LiFePO4 underground storage

[izmail]

I'm currently using AGM batteries and according to all available information they are not good for constant cycling. So using these batteries every day during night hours means that with 50% discharge and 300-400 cycles they will be dead in a year. So I'm looking into replacing them with 2 150ah LiFePO4. This will allow to power the house during non-solar hours for much longer then with AGM and down to 0.25-0.3C But I'm little paranoid about fire. Yes, LiFePO4 are much safer then LI ( or so they say), but still.
Question - is it possible to store LiFePO4 batteries in ground? My whole solar station is outside. I'm thinking about digging a whole ( hydro isolated) and putting batteries in standard plastic battery boxes in there. And covering it all with a plastic box with say 3-4 inches of sand. So in case of Lithium fire plastic will melt and sand will cover the fire. Or lining the hole with fire bricks and covering with concrete lid? Maybe installing a 1/2" breathing tube ( are there any gases from LiFePO4?). Temperature in the ground should be more or less constant or at least not extreme. And in California do not have to warry about freezing. Any thoughts? Thank you

 

[robby]

Why deal with all the problems of putting them underground if you don't have to worry about cold temperatures.
Anything underground is subject to possible flooding. It would be far simpler to make a cabinet above ground and put them in that.

 

[izmail]

Why deal with all the problems of putting them underground if you don't have to worry about cold temperatures.
Anything underground is subject to possible flooding. It would be far simpler to make a cabinet above ground and put them in that.

I'm not sure if metal cabinet can withstand lithium fire. And if it can- what gauge shout it be. And I guess it can get very hot, so there should be a dire distance between cabinet and walls or wooden fence in my case. With cabinet solution, good one may be pouring elevated pad and building a box using fire bricks or even concrete. Underground on the other side looks like more compact solution - nothing outside, just a concrete plate.

 

[robby]

I'm not sure if metal cabinet can withstand lithium fire. And if it can- what gauge shout it be. And I guess it can get very hot, so there should be a dire distance between cabinet and walls or wooden fence in my case. With cabinet solution, good one may be pouring elevated pad and building a box using fire bricks or even concrete. Underground on the other side looks like more compact solution - nothing outside, just a concrete plate.

If your using LiFePo4 the chances of them catching on fire is very small. The chances of them creating a big fire is Zero. If you put them 6ft away from the house you are totally safe.
I would build the room using concrete blocks or bricks and make sure you have some ventilation.
A metal cabinet is going to heat up quickly if the sun hit's it.
It's up to you, if you are sure you can keep them from getting flooded during a rain storm then go with the underground system.

 

[Zoomyn]

I have a buddy in West Texas that re-worked his remote electric cattle fences and some lighting & gates into using lithium batteries - he got mad at Texas sun & heat that was expensively killing lead batteries and endangering his stock...

Yeah he had plenty of scrap to choose from but chose culvert chunks & large PVC pipe to case his cell strings and set the bottoms down five feet with a baffle plug at ground level to keep critters out & then a rain guard above everything. Solar charged & kept cool underground the strings are on their 7th year.

back then I ended up swapping him ten 10w 23% efficient solar panels for a few boxes of old CPUs, cards and memory and the panels are still zapping beef & lighting gates