Storage Safety

By its very nature, any form of stored energy poses some sort of hazard. In general, energy that is stored has the potential for release in an uncontrolled manner, potentially endangering equipment, the environment, or people. All energy storage systems have hazards. Some hazards are easily mitigated to reduce risk, and others require more dedicated planning and execution to maintain safety. This page provides a brief overview of energy storage safety, along with links to publicly available safety research from EPRI.

Energy Storage Roadmap: Safety

As energy storage costs decline and renewable energy deployments increase, the importance of energy storage to the electric power enterprise continues to grow. The unique drivers of lithium ion battery development, including pressures of safe operation and integration into electric vehicles, consumer electronics, and scaled manufacturing, have helped ensure it remains the dominant technology for stationary storage applications. Current lithium ion products pose safety hazards related to their chemical make-up and thermal runaway potential. However, these hazards are not unique. Whenever energy is stored it may be released in an unintended manner—presenting risk if not prevented or mitigated.

The rapid development of lithium ion technology means that its performance is constantly changing—meanwhile, codes and standards are reacting to these new options at a different pace. As a result, leading practices have been sparse, if available at all. Interest in storage safety considerations is substantially increasing, yet newer system designs can be quite different than prior versions in terms of risk mitigation.

Gaps

Hazard Characterization

An uncontrolled release of energy is an inevitable and dangerous possibility with storing energy in any form. Resulting primary hazards may include fire, chemical, crush, electrical, and thermal. Secondary hazards may include health and environmental.

EPRI's Research Activities

EPRI's energy storage safety research is focused in three areas, or future states, defined in the Energy Storage Roadmap: Vision for 2025.

Safety Practices Established

Establishing safety practices includes codes, standards, and best practices for integration and operation of energy storage support the safety of all. Gaps to this future state include:

• Public safety guidelines
• Installation, transportation, and handling safety guidelines
• Operator guidelines
• Maintenance guidelines
• Incident response protocols
• Design and manufacturing safety practices

Asset Hazards Characterized and Minimized

Characterizing and minimizing safety hazards means understanding failure modes and consequences, and developing mitigations to reduce the likelihood and severity of failures and safety events. Gaps to this future state include:

• Battery thermal runaway characterization and mitigation
• Siting risk management practices
• Emerging storage technology safety information and analysis
• Failure modes and effects analyses
• Fire hazard testing and models

Community Resilience and Public Safety Applications Viable

Develop community solutions that demonstrate a range of customer and community resilience applications for disruptions and disasters intended to support public safety, disaster recovery, and environmental quality. Gaps to this future state include:

• Quantification of resilience value for communities
• Energy storage public safety use definition
• Community and customer awareness of options
• Coordination of customer and utility assets

Background

The vast majority of new grid-scale energy storage uses lithium ion battery technology. Lithium ion technology is ubiquitous. Cells and batteries using various lithium ion chemistries can be found in all kinds of consumer electronics and transportation technologies, including electric vehicles, e-bikes, and e-scooters. The main hazards posed by lithium ion systems include electric shock and arcing hazards from the presence of high voltage, and the risk of fire and/or explosion. Failure incidents in commercial and utility-scale storage systems are recorded in a public database maintained by EPRI.

Lithium ion Thermal Runaway

Lithium ion cells can fail due to several factors:

• Manufacturing defects
• Subject to over-voltage condition
• Subject to over-current condition
• Subject to over-temperature condition
• Physical shock, impact, or damage

Any of these failure modes can lead to the cell experiencing high temperatures. If the temperature exceeds a certain threshold, thermal runaway follows. Thermal runaway occurs when high temperatures cause the internal chemical components of the cell to break down, generating more heat in an accelerating manner. The accelerated reaction generates more heat, which causes the reaction to accelerate further, in a positive feedback loop that begins to exceed the ability of the cell to reject heat to its surrounding structure and environment. This reaction then can vaporize the organic electrolyte and release flammable and particle laden gasses at extreme temperatures.

When the flammable gasses mix with oxygen, it creates the potential for fire or explosion. Only an ignition source is required, which is usually present during the thermal runaway process in the form of very hot particulates, high voltage and overheated components. For more information on thermal runaway and fire ignition, review The Difference Between Thermal Runaway and Ignition of a Lithium-ion Battery white paper.

Preventing Failures

Lithium ion cell failures are rare. Cell failures can be avoided through careful monitoring of cell voltage, temperatures, and current, to ensure that cells are maintained with their safe operating ranges. Effective and reliable thermal management is necessary to avoid overheating cells during operation. Additionally, manufacturing and quality controls are necessary to ensure cells perform uniformly and are made without defects that could lead to unexpected failures. As an owner, operator, or customer, choose products that are certified to the appropriate safety standards. Vet suppliers to ensure they have sufficient quality control on their manufacturing. Specify the inclusion of monitoring and safety systems. Homeowners and installers interested in residential energy storage systems can view this Safety Guide for more information.

Mitigation of Fire and Explosion Risk

Once a cell has failed, it is still possible to avoid catastrophic consequences. Mitigation strategies can include design elements to detect and arrest cell failures early in the process, to avoid thermal runaway. Other design elements, like deflagration vents and fire suppression, avoid propagating failures and can reduce the consequences of failures. Much of EPRI's research is focused on system-level and procedural mitigations to limit the risk of lithium ion battery installations. This Reference Hazard Analysis provides a comprehensive overview of threats leading to cell failures, consequences of failures, and barriers to prevent and/or mitigate risks.

Featured Resources

Storage safety research at EPRI is not confined to lithium ion technologies. EPRI evaluates the safety of non-lithium technologies as part of our general technology evaluation research, as well as specific demonstration and testing projects.

EPRI also conducts safety research through the Energy Storage Integration Council (ESIC). ESIC is an open, technical collaborative that brings together various stakeholders to advance energy storage deployments. Anyone can join ESIC, and access the tools and guides, webcasts, and newsletters. Current safety projects through ESIC include the development of a Reference Hazard Mitigation Analysis for Flow Batteries and discussions on safety specifications that can incorporated into storage procurement documentation.

BESS Failure Incident Database

The BESS Failure Incident Database is a public resource for documenting publicly-available data on battery energy storage failure events from around the world. All information listed information, such as the failing system's location, size, application, and date of event, is included and available in publicly linked documents.

Battery Storage Fire Safety Roadmap

EPRI is conducting a phased research program titled BESS Fire Prevention and Mitigation. This program is focused on characterizing the risks of lithium ion technology, especially of thermal runaway failures. The program also develops best practices for deployment and operation of storage, conducting site-specific assessments and studies with industry partners. This research program considers codes, standards and regulations related to storage safety, and provides training for various stakeholders that may interact with storage systems. Through these projects, generalized resources, templates, and guides are developed to support the industry as a whole.

The Fire Prevention and Mitigation research project is currently in Phase 2, focused on the development of a Project Lifecycle Safety Toolkit. Phase 3 will begin in 2024. EPRI continuously publishes research and resources developed through this project, many which are public, listed below. Funders of Fire Prevention and Mitigation Research Project can access the project page with their logins.

Publicly available energy storage safety resources.

Resource	Description
Lithium Ion Battery Energy Storage Fire Safety Measures: An EPRI Perspective	This article provides EPRI's perspective on the current state of lithium ion BESS safety.
EPRI BESS Failure Event Database	Gathers information on battery failures around the world.
Insights from EPRI’s Battery Energy Storage Systems (BESS) Failure Incident Database: Analysis of Failure Root Cause	This report utilizes data from EPRI’s BESS Failure Incident Database, as well as findings from incident reports, root cause analyses, and expert interviews to develop an aggregate analysis of failure causes.
Technology Innovation Spotlight: Lithium Ion Battery Fires in the News	This article looks at lithium ion battery failures across industries and puts the news in context, considering failure rates, risks, and regulations across grid-scale, electric transportation, and micromobility applications.
Lessons Learned: Lithium Ion Battery Storage	Describes trends and lessons learned from failure incidents between 2017-2021.
Safety Implications of Lithium Ion Chemistries	This article looks at the safety implications of different lithium ion chemistries, including NMC and LFP.
Residential Energy Storage Safety Guide	Guide for safe installation and use of residential energy storage systems, for homeowners and installers.
Lessons Learned from Air Plume Modeling of Battery Energy Storage System Failure Incidents	An overview of various plume modeling tools that are available for such simulations, key model characteristics needed, important input metrics, guidelines for scenario building, and current knowledge gaps in the field. The goal is to educate BESS owners and operators, industry professionals, the emergency response community, and researchers as to current practices, drivers of plume evolution, information gaps, and future research needs.
ESIC Energy Storage Reference Fire Hazard Mitigation Analysis	This document uses a bowtie framework to identify hazards, threats, consequences and barriers around fire and explosion risks for Lithium-ion energy storage systems.
Energy Storage Safety Roadmap	This roadmap provides necessary information to support owners, operators, and developers of energy storage in proactively designing, building, operating, and maintaining these systems to minimize fire risk and ensure the safety of the public, operators, and environment. The roadmap processes the findings and lessons learned from eight energy storage site evaluations and meetings with industry experts to build a comprehensive plan for safe BESS deployment.
The Difference Between Thermal Runaway and Ignition of a Lithium-ion Battery	This white paper examines the thermal runaway process to differentiate thermal runaway from battery fire ignition. Understanding how thermal runaway occurs and contributes to battery fire and explosion risks enables improved system design for fire prevention and mitigation.
Thermal Runaway Propagation and Emissions Analysis	Details results of thermal runaway testing on 3 lithium ion NMC chemistry modules, including gas and particulate emissions.
Proactive First Responder Engagement for BESS	Guidance for BESS owners and operators on engagement with fire fighters, paramedics, police on environmental health and safety aspects of storage facilities.
Carnegie Road Energy Storage System Failure Response, Recovery, and Rebuild Lessons Learned	This report conveys the lessons learned from the Carnegie Road energy storage system (ESS) failure event in the UK, including aspects of emergency response, root cause investigation, and the redesign and rebuild processes.

If you have comments, suggestions, or questions, please email Lakshmi Srinivasan.