Number of solar panels to charge 6V 925 AH battery

[fw12]

Solar fanatic, thank you for your answer.

>> For a 1200 watt panel with a MPPT controller takes 100 amps. How did you come up with 45 amps.

Take a look at the specs on the page below,
Scroll down to "2,inverter features".
Under Input, you will see Charging current 45A.

https://www.alibaba.com/product-detail/dc-to-ac-12v-220v-2200W_1933425526.html

If indeed it takes 100A, does it mean the specs are wrong?

>> Throw two of your panels away because they are not being used.

I'm confused. How many amps is a typical 300W solar panel supposed to put out?
For example, looking at this: https://www.alibaba.com/product-deta...391768807.html

I see:
Short Circuit Current(Isc/A) = 8.71
Maximum Power Current(Imp/A) = 8.16

By connecting 4 panels in parallel, the amperage increases.
So, does four panels not therefore, come to roughly 35Amps (4*8.71)?

I know MPPT increases efficiency by about 30%, i.e. about 10A. So the total amps should be 35+10 = 45A.

Please enlighten me where I'm going wrong. Let's focus on this particular question without getting into the weeds.

[Guest]

"For 14 dorm rooms = 23 x 14 = 322W."

322W * 24h = 7728 watt-hours per day. Round it up to 8kWh per day for a safe bet and some padding for the unanticipated such as a student sneaking in a game machine or a DVD player.
On a 5 sun hour day you would need 1.6 Kw (1600W) of panels to collect 8 kWh of energy. 8 kWh/5h = 1.6 kW.

Q1. The charge controller says input voltage is 12V. Assuming I end up getting 24V panels instead of 12V, would this controller still work with it? I get confused when people start talking about nominal voltage, Vmp, Voc, etc. Which one should be looked at as input for the charge controller?

It would be helpful if you post the Make and model number of the hybrid charge controller. With luck we can look up the specifications and give solid advice rather then best guesses.

Q2. Will 4*300W panels charge my 2 batteries? Assuming 5 sun hours per day, and 30-50% DoD.

You would harvest less energy then you consume. 4*300W*5h = 4*300*5*W*h = 6000Wh = 6kWh.

[Sunking]

[USER="3818"]Please enlighten me where I'm going wrong. Let's focus on this particular question without getting into the weeds.

You simply do not understand what is going on. A 300 watt 60-cell panel has a Vmp = 32 volts and Imp = 9.4 volts (32 volts x 9.4 amps = 300 watts.

MPPT Controller Amp Output = Panel Wattage / Battery Voltage
300 watts / 12 volts = 25 amps. 300 watts = 12 volts x 25 amps.

PWM Controller Amp Output = Input Current
9.4 amps input = 9.4 amps output. 9.4 amps x 12 volts = 13 watts from a 300 watt panel.

A MPPT Controller is a Buck Converter and acts like a transformer where current and voltage are are proportionally inverted, Voltage goes down (Buck), and current goes up. Input power = Output power minus some minor conversion losses.

Your mind is stuck on a PWM converter that is nothing more than a series voltage regulator. You take 32 volts @ 9.4 amps input and spit out the same 9.4 volts at 12 volts. You lost 2/3 of your power in your mind.

[Mike90250]

After following your advice, here is what I came up with...

PANELS:
4 x 300W wired in parallel (=12V, 35Amp). I am assuming each panel puts out 8.5A.

Mistake #1
300W panels are not 12V 300w @ 8.5A = 35V panels.
I'd wire them as 2S2P so you end up with 70V , 17A
A true MPPT convertor will give you 15V for charging batteries @ 80a

BATTS:
Trojan solar AGM 6v 315ah
2 x 6V in series (=12V, 315Ah).

CONTROLLER:
2200W 12v Solar Inverter/charge controller 45A
This is a Inverter/charge controller/charger combo.

Whoops. 2200w inverter is a pretty hefty load, from what you listed you need only half that

I have a couple of questions.

Q1. The charge controller says input voltage is 12V. Assuming I end up getting 24V panels instead of 12V, would this controller still work with it? I get confused when people start talking about nominal voltage, Vmp, Voc, etc. Which one should be looked at as input for the charge controller?

Vmp is Voltage max power
Voc is the Open Circuit voltage, which can fry your controller. Your controller has a max voltage spec
watts is only a laboratory value, real life is only 80% of the rated wattage

Q2. Will 4*300W panels charge my 2 batteries? Assuming 5 sun hours per day, and 30-50% DoD.

TIA.

[fw12]

The responses I'm getting here are generalized answers, not tailored to my specific devices. For example one person suggests 2S2P for panels, another says just 2 panels is what is needed.

I'm going to try this again.
Given the panels, batteries, and inverter/charger that I listed, is it safe to say the controller won't fry or smoke, and battery bank will charge to full capacity if I had the following...

2 300W panels in parallel,
2 6V batteries in series?

Here are the devices again:

https://www.alibaba.com/product-detail/dc-to-ac-12v-220v-2200W_1933425526.html

https://www.alibaba.com/product-detail/Bluesun-best-PV-supllier-300-watt_60391768807.html

https://www.ecodirect.com/Trojan-Bat...agm-06-315.htm

[SunEagle]

The responses I'm getting here are generalized answers, not tailored to my specific devices. For example one person suggests 2S2P for panels, another says just 2 panels is what is needed.

I'm going to try this again.
Given the panels, batteries, and inverter/charger that I listed, is it safe to say the controller won't fry or smoke, and battery bank will charge to full capacity if I had the following...

2 300W panels in parallel,
2 6V batteries in series?

Here are the devices again:

https://www.alibaba.com/product-detail/dc-to-ac-12v-220v-2200W_1933425526.html

https://www.alibaba.com/product-detail/Bluesun-best-PV-supllier-300-watt_60391768807.html

https://www.ecodirect.com/Trojan-Bat...agm-06-315.htm

This is how I see your system

Those 300 watt panels have an Imp = 8.16Amps and Vmp = 36.8V

With a 12volt 315Ah battery you need about 30 charging amps.

With an MPPT type charger if you wire those panels in series or in parallel you can generate as much as 50 A of charging which can hurt your battery system

With a PWM type charger the best you can get out of those panels is to wire them in parallel but it will only get you about 16.3 A of charging which is too little for your battery system.

If you had 4 of those 300 W panels and a PWM charger wiring them 2S2P can get you about 36 A of charging which will be ok for your battery system but only utilize about 37% of your panbel wattage which is only about 450 watts out of 1200 watts. That is a waste of panel wattage.

[gbynum]

With 4 panels and using an MPPT controller, you might be able to increase your harvest with 2 panels directed ESE and 2 WSW and not overcurrent the batteries. What and how is beyond my ability with what you've shared.

[Guest]

The responses I'm getting here are generalized answers, not tailored to my specific devices.

Not to beat you up but, the information you provided is too insufficient to get much better. Where you located and the solar resources for your location play a huge role in sizing the system. Also energy usage patterns have an impact on the battery bank size. Without detailed information, detailed answers are not possible.

2 300W panels in parallel,
2 6V batteries in series?

Here are the devices again:

https://www.alibaba.com/product-detail/dc-to-ac-12v-220v-2200W_1933425526.html

https://www.alibaba.com/product-detail/Bluesun-best-PV-supllier-300-watt_60391768807.html

https://www.ecodirect.com/Trojan-Bat...agm-06-315.htm

Panel's VOC of 45.28V is incompatible with the inverter Input DC 11-15V.
You would need 8-10 of the Trojan Battery SAGM 06 315 to store one day's and maintain 50% DOD.
On a 5 sun hour day you would need to have ~ 1600W of panels to cover the energy consumption for one day.

[Sunking]

The responses I'm getting here are generalized answers, not tailored to my specific devices. For example one person suggests 2S2P for panels, another says just 2 panels is what is needed.

I'm going to try this again.
Given the panels, batteries, and inverter/charger that I listed, is it safe to say the controller won't fry or smoke, and battery bank will charge to full capacity if I had the following...

2 300W panels in parallel,
2 6V batteries in series?

Here are the devices again:

https://www.alibaba.com/product-detail/dc-to-ac-12v-220v-2200W_1933425526.html

https://www.alibaba.com/product-detail/Bluesun-best-PV-supllier-300-watt_60391768807.html

https://www.ecodirect.com/Trojan-Bat...agm-06-315.htm

No you are being given correct answers, you just do not understand simple math and answers.

Your batteries cannot tolerate more than 800 watts of panels. With a 800 watt panel using MPPT on a 12 volt battery = 66 amps of charge current the maximum your batteries can tolerate. Those same batteries cannot operate a Inverter larger than 800 to 1000 watts.

So until you learn to accept the limitations, we cannot help you anymore. 1200 watts is too much for a 12 volt system. At 1200 watts is a 24 volt battery system using a 50 Amp MPPT controller with a 24 volt 500 AH battery and 1500 watt Inverter. Everything you propose is not made top work with each other because you do not understand what you are being told.