While it's more likely that something goes wrong with a battery system than it is that the house with the battery system in it gets hit by lightning, neither of those things are remotely likely to actually happen.
If the battery(s) are defect-free and installed correctly, there won't be any problems.
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Home energy storage is a fire hazard; FDNY is on the case
A rare occurrence
Fire safety standards already exist for the lithium-ion batteries in phones, laptops and electric cars. Fires are so rare that experts struggle to quantify them.
Some in the research community ballpark the failure rate at 1 in 5 million to 10 million, said Chris Orendorff, principal investigator for the Battery Abuse Testing Laboratory at Sandia National Laboratories. Even that includes cells that fail "gracefully": They stop working but pose no safety risk.
Nevertheless, the Department of Energy has flagged fire safety as a key issue lithium-ion batteries must overcome to become widely used on the grid.
Paiss of the SJFD wasn't at the Tesla demo, but he noted "it was a demonstration, not a scientific experiment” that a third-party lab ran under controlled laboratory conditions.
He said manufacturers like Tesla are conducting their own safety tests but are wary of sharing their "secret sauce" with independent testers. That's why fire professionals haven't been able to get full systems to do their own tests, he said.
"Manufacturers pay certification labs to test their equipment but are often reluctant to share the failure data produced out of fear of this data being used by competitors or to support more stringent regulatory actions," he said.
Willette said he's not aware of any full-scale independent test that's currently taking place. He said one option is to use government funding to buy a system, then turn it over to a research institution for testing.
https://www.eenews.net/stories/1060029271
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Tesla set fire to a Powerpack to test its safety features – the results are impressive
Nothing exploded. How boring.
They learned from the test that not only did the Powerpack not explode or catch on fire, but the fire created by the heater cartridge also didn’t propagate to other pods.
In fact, NFPA found that the 15 other pods were still functional:
“Following the test, it was determined that only one of the energy pods (the initiator pod) was damaged. The other 15 pods remained operational and had a full SOC. The energy pods were discharged and the Powerpack was recycled.”
That’s very good news. It means that a Powerpack cannot start a fire: even in the unlikely event that one or a few cells explode, it will be contained within the pod and will not unleash the entire 100 kWh of energy capacity of the Powerpack.
But what if the Powerpack doesn’t start the fire, but there’s a fire around a Powerpack? Will it explode and aggravate the situation? That’s the question they tried to answer with their second and more spectacular test.
https://electrek.co/2016/12/19/tesla-fire-powerpack-test-safety/