More than 1,600 battery systems scattered across Germany - most installed to keep the lights on at mission-critical facilities - are about to become active participants in the country's wholesale flexibility markets. That is the core of the multi-asset tolling agreement signed on April 22, 2026, between RWE Supply & Trading and Swedish battery developer Polarium, and it marks a structural shift in how distributed energy resources can be commercialized at scale.
From late 2026, RWE will optimize at least 50 MW of power and 135 MWh of energy from Polarium's distributed battery portfolio within its trading operations. The full Polarium portfolio is expected to grow to approximately 300 MW / 810 MWh across more than 10,000 individual battery systems.
How the Deal Works: A Cloud-Aggregated Virtual Battery
The agreement's commercial architecture is as important as its headline numbers. Rather than a conventional tolling structure centered on a single large-scale asset, the two companies have built what amounts to a software-defined power plant.
Over 1,600 behind-the-meter battery energy storage systems (BESS) located throughout Germany are aggregated via Polarium's cloud platform into one virtual battery, enabling real-time control and secure market participation while unlocking value from underutilized assets and grid infrastructure.
The mechanism is straightforward. Polarium's distributed battery systems are primarily installed to provide backup power for mission-critical customer infrastructure. Any remaining headroom not needed by individual customers is pooled virtually through the Polarium platform and made available to RWE for commercialization.
The arrangement relies on a single technical interface connecting RWE to the Polarium platform, which the companies say simplifies integration of new sites as the portfolio grows. That standardized interface is designed to maintain consistent performance standards across a highly diverse fleet of battery systems distributed across Germany.
Deal Parameters at a Glance
| Parameter | Initial Phase (Late 2026) | Full Portfolio Target |
|---|---|---|
| Power Capacity | 50 MW | ~300 MW |
| Energy Capacity | 135 MWh | ~810 MWh |
| Number of BESS Sites | >1,600 systems | >10,000 systems |
| Asset Type | Behind-the-meter BESS | Behind-the-meter BESS |
| Aggregation Method | Polarium cloud platform | Polarium cloud platform |
| Commercial Structure | Multi-asset tolling agreement | Multi-asset tolling agreement |
| Optimizer | RWE Supply & Trading | RWE Supply & Trading |
What Makes This Model Novel
The distinction from conventional tolling is not merely technical - it is commercially significant.
Traditional tolling structures typically involve a single large-scale storage asset. This first-of-its-kind approach pools numerous distributed systems via the cloud, enhancing flexibility and scalability.
Spreading storage capacity across thousands of locations rather than concentrating it in a handful of large facilities carries several operational advantages: reduced strain on individual grid nodes, improved performance, and potentially extended asset lifespans. It also distributes operational risk across a large number of systems rather than concentrating it in a single installation.
For asset owners, the model opens a monetization channel for capacity that would otherwise sit idle. For RWE, it delivers a scalable, software-extensible resource that can grow without requiring site-specific capital investment at each addition. Polarium grants access to aggregated flexibility for commercialization across all relevant flexibility markets, while RWE connects to the platform to optimize the combined capacity.
Conventional vs. Multi-Asset Tolling: A Structural Comparison
| Feature | Traditional Single-Asset Tolling | RWE-Polarium Multi-Asset Tolling |
|---|---|---|
| Asset Base | Single large-scale BESS | 1,600-10,000+ distributed BESS units |
| Aggregation Layer | Not required | Cloud-based virtual aggregation platform |
| Scalability | Fixed capacity, high capex to expand | Modular - new sites onboarded via software interface |
| Grid Node Risk | Concentrated at single point | Distributed across thousands of locations |
| Primary Asset Use | Dedicated to grid/market services | Backup power primary; surplus flexibility pooled |
| Revenue Unlocked | Owner-operated or tolled as whole | Idle backup capacity monetized for asset owners |
A Well-Timed Market Entry
The agreement arrives at a moment of accelerating demand for distributed flexibility in Germany and across Europe. Germany's utility-scale energy storage installations surged 83.4% year-on-year in 2024, driven by the country's energy transition and growing demand for grid flexibility. according to AltEnergyMag1according to AltEnergyMag
Germany's regulatory environment has also evolved to support aggregated storage. From April 2025, Module 3 of §14a of the Energy Industry Act (EnWG) allows grid operators to offer fully dynamic grid charges that vary by time, with adoption expected to scale through 2026 and create stronger incentives for flexible energy use. Separately, Germany enacted legislation mandating accelerated smart meter rollout and requiring all energy suppliers to offer dynamic electricity tariffs from 2025, establishing the foundational data infrastructure that VPP platforms depend on.
At the European level, the regulatory tailwinds are equally significant. In July 2025, the Agency for the Cooperation of Energy Regulators (ACER) approved a common EU methodology for assessing non-fossil flexibility needs, with member states required to carry out national flexibility assessments by July 2026. With enablers such as real-time pricing and digital tools, flexibility could deliver €350-500 million in annual system savings by 2036, while also lowering consumer bills.
The RWE-Polarium structure sits squarely within this policy trajectory. The project demonstrates that existing assets - batteries already paid for by end customers to ensure backup reliability - can be repurposed as market-facing resources without compromising their primary function. That dual-use logic is precisely what regulators designing capacity remuneration mechanisms and ancillary service frameworks are increasingly seeking to incentivize.
For context on the broader regulatory reforms enabling behind-the-meter assets to access grid service revenue across Europe, see our earlier analysis on how regulatory reforms are unlocking home battery revenue streams.
The Revenue Stack: Where the Value Comes From
A distributed BESS fleet of this type can participate across several layers of the German flexibility market simultaneously - a concept known as revenue stacking.
The primary revenue streams available to an aggregated BESS portfolio in Germany include:
- Frequency Containment Reserve (FCR): Germany's most liquid ancillary service market, requiring assets capable of symmetric response within 30 seconds. BESS units are well-suited to this product given their rapid ramp characteristics.
- Automatic Frequency Restoration Reserve (aFRR): A slower but higher-volume market for frequency restoration services, procured by transmission system operators 50Hertz, Amprion, TenneT, and TransnetBW.
- Intraday and Day-Ahead Energy Arbitrage: Germany implemented a 5-minute settlement period in 2019 following European balancing market harmonization. Shorter settlement intervals increased volatility and amplified the value of fast-reacting, flexible assets in wholesale and balancing markets.
- Capacity and Balancing Market Products: Emerging mechanisms aimed at rewarding dispatchable, reliable flexibility that grid operators can call upon.
The global VPP market is valued at USD 6.28 billion in 2025 and is projected to grow from USD 7.70 billion in 2026 to approximately USD 45.67 billion by 2035, expanding at a CAGR of 22.61%. Europe dominated the global VPP market with the largest share of 41.54% in 2025, according to Precedence Research.
The Scaling Roadmap and Its Challenges
The initial 50 MW / 135 MWh phase serves as an operational proof of concept for a portfolio that could ultimately reach 300 MW / 810 MWh across more than 10,000 sites. That scaling trajectory brings a distinct set of technical and market design challenges that industry observers are watching closely.
Interoperability is the foremost technical hurdle. A fleet spanning thousands of installations will include multiple inverter platforms, battery management system (BMS) protocols, and communication standards. Maintaining consistent performance guarantees - particularly for FCR, which requires response within seconds - across such a heterogeneous fleet demands robust standardization at the software layer.
Cybersecurity is equally significant. A distributed fleet of this scale, accessed via a single cloud interface, presents an expanded attack surface. Grid operators and regulators will scrutinize the resilience of the Polarium platform against both cyber intrusion and cascading failure scenarios.
Revenue transparency for asset owners is a third consideration. Participants whose batteries are pooled into the virtual fleet need clear, auditable reporting on how flexibility dispatch decisions are made and how revenues are allocated - particularly where the primary backup function must take precedence.
Rising demand and new technologies are forcing utilities to coordinate distributed energy resources on an unprecedented scale, a trend likely to continue in 2026, analysts and stakeholders say. The RWE-Polarium agreement is a direct expression of that pressure finding a commercial outlet.
Implications for the German Market and Beyond
If the initial phase demonstrates reliable performance across FCR and intraday markets, the implications for German grid infrastructure planning are considerable. Grid operators may begin treating aggregated distributed BESS - not just utility-scale projects - as a dependable tool for congestion management and balancing. That shift could influence interconnection queue design, distribution tariff structures, and eligibility criteria for new capacity products.
For project developers, the model signals a bankability pathway for smaller, community-scale storage installations that have historically struggled to justify the transaction costs of direct market participation. Aggregation platforms effectively lower the minimum viable project size for market access.
The EU's Network Code on Demand Response will harmonize flexibility rules across member states by 2027, and the RWE-Polarium structure could serve as a template for similar multi-asset tolling arrangements in France, the Netherlands, and Scandinavia - each of which is advancing its own aggregator frameworks.
Key Takeaways
- RWE and Polarium signed a multi-asset tolling agreement on April 22, 2026, aggregating over 1,600 behind-the-meter BESS into a 50 MW / 135 MWh virtual battery, with a target portfolio of 300 MW / 810 MWh across 10,000+ sites.
- The commercial structure - pooling surplus backup capacity via a cloud platform - is explicitly differentiated from conventional single-asset tolling and represents a first-of-its-kind approach in Germany.
- Germany's §14a EnWG reforms, 5-minute balancing settlement, and accelerating smart meter rollout create a supportive regulatory environment for VPP aggregation.
- Technical challenges around interoperability, cybersecurity, and revenue transparency will determine whether the model scales efficiently and earns regulatory confidence.
- If successful, the RWE-Polarium blueprint could inform how EU flexibility markets structure DER aggregation frameworks under the forthcoming Network Code on Demand Response.
