aFRR (Automatic Frequency Restoration Reserve)

aFRR is the automatically activated frequency restoration reserve. After FCR has contained a frequency deviation, aFRR brings system frequency back to the 50 Hz setpoint and releases FCR back to its standby range. Activation is closed-loop: the TSO sends a continuous control signal that adjusts the BSP's output every few seconds.

Activation timing

Full activation is required within roughly 5 minutes of a frequency deviation. The signal cycle in the Continental synchronous area is 4 seconds — every BSP providing aFRR must adjust its asset on that cadence. Compared to FCR, aFRR is slower and more directional: it picks a sign (up or down) per dispatch, where FCR responds symmetrically and instantly to local frequency.

IGCC, PICASSO, BBCM and Estonia

Before any cross-border activation happens, IGCC (the EU imbalance-netting platform) offsets opposing aFRR demand between connected TSOs — a positive need in one area cancels against a negative need in another, so only the residual reaches the activation market. That activation market is PICASSO (Platform for the International Coordination of Automated Frequency Restoration and Stable System Operation): the Continental-Europe-wide aFRR energy exchange that dispatches the cheapest available bid across all member control areas. The 2025 go-live followed years of preparation, including a 2021 joint Baltic frequency-control pilot that allowed Estonian market participants to offer reserves to the Finnish market. Elering connected to PICASSO on 9 April 2025, after Baltic synchronisation with Continental Europe earlier that year. aFRR capacity is procured separately, via the joint Baltic Balancing Capacity Market (BBCM) run with AST and Litgrid; BBCM aFRR capacity procurement started 15 April 2025 (first delivery day 16 April). The market is large, liquid, and increasingly dominated by battery energy storage.

Where it sits in the reserve hierarchy

Three reserve products operate in series: FCR contains the deviation in seconds; aFRR restores frequency in minutes; mFRR takes over for sustained imbalances. Together they form what EU regulators call the operating-reserve hierarchy. aFRR sits in the middle — not the fastest, not the longest-lasting — and the 4-second response window is exactly where 1–2C batteries dominate.