Ensuring Fire Safety in BESS

Unique in the battery industry, EVLO’s next generation BESS contains fire mitigation protection mechanisms at every level above the cell level: module, rack, tray, and enclosure.

 

At the module level, thermal barriers are installed between the cells to slow down and prevent propagation to neighboring cells.

Each tray contains up to six modules.  At the module level, thermal barriers are installed between cells to slow down and prevent propagation to neighboring cells. 

The tray level includes two forms of fire protection: double thermal barriers between each tray, and the arrangement of the trays themselves. The design creates an air gap between each tray. In case of thermal runaway, this gap functions as a chimney by providing a path for gas release that avoids contact with nearby trays, therefore limiting temperature increase on neighboring modules. 

 

At the enclosure level, there are hundreds of sensors as well as proprietary-designed venting panels. Once these sensors detect excess heat, smoke, or hydrogen, they trigger the active mitigation plan: the HVAC goes into Economizer Mode and forces fresh air in from outside the enclosure. Simultaneously, the venting panels open to release hot gas from the enclosure. 

This system works even during power outages, since the venting panels include a failsafe mechanism. In this condition, natural convection alone is enough the meet the performance requirements of NFPA69. 

 

 

The reason we chose to integrate both active and passive safety approaches with our BESS design is simple: to ensure that our BESS are as safe as possible.

The fire mitigation designs of battery energy storage enclosures are governed by NFPA 855, which approves two options to manage thermal runaway. NFPA 69 describes active approaches such as ours, in which the chimney-like design and vents provide ventilation for gas release. NFPA 68 details a passive approach that includes deflagration panels on the container. 

Deflagration panels are sheets of metal that open and release pressure in case of an explosion. This method requires that the container’s design withstand the initial pressure buildup, which ultimately tears the deflagration panel apart and releases the pressure. The process still allows an explosion, which doesn’t allow for individual unit testing (because the process would destroy that unit). The resulting destruction makes it impossible to ensure that this method will work as intended for each unit.

These drawbacks led us to base our fire mitigation approach on NFPA 69, which makes use of sensors, can be tested on a unit-by-unit basis, and is designed to prevent explosions. Our approach also goes beyond NFPA 69’s requirements because we add passive fire mitigation elements on top of our active strategies. Namely, the failsafe venting panels open by themselves to release pressure even during a power outage. We call this approach NFPA 69++.

Our fire mitigation designs also offer flexibility depending on users’ different preferences and requirements. For example, some may need extra sensors, while others may want a different type of detection sensors depending on their climate or requirements. Our engineers can adapt these to meet the most stringent safety standards.

 

 

Like all reputable BESS systems, our EVLO systems are tested using the UL9540A test procedure ⎼ but we go far beyond the minimum requirements to ensure that our batteries are as safe as possible.

The UL9540A test procedure is a set of tests for each succeeding level: cell, module, unit, and system. Currently, the minimum level lithium-ion batteries must pass is the unit level, so many lithium batteries are only tested up to that level. However, this level does not provide a full engineering validation because it doesn’t test all the safety features that must be implemented to meet the requirements of NFPA 855 68 and 69 sections.
 
Testing only up to the unit level also doesn’t reflect all aspects of the real-life conditions within a BESS enclosure. A BESS’s Fire Safety System depends on relationships between the cell, the module, the unit, the enclosure , detection hardware, mitigation hardware, and software. That’s why we have developed our own Engineering Validation Plan consisting of a large scale fire test on a fully functional enclosure following UL9540A system-level guidelines.This test validates the performance as well as active, passive and gas ignition modes.
 
So for us, UL 9540A testing is just one part of the complete Engineering Validation Plan that we provide for our products. Testing the entire system in real-life conditions ensures that our fire mitigation measures will perform reliably on our customer’s sites under any circumstances.  

 

Keeping Firefighters Safe with Distant Fire Resolution