Turbo for the municipal energy transition: Used traction batteries as stationary power storage

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2024/06/11 – With the increasing share of renewable energies in power generation, load management and storage technologies are becoming increasingly important as power production and demand fluctuate over time. In strong winds and low power demand, it is important to store excess electricity to be able to use it when demand exceeds production during calm or dark periods. To ensure reliable power supply, various storage technologies such as pumped storage and compressed air storage, as well as battery storage, are gaining more importance.

In Germany, 14 percent of renewable electricity was curtailed in 2022. This curtailment occurred when more power was generated than the grid could absorb, leading to an overload that prevented the power from being transported to consumers. Dr. Robert Brandt, Managing Director of the Renewable Energy Agency (AEE): “As a society, we cannot afford to lose renewable electricity in this way.”

Solution for local power grids: Second-life batteries from electric cars

Energy storage can be used in many ways to stabilize local power grids, integrate renewable energies into the energy system, and support the energy transition by linking the power sector with transportation or heating. The basis for stationary energy storage is used traction batteries from electric vehicles that are removed at the end of their lifecycle. This typically happens when the capacity of the batteries, which weigh several hundred kilograms, falls below 80 percent, making them unsuitable for vehicle use. Technically, these batteries are completely intact and fully functional for use as stationary storage solutions. An additional advantage is that their continued use extends the lifecycle of electric car batteries, positively impacting the CO₂ balance of energy storage.

Municipalities can integrate these second-life batteries into their local grids for various applications. These include expanding the charging infrastructure for electromobility, ensuring power supply to critical infrastructures such as hospitals or fire stations, supplying power to residential areas, and using electricity for wastewater treatment plants.


“Reusing batteries that have already served in electric vehicles offers a more sustainable way to store excess energy and release it during times of high demand,” emphasizes Brandt. “By giving these valuable resources a second life, we actively contribute to promoting the expansion of renewable energies and conserving the resources needed to manufacture batteries.”

France: Early adopter of second-life batteries

In France, work on the second use of drive batteries has been ongoing for some time: Since 2020, the Munich-based company The Mobility House, together with partners, has set up a power storage facility on the premises of the Renault plant in Douai, France. The storage facility consists not only of used drive batteries from the Renault Zoe but also of first-life batteries. Automakers are required to keep a certain number of batteries in stock at the plant. Since batteries do not store well without losing performance, the solution is to integrate them into a storage facility and slightly charge and discharge them to maintain their optimal charge state.

What does a local power storage system look like? The storage facility in Douai consists of four shipping containers full of electric car batteries. Each container contains 54 battery packs. The total capacity is about 47 MW, exceeding the minimum capacity of 4 megawatts required to participate in the primary control reserve market. The primary control reserve market compensates for short-term imbalances in the power grid through automatic, second-by-second adjustments in generation or consumption to maintain grid frequency stability. The mini power plant is connected to the public power grid as a buffer and compensates for power fluctuations. The four containers can supply almost 370 households with electricity for about a day.

As another pilot project, Renault combined 72 new and used batteries from the compact electric car Renault Zoe at a former coal-fired power plant in Elverlingsen, North Rhine-Westphalia, in 2020, with a total capacity of three megawatt-hours (MWh). This storage facility is also part of Renault's “Advanced Battery Storage” project. A total storage capacity of 70 MWh is planned.

The Fluxlicon project

In Germany, the research project “Intelligent and Flexible System for the Use of All Second-Life Batteries in Municipal Charging Infrastructure” (Fluxlicon) is developing a flexible and modular energy storage system from second-life batteries. Funded by the Federal Ministry for Economic Affairs and Climate Action (BMWK), the consortium of PEM Motion, ConAC, the Chair “Production Engineering of E-Mobility Components” (PEM) at RWTH Aachen University, DEKRA, and the Renewable Energy Agency is working on concepts for municipalities to advance the energy transition locally with the storage system.

Like power generation, the future of storage is decentralized and diversified. Small and large renewable energy plants must be coupled with privately, commercially, and publicly operated storage systems. The latter are still relatively rare in Germany. For example, the WEMAG Group's battery storage power plants “Schwerin 1” and “Schwerin 2,” inaugurated in 2017 and then the largest lithium battery network in Europe, have a combined capacity of 15 megawatt-hours. However, this is only one ten-thousandth of the potential stationary battery storage capacity in Germany in 2040 described by Fraunhofer ISE or the capacity of all storage systems sold worldwide in 2022 of about 140 gigawatt-hours.

The technology is just beginning. It is all the more important now to resolutely advance the expansion of a decentralized storage infrastructure.