In this edition of Voices of the Industry, Steven Joseph, Director of Business Development at Viking Integrated Safety, explores options for reliable fire protection for battery energy storage systems.
Battery energy storage systems (BESS) are reservoirs for electrical energy, typically generated from renewable sources like wind and solar farms, or from the existing power grid. They buffer the energy for use when demand rises, or emergencies occur. Increasingly, BESS are used as emergency power systems (EPS) for data centers, replacing diesel- or gas-based systems. Analysts expect the BESS market to expand to $26B USD by 2026, with 97.8% of systems using lithium-ion (Li-ion) batteries.
Li-ion batteries deliver good energy density in a small, cost-effective footprint — but that comes with a risk. When a Li-ion cell fails or is subjected to abuse, a potentially catastrophic event known as thermal runaway can occur, where chemical energy is converted to thermal energy. Once an ignition threshold is reached the process will continue to propagate, or spread, from cell to cell consuming the BESS, and where adjacent structures are present, the potential for a facility-wide disaster.
Stages of a BESS Fire
BESS fires tend to follow a familiar pattern of stages:
Stage 1) A manufacturing defect or mechanical, electrical, or thermal abuse initiates a thermal reaction in a battery cell.
Stage 2) The damaged cell begins to overheat and vent traces of CO2, Volatile Organic Compounds (VOC), and potentially other compositions of vent-gasses, depending on battery chemistry. Incipient smoke may also be present as a result of the thermal event. Intervention is essential at this stage to mitigate or prevent thermal runaway.
Stage 3) As thermal runaway begins it cannot be stopped, but propagation can be mitigated.
Stage 4) An explosion and/or fire that can consume the BESS and spread to adjacent units.
While investigating this fire threat, NFPA Fire Protection Research Foundation Report confirmed that Li-ion batteries use dissolved lithium salts (LiPF6) rather than free lithium metal, so that water can be used as an extinguishing agent. Of course, the high heat could produce a situation where a steam explosion could occur compounding the threat. Water may not be able to reach concealed or enclosed cells and could also do extensive damage to electrical and mechanical systems not involved in the incident. Further, water may not be readily available for remote locations.
Very Early Warning Sensors for Threat Detection
Fortunately, there are technologies and techniques that can mitigate or avoid battery thermal runaway if threat warning signs are detected early. Effective mitigation techniques can be realized by design, monitoring, and active control using early warning smart sensors and appropriate suppression technologies at the right stage of threat development and before propagation. Sensors recommended for a BESS include:
- Battery Management Systems (BMS) monitor the temperature, voltage, and impedance of individual batteries, and alert when limits are breached.
- Power Quality Sensors can monitor for electrical abuse by analyzing and translating power quality in simple and actionable information.
- Thermal Imaging IR Sensors can monitor battery surface temperatures at up to 9600 discrete points every 2 seconds, highlighting potential hotspots. They can also be used to monitor other equipment like PDUs, CPUs, fans, and other mechanical subsystems
- Typical coolants in a Li-ion BESS consist of 50% ethylene glycol and 50% water. With Coolant & Water sensors, leaks can be detected and immediate action taken to limit a disaster like Victorian Big Battery Fire in Australia.
- Refrigerant (R-134a) Gas sensors can detect leaks from a failing cooling system.
- Shock & Vibration sensors can monitor another root cause of catastrophic battery failures: mechanical abuse. By recording vibrations multiple times per second, potential mechanical abuse can be detected.
A New Sensor for Early Threat Detection
The authors of a study titled Detection of Li-ion battery failure and venting with Carbon Dioxide sensors, concluded that “CO2 and VOC are found in high concentrations in vent-gas from all thermal runaway experiments. Both gas species exist in the first vent-gas, and enable cell leakage detection, so these two gas species are considered good for detection purposes.” VOCs are carbon-based chemicals, like methyl ethyl carbonate (C4H8O3), with propane used as an analog for detection.
As soon as the sensors (or a combination of sensor alarms) detect a threat (Stages 1 & 2), the BESS should be powered down and an automatic suppression system triggered. As mentioned, water should be avoided at these early stages, as it does not reliably reach hidden or obscured fires and could potentially damage electrical and mechanical systems.
Appropriate Suppression Can Prevent Threat Propagation
A fire-suppression system employing inert gas can be effective by both depleting oxygen in the room and extracting the heat from a fire. Inert gases like argon, carbon dioxide, and nitrogen are electrically nonconductive and leave no residue to clean up. Suppression can be directed to specific threat areas or in a total flooding application where the agent fills the entire container or room. Even if a non-battery component of the BESS is involved in a fire, this method can extinguish the fire without causing water damage or requiring post-action cleanup.
Rapidly flooding the BESS with the extinguishing agent prevents the formation of large amounts of an explosive electrolyte-oxygen mixture, reducing a thermal runaway event, and inhibiting the spread to adjacent battery cells. This eliminates secondary fires and the potential for reignition, as the inert gas can remain for an extended period when the system is integrated with the ventilation system.
What is the most suitable extinguishing agent? Chemical extinguishing agents cannot be used in this application scenario because hazardous decomposition products may form, or extended discharge may be necessary. Potential alternatives are three natural extinguishing gases: nitrogen (N2), carbon dioxide (CO2) and argon (Ar). Argon is a single atom molecule and doesn’t react with any element on the periodic table. It does not decompose in high-temperature fire situations, its safe for equipment present and suitable for extinguishing class A, B, C and D fires making it widely compatible with varying battery chemistries. For these reasons, Argon is a suitable extinguishing agent for Li-ion battery storage systems, delivering excellent results.
With renewable energy sources powering the future, the need for reliable and cost-effective energy storage is essential. In the lifetime of any critical infrastructure system like a BESS, reliable fire prevention is a key to lowering total operating costs (TOC) over the lifetime of the system. Very early warning sensors combined with appropriate and effective clean suppression systems can serve that role, detecting threats early and mitigating propagation before disasters result.
Steven Joseph is the of Director of Business Development at Viking Integrated Safety, and has 30+ years in the design and deployment of fire protection solutions for critical infrastructure. Viking Integrated Safety leverages the broad range of Minimax Viking products to provide fully integrated, pre-engineered fire prevention solutions for targeted applications. These solutions combine technologies from industrial IoT smart sensors, flame/heat/smoke/gas detectors, alarm & control panels, notification & A/V appliances, and extinguishment systems into integrated, reliable, and cost-effective kits.