RWE and Polarium, a developer of distributed battery energy storage systems and flexibility solutions, are joining forces to market battery flexibility in the German power market in a new way. From late 2026 onwards, RWE will optimise 50 megawatts (MW) of power (equivalent to 135 megawatt hours (MWh) of electricity) from Polarium’s distributed battery portfolio, within its energy trading operations. 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 underutilised assets and grid infrastructure.
Ulf Kerstin, Chief Commercial Officer at RWE Supply &Trading, says: “Batteries are becoming increasingly important for a stable energy supply, and Polarium’s virtual battery is a strong complement to our rapidly growing portfolio of batteries and generation assets. 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.”
Leif Ottoson, CEO of Polarium:“This agreement shows how distributed battery systems, originally deployed for mission critical infrastructure, can also play a meaningful role in the energy system. By aggregating thousands of batteries through our cloud platform, we can unlock value that supports renewable integration and grid stability — while maintaining the availability originally required by the customers. Partnering with RWE allows us to bring this flexibility to market at scale.”
Polarium is developing a portfolio of distributed BESS installed throughout Germany, providing primarily back-up for customers. Any remaining flexibility not required for back-up is pooled virtually via the Polarium platform into a single, market-ready resource. By late 2026, the virtual battery is expected to comprise at least 50 MW / 135 MWh from more than 1,600 distributed systems.
This capacity is made available to RWE under a multi asset tolling agreement. Polarium grants access to aggregated flexibility for commercialisation across all relevant flexibility markets while RWE connects to the platform to access and optimise the combined capacity. In contrast to conventional tolling structures that 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. Building on RWE’s experience with multi-asset tolling structures, such as its 2025 agreement with Terralayr, this cooperation represents a significant step forward.
The decentralised, behind-the-meter BESS supports system stability by using existing infrastructure and enabling greater integration of renewable energy. Distributing storage across thousands of locations helps reduce strain on individual grid nodes, improves performance and can extend asset lifetime, while spreading operational risk across many systems. A single technical interface to the platform simplifies the integration of new sites and helps maintain consistent performance standards, even across a highly diverse fleet.
Pictures for Media use (credit: RWE) are available at the RWE Media Centre.
