The energy transition creates new opportunities and new risks. With the use of Energie Opslag Systemen (EOS) we can store energy and use it later. EOS is a beautiful, sustainable development, but also raises new and especially different (fire) safety issues.
Insurers are in favour of making society more sustainable and contribute to this by offering insurance solutions. After all, it is important for the insurance industry and all other relevant parties to gain insight into the developments, the most important safety risks and the technical aspects at an early stage, of course insofar as they are currently known.
This brochure is written for and by (policymakers, risk experts, underwriters and loss adjusters working for) insurers. The aim is to provide knowledge and insight into Energy Storage Systems and the developments. Insurers can use this knowledge in-house in their (acceptance) policy and promote the insurability of these systems. Of course, other parties are also free to use the information. The content is derived from various sources and is based on current knowledge and practical experiences of insurers. The purpose of this brochure is to provide knowledge and insight about EOS.
The brochure is informative, but not exhaustive and does not replace applicable standards and laws and regulations. It is a dynamic document that is constantly evaluated and adapted to the (technical) developments and the laws and regulations in force at the time.
In general, each EOS consists of several battery racks, which in themselves consist of several battery modules. A module is a composition of several battery cells. An example of the structure of a typical EOS is shown in Figure 1. It contains a composition of battery cells, modules, and racks.
Figure 1: Royal Haskoning DHV report "Energy storage systems - Guide for insurers" 2024
A typical EOS installation consists of one or more EOSs in combination with other installations with the function of supporting the energy storage and charging process, such as inverters, transformers, control and control equipment (Figure 1-2). In some cases, some of these installations are also located in the EOS
The basis in which electrical energy is stored is a lithium-ion cell. The cell consists of a negative and positive pole with the electrolyte in between. Electrolyte is a material that conducts ions well. A membrane, the 'separator' , prevents the positive and negative poles from touching each other, which would cause a (short) circuit, resulting in a thermal runaway. The lithium-ion moves within the cell between the poles and produces a chemical energy. Electrons move outside the battery and provide electrical energy.
When charging the cell, the process is reversed.
Figure 2 Image of Mirjam van Helvoirt (Achmea)
In a module, several cells are merged. The module is in a unit and can usually be removed in its entirety. By merging the cells, the voltage increases and more currents flow. A module often has monitoring of voltage, current and temperature.
There are several modules in the unit. The unit, also known as a battery rack, is controlled by a battery controller that regulates charging and discharging.
The entire installation includes several units including a battery management system and possibly climate control and power electronics.
The battery management regulates charging and discharging within the EOS. In addition, this includes safety features and control of the system." In addition, the aim is to optimise the lifespan.
The BMS can also balance individual cells. This equalises differences in charge levels. This prevents "cell drift" so that certain cells are not constantly over-discharged or overcharged. With passive balancing, the excess energy is converted into heat via a resistor. This until all cells have the same voltage. In active balancing, the voltage is transferred from the cell that is too high to the cell with a lower voltage. This prevents the energy from being lost.
The energy management of the location is controlled with the Energy Management System. This determines whether energy is imported or exported. This is often linked to control boxes that extract information from the energy markets.
The energy carriers are supplied with direct current. To convert the alternating voltage from the grid, inverters are needed from alternating to direct current. In solar power installations, which also produce direct current, inverters can be combined in which the direct current from the solar panels is converted to alternating current and also the direct current to the energy storage.
Energy storage is temperature sensitive. There are energy losses that cause heat and if the environment is too cold, the storage capacity decreases. For these reasons, climate control is often used.
Energy Storage Systems (EOS) are crucial for a stable and sustainable energy grid. They make it possible to store energy efficiently and use it at the right time. At the same time, these systems entail various risks, such as fire hazards, technical failures and environmental effects. Below is an overview of the most important risks and points of attention when using EOS, risks that also apply to home batteries and storage locations of individual batteries.
Depending on the typical (indoor EOS, mobile EOS, energy storage park, independent EOS in container) and the energy content (kWh), the following may or may not (partially) apply.
- Draw up instructions on how to act and who should be alerted in the event of an emergency (see Appendix A for an example emergency plan).
- Inform family members, staff and possibly emergency response officers about this.
An energy storage system (EOS) is much more than a battery and an inverter, it is not a passive system but an active system that charges and discharges through various systems/software. Typically, organisations such as suppliers, grid operators, energy suppliers can monitor the system remotely. So it's important to realise that you're connected to many third-party systems. Below is an example:
| System | Connected to the Internet | Protocol/Interface | Function |
| BMS, Battery Management System | No (local) | CAN/RS485 | Battery protection |
| EMS, Energy Management System | Yes | TCP/IP, MQTT, REST API | Market communication, charging schedules |
| SCADA, Accessibility from supplier | Yes | Modbus TCP, OCP UA | Monitoring and control |
| Fire detection control panel | Yes/No | BACnet, API | Alarms |
| IT management platform | Yes | HTTPS/VPN | Firmware updates, logging |
There are risks associated with a networked system. As can be seen in the overview above, an EOS has many systems that are connected to the internet. This is for communication with the energy market, for monitoring from, for example, the supplier(s), or to update the software but also the fire alarm system. All in all, these connections pose risks to access the EOS. In addition, an EOS can also be connected to building management systems, solar power installations, charging stations, etc. So many more systems may be accessible to unauthorised persons via the EOS.
It is therefore important that you delve into how the data flows run within the organisation in order to find out vulnerabilities in Information Technology (IT) or Operational Technology (OT). After all, you don't want a hacker to manage your system or end up on your company's server via your EOS.
Cybersecurity
Organisation
External hack despite firewalls cannot be completely ruled out. However, the risk can be greatly reduced by:
The topic of Cybersecurity is becoming increasingly important for EOS. Recently, the EU Cybersecurity Directive (CRA) was adopted, which will also be implemented in the Netherlands. This is the Cyber Resilience Act and this directive is in line with the NIS2. Having a PEN test carried out and ensuring that your system at least complies with the European CRA directive during its lifespan can be wise.
Fire propagation in an EOS is the spreading of a fire in the system. As discussed earlier, there are energy carriers present, namely the battery cells. There are several cells in a battery module, several modules in a rack and several racks in the system. One of the risks is that a battery becomes unstable, resulting in a thermal runaway. This means that the cell temperatures can rise above 550 degrees Celsius. When the temperatures rise, various flammable gases escape from the cell, including the explosive hydrogen gas (H2).
You want to prevent a domino effect from occurring within the module, i.e. that one cell heats up the other cell and that it also becomes unstable. So you want to limit propagation/fire expansion to the cell or at least keep it within the module. To provide insight into this risk, there are fire propagation tests.
Systems that do not pass such a fire propagation test therefore have the risk of rapid internal fire spread, i.e. the cells all ignite each other.
There are currently four main groups in the market:
The IEC method is an international safety standard. The UL method is a defined test method, the entire system can then be tested in a UL laboratory. The UL tests on four levels (cell, module, unit and installation level). It may be that an installation only reaches the cell or module level, then the system test is unfeasible or not tested. Always ask for the result of the test to assess its value. Fail is also a result. Part certificates have little value and are therefore not an installation level test.
In the PGS 37-1, value is assigned to the IEC and UL methods. For example, systems may be placed closer together, the water connection for the fire brigade is no longer mandatory and there are still a number of measures that can be omitted.
The UL method and the IEC standard therefore certainly have added value in terms of (fire) safety. However, you cannot compare them with each other. Of course, you can design a system in accordance with IEC 62933-5-2 and then have the system tested in accordance with the UL9540A. The system that carries both labels has increased safety compared to the four main groups mentioned above.
There are also pitfalls with the UL method that you can deal with, for example, no ignition source is kept at the outgoing harmful and flammable gases, while in reality there may be. The escaping combustible gases have quickly reached the lower volume percentage to form an explosive mixture in atmospheric conditions (LEL/LFL ca 5 - 6%). There are plenty of ignition sources within the EOS with minimal ignition energy. One of the exiting combustible gases is hydrogen gas (gas group IIC) with an ignition temperature of 560 degrees Celsius. Tests from battery suppliers show cell temperatures of 552 degrees Celsius, so there is no wide margin of safety. The equipment inside the enclosure does not comply with a particular appliance category for gas group IIC.
So the ignition of flammable venting gases is underexposed in the test/standard. A highly ventilated arrangement of the system is therefore by far preferable. This is also the focus of attention in the UL 9540A update of 2025. In this UL test, the flammable escaping gas is collected in a sphere and then exploded to determine the Pmax value. A Pmax of 9.98 Bar is not exceptional, this pressure wave can lead to major damage to the casing of the gas being the housing or otherwise the building in the event of an indoor installation.
Familiarize yourself with the test and/or standard before you want to weaken prevention measures, is the advice.
See also (in Dutch) PGS 37-1:2023 version 1.0 (DECEMBER 2023) (publicatiereeksgevaarlijkestoffen.nl)
An up-to-date emergency plan (see Appendix E in the PGS 37.1 for an example) on how to act in the event of incidents has been drawn up. The installation manager is responsible for keeping the emergency plan up to date and distributing it.
The emergency plan is aimed at limiting and controlling calamities, accidents and protecting employees and the living environment. This emergency plan must be available to the party responsible for installation and manager of the EOS and the emergency services.
This contingency plan shall contain at least:
Explanation: In the case of manned locations, align the emergency plan with the internal emergency plan (emergency response, evacuation, employee training, etc.) and review the emergency plan at least every three years and update it if necessary.