Conflicting advice on series vs. parallel for charging 12v Bank. Please advise.

[MikeB]

If your charge controller is only rated for 200 watts (I assume that's if you have a 12V battery bank), and you are going to use a 12 V battery bank, your 2 - 150 watt panels are going to be too much because they will be putting out 300 watts no matter which way you wire them (Series: 36+v x 8.29 amps or parallel: 18+v x 16.58 amps). Typically the wattage rating for the charge controllers is double if you go with a 24V battery though, so assuming that's the case I'd wire the panels in series and wire your 4 - 6v batteries in series for a 24 volt system. Assuming they are rated around 230 Ah that would give you about 2,700 usable watt hours (realistically less because of normal inefficiencies), so as to not run your batteries down past 50%. Not sure what your fridge uses in watts, but you mentioned it was a small one so I think that would work fine. Of course if you have a couple cloudy days in a row you'll need to find a way to help charge the battery bank.

Thanks very much for the clarification. I will wire the panels and batteries in series and the 20a mppt controller does double the watts at 24v. And I do have a generator for backup.

It is somewhat difficult to find reliable information for small systems and I really appreciate this solar forum.

[cmclane28]

Thanks very much for the clarification. I will wire the panels and batteries in series and the 20a mppt controller does double the watts at 24v. And I do have a generator for backup.

It is somewhat difficult to find reliable information for small systems and I really appreciate this solar forum.

Glad I could help. I'm a bit new to all of this myself. It's amazing how much I've learned over the last couple of months, and the help provided on this forum has been great.

[Gajetest]

Gajetest hope this is helpful

I have two 12v-150W panels that I plan to wire in series for 24V, with tracer 20amp mppt CC, and 4-6v batteries connected in series, with 12/24 1500W inverter to run a small fridge. Is this the best plan or should I connect the batteries in series, parallel for 12V.
Thanks in advance.
Greetings,
Well I don't know the model of your refridgerator the going average is around 600 watts to run tht could mean 1000 or more to startup. My advice get a Kill-o-Watt measurer it will tell you how much your fridge uses at startup and running. Two very different numbers. If your in an Ideal sun recieveing place you have about 4 to 5 hours of charge time to fill your batteries and still tun your fridge full time realize the fridge uses more power durring the day as the door is opened and closed a lot. You have a 1500 watt inverter or 1.5K inverter. two 150 watt solar panels will not be able to run this refrigerator without seriuosly depleting your batteries. And

If you do that you will be buying new batteries a lot. Which makes saving money not feasible.
You also need to hook up a meter to your panels at full sun and see what you ar really getting from them. Remember they have to charge your batteries and run your rifrigerrator 24/7. You did not write down what your Amp hours are on your batteries. So since they are 6 volt I'll guess 250ah? Also what is your inverter power input 24 or 12 if it is 12 DO NOT series the 6 volts to get 24 or you will smoke your inverter. From what you said I'm guessing its a 12 volt pure sine wave inverter. It has to be pure sine wave even if your fridge would work on a modified sine wave inverter it would burn up the mothor in the fridge.
So as I see it you have one choice series and parallel the six volt batteries to give you 12 volts and the most amp hours you can get out of them. 2 6 volt batteries joined in a series will give you 12 volts, and I was guessing that you have at least 250 amp hours so that will give you 25o amp hours and 12 volts. Paralleled the two 12 volt batteries you now have. And you will have 12volts and 500 amp hours. Now times the amp hours by the voltage and it gives you 12 * 500 am hours which equals 6000 watt hours or 6 KWH.
I have a Frigidaire 26 cf Side by Side. Manufactured 07/2004 (did I also mention I'm cheap?) I tested it on a Kill-o-Watt meter for 24 hours. In the 24 hours it used 2.9 KWH. This is why you need to see how much your panels actually produce so you can make the right storage choice.

Now on my hypothetical arrangement above at full charge it was 6 KWH. That is if your amperage is 250 or more you’re okay with storage. If less calculate as long as you at least have 4KWH of storage you are okay. Cannot stress this enough do not try to drain your batteries below 50% they will die on you.
Now what do your panels produce in their 4 to 5 hour window? Testing them will let you know for sure and do not trust what it says on the panel. Your panels have to put out enough power to run your refrigerator and on top of that charge on your batteries to full capacity. Do not run your batteries below 50% percent or they will fail on you very quickly. If your panels can't produce enough power then you need to spend a little more and get some more panels. I would be surprised if two 150 Watt panels will be enough to accomplish this. You will not know until you test them to see their real output.
If you would like me to help you figure it out go to my site Gajetest.com there you will find an info email address. Give me the output of your panels amperage at peak sun-time. The amp hours on your batteries are rated at. What voltage they read when they are fully charged and you test them with a multi-meter. And if you do not have a Kill-o-Watt Meter; give me the year and the brand of your refrigerator. Or it may tell you start-up and running Watts inside of the door or on the back by the motor.

And I can tell you what you need to do
Gajetest

[Mike90250]

What is
Vmp ___
Voc ___

it's 8.29 & 22.92

Very strange #'s A Voc of 23V will never be able to charge a 24V battery

Please check the panel specs again. You may have replied with the wrong #'s Voc should only be about 30% higher than Vmp

[MikeB]

What is
Vmp ___
Voc ___



Very strange #'s A Voc of 23V will never be able to charge a 24V battery

Please check the panel specs again. You may have replied with the wrong #'s Voc should only be about 30% higher than Vmp

I assume the two 12v panels wired in series would charge a 24v battery. Am I wrong on this?

[MikeB]

What is
Vmp ___
Voc ___



Very strange #'s A Voc of 23V will never be able to charge a 24V battery

Please check the panel specs again. You may have replied with the wrong #'s Voc should only be about 30% higher than Vmp

I'm sorry, the Vmp is 18.21 voc is 22.92

[Mike90250]

I assume the two 12v panels wired in series would charge a 24v battery. Am I wrong on this?

Could be. We need the
Vmp ___
Voc ___
specs to insure that the panels match correctly. The scant specs 8.29v & 22.92v you gave, made no sense.

Generally, 2, 12V nominal system voltage panels in series, would charge a 24V battery. But this is strange stuff and the numbers don't make sense.