Charge controller for large 1766AH, 48V battery bank with 6 hour peak sunshine

[Sunking]

You will kill your batteries in less than a month. You maybe at 20 degrees with lots of sun, but you also have a lot cloudy and rainy days.

Rolls requires at least a minim C/10 charge current. That means with 1776 AH of batteries you will need 180 amps of charge current. Do the math 180 amps x 48 volts = 8640 watts of solar panels. 3600 Watts is just enough to keep those batteries alive for a couple of weeks before you destroy them.

Your math really sucks To generate 58 Kwh from solar panels where you live will requires (58,000 x 1.5) / 6 Sun Hours = 14,500 watts. That will require 3 very expensive 100 Amp MPPT Charge controllers, and minimum size battery is 48 volts @ 3000 AH

You are not even close to reality.

[NEOH]

SillySnakes,

Trojan states, "The 2,400 Deep Cycles are for estimation purposes ONLY".
Those cycles were performed in a temperature controlled Lab, as quickly as possible, not over 6.5 years - you mileage may ( will ) vary.
The Trojan Premium L16RE-2V has a 7 year warranty = 2 years 100% replacement and then 5 years pro-rated - but only if you keep precise records of each cell.
It will be interesting to see, if you can actually get both: 2,400 cycles at 70% DOD and 6.5 years of aging.


Here is my quick & dirty Watt-Hour math ...

59,337 Watt-Hours = 24 Batteries x 2 Volts x 1,766AH x 70% DOD = Energy Consumed from the Battery Bank every Night ( you said,"every 24 hours" HUH? )
21,600 Watt-Hours = 6 Hours (sun equiv) x 15 panels x 240 watts = PV Energy Generated every Day

You need, at least, TRIPLE the PV Panels ( ~ 45 ), to just "break-even" every day.
Or maybe even 50 Panels = ( 45 Panels / 90% battery efficiency )
I used the NOCT rating, not the STC rating, because your panels will be HOT at 20 Degrees North latitude.

But what about Daytime loads?
Will the PV Panels be required to supply any power to the Daytime Loads and simultaneously re-charge the 70% DOD battery bank?
You seem to have left out some significant details about this project.

The answer to your question about, "... buss bars and cables ..."
No, 231 Amps is not "too much for buss bars and cables", if they are sized correctly.

You will be charging the battery bank over a 10.5 - 13.5 hour period of varying sunlight and varying energy,
which is ~6 Hours of Solar Equivalent time, not 6 hours of clock time.

[SunEagle]

Ok. So you want to use 1160Ah of a 48v battery system. That calculates to over 55kWh a day yet you only have 3600 watt (peak) for 6 hours (maybe) that comes to about 22kWh.

Due to efficiency losses you always need to put back more that what you take out of a battery system so I would say you do not have enough panels wattage.

[SillySnakes]

I see two issues with that plan.

The first is your batteries will barely last a year or so being discharge 70% daily. Check the specs and you will see the number of life cycle drops like a rock once you discharge more than 50%.

The second issue is except for maybe a couple of months a year you will not be getting 6 hours of sunlight strong enough to produce full nameplate panel wattage. You need to design around your shortest time of sunlight which usually happens in the Winter to determine how big to size your panel wattage.

Oh another item. You will need an 80A CC for 3600 watts of panels for a 48v battery system.

These are Rolls Surrette deep discharge batteries and according to the battery specs, at 70% daily discharge, they will last ~2400 cycles, which is about 6.5 years..with maintenance.

There is no Winter at 20N of the Equator...the ~6 hour sunshine window should be fairly steady throughout the year.

[SunEagle]

I see two issues with that plan.

The first is your batteries will barely last a year or so being discharge 70% daily. Check the specs and you will see the number of life cycle drops like a rock once you discharge more than 50%.

The second issue is except for maybe a couple of months a year you will not be getting 6 hours of sunlight strong enough to produce full nameplate panel wattage. You need to design around your shortest time of sunlight which usually happens in the Winter to determine how big to size your panel wattage.

Oh another item. You will need an 80A CC for 3600 watts of panels for a 48v battery system.

[SillySnakes]

Wondering if someone can weigh in on the following...

I am planning on getting a 1766AH, 48V battery bank (24x 2V, 1766AH batteries) that will be discharged daily to about 70% (Dod=0.7)...so I will be using about 1160AH every 24 hours.

My peak sunshine window is about 6 hours....that means that I will need to recuperate my 1160AH of energy in a 6 hour window. I will have 300W panels (300W is the STC rating...at NOCT it's more like 240W).

The MidNite Classic 150 can give me 3 x 5 panel config (3 in series...then 5 such strings in parallel) using the online MidNite string sizing tool. One such controller can provide me with 60A, if the 15 panels can put out 240W. It can put out 80A if the panels approach STC rating...but that will probably not happen Math for one controller:

15 x 240W = 3600W. Then divide by 60V charging voltage:

3600W/60V = 60A

Obviously 60A is not enough to put back 1160AH into my 1766AH bank... so how many such MidNite controllers do I need to be able to recharge my battery bank in a 6 hour sunshine window ?

If I do my math correctly, would it be:

Amount of charge = AH capacity removed / 6 hour window = 1160AH / 6 hrs = 193.3A. So I need to have 193.3A pumped into the bank to recharge it in 6 hours. Taking into account charge efficiency (93%) and battery bank efficiency (90%):

193.3A / (0.93*0.90) = 231A

So would I need to pump realistically 231A into my battery bank to be able to recharge it in 6 hours ??

Does this sound right ? I would need about 4 MidNite 150 Classics, right connected parallel into the battery bank ? Or can I use a better/larger charger ? Wouldn't 231 A be too much for the battery bus bars/cables ??

Much appreciated!