How to wire 13 Sunpower 435W Panels?

LifeWAT

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The way the pallet numbers worked out, I ended up with 13 Sunpower 435W panels, and I need to figure out how to wire this odd number of panels. Here are the panel specs.

Model: SPR-E20-435-COM
Nominal Power: 435 W
Power Tolerance: +5/−3%
Avg. Panel Efficiency: 20.3%
Rated Voltage (Vmpp) 72.9 V
Rated Current (Impp) 5.97 A
Open-Circuit Voltage (Voc) 85.6 V
Short-Circuit Current (Isc) 6.43 A
Max. System Voltage 1500 V UL & 1000 V IEC
Maximum Series Fuse 15 A
Power Temp Coef. −0.35% / o C
Voltage Temp Coef. −235.5 mV / o C
Current Temp Coef. 2.6 mA / o C

My Growatt 5000ES has a max PV input voltage of 450V and max PV amperage input of 100A, so I have plenty of head room to work with.

I assume the common way to wire this for 12 panels would be in 3 paralleled sets of 4 panels in series (85.6V x 4), for a max PV input voltage of 342.4V. My question is how to wire/add the 13th panel?

Thanks in advance.

img_6131828b9cf70.jpeg
 

Lt.Dan

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There is no feasible way because 13 is a prime number. You will need a seperate SCC to use it.
 

MisterSandals

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MisterSandals

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The coldest it gets here in Ohio is about -20F
-28.9C
That is 53.9 deg below what where the panels are rated.

53.9 x 235.5 mV / o C = 12.7V
85.6V + 12.7V = 98.3Voc

450V / 98.3Voc = 4.57 panels (max panels = 4)

So, 4S3P with an extra panel. I do not see a good alternative to a good 2nd system other than 1 or 5 panels (ugh).
 

LifeWAT

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I appreciate that breakdown. In that case I may pick up a separate $100.00 MPPT SCC just to run that one panel.
 

sunshine

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4s-4s-5s all in //,,,whatever that is in proper config!
Amps and voc all well within (edit wrong!) the inverters limits.....blame my caculator!
 
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LifeWAT

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It is acceptible to have 5 in series in one group, and 4 in series for the other two groups? They don't need to be all the same?
 

Lt.Dan

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Well the 5th panel won't do anything because its going to get its voltage puled down to match the other series strings.
 

LifeWAT

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If the 5th panel literally won't produce "anything", it seems the best option is to get an inexpensive MPPT controller, and at least have it producing something rather than having it laying around as a "spare" :)
 

Lt.Dan

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It might do "something" but not enough to be worth the amount of money you spent on the panels, im sure.

My suggestion still stands at a cheaper MPPT SCC to run the single panel alone.

That, or keep your 13th panel as a backup incase something happens to your array. I have 36 total panels, and I keep 1 extra panel in storage for "just in case" circumstances. But granted, my panels were cheap used panels, so it wasn't a big deal to put a cheap panel in storage.
 

MisterSandals

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My suggestion still stands at a cheaper MPPT SCC to run the single panel alone.
If you took this 1 panel and pointed it do east for early morning sun, you could start charging a little earlier in the day. Or, if you're hammering your system to run A/C maybe you want it facing west to top things off late in the day.

Either way, this could be a uniquely useful panel. If it was portable, you could point it east in the morning and west at night for the best of both.

Just a thought.
 

sunshine

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It is acceptible to have 5 in series in one group, and 4 in series for the other two groups? They don't need to be all the same?
The manual always says equal strings but in reality strings are going to have different voltages during certain times of day anyway and it will contribute something.

The 5 does get you very close to the limit,
 

Hedges

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Before you put up the array, you have an opportunity to measure and match the panels.
SunPower is supposed to have low degradation, but you never know ...

Check out my thread on DIY solar panel testing:


Once you have made a list of V(load) & I(load) (or Isc) for your 13 panels, you can select which four to put in each string. Current from each string will be approximately your lowest measured I(load) of panels in that string. Don't worry so much about Voc or Vmp (Vload) variations; the 4s strings should be close enough for that not to matter. If there is much current variation among panels, matching within strings should increase array power.
 

LifeWAT

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Thank you everyone for the feedback! As long as it does not damage the system in any way to have an odd number of panel on one string (SCC limits kept in mind), I think I will do some real world testing to compare 5S-4S-4S vs 4S-4S-4S, and then decide whether to keep the string of 5, or to move that one panel to it's own dedicated charge controller.
 

LifeWAT

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@MisterSandals proved in post #5 that the VOC of 5 panels is much too high for your SCC. Id hate to see you burn it up.
Yes, thank you. I should have articulated that I will likely not leave it 5S-4S-4S, but I am truly curious what the real world difference is on a warm day. I will keep a close eye on the voltage limits during that test.
 

Hedges

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While wired 5s || 4s || 4s, voltage will not appreciably exceed Voc of 4s.
There is a logarithmic I/V curve, and at a voltage hardly any higher than Voc of 4s (where a string conducts 100% of Isc through the photodiodes), the string will conduct 1.5x Isc and suck down its share of the 5s string.

But I still wouldn't leave it that way after testing in warm weather, because in cold weather simply open circuiting the two 4s would let voltage of 5s string be delivered.
 

theshaww

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Amazing! I have this same setup that I'm working on, but I'm using 3 Growatts with 2 strings of 4 to 2 of the Growatts... and 2 strings of 5 going to the 3rd Growatt. Growatts all paralleled.
 
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