Contributed commentary by Laurie Florence, Principal Engineer, UL
Battery energy storage systems are being utilized for numerous applications including support for intermittent renewable energy sources, grid balancing and load leveling, reliability and resiliency, and providing costs savings to users by providing power during peak/high cost times. Utilities have been installing energy storage at various utility controlled areas to provide renewable support or ancillary services. More recently, these systems are being installed at commercial sites, on private property and even within mixed occupied buildings including residential locations. As costs are coming down, new technologies are being employed for these applications such as lithium ion battery systems, and because their performance may be more attractive than lead acid battery systems that have been traditionally employed for these applications. These new technologies do not have a long history of being used safely for stationary storage applications, and in some instances, such as with lithium ion, there have been field incidents in consumer products and other applications that results in concern in the fire safety community regarding their safety for energy storage systems installed within and near occupied buildings.
Manufacturers of these newer technologies such as lithium ion and more exotic type technologies such as flow batteries and sodium beta technologies, etc. are facing some barriers to getting installed due to concerns from the regulatory community with regard to the safety of these systems. This results in delays in being able to install their products and financial setbacks for this relatively new industry. How can the manufacturers of these systems get their systems installed without facing difficult barriers that may prevent installation completely?
The good news is that there have been product safety standards published that can be used to certify their systems to ease the concerns of authorities having jurisdiction (AHJs) who often rely on 3rd party certification referred to as “listing” in the codes to establish the safety of installed electrical equipment. These standards are ANSI/CAN UL 9540, Energy Storage Systems and Equipment and ANSI UL 1973, Batteries for Use in Light Electric Rail (LER) and Stationary Applications, which is referenced in UL 9540 as the requirements for battery systems. These standards are both American National Standards (ANSI) and UL 9540 is also a bi-national standard for both the USA and Canada. The 2nd edition of UL 1973 will also be a bi-national standard for the USA and Canada. Both standards include construction and testing requirements, and certification of these systems by a 3rd party organization such as UL LLC, ensures that there is also ongoing surveillance of production of these systems. UL 9540 also references UL 1741, Inverters, Converters, Controllers, and Interconnection System Equipment for Use with Distributed Energy Resources, for the power conditioning system (PCS) of the energy storage system. The UL 1741 standards panel (STP) recently added a supplement in UL 1741 to address grid support utility interactive inverters, in order for inverters to comply with regulatory requirements in states with a strong renewable policy focus such as California and Hawaii.
In addition to the development of these safety standards, there has been significant work conducted by various code development committees to update the national electric code (2017 NEC) and the model fire codes (2018 NFPA 1 and 2018 ICC IFC) to better address fire safety of energy storage systems. Work has been underway over the past year to develop the first installation standard, NFPA 855, Standard for the Installation of Energy Storage Systems, with the first draft completed and out for public review this summer. The anticipated date of publication for NFPA 855 is scheduled for 2019. Work has also been underway to develop new proposals to further refine the energy storage requirements for the 2020 ICC IFC. Throughout these model codes, there are requirements indicating that energy storage systems shall be listed with some exceptions. The model code definition for listing is an independent 3rd party certification to an approved set of requirements such as an ANSI standard. In addition, the safety standards such as UL 9540, UL 1973 are reference in these codes as the standards to use to evaluate these products. This certification provides a clear path forward to easing installation of these systems in buildings.
Another concern of the regulatory community is the potential for fire from these energy storage systems should there be a fault occurring as a result of a cell failure that propagates. This is a concern due to the field incidents involving propagation of lithium ion systems in other applications including consumer electronics. For new technologies other than lithium ion, there is a concern for potential fire hazards from lack of field experience to establish their safety. Strict limits on sizing of individual systems and separation distances between the systems and between the systems and nearby structures have been added to these codes to try to control the potential of fire spread should there be a fault in the energy storage system that could lead to a fire. However, exceptions to these limits are allowed based upon what the model codes refer to as “large scale fault and fire testing” and upon acceptance by the local authorities having jurisdiction. Proof of compliance to an accepted large scale fire test of the system to be installed is a means for manufacturers to install larger systems and/or install systems closer to each other or closer to building structures per these code exceptions.
To assist in the installation of energy storage systems within mixed use buildings and to allow for larger systems and reduced separation distances, UL has been involved in development of test methods for the large scale fault and fire testing to be published as UL 9450A, Outline of Investigation for Thermal Runaway Fire Propagation within Battery Energy Storage Systems. This test method provides a step by step evaluation of the fire safety of the system starting with the cell and concluding with a complete system (unit level) test where cells are failed to determine the system’s ability to prevent explosion and fire spread. UL has sought input from industry and the regulatory community as well as internal UL fire research experts and others to develop this outline, which will be published in 2017. Future plans for these tests are to include them within ANSI/CAN UL 9540.
The work underway in both safety standard development and model code development will ensure that energy storage systems will meet acceptable levels of safety including fire safety within the built environment. This will help to reassure owners, authorities having jurisdiction (AHJs), regulators and the industry that energy storage systems can be installed and operated safely and will help ease the installation of these systems.
Laurie Florence is the Principal Engineer for batteries at UL since 2003 and had been focused primarily on stationary and motive battery systems since 2010. Laurie is responsible for UL’s certification categories for energy storage and stationary/motive batteries, and represents UL on a number of standards development committees both at UL and through outside organizations such as IEC, SAE, ISO, NFPA and CSA. Laurie is the convener for IEC SC21A working group 5 for industrial lithium ion batteries and the project team leader responsible for developing IEC 62133-1 and IEC 62133-2. Laurie is currently on the committees UL 9540 Standard Technical Panel, IEC TC 120 and NFPA 855 developing energy storage system standards.
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