I think the battery room will be about 40ft from the main structure (assuming 50ft cable run). I can put a mini-split wall unit in the vault if heat becomes a concern (will at least plumb for it, as I'm using a multi-split setup with many taps). Can also make this new room two separate chambers if segregating batteries from electronics is desirable.
Very large off-grid planning considerations - timing
- Thread starter jnmit12
- Start date
Good point. I haven’t determined final mounting height, but want to keep them hidden behind parapet wall. I have a very large roof area, so I won’t be space constrained. Is it wrong to focus on $/watt in this scenario? (If I’m not worried about watts / Sqft)
Hedges
I See Electromagnetic Fields!
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The primary way to stop electrical fires is cut the power. Power is coming from the batteries, so try to stop current by disconnecting load.
Another thread reports a fire involving 16s7p battery. Not certain the cause, but the 7 strings of cells were paralleled through fuses only, no relay or BMS FETs to disconnect. That would be a good addition. Idea is to stop over-charging or over-discharging before there is catastrophic failure, and be able to operate with a string out of the circuit if cells imbalanced.
diysolarforum.com
Heat and smoke alarms could be used to trigger shutdown.
LiFePO4 vents below auto-ignition temperature, but gasses can be ignited by a spark. So want contactors and fuses of an explosion-proof type. And want gasses vented outside, so they won't built up and enter house when door opened. Forced air with fan would be good.
Another thread reports a fire involving 16s7p battery. Not certain the cause, but the 7 strings of cells were paralleled through fuses only, no relay or BMS FETs to disconnect. That would be a good addition. Idea is to stop over-charging or over-discharging before there is catastrophic failure, and be able to operate with a string out of the circuit if cells imbalanced.
House burned down
So, after 4 to 5 years of working flawless, the 100 kwh lifepo4 battery caught fire at night and burned our house down. Luckily our family just made in out on time. Inspection of the fire expert revealed that a melt fuse melted, and created an arc between the 2 points wich ultimatly started the...
diysolarforum.com
Heat and smoke alarms could be used to trigger shutdown.
LiFePO4 vents below auto-ignition temperature, but gasses can be ignited by a spark. So want contactors and fuses of an explosion-proof type. And want gasses vented outside, so they won't built up and enter house when door opened. Forced air with fan would be good.
shadowmaker
Solar Addict
It's always good to focus $/W. Nothing wrong there. Just keep in mind that white shiny TPO is perfect for bifacials and they can give you something like +15% to +30% additional power compared to monopanels depending installation. It's all about getting reflected light to backside of bipanels so installation matters. They like to be elevated and loosely installed and they don't mind being little steeper angle than ideal as the more frontside production you lose because "wrong" tilt angle the more you gain from the backside.
In here mono and bipanels seem to be equally priced now, so I'd go BI if I had your situation.
SilverbackMP
Solar Addict
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- Apr 4, 2022
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I would also go with the Quattros. And maybe some level of AC coupling with Fronius. I will probably go with a similar setup when I build a house except I’ll be using Sunny Boy 7.7s instead of Fronius since I have a plethora of them (no longer made; I snagged the remaining new ones).
(This will be a separate system from the 72 panels, four Sunny Islands, three Sunny Boys, and 135 KWH that are providing power to my shop, mom’s house, misc outbuildings, and a future fairly large greenhouse. Although I might figure out how to switch over to either power to either system from both clusters in case of serious issues with one setup…a couple of transfer switches would probably do it).
Edit: one thing to look out for is the stupid assed battery bank size restrictions in the latest NEC code if your state or local jurisdiction have adopted it. I am in rural MO and my state hasn’t adopted any form of NEC statewide, so I’m good. I have a power shed that’s somewhat sacrificial if magic smoke escapes followed by magic flames.
(This will be a separate system from the 72 panels, four Sunny Islands, three Sunny Boys, and 135 KWH that are providing power to my shop, mom’s house, misc outbuildings, and a future fairly large greenhouse. Although I might figure out how to switch over to either power to either system from both clusters in case of serious issues with one setup…a couple of transfer switches would probably do it).
Edit: one thing to look out for is the stupid assed battery bank size restrictions in the latest NEC code if your state or local jurisdiction have adopted it. I am in rural MO and my state hasn’t adopted any form of NEC statewide, so I’m good. I have a power shed that’s somewhat sacrificial if magic smoke escapes followed by magic flames.
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The only thing I'm not sure of is will the victron system accept soc from a smart shunt or BMV instead of a battery bms?
If so then any lifepo4 better can be used but I'm not sure of that. Do you know?
Want to make sure we don't have the same comms debacle as the sunny island
SilverbackMP
Solar Addict
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- 978
I would either use the REC BMS that I’m using now (with Victron firmware) or SOK batteries that have close loop coms with Victron (at lease I think they do). Maybe even EG4. Current Connected does the Victron + SOK setups as well as the REC.
Id rather get the soc from a shunt. I'll look more into this. Some of these bms are not that good
SilverbackMP
Solar Addict
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- 978
Each REC BMS has a shunt. Of course, they are expensive AF. Not sure what is in the SOKs. Probably not nearly as good as REC but not Daily and Chins level either.
Brucey
Solar Wizard
With a Cerbo or other VenusOS device there's two settings I know of.
You can choose which shunt to use for soc:
You can also select the device that controls DVCC whether that be a battery BMS or you can disable BMS control (I don't have a comms BMS so it doesn't show as an available option for me). So for example if you did have battery comms but didn't want the battery to decide when it should charge etc.
wheelman55
New Member
A couple of things. Shed size, internet and AC in the vault.
Make the shed /vault large enough to accommodate future expansion of solar gear. For instance a 15 ft or 20 ft wall will allow much more room for “what if”.
A wise man who specializes in off grid solar told that there are two kinds of people who he deals with: those who want solar and those who want more.
Plan for when you want more.
How will you run internet to the vault? Put in an additional 2” conduit, spaced far enough from any AC or DC conduit..I think you need 12 inches between conduit…but check.
Plan for the day when the local phone company offers you fiber optic. There is money out there for rural internet.
Our off-grid place sits on 940 acres, some miles off pavement. Our area has zero utilities. The local phone company surprised us with the offer of fiber optic internet. We jumped on it. Our driveway is 3/4 of a mile long. They dug that trench for zero dollars.
Since we had put an extra 2” conduit from electronics shed to house, we had them connect the two buildings with fiber optic cable. 135 ft between buildings in our case.
If you ever get this offer, plan now as to how/where the internet will enter the structure. Make the plan before you do your landscaping. Same for what if your local poco gives you a sweetheart deal on electricity.
FYI we built our shed with 10’ x 11’ interior. Really wish it was 15’ x 20’. Too late now.
It’s pretty simple to add a small panel in the vault for AC. You could then power lights, some outlets and a small mini split for the vault.
Keep in mind that the condensate line for the split needs to run downhill.
Think redundancy for the splits. Having more than one head unit in the rare case where you have a failure.
Sounds like you are having fun with your project.
Make the shed /vault large enough to accommodate future expansion of solar gear. For instance a 15 ft or 20 ft wall will allow much more room for “what if”.
A wise man who specializes in off grid solar told that there are two kinds of people who he deals with: those who want solar and those who want more.
Plan for when you want more.
How will you run internet to the vault? Put in an additional 2” conduit, spaced far enough from any AC or DC conduit..I think you need 12 inches between conduit…but check.
Plan for the day when the local phone company offers you fiber optic. There is money out there for rural internet.
Our off-grid place sits on 940 acres, some miles off pavement. Our area has zero utilities. The local phone company surprised us with the offer of fiber optic internet. We jumped on it. Our driveway is 3/4 of a mile long. They dug that trench for zero dollars.
Since we had put an extra 2” conduit from electronics shed to house, we had them connect the two buildings with fiber optic cable. 135 ft between buildings in our case.
If you ever get this offer, plan now as to how/where the internet will enter the structure. Make the plan before you do your landscaping. Same for what if your local poco gives you a sweetheart deal on electricity.
FYI we built our shed with 10’ x 11’ interior. Really wish it was 15’ x 20’. Too late now.
It’s pretty simple to add a small panel in the vault for AC. You could then power lights, some outlets and a small mini split for the vault.
Keep in mind that the condensate line for the split needs to run downhill.
Think redundancy for the splits. Having more than one head unit in the rare case where you have a failure.
Sounds like you are having fun with your project.
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wheelman55
New Member
PS. Once you get your off grid solar up and running, don’t do any firmware updates, unless you are having issues.
Pretty much all fw updates are for grid tie issues. In more than a few cases these updates have caused off grid gear to be bricked.
Research to see which firmware version works best for off grid and use that version.
PSS. In 8.5 years everything will have changed as far as electronic gear and batteries are concerned.
Pretty much all fw updates are for grid tie issues. In more than a few cases these updates have caused off grid gear to be bricked.
Research to see which firmware version works best for off grid and use that version.
PSS. In 8.5 years everything will have changed as far as electronic gear and batteries are concerned.
Sorry I meant a victron shunt, like a smart shunt.
Thanks! I thought this would be possible with a venus device but I wasn't sure. If I can use a smart shunt for all soc based control I'm good to go. Hard to beat that since almost everyone has a smart shunt already.
Thank you. Thats an impressive offer from teleco! I'm using starlink, which is so much better than the wired service we have elsewhere. In my case, I'm truly off-grid (no address even...) I put in extra 2" runs for future what-ifs, which already paid off yesterday with decision to add a vault. I am adding a couple more 2" runs and 4" for AirCon lineset overhead before backfill.
Got the idea yesterday...Digging the vault today and pouring floor tomorrow... I have 3-4 guys helping me full time, and they just laughed and rolled their eyes when I explained we would be adding more underground concrete...
Planning to be about 8x12, as this vault will only house batteries and related electrical. AC loads and other mechanical items will remain in the original 2-level mechanical room. Mini-split head will primarily address humidity concerns as this area will have a different drainage profile compared to main structure.
I need to work out the mounting geometry, but it definitely looks like I can benefit from some TPO reflection, if only on a portion of the array. The house is dug into a cliff, so I don't have a good spot for the array other than on the roof. Even though the roof is huge, I see that 40k pv will take a lot of space, and cheaper, low watt/sqft panels may require placement on a larger area than intended. Ideal Southern orientation might be difficult to achieve, so I might end of with extra panels to compensate.
Aircon and heatpumps will also sit behind parapet walls, so I want to do a good job hiding everything from view.
thank you the thoughts.The primary way to stop electrical fires is cut the power. Power is coming from the batteries, so try to stop current by disconnecting load.
Another thread reports a fire involving 16s7p battery. Not certain the cause, but the 7 strings of cells were paralleled through fuses only, no relay or BMS FETs to disconnect. That would be a good addition. Idea is to stop over-charging or over-discharging before there is catastrophic failure, and be able to operate with a string out of the circuit if cells imbalanced.
House burned down
So, after 4 to 5 years of working flawless, the 100 kwh lifepo4 battery caught fire at night and burned our house down. Luckily our family just made in out on time. Inspection of the fire expert revealed that a melt fuse melted, and created an arc between the 2 points wich ultimatly started the...
Heat and smoke alarms could be used to trigger shutdown.
LiFePO4 vents below auto-ignition temperature, but gasses can be ignited by a spark. So want contactors and fuses of an explosion-proof type. And want gasses vented outside, so they won't built up and enter house when door opened. Forced air with fan would be good.
This should be easy enough to implement. I'm burying plenty of additional conduit for communication / aircon / AC feed etc. Direct ventilation out doors is also achievable in this location. Imagine a ~100ft tunnel leading to daylight from a lower basement. I've built the first 50ft, so I will simple add this vault at the midpoint and then continue with the tunnel another 50ft later. Pretty good separation from the main structure, but easy to plumb for connections. (I'm just glad my silly tunnel idea is now pragmatic and useful!)
Brucey
Solar Wizard
No problem, I have the following assorted batteries all connected together and using smart shunt to track soc, works fine.
2*24V 100Ah djlb
2*24V 100Ah ecoworthy
1*48V 50Ah ecoworthy
4*12V 100Ah Redodo minis
