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Advice needed on best way to wire my panels  RSS feed

 
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Hi folks!

I have 6 x 320w panels (around 44V output), which should give me around 1.8kw (at optimal conditions, of course).

The diagrams that I got from the seller show how to connect 4 panels or 8 panels, but not 6 panels. I know I can connect 2 groups of 3 panels, or 3 groups of 2 panels, but I don't know which one will be better for the MPPT inverter/controller.

Any advice?

Also, my cable (which will connect the panels to the inverter) is 10mm², which is not a lot.. so I guess a higher voltage is preferred?

thanks in advance!!
 
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What's the maximum PV input voltage of your charge controller?
 
Nuno Donato
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Eric Hammond wrote:What's the maximum PV input voltage of your charge controller?



this is what I can get from the spec sheet

MPPT Range @ Operating Voltage: 60VDC ~115VDC
Maximum PV Array Open Circuit Voltage: 145VDC
Maximum Solar Charge Current: 80A
 
Eric Hammond
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I would put 3 in series and parallel a second string.
 
pollinator
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Add your Open circuit voltage of the panels in the string then multiply by 1.25 as a safety margin. (cold sunny days the voltage goes higher). There is also  a ratio of array voltage to system voltage so what is the voltage of your battery bank? You are really close to the threshold with strings of 3 so unless your system voltage is 48 volts I would suggest 3 strings of 2. As far as wire thickness. 10mm2 for North America translates to between 8 and 7 Guage my chart says up to 60 amps... for 10mm2
Cheers,  David
 
pollinator
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Check your Charge Controller to see how many groups it can accept.
Can you list the model that you have for the both the charge controller and the solar panel?
It sound like you have a setup similar to this:
https://www.wholesalesolar.com/1891351/wholesale-solar/complete-systems/the-cabin-1.83-kw-6-panel-mission-solar-off-grid-solar-system
Most times they will only accept 1 or 2 groups and no more.
So you can have 1 group of 8 solar panels or 2groups with 4each.

In your case you can do either 1 group of 6 panels or 2 groups of 3each.
If you plan on upgrading soon aka buy another 6 panels in a year or so then do just 1 group of 6 now and add the other group of 6 later.
But if you are not going to upgrade, then go ahead now and do two separate independent groups so that you have more ''diversity', redundancy, resiliency in case something happens to one of the groups.



 
Nuno Donato
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thanks all!

Yes my whole system will be 48V. (battery bank is made of 2 groups of 4x12V).

these are the specs of the inverter/controller: http://www.voltronicpower.com/oCart2/index.php?route=product/product&product_id=132 (check the 5K-48 model)

these are the specs of the panel: https://www.distribucionessolares.es/EXT43001892/DOCUMENTOS/EXP0000113000142.pdf
max voltage is actually 37.2. I said 46V in my original post but that is the open circuit voltage
 
S Bengi
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Two solar panels added in series will give you a voltage of 2x37V = 74V
If we were to do just 1 the voltage (37V) would be below the operating range of the Controller (60V-115V)
And if we did 3 in series the voltage (111V) might be okay, but it is best to have a bit more safety cushion
So we 100% need two strings in series.
With the solar panel only outputting 36V to 46V, and the battery requesting over 48V (54V Float Charge), two panels are needed.

Now we have a max current of 80A allowed by the Controller.
Given that each solar panel outputs 9A we could almost do 9 in parallel (9x9=81)
But we need some level of safety so 8 in parallel is the max and 81A is actually above the rated max of 80A.

So you must have at least two strings in series.
And each string can have between 1 to 8 solar panels
With a max solar panel input of 4000W for the charge controller.
We can have at most 12.5 (4000/320)
For a range of 2(2x1) to 12(2x6) solar panels.

In your specific case I recommend
A) 3 panels in parallel (37V and 27A)
B) then another 3 panels in parallel (37V and 27A)
C) finally these two independent strings are joined in series (74V and 27A)

Follow the instruction that came for setting up 8 solar panel but just remove 1 panel from each of the two string to get 6 vs the listed 8.
If possible upload/attach the diagram that came from the seller
 
Nuno Donato
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Many thanks S Bengi for your explanation.

I have a diagram from the seller which uses 6 panels, but its for a 24V system so I dont think I can apply it in the same way (the inverter/controller is also different). But in this case they wire it in 3 groups of 2 panels in series. (check attachment)

It never thought of wiring them as you said, parallel first and series later, I guess because when you place them side by side, its easier to do series since the positive and negative wires will be aligned.

I also need to make some tests in cloudy days and check how much the voltage drops... is it feasible to re-wire according to seasons? probably a bit crazy but I want to maximize the output as much as possible :)
43161213_239697200044538_1991734179498295296_n.png
[Thumbnail for 43161213_239697200044538_1991734179498295296_n.png]
 
S Bengi
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That setup actually work too.
A) Two panel in series (74V and 9A)
B) Another Two panel in series (74V and 9A)
C) Another Two panel in series (74V and 9A)
D) Finally connect all 3 independent strings in parallel (74V and 27A)

There is no need to change the wiring based on the season. It will not change how much each individual panel is outputting or as a sum.
What would make a difference is the angle of the panels, with some type of solar tracking mounting system.
Such a tracking system cost so much it is cheaper to just buy another 2 panels for a 33% increase production. And you don't have to worry about moving parts.

 
pollinator
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[quote=David BaillieAs far as wire thickness. 10mm2 for North America translates to between 8 and 7 Guage my chart says up to 60 amps... for 10mm2
Cheers,  David

I think the chart you have is for automotive, marine, or rv, standalone machine with wires in free air or other situation.


At least in the us and in or on buildings a number 8 conductor is only good for 40a max at 60°c it is a reason to use machine tool wire (MTW) or THHN and specify 75-90 deg°c rated enclosures and accessories.

I commonly install #6 THHN for the ac output of large inverted arrays. It allows me to have smaller conduit, terminate in most terminals and carry up to 20 more amps.

So, a homerun may come to the service entrance on #2 or larger from 350-400 feet away and use #6 to loop through the disconnect and down or over to the mains panel or load center carrying 65-75 amps depending on the other equipment.

Makes the master electricians scratch their heads! But i handle company electricians just fine

Here is an NEC table.

https://www.cerrowire.com/products/resources/tables-calculators/ampacity-charts/
 
David Baillie
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frank li wrote:[quote=David BaillieAs far as wire thickness. 10mm2 for North America translates to between 8 and 7 Guage my chart says up to 60 amps... for 10mm2
Cheers,  David



I think the chart you have is for automotive, marine, or rv, standalone machine with wires in free air or other situation.


At least in the us and in or on buildings a number 8 conductor is only good for 40a max at 60°c it is a reason to use machine tool wire (MTW) or THHN and specify 75-90 deg°c rated enclosures and accessories.

I commonly install #6 THHN for the ac output of large inverted arrays. It allows me to have smaller conduit, terminate in most terminals and carry up to 20 more amps.

So, a homerun may come to the service entrance on #2 or larger from 350-400 feet away and use #6 to loop through the disconnect and down or over to the mains panel or load center carrying 65-75 amps depending on the other equipment.

Makes the master electricians scratch their heads! But i handle company electricians just fine

Here is an NEC table.

https://www.cerrowire.com/products/resources/tables-calculators/ampacity-charts/

Yes we use 40 amps for #8 60 amps for #6 as well. The poster mentioned 10mm2 cable. I pulled from a bad table there. I still think he's better off with the 3 strings of 2 due to the controller max voltage. I'm trying to wrap my head around the example you listed.  AC arrays for us are usually within 200 ft. We get limited in canada to 2 percent loss so the cable costs would be crazy further out.
Always a pleasure.
 
frank li
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Most grid tie string inverter and micro inverter manuals specify maximum 1% on the ac home run. This is often missed as code is much different than industry standard and performance requirements.

I have pulled my share of 1/0 home runs!
 
Nuno Donato
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thanks everyone for your help!
I've decided to go with 2 in series, resulting in 3 strings!
I've just realized, however, that I dont have all the cabling and connectors needed, only the 2 short cables coming out of each panel. So I need to buy some more stuff....

The series part is done with the cabling already in the panels. But for connecting the 3 strings.. whats the best way?
I know there are some triple MC4 connectors, but not sure if they can handle my 10mm² cable! and even if it does, is that the most practical way? Or should I use some other type of connector to get all the 3 together?

thanks!
 
frank li
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You will likely use a combiner between somewhere. At the array, is likely the spot if the 10mm2 wire is long enough.  It can be an upsidedown kombucha bottle with wire nuts ( dont ask) bus bars or teminal blocks in any suitable or a purpose built enclosure with overcurrent protection and switching is a plus. A mindite mnpv3 would be nice. They are inexpensive and weathertite.

Use the plastic cord-grips. Black is best, or conduit depending on if the wire is jacketed for outdoors, burial etc.
 
Nuno Donato
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Alright guys, I'm starting to slowly connect things, and more questions popped up. I'm starting to feel like the guys who sold me the kit didnt send all the necessary components for a proper installation.

As you can see in the diagram I posted above, they consider a 50A fuse coming from the PV panels. But instead they sent me two 20A fuses... So I'm not sure if I'm supposed to get a 3rd one, and have one fuse per string (considering I'll do 3 strings), or if I just forget these ones and get a proper 50A fuse. 20A seems too little for my system since the current will likely be 27A.

Actually, doing only 2 strings (with 3 panels in series) would make my life so much easier in terms of connections, and I would be able to use just two 20A fuses ... however I'm afraid the voltage would get way too close to the max voltage of the controller :/

By the way, I was thinking of getting a weather proof box and set up the fuses and all connections right under the panels, in order to save on mc4 connectors and cable. Is this ok or the norm is to get each string to go for quite some length until the place where the rest of the system is (inverter etc) and have the box and fuses there?

thanks again!
 
S Bengi
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Don't play around with the 20A fuse get the right stuff.
If you can add a few shutoff switches, it will be safer and easier to work on your system in the future.

I would join the strings inside by the converter/inverter.
 
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Maybe things have changed since I saw it, but seeing that wiring diagram for the batteries reminded me of a recommendation to wire up the batteries so that each battery sends/receives the same voltage/current, so each battery is used evenly. Is that actually a thing?
 
Nuno Donato
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Mark Tudor wrote:Maybe things have changed since I saw it, but seeing that wiring diagram for the batteries reminded me of a recommendation to wire up the batteries so that each battery sends/receives the same voltage/current, so each battery is used evenly. Is that actually a thing?



I saw that a few days ago and it made a lot of sense, the guy made some tests and got very different results.
But I guess its more relevant when you have a lot of parallel wiring, as that is when the current matters
 
S Bengi
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The batteries are actually setup exactly like the panel so as to
1) Double the voltage of an individual battery (24V = 2*12V)
2) Triple the current of an individual battery (125A = 3*42)
This works perfectly fine for the 3000W (24V x 125A) System depicted in the diagram.

Except yours is a 48V system vs 24V, so you will need 4 batteries in a string vs just 2.
4000W is just 48V*83A. So your fuse could be just 125A. (technically 83A*1.6=132.8A)

I wonder what size batteries you plan on using
You are generating 2000W * 4Hr  = 8kWHr per day.
I would recommend at least a 16kWHr battery bank.
16 Battery (12V, 83A each)
In a 4 by 4 array.
4 in a series string to get 48V
Then I would connect 4 of said string in parallel, so as to never get below 50%  DOD, and extra for rainy/cloudy days.

If for some reason you only wanted 4000WHr of storage, then just 4 of said batteries (12V, 83A) connected in series would be a ridiculous simple way to connect them.

EDIT: I see that earlier in the thread you mentioned 8batteries. What is the Amp-Hours on each of them. And what is your combined kWHr for the entire thing.
 
Nuno Donato
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Actually I do have 48V on both sides.
I have 8 12v batteries, so my plan is to create 2 banks of 48V (4 in series), and then connect them in parallel

they are rated 260Ah (C100)
 
S Bengi
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8*12v*260AHr=25kWHr.
With a daily production of 8kWHr.
That's 4X, your setup is looking nice.

I checked you manual. The inverter max pull is 110A and the max input during charge is 140A so a 150A fuse?
 
Nuno Donato
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S Bengi wrote:8*12v*260AHr=25kWHr.
With a daily production of 8kWHr.
That's 4X, your setup is looking nice.



I wanted to be on the safe side, since we will depend on electricity for so many things!!
Now I just want to get all this stuff wired up without blowing up anything :D
 
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