First build, I have questions and would like to hear any suggestions.

[JWilliams]

Solar has been fascinating to me for a several years now and I'm finally building my first system. Mostly for a back-up grid goes down scenario to run the well pump, etc. System will be based around the 48V Growatt SPF 6000T, which I am buying barely used next week. I already have the batteries, not my first choice but lithium is so high. I have (12) Fiamm 12flx500 135Ah AGM batteries. These were manufactured at the end of 2021. Then used in a back up power system for I'm guessing some communications company for 2 years. So never really cycled just left on a float charge. I got them for $60 each and they are all very balanced. I haven't got the panels yet but the one's I'm looking at are commercial 520-550W. I think they are all around 50VOC. So my questions are:
1. The Growatt is rated for 250V - 5000W on the PV input. If I do (8) total of these panels... two sets of 4 in series, then hook those two sets in parallel... then I would end up with 200VOC, 25.4A at maximum power, and approx 4,400W. Am I correct with this? Do you think I could squeeze in 2 sets of 5?
2. And this might be a dumb question. Will the charge controller in the Growatt stop charging the batteries once they are full or is there something else I need to add?
3. I will do the batteries in 3 parallel sets of 4 in series to achieve 48V correct?

I'm sure I have more questions but all I can think of right now until I get everything. Will post pictures. Any suggestions or experienced criticism of the components welcomed. Thanks!

 

[JWilliams]

Oh and a 1620Ah battery bank is pretty decent right? What can I expect to get out of that for a small household?

 

[Hedges]

https://www.fiamm.com/fileadmin/user_upload/products/reserve/FLX/FLX_FOLDER-NA_ENG.pdf

12V, 132 Ah. You have 12 of these and a 48V system, so 396 Ah at 48V, about 20 kWh. That's the size of one of mine.

My batteries (SunXtender) are expected to give 700 cycles to 70% DoD.
I don't find cycle life rating for yours, data sheet mentions " EXCELLENT RELIABILITY AND FLOATLIFE", "main application UPS and data centers." Probably much lower cycle life.

They probably won't last long for daily cycling off-grid, but would be great for backup during occasional power failures, what mine are for and your usage too.

$60 each x 12 = $720, great price. Far less than lithium, and won't have any trouble with delivering surge power.
500W per cell, 3000W per battery, could feed 36kW of inverters briefly.

Avoid cycling them deeply at night if possible, run loads during the day when PV supplies it. In my case, several old refrigerators and yard lights run it down.

You could wire the batteries 4s3p, or do 3p4s (interconnect at every tap.)
Try to fully charge all batteries before connecting them.
I picked up a set of FullRiver AGM (36 pieces 6V), and batteries that were same voltage with partial state of charge diverged at full charge (where they will spend most of their life.)

 

[timselectric]

1. The Growatt is rated for 250V - 5000W on the PV input. If I do (8) total of these panels... two sets of 4 in series, then hook those two sets in parallel... then I would end up with 200VOC, 25.4A at maximum power, and approx 4,400W. Am I correct with this? Do you think I could squeeze in 2 sets of 5?

Definitely not 5s.
You have to take into account the record low temperature for your area.
As temperature goes down panel output voltage goes up.
VOC is a hard line that you never want to exceed. (You can't get the magic smoke back in, once it gets out)

2. And this might be a dumb question. Will the charge controller in the Growatt stop charging the batteries once they are full or is there something else I need to add?

It will charge according to your chosen settings.

3. I will do the batteries in 3 parallel sets of 4 in series to achieve 48V correct?

Yes, and you might want to look into a battery balancer. To keep everything charging evenly.

 

[Mattb4]

1. Yes
2. Yes. Choose the right battery type.
3. Yes

Comment: I would anticipate that among 12 used AGM batteries that you have a few duds. Keep an eye on them. Since your intended use is emergency backup and not daily use you might get a few years from them.

 

[JWilliams]

Man you guys are freaking awesome. All great info. Thanks!! Will post pics here, and I'm sure more questions, when I get the rest of the components. Here are the batteries. 94lbs each

 

[OffGridForGood]

For an emergency back up system that will sit long periods at 100%SOC, LFP (Lithium-Iron-Phosphate) would be a poor choice. For your planned use, the AGM are a good option, and should provide the energy you need for short power outages.
I am wondering if you need PV at all for your use, let the batteries charge from Utility - Utility First Mode, put your critical loads in a subpanel fed by the inverter on pass-through, if/when the utility drops out, your inverter will immediately take over. No action required.
In my experience, the utility drops out during storms, when there isn't any significant PV anyway.

edit: ie spend the money on a back up genset instead of the PV may give you better security for emergency power.

 

[Hedges]

True, generator more cost (and labor) effective for backup, as long as the fuel stash lasts.

If net metering is available, then PV can pay for itself and power your backup indefinitely. (what I have.)
Without net metering, zero export supplying loads from power produced at that time may also be cost effective.
But don't let inverter cycle batteries for peak shaving. Save for grid outages.

 

[OffGridForGood]

True, generator more cost (and labor) effective for backup, as long as the fuel stash lasts.

If the OP has Nat.Gas this may be a good alternative, since generally the gas will remain available during a electrical utility outage.
The other option (that I used) is dual fuel and store propane for emergency use. Nice thing about Propane, it doesn't go bad on you in storage.

If net metering is available, then PV can pay for itself and power your backup indefinitely. (what I have.)

Depends on local agreements available, and rates paid. As a back-up system, he doesn't want to be reliant on the grid. Well at least not for the time line of the typical outage he is planning for.

OP may want to plan out his system in two stages, first as a back-up to the grid during outages. In this stage the AGM with a genset and no PV may be the best set up/lowest cost.
In the future (after you catch the solar bug), go to stage two, where PV is added, upgrade the ESS to LFP and add in the grid tie (if net metering is available/worthwile).

 

[JWilliams]

For an emergency back up system that will sit long periods at 100%SOC, LFP (Lithium-Iron-Phosphate) would be a poor choice. For your planned use, the AGM are a good option, and should provide the energy you need for short power outages.
I am wondering if you need PV at all for your use, let the batteries charge from Utility - Utility First Mode, put your critical loads in a subpanel fed by the inverter on pass-through, if/when the utility drops out, your inverter will immediately take over. No action required.
In my experience, the utility drops out during storms, when there isn't any significant PV anyway.

edit: ie spend the money on a back up genset instead of the PV may give you better security for emergency power.

Great to hear that I made a solid choice with the AGMs. So I guess I should have been more specific. I'm building this for a shtf extended grid down scenario, where fuel would eventually run out. I'm all about solar and these panels have gotten so cheap, I guess I keep finding surplus from these solar fields that keep popping up. So I guess in that case I mentioned, the low life cycles of the already 2 year old AGMs would be a problem. Maybe I will aquire some newer ones as back up or LFPs once I get this set up and going. I plan to keep the draw as minimum as possible esp at night. 1# concern well pump, charge my thermal batteries, walkie talkie, flashlights, power tools etc. And hopefully have enough to keep a very small deep freezer running. Not really planning to use the AC. Seems like that would be pushing it.

 

[Hedges]

Try to minimize loads at night, avoid cycling those batteries more than 15% DoD.
Freezers could coast, certainly don't let them do defrost cycles. Old model fridge/freezer can use 3 kWh/day vs. new maybe 600 Wh?
Power a well when sun shines, small booster pump from a tank at night.
A/C is no problem with direct sun.

My PV array can produce in one hour the usable capacity of my battery, although I recharge more gradually to be gentle.
Plenty of surplus production to power things daytime (if not overcast) and the excess is curtailed.
This would not work well during extended time without sun. That's where a battery to provide several days usage would be helpful.
There are reports of FLA forklift batteries lasting 20 years (vs. 7 year powering a forklift). Probably 15% DoD most nights, but can provide 3 days power when needed. AGM on the other hand probably good for 10 years float life.

 

[Mattb4]

.... 1# concern well pump, charge my thermal batteries, walkie talkie, flashlights, power tools etc. And hopefully have enough to keep a very small deep freezer running. Not really planning to use the AC. Seems like that would be pushing it.

Well pump is likely to be your biggest load in terms of starting and running wattage. You should find out what that is so that your planned system can operate it. The deep freeze since it is 24/7 depending on its size is likely around 2kWh for a days worth of power.

Extended grid outage is a bit of a problem for AGM style setups. If you start cycling them on a daily basis for long periods, or very deep daily discharge, they may not last a year if they were new. As a more normal temporary grid outage (say only a couple of days to a week) AGM is actually preferable based on low or no frequency of temporary outages.

For long period daily use the only 2 reasonable choices are flooded lead acid heavy storage type from a good company where you learn how to properly maintain them. Or LiFePO4

 

[OffGridForGood]

The deep freeze since it is 24/7 depending on its size is likely around 2kWh for a days worth of power.

I have three deep freezers, 18cft to 26cft, they use less than 1kWh per 24 hour day - they live in a cool basement area which helps.

I'm building this for a shtf extended grid down scenario, where fuel would eventually run out

In this case, I would recommend you plan to replace the AGM with LFP over the next two year period, they will not be ideal for you to rely upon, especially when the fuel runs out.

 

[JWilliams]

Definitely not 5s.
You have to take into account the record low temperature for your area.
As temperature goes down panel output voltage goes up.
VOC is a hard line that you never want to exceed. (You can't get the magic smoke back in, once it gets out)

It will charge according to your chosen settings.

Yes, and you might want to look into a battery balancer. To keep everything charging evenly.

On the battery balancer, I like this one but seems to require 3 of them for my 48V bank.

https://www.amazon.com/Victron-BBA000100100-Battery-Balancer/dp/B01DH6B2D2/ref=asc_df_B01DH6B2D2/?tag=hyprod-20&linkCode=df0&hvadid=198107824285&hvpos=&hvnetw=g&hvrand=18365809210100140263&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9011087&hvtargid=pla-351132180708&psc=1&mcid=3baec46e3e40397cb325095954ae1b90&gclid=CjwKCAjw_LOwBhBFEiwAmSEQARDnHrDABXG9dkdVZ4ikjQKEMwN68pDYI5amDNpM3mss2ixyEgz5BBoC4SQQAvD_BwE

Do you think this one will do the trick? Or will I still need 3 of them?

https://www.amazon.com/dp/B0CLTZ2XQX/ref=sspa_mw_detail_0?ie=UTF8&psc=1&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9kZXRhaWwp13NParams

 

[timselectric]

On the battery balancer, I like this one but seems to require 3 of them for my 48V bank.

https://www.amazon.com/Victron-BBA000100100-Battery-Balancer/dp/B01DH6B2D2/ref=asc_df_B01DH6B2D2/?tag=hyprod-20&linkCode=df0&hvadid=198107824285&hvpos=&hvnetw=g&hvrand=18365809210100140263&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9011087&hvtargid=pla-351132180708&psc=1&mcid=3baec46e3e40397cb325095954ae1b90&gclid=CjwKCAjw_LOwBhBFEiwAmSEQARDnHrDABXG9dkdVZ4ikjQKEMwN68pDYI5amDNpM3mss2ixyEgz5BBoC4SQQAvD_BwE

Do you think this one will do the trick? Or will I still need 3 of them?

https://www.amazon.com/dp/B0CLTZ2XQX/ref=sspa_mw_detail_0?ie=UTF8&psc=1&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9kZXRhaWwp13NParams

You will need a balancer for each series string of batteries.

 

[JWilliams]

You will need a balancer for each series string of batteries.

Understood. Thanks!

 

[JWilliams]

Anybody have experience with these victron battery balancers? I linked the product ^^^ in my second to last reply to @timselectric . I was on the road working and ordered 3 of them in haste. The product pics clearly showed how you would hook them up for a 48V system, but after I ordered them I saw the pic of the 24V hook ups. WTH. Should I send these right back and can anyone make recommendations for a replacement? Trying to stay around the same price. Battery bank: (4) 12V AGM in series x3. Picture attached of the victron specifications.

Also I now have my panels and the Growatt 6000T! Just trying map all this out on paper before I make any moves.

 

[OffGridForGood]

Generally anything Victron seems to be @sunshine_eggo domain.

 

[timselectric]

Generally anything Victron seems to be @sunshine_eggo domain.

Always and forever. lol

 

[JWilliams]

This attached pic is what led me to believe it was for 48V. Hopefully eggo chimes in. I emailed Victron about it, depending on what they say I'm gonna go ahead and order different ones tomorrow and get them on the way.