German startup Eden Energy is developing commercial battery storage systems using retired e-scooter batteries that still retain much of their original capacity. The Freiburg-based spin-off from the Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) has delivered its first 70 kWh storage system, built from 112 used batteries.
“With this storage capacity, we are initially targeting small and medium-sized enterprises in the region that already have a photovoltaic system but lack a storage solution,” said Florian Bierwirth, who previously worked in Fraunhofer ISE’s power electronics department alongside co-founders Daniel Seeger and Hannes Kurzmann.
The storage systems could also appeal to municipal utilities, as they can be used to optimize self-consumption, reduce peak demand, and facilitate electricity trading.
According to Eden Energy, Germany discards around one million high-performance batteries from e-bikes and e-scooters each year, although many retain much of their original capacity. Unlike second-life batteries from electric vehicles, these smaller batteries have not been widely used for stationary energy storage, largely because of differences in battery designs, cell types, and battery management systems.
Eden Energy aims to address this challenge using power electronics developed at Fraunhofer ISE. “It allows for the interconnection of different storage units and enables communication across various modules, all without the need to dismantle the battery packs,” said Bierwirth.
Few other systems currently offer comparable flexibility when integrating batteries with different designs or levels of degradation. Exceptions include multilevel battery storage systems developed by companies such as Stabl and Sax Power.
Batteries retain more than 90% of original capacity
The company initially screened the 112 e-scooter batteries used in its first storage system before connecting them. Eden Energy currently sources batteries primarily from large e-bike and e-scooter fleet operators, ensuring access to sufficient quantities of identical battery types.
In the future, however, the power electronics developed at Fraunhofer ISE are expected to enable the integration of different battery types. This requires adaptations to connectors, battery management systems, and communication protocols – a significant challenge given the wide variety of batteries on the market.
In the longer term, standardized communication protocols for battery storage systems and regulations governing the second-life use of mobile batteries in stationary applications will be needed.
Initial tests of 350 batteries conducted by Eden Energy highlight the potential for reuse. While the company had expected the batteries to retain around 80% of their original capacity, some retained well over 90%.
The results suggest that the batteries could remain useful in stationary storage applications, where they would be exposed to less mechanical stress, such as vibrations, and fewer temperature fluctuations.
Seeking additional pilot customers
Eden Energy’s technology also enables individual battery modules to be replaced while the storage system remains operational. The modules are monitored through a tracking system and sent to partner companies for recycling once they reach the end of their service lives.
According to Eden Energy, this modular approach turns a potential disadvantage into a technical advantage over conventional battery storage systems. By replacing individual modules, the company says it can maintain the system’s overall storage capacity at a constant level, even after 10 years of operation.
Eden Energy, which now employs three part-time staff in addition to its three founders, plans to scale its storage systems to capacities of up to 300 kWh.
The company is also seeking additional commercial pilot customers in the region. Under the state-funded “Mittelstand trifft Start-ups” (SMEs Meet Start-ups) program, participating businesses can receive a subsidy covering 50% of the cost of an EdenEnergy battery storage system.
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