To ensure sufficient aFRR capacity is available and to maintain the balance of the power grid, TenneT enters into 24-hour contracts with Balancing Service Providers (BSPs). These providers ensure that capacity is always available and receive compensation for doing so. At the same time, they must supply energy whenever their capacity is needed.
Since September, TenneT has been calculating the required aFRR capacity using a new method, known as dynamic sizing. Previously, this was done on a quarterly basis and relied solely on historical data. Now, the specific risks of a given day are also taken into account. This ensures that exactly enough capacity is always available, tailored to what the system actually needs.
Starting November 11, 2025, the system will become even more flexible. In addition to the existing 24-hour contracts,4-hour contracts will also be introduced. This means that capacity is no longer fixed for the entire day but can be purchased in blocks. For now, 90% of the capacity will be allocated through the 24-hour auction, and 10% through six auctions for 4-hour blocks, which take place the day before delivery.
Eventually, TenneT plans to transition entirely to 4-hour contracts. Starting in 2026, capacity can even be allocated per block, making procurement even smarter and faster.
Why this is important
These changes make the aFRR market more flexible and transparent. Technologies such as batteries and renewable energy sources, which are not always available throughout the day, can now participate more easily. The result: a smarter power grid, more participants, and a system that better aligns with actual energy supply and demand.
As a Balancing Service Provider, we operate in various balancing markets and see the 4-hour contracts for aFRR capacity as a great opportunity. We’re working hard to offer the first solar farms on the aFRR market this coming spring, when the sun will be shining brightly again. Interested? We’d love to talk with you!
