Reserve Market Guide

Electricity grid balance is maintained by Fingrid, which procures reserves – the capacity to adjust power – to keep the system frequency around 50 Hz. Reserves are typically divided into frequency containment and restoration reserves (FCR, aFRR, mFRR) and security-of-supply reserves. A market participant offers the capacity to ramp power up or down within a specific timeframe, receiving payment for the committed capacity regardless of whether it is activated.

For battery storage, this is a key difference from conventional backup power: revenue comes from capacity, not fuel consumption. A battery responds in seconds, making it highly competitive, especially in frequency regulation reserves. At the same time, the battery is not locked purely into reserves; it can be sized to participate in electricity price arbitrage and peak shaving simultaneously.

Selling reserves requires registering as a market participant with Fingrid or partnering with an already registered operator. For most industrial and agricultural sites, the latter is the most practical route: the operator manages bidding, metering and settlements, while the asset owner receives their agreed share of the revenue.

In practice, capacity is offered in megawatts and is often tiered: the faster the response, the higher the value of the reserve. A battery storage system can provide multiple reserve types concurrently, provided the power and energy requirements do not conflict. Any conflicts and double compensation are avoided through capacity allocation managed by the operator.

Grid integration consists of four stages: capacity assessment, technical suitability, contracting and continuous monitoring. The assessment determines how much power adjustment the site can deliver and for how long. Technical suitability verifies the inverter and battery response times, protection settings, and the adequacy of metering and communications. The contract defines the reserve type, capacity and compensation model. Monitoring ensures the battery remains operational whenever called upon.

A crucial metric is response time: in frequency containment reserves, activation must begin within seconds. For this reason, the battery management system and grid connection are always configured specifically for rapid response, not just energy storage.

The calculation below is an illustrative example, not an offer. It reflects typical capacity and uses Watti's current partner terms.

Floor: €55,000/MW/year – Guaranteed minimum return, with potential upside from market revenue.

Tolling: €75,000/MW/year – Fixed lease revenue: capacity is leased to the operator at a fixed price.

Revenue under the Market model depends on prevailing reserve prices and fluctuates, so it is always verified during the quotation phase.

Example: With an Emaldo PL-EL-250/836-G400 system, the available power is 250 kW (0.25 MW). Under the Tolling model, annual capacity revenue is around €18,750. Simultaneously, the battery can perform peak shaving, generating separate savings on the demand-based component of the grid tariff.

Figures are based on "Watti / partner offers; Market benchmark: Clean Horizon Battery Index 2h" and are valid from 2026-10-08.

Reserve revenue comes with commitments: cycling degrades battery cells, and reserve contracts mandate high availability. Contracts typically impose penalties if the agreed power response is not delivered. Therefore, battery sizing is carefully engineered to keep cycling within manufacturer parameters and preserve estimated asset life.

It is also vital to ensure the same capacity is not double-sold, and that insurance and tax matters are properly addressed. For instance, changes in electricity tax classification can significantly impact the site's overall economics.