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Energy Storage Systems - Frequently asked questions

What is an ESS?

An energy storage system, often abbreviated as ESS, is a device or group of devices assembled together, capable of storing energy in order to supply electrical energy at a later time. Battery ESS are the most common type of new installation and are the focus of our free fact sheet.


What Are the Advantages of ESS?

ESS have many useful applications, these include:

  • Supplement Renewables
    Renewable energies such as solar panels or wind turbines only produce electricity when the sun is out or the wind is blowing. Supplementing these with ESS allows users to take advantage of the electricity that is generated when the renewable energy technologies are not producing electricity.
  • Peak Shaving
    ESS allows a user to shift where their electricity comes from by drawing power from the batteries during the higher-cost daytime hours then recharging during the lower-cost nighttime hours. This practice is referred to as peak shaving.
  • Load Leveling
    When power generation facilities ramp up and ramp down to keep up with the changing demand for electricity, it puts stress on the system. ESS can help flatten out the demand curve by charging when electrical demand is low and discharging when it is high.
  • Uninterruptible Power Supply
    ESS can provide near instantaneous protection from power interruptions and are often used in hospitals, data centers, and homes.
What Are Some of the Hazards of ESS?

The rise in the number of ESS installations requires the need for a heightened understanding of the hazards involved and more extensive measures to reduce the risks. Those risks include:

  • Thermal Runaway
    Thermal runaway is a term used for the rapid uncontrolled release of heat energy from a battery cell; it is a condition when a battery creates more heat than it can effectively dissipate. Thermal runaway in a single cell can result in a chain reaction that heats up neighboring cells. As this process continues, it can result in a battery fire or explosion. This can often be the ignition source for larger battery fires.
  • Stranded Energy
    As with most electrical equipment there is a shock hazard present, but what is unique about ESS is that often, even after being involved in a fire, there is still energy within the ESS. This is difficult to discharge since the terminals are often damaged and presents a hazard to those performing overhaul after a fire. Stranded energy can also cause reignition of the fire hours or even days later.
  • Toxic and Flammable Gases Generated
    Most batteries create toxic and flammable gases when they undergo thermal runaway. If the gases do not ignite before the lower explosive limit is reached, it can lead to the creation of an explosive atmosphere inside of the ESS room or container.
  • Deep Seated Fires
    ESS are usually comprised of batteries that are housed in a protective metal or plastic casing within larger cabinets. These layers of protection help prevent damage to the system but can also block water from accessing the seat of the fire. This means that it takes large amounts of water to effectively dissipate the heat generated from ESS fires since cooling the hottest part of the fire is often difficult.
What are ESS Failure Modes?

These are ways the batteries can fail, often leading to thermal runaway and subsequent fires or explosions. These failure modes include:

  • Mechanical Abuse
    Mechanical abuse is when a battery is physically compromised by either being dropped, crushed, or penetrated.
  • Thermal Abuse
    Thermal abuse can occur when a battery is exposed to external heat sources.
  • Electrical Abuse
    Electrical abuse can happen when the battery is overcharged, charged too rapidly or at high voltage, or discharged too rapidly.
  • Environmental Impacts
    Environmental impacts that can lead to battery failure include seismic activity, rodent damage to wiring, extreme heat, and floods.
Which NFPA standard covers the installation of ESS?

If you are installing ESS for either new construction or a renovation, you should review the requirements of NFPA 855, Standard for the Installation of Energy Storage Systems.

What is the best extinguishing agent for a fire in a battery ESS?

Testing has shown that water is the most effective agent for cooling for a battery ESS. For this reason, a sprinkler system designed in accordance with NFPA 13, Standard for the Installation of Sprinkler Systems, is required by NFPA 855, Standard for the Installation of Energy Storage Systems.

I’ve heard that an ESS can reignite several days after a fire has been extinguished, is this true?

Lithium-ion batteries have shown they can ignite, or reignite, long after they have been damaged or involved in a fire—hours, days, or even weeks later.

Is it OK to use a fire hose to extinguish a lithium-ion battery fire?

The UL study “Firefighter Safety and Photovoltaic Installations Research Project” (2011) showed that for voltages up to 1000 volts dc, water can be safely applied given the right conditions. This study demonstrated that using an adjustable nozzle at a minimum of a 10 degree fog pattern allowed for the safe application of water at a distance of 5 ft from the 1000 volts dc electrical source; however, due to the potential conductivity of pooling water, contact with it may expose you to shock.