When smart phone batteries catch fire or laptop batteries explode on airplanes, it makes the news. So far batteries used to store energy at the residential and commercial level have avoided those headlines. But eventually there will be a problem.
“Battery fires are rare, but when they happen you have to be prepared,” said Lt. Paul Rogers with the Fire Department of New York’s hazardous materials operations division. Rogers works with a team within FDNY’s hazardous materials operations division, and he has become the point person on energy storage safety issues. “I am a one man show,” he said, operating as a liaison with regulators, researchers and industry.
As the headlines suggest, much of the current safety concerns about batteries revolve around lithium-ion batteries. Those concerns are well founded: Li-ion batteries have a lion’s share of the energy storage market and are the fastest growing storage technology.
Li-ion batteries have become ubiquitous in laptops and smart phones. But batteries used for grid-tied stationary storage applications are quite different than those used in robust, long term use case scenarios such as behind-the-meter applications or on a transmission or distribution system, said William Tokash, a senior research analyst with Navigant Research.
Grid connected batteries have sophisticated software systems that manage the battery during charging and discharging cycles, and they are equipped with thermal control systems and software designed to ensure safe operation, as well as early detection of any operating concerns.
Nonetheless, the rapid growth of energy storage has raised concerns. As a 2014 Department of Energy report noted, most of the safety parameters that are in place for energy storage systems are based on “previous industry knowledge and experience with energy storage for vehicles, as well as experience with grid-scale lead-acid batteries.”
In short, safety issues such as testing and validation, as well as fire prevention and suppression has not evolved as fast as industry has. That could be a hurdle to the expansion of energy storage, unless safety validation techniques are broadened to encompass grid-scale systems, as well as a broader range of stationary storage systems and a much broader range of technologies, the DOE report concludes.
Getting in front of the fire
Rogers is in the forefront of those efforts. As New York began to ramp up its energy storage efforts, Rogers realized that there were not procedures in place to deal with battery fires.
That posed a problem in a densely populated city that in September set a goal of having 100 MWh of energy storage in place by 2020 as part of the city’s effort to cut greenhouse gases by 80% by 2050.
Right now New York City’s fire code “is not restrictive,” Rogers said. It doesn’t address what type of suppression system – water, chemical, water with an additive – would be most appropriate to put out a burning li-ion battery. “We are looking at a dry chemical suppressant, but it is not yet clear if that is the way to go,” he said.
The real problem, Rogers noted, is no so much how to put out a li-ion fire, but how a storage system reacts during and after a fire.
One of the problems with using a dry chemical fire suppressant, for example, is that it does not contain the heat that li-ion batteries can produce.
Water could dissipate heat from a battery, but that could require so much water that drainage and even structure safety from the weight of the water could become an issue.
That is part of a wider problem. Suppression does not penetrate to a battery’s cells, so the heat cannot be absorbed or dissipated. So it can appear that the fire is out, but the heat is actually trapped in a cell. That cell can continue to produce enough heat that it ignites neighboring cells, resulting in thermal runaway.
“Fire is not the biggest problem,” said Rogers. Firefighters are trained to deal with fires, he said, but they need to know what they are dealing with. Li-ion batteries can release toxic acids and flammable vapors. Some of those vapors are consumed by the fire, but if they are not, they could ignite or be a problem for firefighters.
The biggest problem is what happens “post op," that is, after the fire is extinguished. Even if a battery is shut down it could re-ignite for up to 72 hours, Rogers said. And that raises procedural questions. For instance, what agency assumes control and responsibility for the safety of the site after the fire is extinguished? Those hand-off procedures have yet to be worked out, said Rogers.
That is particularly the case when it comes to residential energy storage. The fire department is responsible for storage devices deployed in multi-unit or rental units, but behind the meter deployment in private homes present a gray area, said Rogers.
The explosive growth of energy storage is prompting an array of stakeholders to address the issues and come up with answers.
The FDNY is working with the New York State Energy Research and Development Authority (NYSERDA), the National Fire Prevention Association, insurance companies and with Consolidated Edison to come up with procedures and protocols for battery safety.
NYSERDA is working with Con Ed on a joint battery energy storage safety initiative that aims answer critical safety questions confronting the FDNY and other agencies that are responsible for reviewing applications for energy storage installations.
The initiative was undertaken in support of Gov. Andrew Cuomo’s Reforming the Energy Vision (REV), which among other things looks to reduce peak demand by using battery storage.
The initiative is looking at many of the issues that concern Rogers, including gases released during a fire, suppression methods and re-ignition. A spokesperson said NYSERDA is wrapping up work on the initiative and expects to release its final report by the end of the year.
DNV GL, which won NYSERDA’s request for proposals to examine battery storage issues, is working with Con Ed “in their investigation of the toxicity, flammability, and extinguishing practices for stationary energy storage systems” and aims to make its work public by year end.
Energy storage is spreading rapidly, and stakeholders say they are determined to move quickly to understand the issues and put in place procedures to ensure safe deployment. “We are moving closer and closer to a solution,” said Rogers.