Battery Questions/Suggestions for off-grid home

[Shawn Hayes]

I'm fairly new to solar but have some knowledge. I'm very new to this site. Been reading and searching but so far I can't find enough here to answer my situation. I've used online battery calculators but want the real world opinions/experience from the folks here.
My system has 16,380 watts of solar (51-330w Q cell), two Sol-Ark 12-K (48v) inverters. Yes, I've joined this site to read and learn more due to the complexity of my system. Got my system installed by a professional but want to learn more, be hands on and more educated. I need to have enough battery back-up for approx. 2/3 cloudy/rainy days of power using approx. 32Kwh average usage per 24/hrs. (Location in the southeastern US)
At this time I'm looking for deep cycle FLA (Rolls or Trojan) not really looking at LiFePO4 at this time. 48V strings, so recommend AH per battery/string? Is it possible to have a battery string with the AH being to high (ex: using Rolls 2-YS-62P 2-V 5054 AH..I can't afford that btw) for my system? Any calculations that can be shared would be appreciated. I'm thinking of 2 series of batteries, equaling 48V each string, then paralleled together to increase AH. Please advise, thanks!

 

[Hedges]

FLA has an optimum charge rate.
Does your Sol-Ark allow programming of a max charge rate? That's what I do with my Sunny Island, which has an undersized AGM bank.

If your FLA bank was so large that your PV couldn't hit the desired rate, there could be a negative effect on the battery.
Sounds like if you targeted 75% DoD after 3 days without sun, you'd have a 125 kWh bank and could only reach around 0.1C charge rate part of the day if you minimized loads. See what charge rate your prospective batteries want.

 

[Shawn Hayes]

As an example, I'm looking at the Trojan SIND 6V 920ah @ 100h battery. Not sure how to find the optimum charge rate on the spec sheet, I've looked at it, but maybe I'm missing it?
Sol-Ark does allow you to change your charge/discharge rates, it appears they go as high as 185A. Battery Charge & Discharge Current,
for AGM and Flooded, Sol-Ark recommend Ah battery size x 20% = Charge/Discharge amps.
The Sol-Ark 12K manual says:

Battery (optional) Output Power 9000W
Type	Lead-Acid or Li-Ion
Nominal DC Input	48V
Capacity	90 - 2000Ah

So I assume each inverter is capable is up to 2000AH each, since I've got two I hope that doubles to 4000AH? I can always reach out to Sol-Ark, they're very helpful.

 

[Hedges]

As an example, I'm looking at the Trojan SIND 6V 920ah @ 100h battery. Not sure how to find the optimum charge rate on the spec sheet, I've looked at it, but maybe I'm missing it?
Sol-Ark does allow you to change your charge/discharge rates, it appears they go as high as 185A. Battery Charge & Discharge Current,
for AGM and Flooded, Sol-Ark recommend Ah battery size x 20% = Charge/Discharge amps.
The Sol-Ark 12K manual says:

Battery (optional) Output Power 9000W
Type	Lead-Acid or Li-Ion
Nominal DC Input	48V
Capacity	90 - 2000Ah

So I assume each inverter is capable is up to 2000AH each, since I've got two I hope that doubles to 4000AH? I can always reach out to Sol-Ark, they're very helpful.

Is this the spec sheet?

https://www.solaris-shop.com/content/SIND%2006%20920%20Specs.pdf

"Maximum Charge Current (% of C20 Rate)* 13%"

That says maximum, so best to contact manufacturer, as what charge rate would give best life.

 

[Ampster]

I think it is important to evaluate and compare the long term cost of batteries based on kWhrs.
If one just looks at Amphours, the results can be skewed because of Peukerts law. I recently read an article that uses lifetime storage of kWhrs as another reason that Lithium gives a less expensive long term cost.

 

[Shawn Hayes]

I think it is important to evaluate and compare the long term cost of batteries based on kWhrs.
If one just looks at Amphours, the results can be skewed because of Peukerts law. I recently read an article that uses lifetime storage of kWhrs as another reason that Lithium gives a less expensive long term cost.

Ampster: Yes, i want to explore options, but not sure how to calculate KWH of FLA batteries from the data sheets to compare to LiFePo? Can you share the info or calculation on how to do so?
Thanks.
PS: When it comes to LiFePo batteries, one of my concerns is that the BMS chip inside will give out before the battery does and then no power. (I will be off grid) At least with two strings of FLA, I'll have a backup string if a battery or one stings fails for any reason.

Thanks Hedges, that was what I say but wasn't sure as I'm still learning all of this. Yes, I agree, before I buy anything I would definitely contact Sol-Ark for their advice/recommendations and w/ the battery manufacturer.