help understanding array sizing

[solarnoob22]

I have a 9.2kw battery bank and I am in the US. Will said that to size my array I need to divide the battery bank size by 5 for the hours of sunlight to get my batteries charged in a reasonable time. I currently have 800 watts of panels, 4x200w Rich Solar panels in series into an MPP LV2424(the green one). Today I had 90 volts input into my charger, it was 44 degrees out and making 550ish watts and 20ish amps. How do I determine how many more panels my charger can sustain in series? Do I use VoC or Vmp to decide? What is my manual referring to when it says 145 VDC?

 

[sunshine_eggo]

maybe Will said that, but I don't know if there was a specific context.

Sizing is as follows:

PV minimum array = the minimum array size needed to generate your minimum daily kWh consumption.

The daily CONSUMPTION is typically divided by 5 to approximate your array size.

If your battery is lead acid, then division by 5 is more appropriate because lead-acid needs to be charged at a 10-20% rate to ensure you don't damage them by charging too fast or too slow.

MPPT are rated by output current. That one is rated for 80A output. That means it can deliver a maximum of 80A @ peak battery voltage, so about 80A * 28V = 2240W... and those claim a PV rating of 2000W, so that's pretty accurate.

You have 800W, so you could clearly add more.

That MPPT is limited to 145V maximum, so you need to stay under that. With an input voltage of 90, it sounds like your existing panels configured properly (What is your panels' Voc value?).

You could easily triple your array with the three strings in parallel, i.e., 4S3P and have 2400W available, though it would never deliver over 80A output. You will be slightly over-paneled, but this shouldn't hurt anything.

If lead acid, 9.2kWh = 9200/24V = 383Ah, thus your batteries are charged most healthily between 38.3A and 76.6A, so maxing out your array should be fine.

 

[solarnoob22]

maybe Will said that, but I don't know if there was a specific context.

Sizing is as follows:

PV minimum array = the minimum array size needed to generate your minimum daily kWh consumption.

The daily CONSUMPTION is typically divided by 5 to approximate your array size.

If your battery is lead acid, then division by 5 is more appropriate because lead-acid needs to be charged at a 10-20% rate to ensure you don't damage them by charging too fast or too slow.

MPPT are rated by output current. That one is rated for 80A output. That means it can deliver a maximum of 80A @ peak battery voltage, so about 80A * 28V = 2240W... and those claim a PV rating of 2000W, so that's pretty accurate.

You have 800W, so you could clearly add more.

That MPPT is limited to 145V maximum, so you need to stay under that. With an input voltage of 90, it sounds like your existing panels configured properly (What is your panels' Voc value?).

You could easily triple your array with the three strings in parallel, i.e., 4S3P and have 2400W available, though it would never deliver over 80A output. You will be slightly over-paneled, but this shouldn't hurt anything.

If lead acid, 9.2kWh = 9200/24V = 383Ah, thus your batteries are charged most healthily between 38.3A and 76.6A, so maxing out your array should be fine.

Thank you for your response. The panels have a Voc of 24.3

I have a slight hodgepodge of batteries. I have a 100ah lifepo4 rich solar parallelled to a 260ah lifepo4 eco-worthy, and that same setup wired in series to get my 24v. The eco-worthy's were a gift so I decided this was the best way to put them to use. I'm thinking of ordering 2 more panels to wire in series and help speed the charging along.

 

[sunshine_eggo]

Thank you for your response. The panels have a Voc of 24.3

I have a slight hodgepodge of batteries. I have a 100ah lifepo4 rich solar parallelled to a 260ah lifepo4 eco-worthy, and that same setup wired in series to get my 24v. The eco-worthy's were a gift so I decided this was the best way to put them to use. I'm thinking of ordering 2 more panels to wire in series and help speed the charging along.

100+260 parallel in series with 100+260 parallel?

personally, I would spit them out.

2S 100Ah
in parallel with
2S 260Ah

This gives you the ability to monitor the individual 12V batteries.

Since they're LFP, the only consideration is max rated charge current, which should be at least 180A. The 80A controller is under that no matter how much power you put on the MPPT.

 

[solarnoob22]

100+260 parallel in series with 100+260 parallel?

personally, I would spit them out.

2S 100Ah
in parallel with
2S 260Ah

This gives you the ability to monitor the individual 12V batteries.

Since they're LFP, the only consideration is max rated charge current, which should be at least 180A. The 80A controller is under that no matter how much power you put on the MPPT.

So, just to be clear you're saying I should go (Positive cablefrom inverter-->) 2-!00ah in parallel (0/0awg cable--->) 2-260ah in parallel (negative cable back to inverter)?

 

[sunshine_eggo]

Shit no.

This:

 

[solarnoob22]

Shit no.

This:


View attachment 206375

I'll wire it up like this! because the way it is right now is... not that. this makes way more sense and will probably solve another issue I'm facing which I assume to be uneven discharging, the 2 batteries on the negative side of the 0/0 always hit their low cutoff before the others

 

[sunshine_eggo]

If you're already having problems, it is very important that the 12V be fully charged individually before they are placed in series. If they are not both at the same state of charge, both charging and discharging can be interrupted resulting in a loss of capacity.