An unconstrained two-hour battery in Germany could have earned €215k/MW/yr in September 2026. That is 12% more than in August, as say-ahead spreads in September were the widest since the energy crisis in 2022.

But the same battery could have earned €351k/MW/yr in September 2025. Revenues fell 39% in a year, although the underlying spreads were far wider this year.

Two forces explain the gap. Gas prices more than doubled, which pushed evening power prices up and widened spreads. At the same time, the reserve markets that paid most of last year's revenue have begun to fill up with batteries. Wider spreads added money, but nowhere near enough to replace what reserve prices lost.

Key takeaways

• Gas prices set the revenues last month, explaining much of the month-on-month increase. TTF averaged about €76/MWh in September, against about €33/MWh a year earlier. That roughly doubled the fuel cost of the gas plants that set Germany's evening price.
• The day-ahead TB2 spread averaged €220/MWh, the widest since 2022. A pure energy trading strategy could have earned about €148k/MW/yr, almost 20% more than a year ago.
• Two windless weeks created system tightness with high net load to be met with gas, and evening prices in those weeks averaged €261/MWh.
• While aFRR capacity still contributed the largest part of the stack at €116k/MW/yr, its dominance in the stack compared to last year has shifted.
• Month-on-month, aFRR up prices recovered 66% to €12.2/MW/h, which drove most of September's rise. But they are about 50% lower than a year ago.

High gas prices lifted spreads, but cheaper reserve pulled revenues below last year

Last September, aFRR capacity made up 94% of what the battery could have earned. Trading energy was less profitable and effectively only used for state-of-charge management, at 5% of the stack.

This September looks very different. aFRR capacity fell to 54% of the total, and day-ahead plus intraday rose to 30%. FCR added another 16%. The battery now earns from more places, but less in total. aFRR still dominates - saturation is not fully here yet. But the premium from being active in ancillary markets has shrunk.

Ancillary revenues, not the day-ahead part, drove the rise from August

Compared with August, the battery could have earned €24k/MW/yr more. aFRR capacity added €20k/MW/yr of that, almost all from the upward product. Intraday added €6.8k/MW/yr and FCR €2.3k/MW/yr.

Day-ahead revenue barely moved, even though spreads widened. aFRR prices increase together with their opportunity cost on the day-ahead market, giving an incentive to keep putting capacity into ancillary markets.