I emailed Jeff Spies and Carl Arellano of Planet Plan Sets, with a question about California ESS-installation permitting requirements (ESS ~ Energy Storage System).
Carl gave me a thoughtful email reply. Jeff gave me a 90-minute night-time phone call. THANK YOU.
Here are my notes:
Mike's (naive) email:
I have a prospect who got some high PV / battery quotes. He decided to "stick it to the man" by buying equipment himself. He bought sixteen 280Ah 3.2V battery cells. He'd like me to pick a BMS and charge-controller inverter, and install the system. I'd like to take this on.
I understand that PV modules and inverters must be on the CEC list in order to be interconnected.
To qualify for interconnection, do batteries / energy-storage systems need to be on the CEC battery list? Otherwise... Is the UL 9540 certification required for the entire energy-storage system (whether an integrated option from one company, or a particular equipment combination from 2+ companies)? Or maybe it's less strict... maybe the battery inverter needs UL 1741 certification while the battery cells need UL 1973 certification.
Carl's reply:
There does appear to be a CEC approved battery list, I think perhaps they might need to be, if we are dealing with a grid-tied system. The Energy Storage system will need UL 9540 certification to be able to be legally installed in California. An ESS unit can be just the Battery modules and their Battery Management System (BMS), and this assembly will need UL 9540 certification. Typically batteries, BMS and enclosure(if applicable) come from the same manufacturer for the UL 9540 listing. The battery inverter would also need 1741 SB compliance, which can be found on the CEC approved list as well, for interconnection approval.
Jeff's feedback over the phone (paraphrased):
The prospect-purchased (LFP) cells are from a company whose LFP battery caused an explosion in a German home last year (source, in German). Batteries (and cells) from this company should be avoided. Besides, they aren't UL 9540 listed.
While fires and explosions for home ESS have been rare to date, both of the major lithium battery types (NMC and LFP) can go into thermal runaway... which can cause a fire or explosion. In the unlikely event of thermal runaway: NMC is more prone to fire while LFP is more prone to explosion. LFP batteries can seep four times as much combustible gas as NMC batteries in a failure situation. Poorly made LFP batteries are dangerous.
There are only a few major NMC battery makers. Apart from LG Chem, they've demonstrated good quality control. On the other hand, there are hundreds of obscure LFP battery makers. ...This makes it harder to assess and trust quality.
In general, "you get what you pay for". Second-tier battery makers offer lower prices. But they tend to have little (or no) tech support or real warranty coverage.
It's difficult to assess battery-cell construction characteristics. The fire-causing defect is sometimes in the battery electronics, not the cells.
The first-tier battery makers provide safer ESS, but need to better differentiate themselves around safety and durability.
Just because a low-price battery is UL 9540 listed... doesn't mean it's as safe and durable as one from the higher-quality battery makers. UL 9540 is a minimum-requirement standard. Some companies put more effort than others into meeting (or exceeding) UL 9540 requirements, and documenting the process.
For the UL 9540A test method (not a listing), many companies do the bare minimum. Some UL 9540A test reports are very cryptic. When a company only indicates "UL 9540A" for a battery without having a 9540 certification... it only means: "We burned this uncertified battery".
WORD OF WARNING: THE ESS MUST BE LISTED TO UL 9540! Some budget batteries show 9540A on their documentation while not being 9540 listed. This is sleazy and disingenuous, as they're implying that they are listed to 9540. There is no 9540A listing... this is only a a test.
It may be advisable to purchase an inverter and battery from the same company. ...It's less likely that problems will arise over time (e.g. remote firmware upgrades causing incompatibility).
With minimum charges of 20% and maximum charges of 80%, a battery will last longer. 10% to 90% is the norm. Sometimes, 5% to 95%. Jeff would like to see more data on discharge / charge range versus durability.
When practical, install lithium batteries outside. If installing inside a garage, heat detection and (when applicable) vehicle-collision barriers (bollards) are required.
Thanks so much Jeff and Carl for the awesome guidance.