RWE (electricity and gas suppliers) Supply & Trading and Swedish battery developer Polarium have signed a multi-asset tolling agreement that will pool more than 1,600 behind-the-meter battery energy storage systems located throughout Germany into a single virtual battery, the companies announced on April 22, 2026.

A New Model for Distributed Storage

Under the agreement, RWE will begin optimizing at least 50 megawatts of power, equivalent to 135 megawatt hours of electricity, from Polarium's distributed battery portfolio from late 2026 onwards.

The arrangement operates through Polarium's cloud platform, which aggregates the individual battery systems in real time, creating what the companies are calling a market-ready virtual battery.

RWE will connect directly to that platform to access and optimize the combined capacity across relevant flexibility markets in Germany.

Polarium's distributed battery systems are primarily installed to provide back-up power for mission-critical customer infrastructure. The flexibility made available to RWE represents capacity that is not required at any given moment for that back-up function.

Any remaining headroom not needed by individual customers is pooled virtually through the Polarium platform and made available to RWE for commercialization.

The structure distinguishes itself from conventional tolling arrangements, which typically center on a single large-scale storage asset. By aggregating numerous smaller distributed systems via cloud technology, the companies say the approach enhances both flexibility and scalability in ways that a single centralized asset cannot replicate.

Scale and Growth Ambitions

The initial tranche of at least 50 megawatts and 135 megawatt hours, drawing on more than 1,600 systems, is expected to be operational by late 2026. However, the two companies have outlined considerably larger ambitions for the portfolio.

Polarium's total distributed battery portfolio is expected to grow to approximately 300 megawatts and 810 megawatt hours, spread across more than 10,000 individual battery systems.

That trajectory would represent a roughly sixfold expansion from the initial capacity being made available to RWE under the current agreement. The companies did not specify a timeline for reaching the 300 megawatt threshold in their announcement.

What Each Party Brings to the Table

For RWE, the deal extends a strategic direction the company has been pursuing in the flexibility and storage market. Ulf Kerstin, Chief Commercial Officer at RWE Supply & Trading, described distributed batteries as an increasingly important component of a stable energy supply.

He said the virtual battery from Polarium complements RWE's existing portfolio of batteries and generation assets, and emphasized the role that smaller storage units can play when brought into organized flexibility markets.

"By working with Polarium, we are bringing thousands of smaller storage units into the flexibility market, where they can contribute to make the energy system more robust, generate additional value, and help to keep the system in balance in real time," Kerstin said.

For Polarium, the agreement opens a route to monetizing stored capacity that would otherwise sit idle. Leif Ottoson, CEO of Polarium, said the deal demonstrates how distributed battery systems originally deployed for mission-critical infrastructure can take on a broader role in supporting the energy system.

He cited renewable integration and grid stability as the primary systemic benefits, while emphasizing that the original back-up availability required by customers would be maintained throughout. "Partnering with RWE allows us to bring this flexibility to market at scale," Ottoson said.

Technical Architecture and Grid Benefits

The arrangement relies on a single technical interface connecting RWE to the Polarium platform, which the companies say simplifies the integration of new sites as the portfolio grows.

That standardized interface is designed to maintain consistent performance standards across what is described as a highly diverse fleet of battery systems distributed across Germany. Spreading storage capacity across thousands of locations rather than concentrating it in a small number of large facilities carries several stated operational advantages.

According to the companies, this distributed approach helps reduce strain on individual grid nodes, improves performance, and can extend the working life of individual assets. It also distributes operational risk across a large number of systems rather than concentrating it in a single installation.

The behind-the-meter positioning of the battery systems means they make use of existing infrastructure, which the companies say supports greater integration of renewable energy into the grid while avoiding the need to build entirely new grid-connected assets.

Building on Prior Tolling Experience

The Polarium agreement follows a similar structure to a multi-asset tolling deal RWE concluded with Terralayr in 2025, which the company cited as a precedent for this type of arrangement.

RWE described the Polarium cooperation as a significant step forward from that earlier agreement, noting that the pooling of distributed systems through a cloud platform represents a first-of-its-kind approach compared to conventional tolling structures.

The deal was announced from Essen, where RWE is headquartered, and Stockholm, which is the base for Polarium.

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