We have installed many LG RESU battery backup systems with our new solar installations and some time this winter I will be installing one in my own house to offset the recent rash of NHEC grid outages. Five this year all ready this since their big rate increase! and ranging from 2 hours to 5 hours. Plus at least once a month the Co-op grid drops out just long enough to kick out the modem and require re-setting anything with a timer.
I'd prefer using a LFP (litho ferro phosphate) battery chemistry because as already pointed out they are inherently far safer than a NMC battery, but my SolarEdge system will only work with the LG 400 volt Li-ion batteries. Tesla Powerwall Li-ion batteries are similar in design to the LG RESUs, but are packaged with their own inverter and this is why they are sometimes used for backup sans solar array.
I do think that when I add my storage system I'll be building a remote insulated shed that will house both my old generator and the new LG battery. It will only take a very small heater to keep the battery above freezing and I'll have the security of having both the generator and battery in a weather tight enclosure and well away from my dwelling. We recently set up a similar battery shed for a client this way and the more I thought about it the more I liked the idea.
The impetus for the client's shed was the new code, NFP 855, that went into effect in July. In a nutshell all residential home energy storage batteries are now required to be either remote and/or enclosed in a one hour fire rated closet. This came about because the fire chiefs were reacting to ten house fires in the USA in the last couple of years that were proven to have started with the battery storage systems. Even though in the overall national scheme of things ten fires is a miniscule amount, it was still ten preventable fires. My only issue with the code is that it states all batteries when the culprits were all either NMC or acid based. Hopefully going forward the fire chiefs will exempt the far more stable LFP battery technology. An added benefit to LFPs is that they have an extremely long cycle life, Simpliphi warranties their LFP batteries for 10,000 cycles! That is literally a lifetime folks, and they are totally maintanence free.
The sulpher based batteries also hold promise too, but they are still working on perfecting the chemistry. Right now they are somewhat limited because of minute but constant mineral exchange between the cathode and anode and this leads to a relatively short life cycle.
After many discussions my partner and I have made a decision to move away from the SolarEdge/LG battery Li-ion system and will be instead installing either Outback or SolArk systems for our clients wanting battery backup and the advantages of daily self consumption. Both inverter systems use the much more stable LFP batteries, and an additional advantage to that is that the batteries are "stackable". What that means is that the client can add a nearly unlimited number of batteries after the initial installation. We have been using LFPs in our off-grid systems for three years now and have had multiple clients upgrade their systems with more storage capacity as their needs changed. Right now LFPs are the way to go!
Lastly, it is important to note that the battery setup that caused the Sanbornton fire was a home built system using used automotive NMC batteries, not a carefully engineered system from a major company like LG or Tesla and definitely not carrying a UL rating. It is an unfortunate situation but certainly there is something to be learned from bot this poor souls misfortune and the Moultonboro generator fire.
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