BESS multi-use marketing – five markets, one capacity window

Multi-use done right: sequential, not parallel

Multi-use is often mis-sold. The promise sounds like this: one battery earns on several markets at the same time. Physically, that is not true.

A battery has only one capacity window per time slot. Peak shaving, arbitrage, FCR and aFRR cannot be stacked within it simultaneously. Multi-use means something more demanding – the daily, EMS-controlled choice of the most valuable market for each time slot. Sometimes the storage earns with frequency containment, sometimes with arbitrage, sometimes it shaves the peak load of the on-site customer. Sequential, not additive.

This discipline is exactly what separates serious BESS planning from over-optimistic sales brochures: calculate honestly instead of summing up revenues that never occur at the same time. All revenue ranges in this article are therefore the best possible daily mix under optimal control – not the sum of markets served simultaneously.

The five revenue sources at a glance

Five markets are relevant for a battery storage system.

FCR (primary control reserve) keeps the grid frequency stable and is remunerated solely for the reserved capacity. aFRR (secondary control reserve) balances larger frequency deviations and remunerates capacity plus the energy actually delivered. Arbitrage exploits price differences on the power market: charge cheaply, discharge expensively. Peak shaving lowers the on-site customer's grid fees by breaking their annual peak load. Self-consumption optimisation maximises the on-site use of PV power instead of the lower-remunerated grid feed-in.

What each source is, is set out here. How it works – and why the sources cannot be used simultaneously – is shown in the next section.

How the daily best-market selection works

At the centre sits the Energy Management System, EMS for short. In real time it weighs which market will bring the highest contribution margin in the next time slot – while respecting technical limits: state of charge, cycle budget and warranty limits.

The market options behave differently. FCR reacts fully automatically via a local frequency sensor, full activation within 30 seconds; only the reserved capacity is remunerated, not the energy (a minimum holding time of around 15 minutes should be treated as an estimate). aFRR is controlled centrally by the transmission system operator via a digital setpoint, full activation within 5 minutes; here both capacity and delivered energy count. Arbitrage requires a roundtrip efficiency of at least 85 percent (LFP standard) and free cycle budget; on the Continuous Intraday market (XBID) the position can be readjusted up to 5 minutes before delivery, which absorbs short-term PV or weather forecast errors.

The core stays simple: each of these options occupies the same capacity window. Whoever reserves the battery for FCR runs no arbitrage in the same slot. The EMS therefore decides anew for each time slot and balances the cycle budget between the markets. That is the actual multi-use performance. Both control reserve markets require prequalification with the transmission system operator (details in the implementation part).

What multi-use delivers economically

Now it gets concrete – and here is where the sequential logic matters.

The following ranges refer to the revenue per installed megawatt and year. This is a normalisation for comparability; the market standard quotes €/MW capacity price and €/MWh energy price respectively. Pure FCR marketing was roughly 25,000 to 60,000 EUR per MW and year in 2025/2026, fluctuating strongly by market phase; aFRR is in a similar order of magnitude. Arbitrage delivers considerably more in volatile weeks and considerably less in quiet phases. Peak shaving generates no market revenue but grid-fee savings – for an industrial operation with a reducible annual peak load, quickly six figures per year.

The decisive point: these values do not add up. The realistic multi-use blended revenue is the best possible daily mix across all time slots of a year, not the sum of the individual markets. All figures are market assessments, project-dependent and not guaranteed revenues.

Three example calculations

Three anonymised cases make the blended-revenue logic tangible.

Case A – 1 MW / 2 MWh commercial storage: CAPEX 600,000 to 800,000 EUR, OPEX 15,000 to 25,000 EUR per year, blended revenue around 80,000 to 100,000 EUR per year, payback about 7 to 9 years. Here the investment deduction under § 7g EStG (German Income Tax Act) can improve the tax effect, provided the profit threshold of 200,000 EUR is met in the relevant financial year.

Case B – 5 MW / 10 MWh industrial BESS: CAPEX 2.5 to 3.5 million EUR, OPEX 60,000 to 90,000 EUR per year, blended revenue including peak shaving 300,000 to 500,000 EUR per year, payback 6 to 8 years. Important: § 7g EStG is generally not usable here because the 200,000 EUR profit threshold at company level is usually exceeded.

Case C – 20 MW / 40 MWh standalone large-scale storage: CAPEX 8 to 11 million EUR, OPEX 150,000 to 250,000 EUR per year, revenues 1.2 to 2.0 million EUR per year, payback 5 to 7 years; here too § 7g EStG is practically ruled out because the profit threshold is exceeded.

All three cases are example calculations, not guaranteed values – they illustrate the logic explained above.

Legal framework: tax, electricity tax, REMIT, registration

Anyone entering multi-use must know four legal fields. They are relevant to profitability but must be considered separately from it – readers interested only in the revenues can skip to the next section.

Tax. § 7g EStG (German Income Tax Act) offers the investment deduction: up to 50 percent of the expected acquisition costs can be deducted in advance to reduce profit, complemented by the special depreciation under § 7g (5) EStG of 40 percent. Since the 2020 reform, the prerequisite is a uniform profit threshold of 200,000 EUR in the relevant financial year – equally for balance-sheet accounting (§ 5 EStG) and cash-basis accounting (§ 4 EStG). Businesses above this threshold cannot use the deduction.

Electricity tax. The common reference to § 9 (1) no. 2 StromStG (German Electricity Tax Act; electricity used for generating electricity) does not hold for battery storage: in its judgment of 19 June 2012 (VII R 33/10), the Federal Fiscal Court ruled that storing electricity in an accumulator is not electricity generation in this sense. Instead, § 5 (4) StromStG applies. Storage in which a supplier temporarily stores electricity and feeds it back into the supply grid is deemed part of the supply grid in this respect – provided it is registered in the Market Master Data Register. The storing is then not a taxable withdrawal. A separate permit from the main customs office has no longer been required for this since July 2019; however, notification and cooperation obligations remain (description of storage, use and contracts), and supplier status must be clarified with the responsible main customs office.

REMIT. Here too a misconception circulates. The frequently cited threshold of 600 GWh per year concerns the consumption capacity of final customers in the definition of wholesale energy products (Art. 2 no. 4 in conjunction with no. 5 REMIT), not the trading turnover of storage operators. For market participants with wholesale energy transactions (FCR, aFRR, spot) no such minimum threshold applies; the registration obligation under Art. 9 REMIT can apply regardless of volume.

Registration. From an administrative standpoint, the following are added: entry in the Market Master Data Register (MaStR) within one month of commissioning, for grid connection from 135 kW the registration as a generation plant under VDE-AR-N 4110/4120, and metering point operation under the MsbG (German Metering Point Operation Act). For PV-coupled storage, the MiSpeL ruling of 1 October 2026 allows mixed operation via the delineation option (Abgrenzungsoption) and, for PV up to 30 kWp, the flat-rate option (Pauschaloption). Until 30 September 2027 this requires consent of the grid operator and the metering operator; the flat-rate option also requires EU state-aid approval. It applies to the market premium and direct marketing, not the fixed feed-in tariff. Separate metering (Ausschließlichkeitsoption) remains available alongside it.

Implementation: EMS, marketing partner, prequalification

Once the decision has been made, implementation follows in three steps.

First, the EMS as the control layer. Mandatory interfaces are SCADA to the battery management system, the market connection to the marketer, and the TSO interface for aFRR setpoints (IEC 60870-5-104, ICCP). Cyber security under IEC 62443 and ISO 27019 is increasingly required, especially for aFRR; for critical revenue streams a second EMS instance or a failover mode is worthwhile. Setup costs vary strongly and are project-dependent (estimate).

Second, the marketing. Individual plants often do not reach the minimum bid size of the control reserve markets – 1 MW for both FCR and aFRR – on their own. Pool marketers therefore bundle several plants. Aggregators active on the market include, for example, Next Kraftwerke, EnBW, MVV Trading, Entelios or Entrix; Statkraft and BayWa r.e. are also real market participants. I name these companies as examples from the market, not as partners. The same threshold applies to the minute reserve (mFRR): the Bundesnetzagentur lowered it from 5 MW to 1 MW by decision BK6-21-042 of 28 April 2022. Selection criteria are contract duration, fee structure and billing transparency.

Third, the prequalification (PQ) with the transmission system operator – site-specific and non-transferable. Market sources cite roughly 4 to 8 weeks in duration and 15,000 to 50,000 EUR in effort; higher values are possible. Treat these ranges as a market assessment, not a fixed figure. For peak shaving, § 19 (2) sentence 1 StromNEV (German Electricity Grid Fee Ordinance; atypical grid use) applies from a regulatory standpoint.

Anyone who builds a cluster of many small storage units instead of a single storage reaches the minimum bid sizes jointly. The cluster model structures 10 to 100 individual storage units via purchase contracts with a condition precedent (§ 158 BGB, German Civil Code) and an escrow account: each owner remains the sole owner of their unit – without pooled assets and without KAGB (German Investment Code) risk. Details on the homepage and the BESS knowledge page.