To ensure sufficient aFRR capacity is available, TenneT enters into daily 24-hour contracts with Balancing Service Providers (BSPs). These providers receive compensation for keeping their ramp-up or ramp-down capacity available for 24 hours. In addition, they are required to submit energy bids for the use of this capacity during the designated delivery periods.
Procurement takes place via a daily auction at 9:00 a.m. on the day before delivery. This determines the minimum required aFRR capacity, ensuring that the grid remains stable under varying conditions.
Since September 15, 2025, TenneT has been using a new method to determine the minimum aFRR capacity: dynamic sizing. Previously, this capacity was calculated twice a year based on worst-case scenarios. Now, this is done daily, using up-to-date system forecasts. The results are published at 6:00 a.m. on the day before delivery, three hours before the auction closes.
The result: more accurate procurement and likely lower contracted capacity. The obligation for BSPs to keep capacity available 24 hours a day remains in effect, at least until the planned transition to 4-hour capacity contracts in November.
In short, the aFRR market is changing rapidly. With dynamic sizing and the upcoming 4-hour structure, TenneT is taking steps toward a more flexible and responsive system that better aligns with the changing needs of the power grid.
