Enervis Battery Storage Index: December revenues fall to multi-month low

With the current publication, we are, for the first time, covering a full annual period since the launch of the Enervis Battery Storage Index at the beginning of 2025. In addition to analyzing the revenues achievable in December, this edition therefore also provides an opportunity to review the completed year 2025. The index is based on historical market data and reflects revenue opportunities for battery storage systems from participation in both the intraday market and the balancing power markets. For each month of the past 13 months, the respective achievable revenues are reported.

New revenue figures for December 2025

Achievable BESS revenues in December continued their pronounced decline and reached exceptionally low levels. Revenues fell to approximately €5,000 per megawatt, representing a 30% decrease compared with November and standing 49% below December 2024. This marks some of the lowest values ever observed. Volatility in the spot markets weakened significantly, with the average spread declining by 29% compared with November, thereby severely limiting arbitrage opportunities for battery storage systems. At the same time, ancillary services prices fell to very low levels, even compared with December results over the past four years, further constraining revenue potential.

2025 review

The monthly revenues achievable by battery storage systems in 2025 exhibited a pronounced seasonal pattern. Revenues typically increased from spring into the summer months and declined significantly toward the end of the year. Higher revenue levels occurred particularly during periods of elevated renewable electricity generation, especially from photovoltaics, which led to increased intraday volatility and system imbalances, thereby supporting both intraday trading and ancillary services revenues.

Monthly achievable revenues fluctuated substantially over the course of 2025. They ranged from a low of approximately €5,000 per megawatt per month in December 2025 to peak values of around €19,000 per megawatt per month in May and September. The generally seasonal pattern was interrupted during the summer by a pronounced revenue decline in July and continued moderate volatility in August. A key reason for this was comparatively low solar irradiation in July.

Overall, 2025 was characterized by pronounced monthly revenue volatility, with average month-to-month fluctuations of around 31%, featuring a strong increase in spring followed by an equally pronounced decline in autumn.

Over the past twelve months, this resulted in an average monthly revenue level of approximately €12,370 per megawatt, corresponding to an annual value of around €148,500 per megawatt. This level is broadly in line with 2024 and around €4,300 per megawatt higher (+3%) than the average annual revenues achieved in that year.

Expected revenues for 2026

Analogous to the approach used for the historical analysis, the Enervis Battery Storage Index also provides a forward-looking perspective. Based on our current power price forecasts, the operation of a typical stand-alone battery storage system is modelled for the year 2026.

For the projection of achievable revenues, the underlying Enervis electricity price scenario has been updated to the Current Efforts Q1/2026 scenario. The modeled revenues under the new scenario are close to those of the Q4/2025 scenario. Overall, revenues decline by approximately €3.7 thousand per megawatt, corresponding to a reduction of around 2.5%. Higher spreads in the day-ahead market are partially offset by lower balancing power prices in the new scenario, resulting in a slightly lower overall revenue level.

The forecast revenues for 2026 amount to €145,900 per megawatt per year, slightly below the average achievable revenues of the past twelve months, but still within a comparable range, as shown in the Battery Storage Index. Storage parameters were kept unchanged.

Methodological explanation: The Enervis Battery Storage Index shows the monthly net revenues that can be achieved historically and in the future in Germany for a 1 megawatt capacity and 2 megawatt hours storage volume (2 hours) battery storage system. The storage system was modeled with a use restriction of 1.5 cycles per day, a maximal depth of discharge of 90%, a technical availability of 97% and a round-trip efficiency of 87%. The index takes into account participation in the following markets: Intraday, Frequency Containment Reserve (FCR) and automatic Frequency Restoration Reserve (aFRR). Imperfect foresight and no revenues from aFRR energy are modeled. The respective prices of the markets for the historical analysis are taken from publications of the transmission system operators and EPEX-Spot. The future outlook is based on the same modeling and parameters and prices from the current Enervis power price scenario Current Efforts Q1/2026.

Further information:

More detailed analysis and the full report can be requested here.

About the authors: 

Mirko Schlossarczyk, managing director of enervis energy advisors, is an experienced energy market expert. His consulting focus is on electricity price forecasts, electricity market scenarios, and the asset valuation of BESS.

Jonas Anthonioz is a consultant at enervis energy advisors, where he is responsible for battery energy storage related topics. In addition to his tasks in revenue assessment and profitability analysis of battery energy storage projects, he developed the enervis “BESS Index” and the associated “BESS Index Report.“