Wind mill and panels


A MYRIAD OF CHALLENGES face our electrical grid in the United States, including disaster resilience, aging infrastructure, environmental concerns (greenhouse gas emissions, solid waste generation, etc.), and cybersecurity.[1,2,3,4] These challenges are likely to increase in importance, as energy consumption in the United States has increased every year since the 1950s. Even though the rate of increase has slowed,[5] electrical energy consumption still outpaces growth in transmission capability.[6,7] Fortunately, advances in technology will help us overcome the challenges of our electric grid.

Renewable energy sources (e.g., rooftop photovoltaics, wind turbines) are capable of addressing many of our grid challenges, such as reduced environmental impact, increased resilience, and an inexhaustible supply of input energy. However, renewable energy sources alone are not a panacea.[8] The generation of power from renewable energy sources fluctuates with the weather, creating significant challenges in matching electrical power generation to electrical power consumption. Renewable energy power generation sources are a much more valuable technology when paired with another relatively recent technology, electrical energy storage systems (ESS), which can store excess power generated from renewable energy when it is not consumed and deliver that power at a later time when demand exceeds base power generation. Current practice within the electrical power industry is to use “peaker” plants, which are fossil-fueled power plants turned on for hours at a time to quickly ramp up generation to meet demand (i.e., load leveling). Energy research firms now expect the addition of electrical ESS to renewable energy generation will soon eliminate the need for peaker plants.[9]

Beyond balancing our grid, ESS will provide many other benefits. These include backup power, peak shaving (reducing the demand on the grid), capacity firming and power quality (reducing voltage swings on the grid), and frequency regulation (maintenance of 60 Hz AC). Energy storage has been developed using a range of technological approaches. The predominant technologies are electrochemical batteries (e.g., lithium-ion, lead acid), chemical systems (e.g., hydrogen storage paired with energy conversion equipment such as a fuel cell system), mechanical systems (e.g., flywheels, compressed air), and thermal energy storage (e.g., sensible heat, latent heat storage paired with energy conversion equipment such as a steam turbine and generator).

As of June 2018, the United States had over 25.2 GW of rated power in energy storage, compared with 1,082 GW of total generation capacity. Ninety-four percent (23.6 GW) of that energy storage capacity is from pumped hydroelectric storage,[10] as hydroelectric storage has been deployed for nearly 100 years. [11] However, rapidly advancing technology and falling battery costs have resulted in a surge in the permitting requests and deployment of electrochemical battery energy storage,[12] specifically lithium-ion. In 2015, lithium-ion ESS made up approximately 90 percent of utility-side energy storage deployments.[13] With the cost barrier for lithium-ion batteries lowering from roughly $1,200 per kWh in 2010 to less than $200 per kWh in 2018,[14] eight U.S. states have set aggressive implementation goals to quickly achieve the benefits of energy storage. Table 1 (see page 21) provides a summary of these goals at the time of this writing.

Demonstration of a Full-Scale Fire Test
FIGURE 1. UL Demonstration of a Full-Scale Fire Test of a Lithium-Ion Energy Storage System According to UL 9540A, Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems

While the ESS will be essential to modernize our grid, current ESS technologies are not without their own implementation challenges. The key challenges for the fire safety industry, especially regarding lithium-ion technologies, are fire and explosion hazards resulting from thermal runaway. In South Korea, currently the global leader in ESS deployment, 23 large-loss fires were reported since 2017[24] (across an estimated 1,500 installations[25]). The United States has experienced only a handful of ESS fire incidents but has less than half of the installed capacity of ESS compared to South Korea.[26] In South Korea and the United States, the cost of ESS fires has been primarily property loss, as fire incidents to date have occurred in installations with minimal life-safety exposures. However, nine first responders were injured on April 19th by an explosion that occurred while investigating smoke from a dedicated use ESS building in Surprise, Arizona.[27]

Energy storage hazards are not new to the international codes and standards development community. An exhaustive 2014 inventory of codes, standards, and regulations (CSRs) applicable to ESS safety identified 38 for ESS components, 36 for “entire” ESS (the system of interconnected components), 56 for ESS installation, 12 for commissioning and maintenance, 8 for incident response and 3 for the transportation of ESS parts.[28] Since 2014, new CSRs have been developed and existing CSRs updated. Developments were rapid due to the surge in demand for energy storage. Table 2 provides a summary of CSRs addressing fire and explosion safety, adapted from a recently issued Department of Energy brief.[29]

The new CSRs and updates to existing CSRs were driven by the need to address propagation of thermal runaway and the resulting development of fire and explosion hazards associated with lithium-ion ESS. Previous CSRs focused on the hazard characteristics of lead-acid chemistry batteries, as other ESS chemistries were relatively uncommon. For example, the 2015 editions of NFPA 1 and the International Fire Code safety requirements for stationary storage battery systems covered siting, spill control, ventilation, signage, and smoke detection based on lead-acid systems. Though identified, no specific requirements existed for lithium-ion chemistries, and other chemistries were not addressed. The 2018 editions of NFPA 1 and the International Fire Code now contain updated safety requirements based on flow, lead-acid, lithium, Ni-Cd, and sodium chemistries. Provisions have been made to enable safe installations of unidentified chemistries that may become viable in the future. In effect, the recognition of fire and explosion hazards for lithium-ion ESS has resulted in the development of safety requirements for all viable ESS technologies, as reflected by Chapters 9–12 of NFPA 855[30] and Chapter 12 of the International Fire Code (IFC).[31]

Table of Energy Storage Implementation Goals
Table of Codes and Standards

Table 2 is arranged in a top-down order beginning with the model codes, which establish the overarching ESS safety performance requirements for building and life safety**. The CSRs that follow in descending order contain specific safety requirements for locations where ESS are installed, the design of the ESS, and the safety of individual ESS components. Collectively, the CSRs in Table 2 address the design, manufacture, installation, construction, commissioning, operation, and maintenance of the ESS and its component parts. The different levels of CSRs exist because of the necessary complexity for an ESS to perform its functions. System safety is dependent on the reliability of individual components, the safe interoperability of those components as a system, the safe interconnection and implementation of the system at the installation site, and any additional considerations necessary for safe installation with respect to life and property protection near, on top of, or inside buildings. Those seeking to better understand the process of demonstrating ESS compliance to CSRs are encouraged to read the DOE report “Energy Storage System Guide for Compliance with Safety Codes and Standards.”[44]

UL 9540A is an unusual fit within Table 2 (opposite page) because it is not a product or installation standard. UL 9540A is a test method developed to provide fire and explosion performance data for ESS when required by the model codes. The model codes require large-scale testing to demonstrate whether there are fire spread or explosion hazards when individual ESS units or ESS installations exceed certain total electrical capacities, or when it is desired to install equipment with less than the minimum spacing. The test methodology within UL 9540A was designed to output the types of measurement data needed to enable evaluation of the safety performance of an ESS product to the performance requirements established by the model codes (e.g., propensity of fire spread from one piece of equipment to the next or quantification of explosion hazard characteristics).

Testing within UL 9540A begins at the component (cell) level. If test data shows fire and explosion hazards not controlled by the product at the cell level, tests are conducted at increasing product scales (module level, unit level) until it is demonstrated that either safety features within the product control the hazards or that supplementary fire protection equipment is required to achieve the safety performance established within the codes and standards for other equipment integrated into our ever-improving infrastructure.

In the future, CSR requirements will be further refined for specific technologies and end-use applications, and listings will be available for pre-engineering and pre-packaged ESS equipment. At present, successful permitting of an ESS installation requires analysis of documented UL 9540A test data and reports to validate a given ESS installation will meet the performance requirements of the model codes. Fire protection engineers are needed as fire and explosion hazard subject matter experts and will play an important role in helping states meet their ambitious and much-needed energy storage objectives.

* UL 9540A, while not an installation standard, has been developed to document validation of compliance of a proposed ESS installation with the safety requirements established by the model codes and NFPA 855.
** The CSRs shown in Table 2 apply primarily to “behind the meter” installations, where ESSs are interconnected to a commercial, industrial or residential network behind the meter to the utility. ESS installations in “front of the meter”, connected to the transmission and distribution networks owned by grid operators, are subject to the requirements developed and adopted by the utilities. UL 9540 is intended for both in front of and behind the meter applications.

ADAM BAROWY is with UL’s Fire Research and Development Group.


1. M. Henderson, D. Novsel and M. Crow, “Electric Power Grid Modernization Trends, Challenges, and Opportunities,” IEEE, Piscataway, NJ, November 2017.
2. J. M. Barrett, “Challenges and Requirements for Tomorrow’s Electrical Grid,” Lexington Institute, Arlington, Virginia, June 2016.
3. United States Environmental Protection Agency, “About the U.S. Electricity System and its Impact on the Environment,” [Online]. Available: [Accessed 7th July 2019].
4. U.S. Energy Information Administration, “How Electricity Is Delivered To Consumers - Energy Explained, Your Guide To Understanding Energy - Energy Information Administration,” 31 August 2018. [Online]. Available: [Accessed 7 July 2019].
5. L. Schwartz, M. Wei, W. Morrow, J. Deason, S. Schiller, G. Leventis, S. Smith, W. Ling Leow, T. Levin, S. Plotkin, Y. Zhou and J. Teng, “Electricity end uses, energy efficiency, and distributed energy resources baseline,” Lawrence Berkeley National Laboratory, Berkeley, California, 2017.
6. Litos Strategic Communication, “The Smart Grid: An Introduction,” U.S. Department of Energy.
7. U.S. Energy Information Administration, “Record U.S. electricity generation in 2018 driven by record residential, commercial sales - Today in Energy - U.S. Energy Information Administration (EIA),” 6 March 2019. [Online]. Available: [Accessed 7 July 2019].
8. M. S. Whittingham, “History, Evolution, and Future Status of Energy Storage,” Proceedings of the IEEE, vol. 100, pp. 1518 - 1534, 2012.
9. C. Newberry, “Energy Storage Poses a Growing Threat to Peaker Plants,” General Electric, 1 October 2018. [Online]. Available: [Accessed 7 July 2019].
10. Center for Sustainable Systems, ““U.S. Grid Energy Storage Factsheet.”,” University of Michigan, 2018.
11. United States Department of Energy, “History of Hydropower | Department of Energy,” [Online]. Available: [Accessed 7 July 2019].
12. M. Froese, “What’s new in energy storage,” Windpower Engineering and Development, 13 May 2019.
13. D. Ola, “20% increase in grid-connected storage pipeline, says IHS | Energy Storage News,” 12 July 2016. [Online]. Available: [Accessed 8 July 2019].
14. D. R. Baker, “Battery Reality: There’s Nothing Better Than Lithium-Ion Coming Soon - Bloomberg,” 3 April 2019. [Online]. Available: [Accessed 14 July 2019].
15. A. Colthorpe, “Arizona’s 3GW energy storage target, Clean Peak plan; part of a wake up call to other states | Energy Storage News,” Energy Storage News, 31 January 2018. [Online]. Available: [Accessed 15 July 2019].
16. State of California Office of Legislative Counsel, “Assembly Bill No. 2868,” State of California Office of Legislative Counsel, 2016.
17. Public Utilities Commission of the State of Hawaii, “Providing Guidance of The Hawaiin Electric Companies’ Phase 2 Draft Requests for Proposals for Dispatchable and Renewable Generation,” Public Utilities Commission of the State of Hawaii, 2019.
18. Commonwealth of Massachusetts, “Energy Storage Target |,” Commonwealth of Massachusetts., 8 August 2016. [Online]. Available: [Accessed 19 July 2019].
19. Maine Office of Legislative Information, “HP1166 Resolve, Establishing the Commission To Study the Economic, Environmental and Energy Benefits of Energy Storage to the Maine Electricity Industry,” in 129th Maine Legislature, 2019.
20. A. Colthorpe, “Energy storage procurement targets could work for Nevada, PUCNcommissioned study says | Energy Storage News,” Energy Storage News, 4 October 2018. [Online]. Available: [Accessed 5 August 2019].
21. New York State Energy Research and Development Authority, “Energy Storage in New York - NYSERDA,” New York State Energy Research and Development Authority, 2019. [Online]. Available: [Accessed 5 August 2019].
22. P. Maloney, “Oregon PUC release guidelines for energy storage mandate,” Utility Dive, 6 January 2017. [Online]. Available: [Accessed 5 August 2019].
23. State of New Jersey - 218th Legislature, “A3723,” State of New Jersey - 218th Legislature, 22 March 2018. [Online]. Available: [Accessed 5 Augst 2019].
24. C. Yun-Hwan, “ESS units caught on fire due to bad management-INSIDE Korea JoongAng Daily,” 12 June 2019. [Online]. Available: [Accessed 9 July 2019].
25. S. Ji-hye, “Ministry postpones ESS fire probe report, industry suffers setback,” 2 May 2019. [Online]. Available: [Accessed 9 July 2019].
26. J. St. John, “Global Energy Storage to Hit 158 Gigawatt-Hours by 2024, Led by US and China,” 10 April 2019. [Online]. Available: [Accessed 9 July 2019].
27. R. Randazzo, “Arizona Public Service provides update on investigation of battery fire,” 23 April 2019. [Online]. Available: [Accessed 10 July 2019].
28. D. R. Conover, “Inventory of Safety-related Codes and Standards for Energy Storage Systems,” Pacific Northwest National Laboratory, Richland, WA, 2014.
29. D. R. Conover and D. M. Rosewater, “Energy Storage System Safety - Development and Adoption of Codes and Standards,” Department of Energy, 2018.
30. NFPA 855: Standard for the Installation of Stationary Energy Storage Systems, Quincy, MA: National Fire Protection Association, September 2019.
31. International Code Council, International Fire Code, Falls Church, Va: International Code Council, 2018.
32. National Fire Protection Association, NFPA 1: Fire Code, Quincy, MA: National Fire Protection Association, 2018.
33. National Fire Protection Association, NFPA 70: National Electrical Code, Quincy, MA: National Fire Protection Association, 2017.
34. International Code Council, International Fire Code, Country Club Hills, IL: International Code Council, 2017.
35. International Code Council, International Residential Code, Country Club Hills, IL: International Code Council, 2017.
36. The Institute of Electrical and Electronics Engineers, Inc., 2017 National Electric Safety Code (NESC), New York, NY: The Institute of Electrical and Electronics Engineers, Inc., 2016.
37. Underwriters Laboratories, Inc., Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems, Northbrook, IL: Underwriters Laboratories, Inc., 2018.
38. Underwriters Laboratories, Inc., UL Standard for Safety for Energy Storage Systems and Equipment, Northbrook, IL: Underwriters Laboratories, Inc., 2016.
39. ASME Codes and Standards, TES-1 Molten Salt Thermal Energy Storage Systems, New York, NY: ASME Codes and Standards, 2017 DRAFT.
40. Underwriters Laboratories, Inc., UL Standard for Safety for Batteries for Use in Stationary, Vehicle Auxiliary Power and Light Electric Rail (LER) Applications, Northbrook, IL: Underwriters Laboratories, Inc., 2018.
41. Underwriters Laboratories, Inc., UL 1974: Standard for Safety for Evaluation for Repurposing Batteries, Northbrook, IL: Underwriters Laboratories, Inc., 2018.
42. Underwriters Laboratories Inc., UL 810A: UL Standard for Safety for Electrochemical Capacitors, Northbrook, IL: Underwriters Laboratories Inc., 2008.
43. Underwriters Laboratories, Inc., UL 1741: Inverters, Converters, Controllers and Interconnection System Equipment for Use With Distributed Energy Resources, Northbrook, IL: Underwriters Laboratories, Inc., 2010.
44. D. R. Conover and P. C. Cole, “Energy Storage System Guide for Compliance with Safety Codes and Standards,” U.S. DOE, Alexandria, VA, 2016.