Charging large capacity batteries with less than optimum PV arrays

[russ_drinkwater]

I know that the recommendation for charging batteries (fla) is 20% amps in of stated capacity of cells and 10% will do the job in a pinch.
But what if your amps in is less than that and much higher than what you consume in a 24 hour period?
I do not want to up the voltage of the battery bank and change the system voltage!
20% of 2700 amp hour in theory would require 540 amp of charge from the solar arrays.
10% of same would require 270 amps.
Both are staggeringly high amounts of power to be made!
Best I can provide is 4400 watts of array and 80 amps for 5-6 hours during summer time.
This winter the arrays have been making 12 kws a day on average.
And summer should push this to near 20 kws on our normal long summer days.
Sunrise at 4.30 - 5 .00 hrs and sunset at 1900 - 1930 hrs.
These batteries will be powering nothing during the daylight hours and will only have a draw after sunset when the daylight bank is switched over.
10 panels is the max each reg can handle (0.9) in summer according to the calculator.

[Vic]

Hi Russ,

The customary advice for Flooded batteries,  is the try to have 10% of 20-hour Capacity,  5% can be adequate,  in  a pinch,  and  13% Maximum rate into the battery.  Just a rule of thumb.

If your 4KS25s have 1.265% SG electrolyte,  the real AH Capacity is about 1280 Ah  --  a 5% reduction in C,  because that 1350 Ah C is if the battery had 1.280 SGs,  which they rarely do,  if they are in NA,  anyway,  so,  there is a slight gift right there, depending on your SGs.

If you are not deeply-cycling your batteries,  then you can probably get a full charge done in one day,  perhaps.  Load Shedding is also a large help,  or perhaps selling a bit less to the Grid on some days ...

FWIW,   Vic

[Westbranch]

Ross sounds like you are in the > 90% crowd....How do the numbers work out for load vs Pn incoming?  you sound like you will be well over 110% of your load in replacement Amps...

[sigp2101]

I know that the recommendation for charging batteries (fla) is 20% amps in of stated capacity of cells and 10% will do the job in a pinch.
But what if your amps in is less than that and much higher than what you consume in a 24 hour period?
I do not want to up the voltage of the battery bank and change the system voltage!
20% of 2700 amp hour in theory would require 540 amp of charge from the solar arrays.
10% of same would require 270 amps.
Both are staggeringly high amounts of power to be made!
Best I can provide is 4400 watts of array and 80 amps for 5-6 hours during summer time.
This winter the arrays have been making 12 kws a day on average.
And summer should push this to near 20 kws on our normal long summer days.
Sunrise at 4.30 - 5 .00 hrs and sunset at 1900 - 1930 hrs.
These batteries will be powering nothing during the daylight hours and will only have a draw after sunset when the daylight bank is switched over.
10 panels is the max each reg can handle (0.9) in summer according to the calculator.

No! you should be between C8 and C12 charging value. Ideally, C10 for FLA batteries only.

[russ_drinkwater]

There will be no draw on the rolls batteries during the day.
As the 2nd system with the trojans does all the day work.
During the day the draw is 5kws on average.
Overnight the draw is 7kw and maybe 9kw in summer as the refrigeration units have to run longer.
The 2 solar arrays feeding the rolls are purely standalone with no grid tie connection.
The 4400 watts should give approx 20kws plus as we have long days in summer.
The grid tie arrays of similar size and output do up to 30kws a day.
So the input from the solar is 3 times the consumption from the batteries/solar.
Not sure how that equates in amps in and out.
But as I said best case is 80amps per hour in summer with a 5 hour windows for maximum pv output.
The batteries are only hitting 95% soc after a night of running, but it is winter at the moment.
I would imagine I will pull them down to 85% absolute maximum in summer and most likely far less than that!