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Steve Cummings

Utility, industrial, commercial and government facilities are increasingly turning to battery energy storage systems (BESSs) in a variety of sizes and power outputs for reliable back-up power, to avoid peak demand charges and to store energy generated by renewable power systems for use at a later time.

Given the expected growth in this sector, coupled with the fact that most energy storage systems are designed by interconnecting a series of lithium-ion (li-ion) batteries, the industry is continuing to focus attention on measures designed to all-but-eliminate any potential for dangerous thermal runaway conditions.

To examine the benefits of off-gas detection in li-ion battery energy storage systems up to 30 minutes before dangerous thermal runaway events, which enables action to deter potentially catastrophic cascading failure, we discuss this development Steve Cummings.

Cummings is director of the sensors business unit at Nexceris, a developer of gas sensors and monitors.

Q: How would you explain thermal runaway and its danger?

A: Thermal runaway occurs when excess heat caused by defects, mechanical failures from damage or improper operation of the system creates a reaction that further increases the temperature. If left unchecked by built-in system protections or the battery management system (BMS), this process can continue to drive up temperature and pressure until the battery cell ruptures, which can cause fires in affected and adjacent cells.

Q: How is the industry responding to the danger of thermal runaway?

A: Fortunately, early detection systems have been developed that can now detect a unique pre-cursor event to thermal runaway – an off-gassing in the battery cell that occurs up to 30 minutes prior to a cascading failure. This distinctive and recognizable early warning sign enables the problem to be mitigated or the system shut down before thermal runaway can even begin.

Although virtually all quality BMS equipment monitors temperature and other variables to prevent thermal runaway by triggering protections before temperatures change in an unplanned way, the early detection of off-gassing provides a critical additional layer of protection for the entire system, the facility and even personnel.

There are hundreds, if not thousands of battery energy storage systems already deployed where single cell failure could result in loss of the system. So, the ability to detect cell failure before it results in thermal runaway – and stop it – could literally save the system, adjacent property, and human lives.

Q: How does early detection of li-ion battery thermal runaway work?

A: The early detection of thermal runaway relies on four sequential stages of li-ion battery failure. A li-ion battery cell first begins to fail when it is subjected to an abuse factor like heat, overvoltage, etc. The second step is off-gassing. The third step is smoke, and the fourth step is fire. But smoke and fire often occur almost simultaneously. So, by the time smoke is detected, thermal runaway has typically already begun.

Off-gassing usually occurs due to a breakdown of a li-ion battery cell electrolyte, as a result of pressure buildup. Later, temperature increases, smoke is emitted and then fire breaks out.

To enable off-gassing detection at the earliest stage of a battery event after the initial abuse, the li-ion Tamer system offers a battery off-gas monitor and sensor network designed specifically for lithium ion batteries.

Because the system can detect off-gassing at the ppm-level concentration range, it can detect individual cell failures without contacting the cells. This enables action to prevent thermal runaway and its spread to adjacent cells as soon as a single battery cell begins to fail.

Q: What role do BMS systems play in thermal runaway? Are there limits to this?

A: When working with Tier 1 providers, it is typical to have a well-integrated BMS with enough sensors to properly monitor various aspects of li-ion usage, including the state of charge of individual cells and temperature in the system. However, this may not be the case when dealing with Tier 2 or 3 providers that sell batteries only and leave the BMS to the engineering, procurement, construction (EPC) contractor.

Lower end, offshore battery manufacturers have generally gone from monitoring every small cell group to having one thermocouple run an entire module, monitoring dozens of cells.

As a result, the battery management system is completely dependent on a voltage indication to detect any problems with the cells. But in many cases, voltage is not the perfect indicator of something potentially going wrong in the cell.

Even in the case of qualified Tier 1 battery suppliers, having an independent, redundant system like li-ion Tamer is recommended. In the same way that seatbelts and airbags combined can reduce the risk of injury in a car crash, such an approach can help a qualified EPC integrate additional complementary safety measures into a safer, more comprehensive solution.

Q: How does the detection system’s sensitivity to li-ion electrolyte off-gassing compare to sensors for other kinds of gas monitoring?

A: The detection system’s sensitivity to li-ion electrolyte off-gassing is much greater than traditional sensors for other kinds of gas monitoring. Most sensors that detect gases are either looking for a generic hydrocarbon gas or generic level of gas, and are only detecting at one physical location. The value of a li-ion Tamer sensor is that it is specifically looking for the gas that is emitted from li-ion batteries. It is incredibly sensitive and able to detect it at much lower levels than any other sensor.

Another advantage of such an advanced li-ion specific system is that it is designed to function as a network of sensors, which enhances its effectiveness in li-ion off-gas detection. Because it also allows multiple sensors to be deployed, it is much more effective at detecting gas as it disperses through the container. So, when off-gassing occurs, it is detected immediately and an alarm is sent.

Q: How cost effective is the li-ion specific system compared to traditional fixed gas sensors?

A: The ability of an advanced li-ion specific system to be designed and function as a network of sensors makes them significantly more cost effective than conventional fixed gas sensors.

Typical fixed gas sensors are usually intended to have two or three installed and cost from $1,500 to $4,000 each. But they only measure at a certain point. If you want to extend that, you would need to buy and install 10 to 20. Then you would need to activate each individually to control the system, which adds to the cost.

Q: Can you give an example of a li-ion specific off-gas detection system installation?

A: Because of the benefits of li-ion BESSs, along with li-ion specific off-gas detection systems, a growing number of facilities are installing them together. As an example, Northern Reliability, Inc. (NRI) of Waterbury, VT was selected by the Palo Alto, CA-based Electric Power Research Institute (EPRI) to design and build two transportable microgrid BESSs for the U.S. Navy.

EPRI’s $2 million contract with NRI was finalized in August 2019. The project is funded in part through the California Energy Commission’s Electric Program Investment Charge (EPIC) program, and the Department of Defense’s Environmental Security Technology Certification.

Microgrids are small electrical systems that can operate both independently and together with the larger local electrical grid. Microgrids are being increasingly deployed at critical, nonmilitary facilities such as hospitals, fire stations, and airports to provide uninterrupted power during local electric utility outages.

The microgrid in the project will use solar energy and the BESS, along with Navy site generation, to provide emergency backup for blackout recovery, disaster recovery and weather/fire storm response.

Each NRI BESS is lithium-ion based and can deliver 250kW of power on demand. The two microgrid BESSs will go through testing at the Port Hueneme Naval Base in Ventura County, CA. They will then go through testing and operational use at a Naval Surface Warfare Center-Port Hueneme division data center in Southern California.

Based on EPRI’s recommendation, NRI integrated the Navy-approved off-gas detection system into the unit’s system supervisory controller as a redundant safety solution and on-board fire protection/suppression system.

Author: Steve Cummings is director of the sensors business unit at Nexceris, a developer of gas sensors and monitors. The company worked with the U.S. Navy a decade ago to develop an off-gassing detection technology for li-ion BESSs that would later be commercialized in a product called li-ion Tamer, compatible with all li-ion chemistries. For more info, contact Nexceris: (614) 842-6606.