Within the first of a three-part collection, Greentech Media’s Julian Spector seems to be at implications and classes from final yr’s APS battery hearth.


The vitality storage business did not look forward to the end result of Arizona Public Service’s year-long investigation into the battery hearth that injured 4 firefighters in April 2019 to begin bettering the protection of grid batteries.

The McMicken hearth set off a collection of shadow investigations, as battery suppliers, builders and prospects pieced collectively proof to establish the dangers posed by their very own methods. New seems to be at potential failures prompted product redesigns, together with hardware and software program updates to current methods.

“Due to our personal analysis into the causes of the APS occasion, we have been conscious of what the report was principally going to say,” mentioned Danny Lu, senior vp at storage integrator Powin Vitality, in an e mail. “We had instantly began engaged on options to these issues a few yr in the past.”

By the point the APS battery report got here out final month, main vitality storage suppliers, together with Fluence, which equipped the McMicken vitality storage system, had already adopted key security enhancements. They engineered methods to detect and take away harmful gases so they can not construct up and explode. In addition they addressed the structure of battery cells in order that if one heats up, the issue doesn’t unfold.

A high-profile failure just like the McMicken hearth is perhaps anticipated to carry again development of extra grid batteries. Quite a few startups hawk various storage applied sciences on the idea of being safer than lithium-ion.

However the U.S. vitality storage market didn’t cease increasing because of security considerations. As an alternative, the business has skilled meteoric development, with report procurements introduced nearly weekly this summer season. An unprecedented variety of utilities and energy producers are investing in batteries as a pillar of a cleaner electrical grid.

The current modifications to top-tier battery choices have diminished the chances of a repeat of the damaging occasion on the APS facility, which got here on-line in 2017. APS now applies stricter standards to the batteries it buys, and different utilities could observe swimsuit.

“General hearth security is definitely a key precedence, and we’re happy by the progress round standardization of security options,” mentioned Benoit Allehaut, managing director for clear vitality infrastructure at Swiss asset supervisor Capital Dynamics, which is at the moment setting up 1.9 gigawatt-hours of storage.

Lesson 1: Remove root causes

A number of weaknesses made the McMicken Battery hearth doable.

One thing precipitated one lithium-ion cell to warmth up, though what that one thing was stays a matter of dispute. APS concluded it was “an inner cell defect.” However battery producer LG Chem challenged that conclusion, contending that the bodily proof suggests an exterior warmth supply, reminiscent of electrical arcing outdoors the cell, precipitated it to warmth up. (For extra on this, learn the second half on this collection, to be printed later within the week.)

There may be settlement on what got here subsequent: The clear agent hearth suppressant didn’t cease the fireplace. The hearth unfold to neighboring cells all through a single vertical rack. The warmth precipitated the cells to launch harmful gases, which constructed up contained in the container, which lacked air flow or a way of detecting these gases. When the hazmat staff opted to open the door, the setting contained in the container shifted in such a manner that it triggered an explosion.

To make sure that an explosion like McMicken by no means occurs once more, the folks placing collectively grid batteries want to stop this chain of occasions from ever being repeated. The vitality density and chemical attributes of lithium-ion cells carry an inevitable threat of thermal runaway, however the decisions a system integrator makes will decide if an surprising occasion burns up one cell or explodes a complete facility.

Lesson 2: No extra explosions

The explosion is what set this occasion aside from different battery mishaps. When dozens of batteries caught hearth in South Korea, they burned down however didn’t harm folks.

In Arizona, the explosion — not the fireplace — despatched first responders to the hospital. It unleashed a lot power that it threw one firefighter 73 toes by way of a chain-link fence.

However the explosion may be the best failure mode to handle: Prevention requires letting harmful gases out, reasonably than holding them in.

“The APS occasion was a studying expertise for the entire business to come back out with safer requirements and practices,” Lu mentioned. “It’s [no longer] affordable…to construct an answer that does not have the power to vent gases.”

Ought to explosive gases accumulate nonetheless, using a “deflagration panel” can channel the explosive power up and out of a construction, reasonably than outward horizontally the place they’re extra prone to harm folks. Deflagration panels now come normal on storage enclosures reminiscent of Fluence’s new Dice design.

“The strain launch serves to attenuate structural and mechanical harm, and extra importantly, to attenuate the protection threat to operators or first responders,” mentioned Fluence COO John Zahurancik.

Ideally, batteries would by no means arrive at that state of affairs. To this finish, Fluence added an “incipient gasoline detection system” that triggers a shutdown if it spots the sorts of explosive gases that lithium-ion cells are recognized to emit when heated. The mix of early detection methods and air flow signifies that newly constructed storage crops ought to have the ability to establish the presence of gaseous buildup and expel it earlier than there’s any threat of it igniting.

The bodily form of the battery enclosure has developed too. McMicken housed its battery racks in a big transport container, with house for folks to enter and stroll round. That spaciousness set the scene for gasoline to construct up and for firefighters to enter in an effort to work out what was occurring.

Extra lately, storage designs have shifted to smaller, modular, cabinet-based designs. The Fluence Dice is eight toes on all sides. The Tesla Megapack can also be tightly packed and cabinet-based. That leaves no room for responders to enter.

Lesson three: Cease the unfold

Stopping the unfold of thermal runaway from cell to cell would take away the reason for gaseous buildup within the first place. Storage plant designers at the moment are doing simply that.

It didn’t assist that the Novec 1230 clear agent hearth suppression put in at McMicken was, based on producer 3M, incapable of stopping thermal runaway in lithium-ion battery methods. That declaration got here after McMicken was designed and constructed, the report notes.

The bodily design of the battery modules and racks performs a job as nicely. After the primary cell heated up, “the shut packing of the battery cells inside every module allowed that cell to set off thermal runaway in its neighbor, which unfold to the subsequent cell, and so forth,” the report notes. “The cell-to-cell packing and module-to-module placement supplied no safety to stop this from occurring.”

The report suggests two key antidotes: separating cells with boundaries or house and cooling down cells to cease thermal runaway. Aluminum plates separating cells can gradual the switch of warmth; connecting it to a liquid cooling system is even higher. The report notes that “a number of suppliers” are incorporating such measures into new product generations.

The Fluence Dice makes use of batteries that handed the UL 9540A take a look at for non-propagation of thermal runaway from a single cell, Zahurancik mentioned. The design works with a number of battery sorts, together with air and liquid-cooled batteries, he famous.

Powin makes use of lithium-iron-phosphate chemistry due to its “minimal” threat of thermal runaway, Lu mentioned. It handed checks that confirmed no propagation on the cell, module or stack stage, he added.

Tesla didn’t reply to a request for touch upon its battery security, however a significant buyer did. Capital Dynamics is shopping for Tesla Megapacks for the most important behind-the-meter storage venture on the earth, by the way positioned on the Swap knowledge middle down the street from Tesla’s Gigafactory close to Reno, Nevada.

Tesla’s use of liquid cooling, reasonably than air cooling, was a gorgeous characteristic, mentioned Capital Dynamics’ Allehaut. Different firms are additionally adopting liquid cooling.

“We observed that the [APS] report recommends that modules of cells must be totally separated to keep away from propagation,” Allehaut mentioned. “That’s already within the design of the Megapacks, and that is seemingly going to be an business normal.”

Notably, the house and materials separating every vertical rack of batteries blocked warmth switch to adjoining racks at McMicken; solely the one rack was destroyed. Equally, spacing out battery containers at bigger initiatives reduces the danger of fires leaping between them. And people measures require no new know-how to attain.

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