Flexibility marketing for BESS operators: Models, contracts, aggregators in comparison

Anyone who is planning or already operating a front-of-the-meter (FTM) battery energy storage system cannot avoid one question: Who markets the system's flexibility on the electricity market—and under what conditions? In most cases, the answer is a specialized flexibility aggregator. This article explains what Flexibility marketing specifically, what contract models exist, what operators should look for when choosing a partner, and which providers are active on the German market.

What is flexibility marketing?

Flexibility marketing refers to the sale of an asset's ability to increase or decrease its feed-in or consumption on short notice in exchange for compensation on electricity and balancing energy markets. In the case of battery storage systems, this flexibility consists of the charging and discharging power as well as the available capacity. A flexibility aggregator pools this flexibility, trades it on exchanges such as EPEX Spot or EEX, and handles the technical connection, market access, and frequently also the balancing group responsibility.

For operators, this means they do not have to set up their own exchange membership, trading desk, or real-time trading algorithms. The marketer takes on these tasks as part of a flexibility marketing agreement.

Comparison of flexibility marketing, direct marketing & tolling

In practice, the three terms are often used synonymously, but they are neither legally nor economically identical—and not every model fits every type of investment.

Direct marketing

Direct marketing is a legally defined term pursuant to Section 20a of the Renewable Energy Sources Act (EEG) and generally refers only to EEG-subsidized green electricity generation plants (PV, wind, biomass, etc.). Instead of a fixed feed-in tariff, the plant operator—or a commissioned direct marketer—markets the generated electricity themselves on the market and additionally receives a floating market premium to compensate for the target value.

A Standalone Storage basically without own EEG-subsidized generation not into this category. Direct marketing for storage systems only becomes relevant if they are directly coupled with an EEG-subsidized system and – depending on the metering concept – store and discharge green electricity. Exactly this distinction is the subject of the MiSpeL reform. Read more in our articles “MiSpeL: More Market & Opportunities for Large-Scale Storage?”and“MiSpeL 2026: When does the determination apply and what does it mean for BESS projects?“

Flexibility marketing

For the classic standalone BESS in FTM operation, which operates on the market independently of a subsidized generation plant, therefore the relevant approach is not direct marketing, but rather Flexibility marketing the relevant model or designation. This is a purely contractual construct with no reference to the EEG [Renewable Energy Sources Act], in which the operator participates in the actual trading result. They also usually determine the marketing strategy in advance together with the marketer. This often depends on the technical design of the storage facility, market conditions, and the operator's economic objectives.

Tolling

Tolling is also not an EEG term, but originates from the gas-fired power plant business. There, a tolling partner pays a capacity fee, supplies the fuel themselves, and markets the generated electricity entirely under their own direction. With battery storage systems, the principle works analogously, just without fuel: a tolling partner—usually an energy trader or financial investor—rents the complete storage capacity for a defined period. They take over full dispatch control (when and how charging and discharging take place), bear the entire market risk, and keep all trading proceeds. In return, they pay the operator a fixed, predictable remuneration per MW and year—regardless of the actual market outcome. The operator thereby completely relinquishes operational control of the plant.

Direct comparison

Thus, the essential difference between flexibility marketing and tolling lies not in the legal framework, but in the Control and risk allocationUnder tolling, the operator completely relinquishes dispatch control in exchange for planning certainty. With flexibility marketing, the operator retains influence over the plant strategy—at least within defined limits—and participates directly in the market outcome, but consequently also bears its volatility.

How a flexibility marketing contract works

At its core, a flexibility marketing contract governs three things:

• Market access
• Control sovereignty over the facility
• Compensation

For operators and investors, it is crucial in practice to clarify these relevant contract components with potential marketers at an early stage before a plant concept is finalized:

• Multi-market capability: Can the marketer flexibly switch the asset between intraday, day-ahead, and balancing energy markets (aFRR, mFRR) to choose the most lucrative marketing option in each case? What maintenance and calibration times must be taken into account?
• Balance group and metering concept: Who assumes the balance group responsibility, and how is the system connected in terms of measurement technology (separate metering location, summation meter, remote control technology)?
• Control sovereignty To what extent is the marketer allowed to remotely control the system, and what limits (state of charge, maximum number of cycles) does the operator specify? Are there time windows for BTM applications that need to be observed?
• REMIT-Compliance: Who ensures that trading activities comply with the transparency and reporting obligations of the REMIT Regulation?
• Term and exit options: Notice periods, change of marketer, procedure in the event of a technical failure of the system.

Remuneration models: Profit-Share & Floor-Price

In flexibility marketing, two basic models have been established, which are also frequently combined:

Profit-Share: The marketer or aggregator receives a percentage share of the trading result achieved, with figures of 20 to 30 percent being customary, depending on the plant concept and the technology used. The operator bears the full market risk, but in return benefits fully from strong market phases.

Floor Price (Minimum Guaranteed Revenue) The marketer guarantees a minimum remuneration per MW and year, regardless of the actual market outcome. If the revenue achieved exceeds this, the surplus is usually shared. This model reduces the risk for the operator, but is typically accompanied by a lower revenue cap.

For companies that purchase a battery storage system and use third-party financing, a variation of the floor price model is usually more cost-effective because it significantly improves bankability. This keeps the risk lower and more predictable. CUBE CONCEPTS, as the operator, frequently agrees on a profit-share model with BESS Contracting or CPFS. Companies benefit from this right from the first day of operation. However, which model makes more economic sense in the end depends on the operator's risk-bearing capacity, the project's financing structure, and the expected market volatility.

What operators should look for when choosing a flexibility aggregator

Companies wishing to transfer the marketing of their FTM battery storage capacities to a flexibility aggregator should consider various technical, economic, and contractual criteria when selecting a partner. CUBE CONCEPTS relies on cooperation with renowned and experienced marketing partners to ensure reliable marketing and long-term revenue optimization.

• Market access and experience: Is the aggregator actively licensed in all relevant markets (intraday, day-ahead, balancing energy), and what generation portfolio does it have proven experience with – specifically with battery storage systems?
• Track Record in BESS: Are concrete, referenceable revenue figures for comparable storage projects disclosed?
• Technical Integration: What telecontrol technology and interfaces (e.g., to the plant's EMS) are required, and who bears the integration costs?
• Transparency: Does the operator get insight into individual trades, or is only an aggregated result shown?
• Contract flexibility: How short-notice can the marketer be changed if the cooperation is not convincing?
• Credit rating and default risk: Especially in the case of floor price models, the economic substance of the marketer is relevant because they must bear the guarantee themselves.

Aggregator landscape in Germany and Europe

The market for flexibility trading has grown significantly in recent years, ranging from established energy traders and municipal utilities to specialized aggregators and algo-traders that focus specifically on battery storage systems.

CUBE CONCEPTS collaborates with specialized flexibility marketers, algo-traders, and optimizers on FTM projects – including with Second Foundation and Inspired, two providers active in the German and European markets that specialize in the algorithmic marketing of battery storage flexibility at Control energy, Day-Ahead Trading and Intraday Trading specialized. As a project developer and integrator, CUBE CONCEPTS assumes the interface function: from the technical design of the system for FTM capability and the selection of the suitable marketing partner to the contractual connection.

This choice of partner is made on a project-specific basis – depending on the plant size, location, grid connection point, and the operator's individual requirements regarding the risk profile and contract duration.

Regulatory Framework

The flexibility marketing of battery storage systems in Germany operates within the interplay of EU electricity market law, the Energy Industry Act, redispatch rules, and the regulations for controllable consumption devices. At the European level, the primary focus is on the Directive (EU) 2019/944 relevant, that is in Article 32 provides for market-based, non-discriminatory procurement of flexibility services. In Germany, this framework is essentially established via the EnWG, the Redispatch 2.0regulations as well as the guidelines of the Federal Network Agency are specified. For operators of FTM battery storage systems, this means: flexibility may be marketed, but the technical and balancing integration must be properly regulated.

For standalone BESS, the distinction from EEG direct marketing is important. Direct marketing according to § 20a EEG concerns fundamentally EEG-subsidized generation plants, but not a pure grid storage facility without a coupled green electricity plant. The classic FTM storage facility is therefore usually used in practice via a flexibility marketing or tolling agreement. In addition Section 14a EnWG For controllable consumer installations: As soon as the storage system acts as a controllable load in the grid during charging, the requirements for controllability, grid fee regulation, and grid connection must be observed. Depending on the system design, metering concepts, balancing group allocation, telecontrol technology, and REMIT obligations may also apply. For operators, it is therefore crucial to set up marketing correctly from the start, not only economically, but also regulatory and technically.

Queen Green electricity storage, which previously applied Exclusivity option pursuant to Section 19 (3a) of the Renewable Energy Sources Act (EEG) and receive an EEG remuneration for the fed-in electricity, have previously hardly been able to benefit from flexibility marketing. They exclusively charge electricity from their own RES systems and are only allowed to feed green electricity into the public grid. As a result, an actual marketing of flexibility has not been possible to date. Grey Water Storage Tank on the other hand, can also draw electricity from the public grid and thus become full market participants. However, if they are coupled with a renewable energy system, the EEG (Renewable Energy Sources Act) surcharge has so far been omitted. With the Solar peak law on February 25, 2025, the legislature broke this logic. The new Accrual option (Section 19 (3b) EEG, Section 21 (1–4) EnFG) will in future enable an energy storage system to absorb both green and grey electricity components—and still proportionately receive EEG funding for the green component.

FAQ: Flexibility Marketing for BESS Operators