The Belgian automatic Frequency Restoration Reserve (aFRR) market has hit a turning point.

Market Structure

Belgium operates two reservation auctions – 4h and 24h product – with the 4h product dominating volumes over the past year.

What changed?

A wave of new BESS capacity came online in 2025, as major 4h storage projects reached COD in Belgium, totalling 325 MW of newly commissioned batteries.

Impact on Prices

As these assets entered the market, competition intensified and reservation prices dropped sharply.
The Belgian aFRR reservation market — relatively shallow — is now effectively saturated under current market conditions.

Strategic Shift

Market players are no longer bidding based on standalone aFRR value.

Instead, bids are increasingly driven by opportunity cost:
– Day-ahead spreads are acting as a price floor
– aFRR revenues are now converging with single-cycle day-ahead trading revenues for 4h systems

Bottom line: aFRR is no longer a standalone business case — it’s becoming part of a broader optimisation strategy.

Thanks to Vitor Gialdi Carvalho and Jules Gallazzini, Clean Horizon consultants, for this analysis.

Want to go deeper?
Learn more in our Clean Horizon Belgium Price Forecast