While not the person you were asking the question of - I recently installed 40kwh of batteries to complement my 20kw of solar. I'm using Enphase for both the solar micro-inverters as well as the batteries. The batteries are LiFePo, so fire risk is very very low. The cars in my garages with gasoline represent a much greater risk.

I ended up with Enphase instead of Tesla Powerwalls primarily because the Enphase system supports direct generator integration, which allows smart generator use to offset the battery/solar system in a grid-off situation. The combo of batteries and genset makes for a very reliable scalable solution.

Definitely make sure you have that generator and also setup a local only monitor of the state of the system. In hurricane Ida's aftermath a lot of Enphase systems bricked themselves because the cell and internet service was down and there's nothing to indicate state of charge etc without external connections.

> The batteries are LiFePo, so fire risk is very very low. The cars in my garages with gasoline represent a much greater risk.

Is this really true, and do you have a source on this? Gas vehicles are extensively tested to ensure the integrity and safety of their gas tanks, even in extreme crashes, so I feel like the danger is actually very low.

I’m also curious what batteries you specifically used and how they are doing in terms of holding capacity after hundreds of cycles. Also, do you live in a cold location?

In looking at risk, I would be most concerned with what kind of malfunction could lead to what outcome. LiFePO batteries can be punctured without catching fire, and if a fire is caused by something else, they are not fundamentally very combustible. This chemistry is very different from Lithium-ion. In terms of add this to your house, there is low risk of them starting a fire, and low risk of them contributing to a fire in a significant way.

Gasoline in a car has a low risk of starting a fire, but a higher risk in the event of being exposed to a fire. Storing gasoline in a jerry can probably has higher risk of the first, and certainly the second.

Keep in mind both of these risks are much much lower than so many other things in your house that you do every day. Extension cords, faulty wiring, arcs, heaters, kitchen fires, etc.

I am using Enphase Encharge batteries, which are a LiFePO4 chemistry. They are in my garage, which is heated, so outdoor temperatures don'r make a difference. If they were outdoors, cold temperatures would be a problem below 0F, so if that is your situation I would only do an inside mount. I only have 20-30 cycles so far, but the cycle count is generally well regarded with this chemistry. Still, I don't expect these to last more than 15-20 years.

Thanks for the details. How do you scale this up to power the whole house? On the low end I would imagine you need 30 kWh worth, along with the appropriate equipment (5 kW inverter, cabling, enclosures) to tie it all together into a single system, manage charging, connect it to your home’s circuit safely, and so on. Do you buy off the shelf solutions for all that or pay for some kind of ongoing service or DIY?

The scale is based on two things - storage capacity, and power capacity. Storage is the kwh of storage, which will determine how long you can run off-grid. The power capacity is the peak output power of the system when off-grid, and is usually limited by the inverters.

I am using the Enphase Encharge system, in which each battery unit also includes grid-creation capable micro-inverters. They are integrated into the same boxes, and can provide both grid offset, or grid generation. There is also a 'smart switch' that does the interconnects to the grid, and provides the autotransformer capability ( needed to have 120V split phase ).

There are some more details in my house/shop build thread on garage journal: https://www.garagejournal.com/forum/threads/jeffs-mountain-s...

Thanks for sharing - that seems like an ambitious (and expensive?) project. Are you planning to do an all-up retrospective on it (not just the backup power but the entire site and building)?

Your feelings are ignoring basic physics of the materials which is well known.

Danger is contextual though. My LiPo burning down in the middle of a concrete patch is no risk to anyone, but having it burn down in a backpack in my cupboard will probably burn the house down.

Petrol inside a petrol tank inside a modern car is not the same risk as petrol sitting in a jerry can by the stove for another example.

Agreed on the petrol - The risk of starting while in a car is very low (at least a modern one), but the risk if you have a fire from another cause is certainly higher. 50 gallons of gasoline is lot of stored energy (as is a couple of propane tanks). All of this risk is still very low, and I would be most concerned with something that can start a fire. Of course some electric cars like the Bolt have been problematic.

I have 2 Tesla Powerwalls. I'm not too worried about the fire risk, as I haven't heard of any case of powerwall fire. The city seems worried about it though, my permits and inspections all have to go through the fire department which has slowed things down a lot.

Probably a good idea to install them somewhere that would be easy to flood with water if there was a problem though.

If there is a fire indoors that you cannot extinguish very, very quickly, you need to immediately get out and call the emergency services. The longer you wait, the larger the fire gets and the less professionals can do about it.

Don't try to be a hero and flood batteries from your 10 litres/minute faucet. Just get out before you inhale too much smoke, faint, and die.

It might be a horrible idea to attempt to extinguish a lithium fire with water. [1]

[1] http://electronics.stackexchange.com/questions/290443/ddg#29...

Tesla's guidance for dealing with battery fires in their cars is to basically flood them. I think the idea is to keep the temperature down. The water won't extinguish it because it's a chemical fire, but you can use water to keep it from spiraling out of control.

Yes, it’s to keep the temperature down to not start secondary fires. You cannot stop thermal runway and must let it take its course.

However dumping water on mass amounts of stored electricity sounds scary.

This is something that I’ve wondered about. I’ve got a trio of Powerwalls in my unfinished basement. My town seemed cool with that - for the most part the inspector was totally geeking out over the setup and how clean the installation was.

I read about a lot of places that require Powerwalls to be outside or have additional fire suppression for inside. Anyone have suggestions for what I can do given that I’ve got these guys installed? I haven’t found much help on how to protect myself there.

> Probably a good idea to install them somewhere that would be easy to flood with water if there was a problem though.

I can see why the fire department was concerned with these batteries: https://youtu.be/cTJh_bzI0QQ?t=344

That's lithium metal though, lithium ion batteries don't behave like that. The flammable part is the electrolyte, and the high power density of lithium cells which produces a lot of heat when short-circuited.

I believe the FDNY has not yet approved battery systems like the Tesla Powerwall for use in residential solar systems.

They have -- there are limits to the storage capacity. I cant remember what it is off-hand.