Case Lempäälä | Second-Life EV Battery as Stationary Energy Storage

Author: Jari Saukko, Ekokumppanit

In the municipality of Lempäälä, Finland, we piloted the installation of a second-life electric vehicle (EV) battery system in a public building, Lempäälä House. The goal was to explore the potential of reusing EV batteries for stationary energy storage to support solar energy self-consumption, reduce peak loads, and provide grid services.

Read our best practices for replication:

At Lempäälä House, the main role of the battery system is to store surplus solar energy produced by the rooftop panels. This stored energy can then be used during expensive peak electricity hours, helping to reduce demand on the grid and lower energy costs. That happens inside Lempäälä house.

In addition, the system enables Lempäälä House to participate in national electricity balancing markets by offering flexibility services via Fingrid. This means the battery can support the grid by responding to changes in supply and demand, for example, by injecting or absorbing power to help maintain frequency stability or by shifting energy use to off-peak times. These capabilities not only improve grid reliability but also create potential revenue streams through market participation.

Lempäälä House is a multipurpose municipal building equipped with a battery-based energy storage system. The system has an energy storage capacity of 80 kWh and a power output capacity of 40 kW. Solar panels are installed on the roof, and the battery is primarily used to store excess solar energy for self-consumption, smooth out consumption peaks, and provide grid support and frequency regulation services.

Testing

The battery packs used in the Lempäälä House were removed from Nissan Leaf vehicles. They were tested according to established procedures, and their lifespan can be extended by up to 15 years before being sent for dismantling and shredding-based recycling.

Location

After selecting the appropriately sized energy storage system and its supplier the process began with identifying a suitable room for the battery system. The room had to meet strict requirements for weight-bearing capacity, ventilation, temperature control, and safety.

Collaboration

We collaborated closely with the local fire department, grid operator, and municipal building authorities to ensure full compliance with all relevant regulations.

Security and Tracking

Auxiliary systems were installed in advance, including an aerosol-based fire suppression system and an air-to-air heat pump to maintain optimal room conditions. The battery system was integrated into the building automation system, with power meters added for monitoring and performance tracking. After installation, the system underwent inspection by certified professionals and was successfully connected to both the grid and the building’s solar panel system.

Replication

The process we describe applies to both new and second-life batteries, as the core system architecture is essentially the same. In the end the electrical energy storage consists of a metal enclosure housing power electronics, battery modules inside, and external connections to the building’s electrical and data networks, as well as its automation system from the metal enclosure.