On 2024-02-13, I went down to Palo Alto for the Sustainable Energy Action Committee's (SEAC) Energy Storage Systems (ESS) workshop.

I'm glad I did. The workshop was hosted by Jeff Spies, who always provides both humor and zero-bullshit professionalism.

Here are some things I learned at the workshop:

SEAC started in 2015. It's now run by the International Renewable Energy Council (IREC). It's a hub for electrical-code engagement. It has monthly online meetings (fourth Thursday), that are open to the public.

Last March, the Underwriters Laboratories (UL) had a workshop on lithium-ion-battery technology and fire risk. Six hours of event video is available here (form submission required).

UL 9540 is a standard for ESS... a set of safety requirements. Any ESS installed in California needs to be UL 9540 listed.

Separately, there's UL 9540A. This one is a test method, not a standard. Because it's only a test method, an ESS can't be "UL 9540A listed".

If a lithium-ion battery is poorly made or managed, it can erupt into flames. ...Self-sustaining flames, roaring from the bowels of hell. "Thermal runaway."

If an ESS does go into thermal runaway and there are flames... throwing water at the ESS won't affect the hell box. BUT, the water will cool the surrounding area... reducing the likelihood that the building burns down. So water good (despite this being an electrical fire).

A manufacturer can pay a testing lab to put their ESS through the UL 9540A gamut... which includes disabling the ESS's safety system, and inducing thermal runaway. The ESS is wrapped in flammable cheesecloth. If the cheesecloth chars or burns... FAIL. The chaos needs to stay contained in the box. A big test-results report is prepared, that the manufacturer can provide to interested parties.

The UL 9540A report can be helpful when trying to get a non-standard installation approved. ...Like installing the ESS within three feet of a door or window. Or featuring the ESS in the dwelling area, like in all that Sonnen marketing.

There was some lamentation at the workshop that UL 9540A isn't a standard. Because a listing checks a box. While a test-results report makes grown men cry.

I learned at the workshop that there are three types of lithium-ion cell construction: pouch, prismatic, and cylindrical. None of these are straight-up superior. There are tradeoffs.

A lot of the bargain batteries available on Amazon don't meet a standard. Watch out.

If an ESS "unit" is over 20kWh... more rigorous commercial code requirements apply. It seems that there isn't complete clarity on what constitutes a "unit". If there's a rack / cabinet for modular ESS systems... is that the unit?

There are solid learning resources at: code-authorities.ul.com.

A listed ESS can be a black box or a matched assembly. If the latter, the likely interplay of the components is considered. I was happy to hear that a matched assembly can qualify... this seems to make the standard friendlier to grassroots open-source ESS.

I have more notes, but let's get this out there.