aFRR explained: how France's automatic frequency reserve market works
aFRR explained: how France's automatic frequency reserve market works
aFRR (automatic frequency restoration reserve) is currently the most lucrative revenue stream for battery energy storage in France.
RTE, France's transmission system operator, reopened the aFRR capacity auction in June 2024 after a two-year suspension during the energy crisis. In April 2025, RTE connected to PICASSO, the European aFRR activation platform, linking French providers to 20 TSOs.
This article explains the full aFRR market structure, from auction mechanics to qualification rules, based on RTE's Market Rules.
For any further information on this topic, reach out to the author — timothee@modoenergy.com.
Where does aFRR sit in France's reserve stack?
RTE procures four frequency reserves, activated in sequence:
- FCR (containment, 30 seconds)
- aFRR (automatic restoration, 67-300 seconds)
- mFRR (manual restoration, 13 minutes)
- RC (complementary, 30 minutes)
aFRR bridges the gap between FCR's fast but limited response and the slower, larger tertiary reserves.
Activation is fully automatic, response times match BESS ramp capabilities, and operators can cross-optimise between aFRR capacity, aFRR energy, and wholesale trading daily.
The mechanism is similar across European markets.
The volume of aFRR that RTE contracts varies throughout the day and across seasons. Requirements are calculated semi-annually.
Winter upward requirements stay below 820 MW. In summer, the 16:00–20:00 block reaches 1,500 MW.
The summer evening spike reflects a specific grid dynamic. When negative-price episodes end, renewable output ramps back up and cross-border flows shift abruptly.
This transition generates sharp upward imbalances in the minutes leading up to spot prices turning positive. As a result, RTE sizes the upward requirement for 16h–20h at nearly twice the winter peak.
For BESS operators, this pattern aligns well with how batteries operate. During negative-price hours, a battery can charge at minimal cost on the spot market. When the episode ends, and upward aFRR demand surges, that stored energy becomes available for reserve activation.
How does the aFRR capacity auction work?
The aFRR market has two distinct revenue streams: a capacity payment for availability and an energy payment for actual activation.
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