Fox ESS has seen a growing number of customer inquiries regarding battery protection and safety, often driven by requests from insurance companies. To address these concerns, we have outlined the key protection mechanisms and fire mitigation measures in our battery storage systems.
Battery Chemistry and Safety
Fox ESS uses cobalt-free LiFePOâ‚„ (Lithium Iron Phosphate) cells across its battery storage products. This chemistry is the most stable of all lithium-ion variants, offering exceptional chemical stability and thermal resilience. Unlike other lithium-ion chemistries, LiFePOâ‚„ is significantly less prone to thermal runaway, making it the preferred choice for residential energy storage due to its superior safety, longevity, and reliability.
Fox batteries incorporate industry-leading protection and fire prevention technologies. To date, we have deployed over 500,000 battery systems worldwide, each containing multiple battery cells. Despite this extensive deployment, there have been zero recorded incidents of battery combustion.
System Protection Measures
Fox battery systems implement three layers of protection within the inverter and Battery Management System (BMS):
Primary Protection
Primary protection provides an immediate response to potential issues such as overvoltage, undervoltage, overcurrent, and extreme temperatures. If any of these conditions arise, the system will automatically regulate operation or shut down to prevent damage.
This protection operates in real time through a proprietary communication protocol between the inverter and battery, ensuring that the system functions strictly within safe operating limits. The BMS continuously monitors individual cell temperature and voltage, preventing overcharging and overheating at the cell level.
If the BMS itself fails, a communication error will be triggered, notifying the inverter that the system is non-functional. As a result, the batteries will automatically enter an idle state, ceasing all charge and discharge activity. This built-in fail-safe ensures that, in the absence of active monitoring and control, the system remains in a secure, non-operational state until the issue is resolved.
Secondary Protection
Secondary protection consists of monitoring and management features that help prevent primary protection from being triggered. This includes balancing cell voltages, managing charge/discharge rates, and ensuring that batteries do not exceed their safe charging limits.
The inverter firmware plays a critical role in regulating the current flow to and from the battery. If the BMS detects an abnormality and issues a warning, it will automatically open its circuit to halt all current flow, preventing further risk.
Tertiary Protection
Tertiary protection is built into the mechanical design of the system to serve as a final safeguard in the unlikely event that primary and secondary protections fail. These include:
- A fused BMS to prevent excessive current draw.
- DC circuit breakers to protect against short circuits and overloads.
- Online monitoring and early warning alerts through the Fox monitoring platform and mobile app.
Additionally, both the battery and inverter feature visual indicators that alert users to any warnings or errors. With a carefully engineered multi-layer protection system, Fox battery systems are designed to prevent overcharging or overheating under normal operating conditions.
Fire Suppression Technology
The latest Fox battery models are equipped with an advanced thermal aerosol fire extinguishing system. This device activates when the internal temperature reaches 170±10°C and has been tested to successfully extinguish internal fires within 30 minutes without re-ignition.
Unlike gas-based suppression methods, this aerosol exists in a solid state before deployment and remains contained within the battery enclosure after activation. It is designed to settle within 20 minutes, eliminating the risk of external dispersion.
Battery Enclosure and Containment
Fox battery cells are housed within a fully sealed enclosure, which:
- Prevents external fire spread.
- Limits heat transfer.
- Incorporates a pressure release valve to control the safe expulsion of gases in the event of an internal fire.
Summary of Safety Measures
- Stable LiFePOâ‚„ Chemistry: LiFePOâ‚„ offers inherent stability, significantly reducing the likelihood of thermal runaway.
- Multi-Layered Protection: A robust BMS system, inverter protections, and physical safeguards minimize safety risks.
- Fire Suppression Technology: Integrated aerosol extinguishing systems prevent fire spread in case of a thermal event.
- Enclosed Design with Gas Control: Fully sealed enclosures and pressure relief valves mitigate explosion risks.
Fox ESS battery storage solutions are engineered to exceed industry safety standards, offering superior protection and fire mitigation compared to other battery types used in residential installations.
Fox ESS battery modules are compliant with all required battery fire and impact regulatory requirements. Certification available on request.
