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Raising serious concerns about the safety of battery storage,
investigators into the alarming spate of lithium-ion battery fires
in South Korea said one of the primary causes was the practice of
using nearly the full charging and discharging battery capacity on
a daily basis—a pattern that can roughly correspond with plans
by U.S. operators to use storage to shift wind and solar generation
to the evening periods of peak demand.
Last year, South Korean government officials largely halted
deployment of new lithium-ion battery systems and urged operators
to curtail operations of existing ones after 23 battery fires broke
out over a year-and-a-half. Many owners continued operating,
however, and in recent months another five battery fires have been
reported in South Korea, which had represented the world's largest
market for stationary battery storage before the fires cratered new
deployments.
South Korea's Ministry of Trade, Industry and Energy completed a
months-long investigation into the fires in June, generally
concluding that they were caused by a range of issues including
lack of protections against shocks, faulty installation practices
and control systems that were incompatible with some
components.
More broadly, though, investigators at DNV GL—a global
engineering standards firm contracted to investigate the root cause
of one of the fires—said the common practice in South Korea of
cycling the lithium-ion batteries from close to 0 percent to 100
percent and then back down again on a daily basis has led to
extreme wear-and-tear on the systems and was an underlying cause of
failures in the battery cells that sparked the fires.
That hard-driving cycling pattern, which has been common in
South Korean storage systems co-located with wind and solar farms
to shift the output to periods of higher demand, is different from
most batteries deployed to date in the United States, where they
have been used primarily for fast-responding frequency regulation
within a narrower and less-stressful band.
"If we start cycling those batteries as aggressively as we do in
Korea, we will likely see similar failure rates," George
Garabandic, DNV GL's energy storage leader for the Asia-Pacific
region, told The Energy Daily. "It should be expected that
a higher component stress will result in higher levels of random
component failures. In other, more developed energy storage system
(ESS) markets, the batteries are providing services similar to
frequency regulation, and the component stress is relatively
milder."
If accurate, that assessment could prove problematic for U.S.
utility-scale battery developers, who are increasingly co-locating
storage with solar generation and touting its ability to charge up
during the day when the sun is shining and then discharging that
power in the late afternoon and evening—a cycle that more
closely resembles the pattern in South Korea where the dozens of
fires have broken out.
In fact, most of the fires under investigation in Korea were at
facilities co-located with renewable resources, according to Korean
media accounts.
Such deep cycling to shift load has long been known to
accelerate degradation of lithium-ion batteries, with researchers
at the National Renewable Energy Laboratory (NREL) reporting in
2017 that batteries used daily for such utility-scale applications
will wear out in seven years even if depth-of-discharge (DOD) is
limited to 74 percent. Batteries will wear out in 10 years if DOD
is further limited to just 54 percent, according to NREL's
estimates.
Given that accelerated degradation and the potential to raise
risks of fires that comes with deep cycling, U.S. battery operators
often strictly limit the depth-of-discharge, but that can severely
constrain the system's ability to significantly shift renewable
energy to periods of high demand as advertised. Battery experts
also stress that there are ways to limit the threat of fires even
with more aggressive cycling, which the industry is rapidly
developing and working to adopt.
The risk of battery fires gained prominence last April when an
explosion at Arizona Public Service's McMicken battery facility
near Phoenix sent several firefighters to the hospital. Arizona
regulators were subsequently surprised to learn that a fire in 2014
also destroyed APS's Mt. Elden battery storage system.
The cause of the McMicken fire is still under investigation, but
in the meantime APS has suspended plans to deploy 850 megawatts of
battery storage—which had been the nation's largest battery
storage initiative—until the utility can figure out what
happened.
Lithium-ion batteries can present heightened risks of fire, in
part due to a phenomenon called "thermal runaway," in which
excessive heat in the battery can create more heat that can then
cause cascading fires in adjacent battery cells, according to a
battery risk assessment compiled by the insurance group AIG.
The burning batteries also release highly toxic hydrofluoric
acid, cyanide and other gases that can explode upon ignition, which
is what appears to have happened in the McMicken fire, according to
a November 5 preliminary report from APS.
While the chances of an individual battery cell failing and
starting a fire is extremely remote, Garabandic from DNV GL noted
that large battery storage systems can have the equivalent of 10
million or more lithium-ion cells packed into a small space.
"One cell out of those 10 million will fail and if, in such
circumstances, we don't implement adequate safety measures, a
cascading effect will certainly lead to a large-scale fire," he
said. "The lack of such safety measures has been the main reason
why the accidents in Korea had such catastrophic outcomes; and
consequently, the entire Korean ESS industry was brought to a
halt."
To strengthen safety, battery operators must recognize that an
individual cell is likely to fail at some point, and therefore use
monitoring analytics to replace cells that present risks before
they fail, Garabandic said.
Beyond that, developers must implement "all technical and
operational measures that will prevent the cascading effect of
failures and contain the damage to a reasonable level," he
said.
Those measures include barriers between cells to prevent
cascading fires, adequate control and monitoring systems and proper
ventilation of potentially explosive gases, along with systems that
can douse a burning battery cell quickly with water, which
counterintuitively has been shown to be the best way to extinguish
a battery fire.
Battery experts have reported that various technologies already
exist that effectively reduce lithium-ion battery fire risks, and
that safety will improve in the still-nascent storage industry as
these are scaled up and integrated into manufacturing and
installation processes.
Korean battery makers LG Chem and Samsung have recently attained
compliance with newly developed international battery fire
prevention standards, and the U.S. Energy Storage Association last
year released guidelines for best practices to reduce fire risk in
an effort to address what is emerging as a serious threat to the
fast-growing industry.
Several battery makers also are touting different chemistries as
inherently safer alternatives to traditional lithium-ion batteries.
Among these are Sonnen, SimpliPhi and Chinese battery giant
Contemporary Amperex Technology, which are marketing lithium iron
phosphate batteries they say are less likely to catch fire and are
less toxic if they do start to burn.
Reprinted from The Energy Daily. For more
comprehensive daily coverage of US energy policy, regulatory, and
business trends from IHS Markit, visit
The Energy Daily website.
