How to Install a Second-Life EV Battery in a Municipal Building

Author: Jari Saukko, Ekokumppanit

As public buildings look for smarter, greener ways to manage their energy use, electric vehicle (EV) batteries can serve as a promising solution for local energy storage. By repurposing or integrating EV batteries into building systems, it can enhance energy efficiency, reduce electricity costs, and support the broader transition to renewable energy. This article explores the key considerations for utilizing EV battery storage in public facilities, using the Lempäälä House as a real-world example of an innovative, multi-use energy storage setup.

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. To replicate this solution, follow the steps described in this article.

Read more about how we did it in the Municipality of Lempäälä, Finland:

The Most Important Requirements for Success

1. Define the Target Electricity Markets

The main role of the battery system can be also to store surplus solar energy produced by the rooftop panels and this stored energy can then be used during expensive peak electricity hours, helping to reduce demand on the grid and lower energy costs.

Fingrid’s reserve market ensures the real-time balance between electricity consumption and production in Finland’s power system. The market operates continuously, with reserves made from balancing service providers on an hourly basis. Detailed information on how to participate in these markets, including the required battery capacities for each market segment, can be found on Fingrid’s website. This resource provides essential guidelines and criteria for market entry, helping you align your battery system with the specific demands and opportunities of the reserve markets.

2. Assess the Installation Site

Select a room that meets structural and environmental requirements. Ensure the floor can support the battery weight, and that the space allows for safe ventilation, temperature control (10–30 °C), and humidity management. This foundational step ensures the physical environment is suitable for safe and efficient battery operation. In Lempäälä House demo assembly the battery system is located inside the building.

3. Apply for Permits

Permitting processes can take time. It is important to start early to keep the project on schedule.
Start early with all required permits, as delays can significantly affect the project timeline. The following permits and approvals are typically needed for battery energy storage systems in Finland:

Building Permit

If the battery system is installed in an existing building (e.g. converting a storage room into an electrical room), a building permit is required. This includes structural modifications, ventilation systems, and fire safety installations. The permit process is handled by the local municipal building control authority.

Grid Connection Permit

Grid connection is not governed by a single national law but is based on a bilateral agreement between the installation owner and the local Distribution System Operator (DSO). The process typically includes:

• Technical review of the inverter and protection systems
• Capacity assessment of the local grid
• Payment of a grid connection fee within 30 days of agreement
• Compliance with Fingrid’s Grid Code Specifications (e.g. VJV2018, SJV2019) depending on system size and voltage level 

For small-scale systems, connection is usually granted if technical and safety requirements are met, and the grid has capacity.

Fire Safety Documentation

The local fire department must assess the suitability of the battery room. This includes:

• Fire load assessment
• Recommendations for fire suppression (e.g. aerosol-based systems)
• Room classification (e.g. EI60 fire rating)
• Emergency access and signage

Electrical Safety Compliance

All electrical work must comply with Finnish electrical safety law (Sähköturvallisuuslaki 1135/2016). Only certified professionals may perform installations. A certified inspector must inspect the system within six months of commissioning, and the inspection report must be submitted to the insurance company and fire authority.

Office Holder Decision (for Municipal Buildings)

In public sector projects, an official decision must be made and published for at least 30 days before implementation. This ensures transparency and legal compliance.

4. Install Auxiliary Systems

Set up fire suppression (e.g. aerosol-based), ventilation (e.g. air-to-air heat pump), and electrical cabinets before battery delivery.  These systems are critical for operational safety and must be in place before battery installation.

Before the battery system is delivered, it is essential to ensure that fire suppression, ventilation, and electrical cabinet systems are fully installed and operational. These systems are critical for operational safety and must be in place prior to battery installation. Fire suppression solutions, such as aerosol-based systems, are particularly important, but it’s worth noting that requirements may vary between municipalities, building owners, and insurance companies. These differences should be carefully reviewed to ensure compliance with all relevant regulations and expectations.

From a risk management perspective, it is also important to consider the potential consequences of a battery explosion. The design of the battery room should account for how pressure would be released in such an event, ensuring that any pressure buildup can be safely and controllably vented out of space.

To maintain optimal performance and safety, the battery room must also meet the environmental conditions recommended by the battery manufacturer. This includes maintaining appropriate humidity and temperature levels. The manufacturer’s specifications typically outline the maximum thermal energy output of the battery system and its auxiliary components, as well as the optimal operating temperature range for the battery.

5. Integrate with Existing Systems

Connecting the battery to solar panels and the building automation system requires power meters and monitoring tools for smart energy management. A dedicated substation for the battery system was needed within the building automation infrastructure at the demo site. Ideally, both the battery and building main switches should be controllable via the building automation or battery management systems.

Our demo case includes a manual, independent disconnect switch between the battery and building main switches, as required by the electricity distribution company. This switch can disconnect the battery due to minor grid fluctuations, even without the battery or building automation system being aware. Requirements for this switch vary by grid operator and country. It’s highly recommended that this switch be automatically resettable; otherwise, manual intervention is needed to reconnect the battery.

Data network integration at the demo site was a significant challenge: securely connecting the battery system (already on building networks) to the supplier’s external network. This raises cybersecurity concerns, especially with robust firewalls in municipal buildings. One solution is to use an independent 4G/5G cellular connection for the battery system, creating a secure, isolated channel for supplier monitoring without compromising the building’s internal network.

6. Implement Safety Protocols

Integrating the battery storage system at the demo site securely into the supplier’s external network is a key challenge. The system needs to share operational data, but this data network integration must not compromise the building’s internal ICT security. Local ICT professionals must carefully plan the connection, ensuring firewall changes don’t disrupt existing services.

One secure solution is using an independent 4G or 5G cellular connection dedicated to the battery system, bypassing the building’s firewall entirely. This creates an isolated channel for supplier monitoring and maintenance, protecting the internal network from external risks.

Cybersecurity is paramount, demanding resilience against vulnerabilities. For municipal buildings with robust firewalls, evaluating a separate radio link is even more critical.

Furthermore, automation system safety and reliability are crucial. In a fault, both the battery and building automation systems must respond coordinately, requiring clearly defined control logic, fallback modes, and communication protocols.

Finally, personnel access to the battery room must be strictly controlled, with clear instructions for emergency shutdown procedures, including E-stop switch locations.

7. Conduct Inspections and Notify Stakeholders

In Finland, certified electrical inspections are legally required within six months of commissioning new installations. These inspections, mandated by the Finnish Safety and Chemicals Agency (Tukes), include a commissioning inspection by a qualified professional for all installations, and a verification inspection (varmennustarkastus) for larger systems like battery storage connected to main electrical infrastructure.

The purpose is to ensure electrical safety and regulatory compliance through visual checks, measurements, and testing, all documented in a report provided to the client. This documentation is also crucial for insurance providers and fire authorities, who may have specific requirements. For municipal or institutional buildings, these reports are often required for quality management systems and potential internal or external audits, sometimes including data privacy and cybersecurity assessments for networked systems.