January 2026 Update

Clean Horizon has launched the index in January 2025 simulating past revenues of a storage project across European markets. The methodology to compute the index changes in January 2026 to better reflect realistic average battery revenues in the different markets:

• Before January 2026, the index showed the potential revenues of a marginal MW of battery, operating freely on all the markets available to storage, therefore capturing the best marginal revenue (even though this revenue might only be considered for a small portion of the storage capacity).
• Starting January 2026, the index now takes into account the actual volumes available on both capacity reservation and energy activation markets, as well as the installed storage capacity in the country. The result of the index thus shows the potential revenues not of the marginal MW of battery anymore, but rather of the average MW of battery operating on the markets, and evolving among the pool of other projects also operating on the markets. This approach allows better considerations of market conditions, and volumes, especially as deployed storage volume grows and optimizers have to split their assets on the different markets.

Besides, the computation tool behind the index (COSMOS) is now able to optimize battery operations at a 15-minute timesteps instead of 1h as of 2025, following the recent change in the day-ahead market products.

In addition to these changes, the following country specific elements have evolved:

• Capacity mechanism revenues have been removed in the calculation of the index for France.
• Portugal and Romania are now covered by the index.
• Intraday revenues have been added based on historical transactions in each country.

What is the Storage Index?

The Storage Index is calculated monthly and represents the annualised gross revenue of a storage asset based on the energy, capacity and ancillary services prices observed during that month. In other words, the calculated value assumes that the year consists of 12 repetitions of the same month; the Storage Index thus provides accurate information on how the specified month’s prices impact the revenue of a storage asset.

How is it computed?

The Storage Index is calculated using COSMOS, Clean Horizon’s sophisticated energy storage simulation tool. For more information about COSMOS, please visit our web-page or contact our business development team at sales@cleanhorizon.com.

The Storage Index calculation considers the following parameters:

• Round trip efficiency (measured at grid connection point): 85%
• Cycles: 1.5 cycles per day (Clean Horizon’s reference cycling constraint)
• System availability : 100%
• The BESS duration is calculated based on the usable AC BESS energy
• Prequalification requirements tailored to each market and country and based on Clean Horizon’s expertise
• Complete knowledge of day-ahead market price. D-1 auction markets prices for ancillary services are almost completely known (e.g. FCR, aFRR capacity reservation, etc…): the forecast excludes rare prices spikes, ensuring more realistic decisions without assuming perfect prediction of extremes.
• No information on prices from other markets; estimates are derived from a statistical analysis of historical prices (e.g., aFRR energy, mFRR energy).
• Index revenues are gross revenues: grid fees, taxes and SOC management costs are not taken into account in the calculation.

The Storage Index is based on historical market data for each month. This data automatically collected by Clean Horizon ensuring that the revenue calculations reflect realistic operating conditions.

Which revenue streams are currently considered for each country?

• Belgium: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, aFRR and imbalance.
• Denmark DK1: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, FCR, aFRR (capacity and energy since October 2024), and mFRR capacity reservation.
• Denmark DK2: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, FFR, FCR-N, FCR-D, aFRR (capacity and energy since October 2024), and mFRR capacity reservation.
• Estonia: Revenues are calculated based on participation in the Day-Ahead market, FCR, aFRR and mFRR.
• Finland: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, FFR, FCR-N, FCR-D, aFRR, and mFRR capacity reservation and energy activation markets.
• France: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, FCR, aFRR, mFRR and the Capacity Mechanism.
• Germany: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, FCR, and aFRR.
• Italy: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, MSD (ex-ante) and MB, using SUD zone prices.
• Latvia: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, FCR, aFRR and mFRR.
• Lithuania: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, FCR, aFRR and mFRR.
• Poland: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, FCR Up and Down, aFRR and mFRR.
• Portugal: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, aFRR and mFRR.
• Romania: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, FCR, aFRR and mFRR.
• Spain: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, aFRR and mFRR.
• Sweden: Revenues are calculated based on participation in the Day-Ahead market, the Intraday market, FCR-N, FCR-D, and mFRR, using SE3 zone prices.

How often is the Storage Index published?

It is updated every month.