cogeneration units. 

At the same time, energy is taken out of the grid by various types of users:  

  • large factories;
  • SMEs;
  • institutions (such as hospitals);
  • homes. 

But there is one problem: electricity cannot be stored in large quantities. This means that production must be adjusted continually in line with consumption. Transmission system operators (such as Elia) keep an eye on balance in their own control areas. They comply with the joint rules agreed at European level. 


Ancillary services

Ancillary services enable Elia to maintain frequency and voltage at appropriate levels while managing balance and congestion in three different ways: 

Primary reserve (R1)

The turbines at some production units can automatically detect frequency fluctuations and, where necessary, adjust production within 0 to 30 seconds.  

If an imbalance is detected, the system operator can count on contributions to the primary reserve from all European transmission system operators. The primary reserve is able to compensate for two simultaneous serious incidents (the loss of two 1500 MW production units). It is delivered up to 15 minutes after the incident.  

Secondary reserve (R2)

The secondary reserve is automatically and continually activated both upstream and downstream (upward/downward regulation). It kicks in quickly (between 30 seconds and 15 minutes) and remains active as long as it is needed. Grid users that provide secondary reserve must have the appropriate facilities for communicating in real time with Elia's national control centre, and their production units must comply with certain technical requirements. 

Prior to the activation of secondary reserves, TSOs participating in IGCC (International Grid Control Cooperation) exchange imbalances:

  • In Entso-E RG Continental Europe, secondary control reserve is activated automatically and in accordance with the source of imbalances. Within a region with several control areas, for a given point in time a counteracting deployment of reserves is possible and not unusual.
  • IGCC aims to prevent these counteracting deployment of reserves by exchanging opposing imbalances between TSOs. This leads to a more efficient activation of ancillary services and improves the quality of the regulation.
  • To do so, the IGCC participants compare in realtime the imbalances of their zones and exchanges them when possible. The remaining imbalance of a zone will be corrected by the responsible transmission system operator with his own means.
    • In order not to hamper the grid security or influence the interconnection capacity made available for the market, the exchanges are limited tothe remaining available transfer capacity after closure of the market, with a maximum of 140MW.

The IGCC participation of Elia was in a trail phase running from 01/10/2012 until 01/10/2013 to test the liability of this system. The IGCC participation of Elia is now extended for an indefinite period.

Tertiary reserve (R3)

The tertiary reserve enables Elia to cope with a significant or systematic imbalance in the control area and/or resolve major congestion problems.  

The tertiary reserve has two components:  

  • the tertiary production reserve: injection of extra capacity by producers who have signed a contract for tertiary reserve;
  • the tertiary off-take reserve: reduction in off-take by grid users who have signed an interruptibility contract.  

Unlike the primary and secondary reserves, the tertiary reserve is activated manually at Elia's request. Any grid user whose facilities comply with certain technical requirements can sign a contract with Elia to take part in the tertiary reserve. 

Compensation for grid losses

Elia itself also purchases electricity to compensate for part of the losses on its grid. Domestic and foreign suppliers can submit bids for such purchase. More info about these purchases on the 'Energy purchases' page

Black Start

Just imagine a total outage of the Belgian grid, meaning that grids in neighbouring countries are also unavailable. In that case, certain power stations must be able to start up without being able to draw power from the grid. This is called the 'black start service'.