Primary reserve capacity (FCR) must be available within 30 seconds, and delivery must continue uninterrupted for at least 15 minutes. Checks are conducted as part of prequalification tests to identify how much positive and negative capacity can be produced in this time frame. This ‘capacity range’ can be sold on the control reserve markets after a bidding process conducted in advance. Unlike the tertiary or secondary reserve, primary reserve is not activated by a command from the TSO. Instead, it is triggered by grid frequency. This is measured directly on the biogas asset; depending on the deviation, the asset immediately delivers positive or negative primary reserve. Due to the constant availability, there is no difference between the capacity price and the energy price - compensation is automatically set at the capacity price. The Belgian TSO Elia procures four different FCR products: two symmetrical and two assymetrical. The symmetrical products are FCR 100 mHZ and FCR 200 mHZ, respectively responding in a frequency deviation band of +- 100 mHz and +- 200 mHz around 50 Hz. The assymetrical products require an activation in only one direction, respectively upwards or downwards for FCR upward and FCR downward. The different products are shown in the figure above.