September showed just how quickly conditions can change in the German electricity market. While high gas prices continued to support wholesale electricity prices, the declining influence of summer solar generation made periods of low renewable output increasingly significant. This was particularly evident during extended periods of low wind generation, which led to pronounced price peaks and wider price spreads.
September in Numbers
To assess how these market developments affected battery revenues, we analyzed simulated earnings for a representative 10 MW / 20 MWh grey standalone storage in Germany. As in previous months, we compared individual wholesale and ancillary service strategies with suena energy’s forecast-based cross-market optimization approach.
Wholesale strategies recovered strongly compared with August. Continuous intraday trading remained the strongest individual spot-market strategy, with revenues rising 36% to €17.5k per MW per month. Day-ahead trading and intraday auctions also improved, reaching €13.8k and €13.2k per MW per month respectively, up from €10.8k and €10.5k in August. The stacked wholesale strategy recorded an even stronger result, climbing from €15.4k to €20.9k per MW per month, the strongest single-stack result in our observed series.
Ancillary services presented a more mixed picture. FCR declined slightly to €14.3k per MW per month, while positive aFRR recovered significantly, rising 50% to €8.4k per MW per month. Negative aFRR, by contrast, fell to €11.3k per MW per month, while the stacked aFRR strategy remained broadly stable at €9.9k per MW per month. The aFRR energy benchmark reached €7.9k per MW per month under a revised calculation methodology and is therefore not directly comparable with previous months.
The strongest overall result once again came from cross-market optimization. suena energy’s approach generated €25.5k per MW per month, slightly above August’s €25.3k. This was 22% above the combined wholesale benchmark, although the advantage narrowed considerably as wholesale trading revenues recovered.
Higher Prices, Wider Spreads
Wholesale electricity prices continued to rise in September. The average day-ahead price reached €144.80/MWh, around €18/MWh above August and more than 50% higher than in September 2025. Higher fuel costs remained a major driver. Spot gas prices averaged €76.20/MWh and exceeded €80/MWh towards the end of the month, while coal and carbon prices added further upward pressure.
Despite unusually sunny and dry weather, renewable generation was less able to cover demand than in previous months. Solar output remained strong for September but declined seasonally compared with August, while wind and hydropower generation also weakened. Renewables accounted for around 66% of German electricity generation, with a larger share of residual demand covered by conventional power plants, particularly coal. Negative day-ahead price hours also became less frequent, falling from 55 in August to 39 in September.
The effects were especially noticeable during two extended periods of low wind generation, when evening price peaks became particularly pronounced. Evening electricity prices averaged around €261/MWh during these weeks, while the monthly day-ahead top-bottom spread for a two-hour battery reached approximately €220/MWh, its widest level since the 2022 energy crisis. These pronounced price differences created more attractive opportunities for battery arbitrage, helping explain the recovery in wholesale trading revenues.
The divergence between wholesale and ancillary service revenues also became more apparent. Greater demand for upward flexibility during periods of tight supply supported the recovery in positive aFRR revenues, although these remained below September 2025 levels due to growing competition from battery storage. Negative aFRR revenues, meanwhile, declined as periods of surplus electricity became less frequent.
Flexibility in a Changing Market
September highlighted how quickly battery revenue opportunities can shift between markets. Following August’s weaker wholesale performance, wider price spreads brought a substantial recovery in day-ahead and intraday revenues. At the same time, ancillary service markets followed different trajectories, reinforcing the importance of flexibility across trading strategies.
Looking ahead, shorter days and more variable renewable generation are likely to further influence electricity price patterns as autumn progresses. In the longer term, the continued expansion of battery storage is also likely to play an increasing role in shaping electricity prices, affecting the frequency and duration of extreme price movements.
As battery storage increasingly shapes the markets in which it operates, accurate forecasting and the ability to respond dynamically across markets will therefore become even more important for capturing revenue opportunities.
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