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Energy Storage System Gas Protection – NFPA855
What is an energy storage system?
An energy storage system (ESS) is pretty much what its name implies—a system that stores energy for later use.
ESSs are available in a variety of forms and sizes. For example, many utility companies use pumped-storage hydropower (PSH) to store energy. With these systems, excess available energy is used to pump water into a reservoir during times of low demand. When energy demands rise, the water is discharged from the reservoir and drives a turbine which produces electricity.
PSH systems, though an efficient method of storing energy, are logistically complex and infrastructure intensive. Therefore, they typically are only used in utility-grade installations. And while PSH currently commands a 95% share of energy storage, utility companies are increasingly investing in battery energy storage systems (BESS).
Photo Courtesy of NFPA
These battery energy storage systems usually incorporate large-scale lithium-ion battery installations to store energy for short periods. The systems are brought online during periods of low energy production and/or high demand. Their purpose is to increase the reliability of the grid and reduce the need for other drastic measures, such as rolling blackouts.
BESSs for both commercial and residential applications represent a small—but rapidly growing—sector of the ESS community. Increasingly, homes and businesses that use renewable energy generators (e.g., solar panels and wind turbines) are also including a lithium-ion BESS into their installation. This allows the storage of power during times of excess energy production and is a better value than selling the power to the grid and then buying it back at a higher price. It also functions as a back-up during instances of power outages.
It is estimated that in terms of BESSs, lithium-ion has a 90% market share worldwide. Applied research and scales of economy in manufacturing have led to decreasing financial outlays for their installation. BESSs’ market share is forecast to grow in exponential terms due to their potential for applications on the horizon as well as the expected increase in traditional usage modes.
What are the risks/hazards with battery energy storage systems?
When dealing with any form of energy and its storage, there is always some degree of risk with an associated hazard involved. With PSH, there is a risk that the containment could fail producing the hazard of cascading water rushing through the surrounding area.
BESSs produce a large amount of energy in a small area. This design, while efficient, creates a risk that must be managed. Big energy + small space = potential for problems. While most BESSs operate without experiencing any unfortunate incidents, the risk of failure of one or more of the cells must be taken into consideration and addressed.
The primary risk with BESSs is battery case damage or overheating of the system from an internal fault or externally from exposure to fire. If the risk scenario comes to fruition, the hazard side of the failure equation comes into play. The hazards are the release of toxic and/or flammable gases which often lead to a probable fire and potential explosion. When risks and hazards are identified in any system, it is incumbent upon the owner or operator to take steps to minimize them.
How is the risk in battery energy storage systems managed?
Fortunately, owners and operators of BESSs have guidance to manage these risks. The increasing popularity and use of lithium-ion battery systems has given rise to standards governing their use. The first such standard was UL® Standard 9540 released in 2014. In 2017, UL released Standard 9540A entitled Standard for Test Method for Evaluating Thermal Runaway Fire Propagation in Battery Energy Storage Systems. Following UL’s lead, the NFPA® introduced the 2020 edition of NFPA 855: Standard for the Installation of Stationary Energy Storage Systems®.
Before delving into specific risk management strategies, it is necessary to understand the failure model for BESS.
A battery cell becomes compromised through mechanical damage, an internal or external thermal event, or through an electrical fault.
Small amounts of gas, typically hydrogen, are generated and released from the cell with an accompanying release of heat; this is known as “off-gassing.”
With increasing heat levels, smoke begins to emit from the cell. The presence of smoke is indicative of an impending catastrophic event in which ignition and thermal runaway are the likely outcomes.
Fire ensues and a chain reaction failure of adjoining cells is probable, along with the possibility of explosion.
Thermal runaway is defined as the situation in which the heat inside of a cell rises much faster than it can be dissipated. This leads to a rapid release of energy which ignites the flammable vapors present from the off-gassing phase. Adjacent cells are adversely impacted by the fire and in turn fail in a similar fashion. This can lead to a domino-like effect in which cell after cell fails and ignites, often with disastrous results.
Test Demonstration of the Speed of Flame Propagation in BESSs (in seconds)
Photo Courtesy of NFPA
The first line of defense is a battery management system (BMS). The purpose of the BMS is to monitor the charge at the cell as well as the temperature during the charge and discharge phases. Upon detection of temperatures exceeding the safe range, the BMS may shut off power to prevent continued escalation of internal cell temperature.
A BMS is often complemented with the addition of a device designed to monitor the enclosure for the presence of flammable or toxic vapors released during the off-gassing phase. These devices have a quick response time, i.e., ≤ 5 seconds. Upon detection, a signal is sent to the BMS to shut off power to the batteries. A ventilation system may also be activated to expel the flammable vapors from the BESS enclosure.
What happens if there is a fire and how can it be managed?
Fires involving BESSs are problematic for a number of reasons:
Thermal runaway causes an ever-escalating fire.
The consumption of the cathodes in the cell are believed to self-generate oxygen.
Thermal runaway events are exothermic, and the heat release makes extinguishment by cooling difficult.
There are a variety of fuels available to be consumed:
Class A: wire coverings, polymer components, etc.
Class B: electrolytes, solvents, and flammable gases
Class C: electricity / remaining voltage in unburned batteries
Class D: combustible metals in cathodes (Momentary event)
The design of the cell necessarily results in a deep-seated, hard-to-reach fire.
KELISAIKE GAS DETECTOR on ESS
Given the special hazard nature of lithium-ion BESSs, special gas detection systems are in order. Traditional gas detection systems are often ineffective or inefficient.
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