The new solution extends battery life, reduces environmental impact and energy-storage costs, and helps stabilise the power grid.
The topic of second-life battery use is highly relevant today, as the first generation of traction batteries in electric vehicles is now reaching the end of its operating life. “Their capacity no longer meets mobility requirements, but for stationary storage it is still sufficient. Second-life use extends the battery life cycle, postpones recycling, reduces material and environmental burdens, and improves the economics of energy storage,” explains Prof. Radomír Goňo, Head of the Department of Electric Power Engineering at FEI.
What is the potential of retired batteries for renewable energy sources?
As the number of electric vehicles grows, so does the supply of batteries with residual capacity suitable for stationary storage. Second-life use of these batteries can reduce the cost and accelerate the deployment of energy-storage systems that help balance peaks in generation and consumption, integrate variable (intermittent) sources, provide ancillary services, and increase the energy self-sufficiency of buildings and municipalities. With appropriate diagnostics and control, it is possible to safely connect batteries of different types and ages, increasing grid flexibility and supporting the development of renewable energy.
What is the main technical and research challenge of the project? Why is there still no universal control unit for different battery types?
Each electric vehicle manufacturer uses its own battery design and Battery Management System (BMS), which often cannot communicate with each other. There is no unified documentation or standardisation, which has complicated their further use. Our team is therefore developing a universal device that overcomes this issue – it safely connects a wide range of used batteries and enables their efficient integration into a single storage system.
What types of batteries are you testing?
We are testing three main cell types: cylindrical, pouch, and prismatic. Beyond mechanical design, the cells also differ in chemical composition, which affects the weight, performance, and capacity of the resulting battery pack. From this perspective, we work with selected variants of Li-ion and LiFePO₄. Individual second-life cells must be measured and thoroughly sorted according to their technical condition. Only batteries with the most similar parameters are then interconnected so that the new storage device is assembled from cells with comparable characteristics, ensuring optimal performance and service life.
What will the semi-operational testing verify?
The tests will run throughout the year to capture various operating conditions. In individual stages, we will verify control efficiency and stability, BMS functionality (voltage, current and temperature monitoring, and balancing), energy-storage efficiency, and long-term reliability. We will also assess the compatibility and mutual behaviour of different storage devices and combinations of battery modules. Testing will be conducted on assemblies connected to the two most common types of renewable energy sources—photovoltaic and wind power plants—taking into account the availability of energy sources during different periods of the year.
How can the project influence the development of energy storage?
The device under development may be a key step toward wider utilisation of second-life batteries. It provides more affordable storage solutions, supports renewable-energy integration, reduces environmental impact, and contributes to energy security. If the prototype is successfully deployed in practice, it could positively influence the development of energy storage not only in the Czech Republic but also across other European countries.
Project No. FW10010003, Control System for the Use of Lower-Capacity BEV Batteries for Renewable-Energy Storage, is co-funded with state support from the Technology Agency of the Czech Republic under the TREND programme.
