Series vs Parallel Question with odd number of panels

[kfulmer]

I have 5 330 watt panels that I am planning to install on a cargo conversion trailer (24ft)

In series, the system produces ~80 amps and ~250 volts. This has made it hard to find a good "all in one" unit and requires me to find ad hoc components (= expensive)

Question - is it safe/possible to have a 2 panel series and a 3 panel series wired in parallel. Is it ok to have odd number of panels in each group? This would allow me to get at ~100 volts which opens up the market for an all in one.

What are the pros and cons of this approach?

Thanks!!

 

[MisterSandals]

is it safe/possible to have a 2 panel series and a 3 panel series wired in parallel.

No.
What SCC are you considering?
What is the panel Voc as stated on panel?

 

[sunshine_eggo]

I have 5 330 watt panels that I am planning to install on a cargo conversion trailer (24ft)

In series, the system produces ~80 amps and ~250 volts.

No it doesn't. It may produce about 250Voc and about 200Vmp, but it only produces the current of ONE panel, presumably about 8.25A.

This has made it hard to find a good "all in one" unit and requires me to find ad hoc components (= expensive)

Question - is it safe/possible to have a 2 panel series and a 3 panel series wired in parallel.

Absolutely not. Array will either not perform at all or perform very poorly.

Is it ok to have odd number of panels in each group? This would allow me to get at ~100 volts which opens up the market for an all in one.

If by odd you mean, 3, 5, 7, etc., yes. If you mean different numbers of panels in each parallel string, no.

 

[kfulmer]

No.
What SCC are you considering?
What is the panel Voc as stated on panel?

Voc is 41.3

Was looking at Growatt 24v ( I will have 4 100ah battery bank)

Currently have a Victron 250/60 MPPT on order

 

[kfulmer]

No it doesn't. It may produce about 250Voc and about 200Vmp, but it only produces the current of ONE panel, presumably about 8.25A.


Absolutely not. Array will either not perform at all or perform very poorly.


If by odd you mean, 3, 5, 7, etc., yes. If you mean different numbers of panels in each parallel string, no.

Your right, I had 80amp in my head when I typed. its rated for 10.24A

OK. this is what I was concerned about.

 

[sunshine_eggo]

Your right, I had 80amp in my head when I typed. its rated for 10.24A

OK. this is what I was concerned about.

You need to match series Vmp within about 5% to be confident the array will perform well. You need to either go parallel or add or drop a panel for 2S2P or 3S2P.

 

[Rocketman]

Assuming 6 won’t fit…
What may be easier is to hook four up to the all-in-one (maybe 2s2p?) then hook the fifth one up to its own SCC - something like a Victron 100/20 - connected directly to the batteries.

 

[MisterSandals]

Was looking at Growatt 24v

What is max input voltage an coldest temp on record in your area?
The voltage increases as it drops below 25C (77F) so its important to NEVER exceed max input volts.

You need to either go parallel or add or drop a panel for 2S2P or 3S2P.

Ah, Rocketman types faster but we're on same page:

Or add one panel similarly spec'd panel to make 2S3P or 3S2P (and restricted by SCC max input voltage)
Or configure 2S2P and use 5th panel with separate SCC (like a Victron 75/15).

 

[kfulmer]

What is max input voltage an coldest temp on record in your area?
The voltage increases as it drops below 25C (77F) so its important to NEVER exceed max input volts.

Ah, Rocketman types faster but we're on same page:

Or add one panel similarly spec'd panel to make 2S3P or 3S2P (and restricted by SCC max input voltage)
Or configure 2S2P and use 5th panel with separate SCC (like a Victron 75/15).

Attached is a pic of the panel label if that helps. I will never be somewhere where the temp will be below 25 degress F. I live in FL so mainly south east travel.

 

[MisterSandals]

never...below 25 degress F

When i bought my RV in January 2011 it was 28F in Miami at night. The iguanas were falling out of the trees.
25F = -3.9C
delta temp 28.9 deg C
Anyway with rough temp coefficient of roughly .3% some rough math:

41.3V x .003 x 28.9 = 3.58V
temp adjusted Voc is 44.9V

Still need to know SCC max input volts to put this to use configuring an array....

 

[kfulmer]

When i bought my RV in January 2011 it was 28F in Miami at night. The iguanas were falling out of the trees.
25F = -3.9C
delta temp 28.9 deg C
Anyway with rough temp coefficient of roughly .3% some rough math:

41.3V x .003 x 28.9 = 3.58V
temp adjusted Voc is 44.9V

Still need to know SCC max input volts to put this to use configuring an array....

True. Going to be 28 in Tampa Saturday.

This is the all in one I was looking at (150v max)

Growatt (24V / 3kW / 120VDC) Stackable Inverter

USA OFF GRID BATTERY BACKUP SPF 3000TL LVM – On grid solar inverter Sma Sunny island Growatt spf 5000 es Spf5000es Sunny Growatt Hybrid grid tie inverter JACKERY 1000 1KW 1000W SOLAR SUN POWER SOLAR COMPANIES SOLAR TEXAS CAR INVERTER SOLAR SHINGLES LG SOLAR 100+ WATT SOLAR SOLAR POWERED KIT...

www.signaturesolar.com

 

[MisterSandals]

This is the all in one I was looking at (150v max)

Growatt (24V / 3kW / 120VDC) Stackable Inverter

USA OFF GRID BATTERY BACKUP SPF 3000TL LVM – On grid solar inverter Sma Sunny island Growatt spf 5000 es Spf5000es Sunny Growatt Hybrid grid tie inverter JACKERY 1000 1KW 1000W SOLAR SUN POWER SOLAR COMPANIES SOLAR TEXAS CAR INVERTER SOLAR SHINGLES LG SOLAR 100+ WATT SOLAR SOLAR POWERED KIT...

www.signaturesolar.com

So that would accept 3S if you were to get a 6th panel to make 3S2P (best way to use your 5 would be to add a 6th).

Otherwise 2S2P and 5th panel on separate SCC (not as bad as it sounds, it provides redundancy and possible carryout flexibility).

 

[kfulmer]

So that would accept 3S if you were to get a 6th panel to make 3S2P (best way to use your 5 would be to add a 6th).

Otherwise 2S2P and 5th panel on separate SCC (not as bad as it sounds, it provides redundancy and possible carryout flexibility).

Thank you and the others for your input. This is the most responsive forum i have ever participated in!

I am going to see if I can squeeze another panel on the roof. If so, I will do the 3S2P. If not, I will do the backup. This will make my install so much simpler.

I will add pics of the install once i get it going.

 

[sunshine_eggo]

that Victron 250/60 MPPT will do 5 panels in series. if you can add another 5 later and parallel them together it will handle 10 panels.

Nope. It can handle 35A in the PV input, which allows for a 5S3P array (15 panels).

every mppt controller can handle 33% more input from solar panels it just wont use it.

Arbitrary and wrong.

the 60 means it will charge with 60 amps max. the 250 means it will use 250 volts max but 300 volts coming at it wont hurt it.

Completely wrong. 300V coming at it will destroy it.

 

[BenFromSignatureSolar]

that Victron 250/60 MPPT will do 5 panels in series. if you can add another 5 later and parallel them together it will handle 10 panels. every mppt controller can handle 33% more input from solar panels it just wont use it. the 60 means it will charge with 60 amps max. the 250 means it will use 250 volts max but 300 volts coming at it wont hurt it.

You're going to cost someone a lot of money with this advice. I would never advise anyone to go more than 15% over spec.

 

[sunshine_eggo]

You're going to cost someone a lot of money with this advice. I would never advise anyone to go more than 15% over spec.

Disagree. 15% is completely arbitrary. Victron regularly allows 30% over-paneling on their MPPT calculator.

Over-paneling is done for a reason. One should make sure they're doing it for the right reason and how much is needed, THEN determine the correct charge controller for the system design incorporating over-paneling.

Someone might want to overpanel it with multiple arrays facing different directions.
Someone might want to overpanel it by 2-3X because of horrible weather.

At about $0.50/W these days, PV is relatively cheap.

Given that you're now supporting Victron, you should know their rules:

1) do not exceed Voc
2) do not exceed PV input current limit (and they're kinda flexible on this)

Those could result in an array substantially larger than the MPPT output power - possibly by several multiples.

A 250/60 can accept a ~6300W array of 6S 60 cell panels regardless if it's on a 12, 24 or 48V system. That's extreme, but someone might have a use case.

 

[sunshine_eggo]

I disagree. so please master inform me how we break the chains of law. every inverter which has an mppt controller is bound by law. ITs 33%. so please explain to me how you do nto agree and show me the law that violate it?

Inverters don't have MPPTs. All-in-ones do. Inverters invert. MPPTs convert PV to DC battery current/voltage.

Victron explicitly states that over-paneling provided Voc and PV input currents aren't exceeded. This can allow for an array several times larger than the output can support.

You claim this "33%" number. Source?

 

[12VoltInstalls]

You claim this "33%" number. Source?

Well two things.
I like little ‘rules’ that let one make wildhat guesses but other than sometimes people saying 25% or 1/3 or 50% I’ve never heard of that as a rule and I would have OCD’d on that ? - I would have noticed!
Second, this thread went stale 11mos ago ?