How do I connect 5 solar panels?

[MisterSandals]

Ahhhhhh worse than all that... 30A at 50' needs 2AWG

Does that apply to ALL the wiring in parallel? So even the rooftop solar panel leads become woefully inadequate?

 

[Justin Laureltec]

Does that apply to ALL the wiring in parallel? So even the rooftop solar panel leads become woefully inadequate?

Waaaaaiiiiiiit I'm an idiot... hang on, what voltages are we talking about here? I was thinking 12v, but obviously at the panel side of the controller the voltage is way higher, and the amperage way lower, which of course means you can use lighter-gauge cables.

 

[Justin Laureltec]

Okay, I've read back... the panels on the roof are roughly 18.2v, 5.5A, so in parallel they're fine all the way to 12AWG.

The suitcase is a little funky... does it have an SCC built-in, or is it just the panels? If it has an SCC built-in, then it's stepping down the voltage/up the amperage, in which case you're back to using 2AWG at 50'. If it's just the panels out 25' away, then you're still high-voltage low-amperage, in which case you're good to stay at anything heavier than 12AWG going to the SCC, then of course heavier gauge from the SCC to the battery.

 

[MisterSandals]

Yea, and after I just read back, I am wondering why we didn't suggest connecting the 4 roof panels in series?
Is there a limitation on the SCC for input volts?
(panels in series add the volts, and as we discussed, panels in parallel add the amps).

 

[Supervstech]

Just keep an eye on amps...dont go over the current rating of the wire.

 

[Santa]

Ahhhhhh worse than all that... 30A at 50' needs 2AWG to keep the voltage drop under 3%, though 4AWG puts you at 3.2%, which... eh... could be lived with I guess.
8AWG at that distance puts your voltage drop at 8.08%, which is simply untenable. Then again, running 2ga wires 25' out is also pretty untenable... I strongly recommend just not putting your suitcase that far away, @Santa .

EDIT: I'm an idiot... what voltage are your panels running at? I was using 12v as the voltage in my calculator and on the panel side of the controller, that's obviously not the case.

You seem pretty smart to me. ;-) 18 on the (4) 100 watt panels and 18.2 on the suitcase

Yea, and after I just read back, I am wondering why we didn't suggest connecting the 4 roof panels in series?
Is there a limitation on the SCC for input volts?
(panels in series add the volts, and as we discussed, panels in parallel add the amps).

Yes. There is a limit of 30 amps on this SCC. I HAVE to wire them in parallel with this system. Adding the 5th panel is not what Will recommended in his blueprint and will be close to the max the SCC can handle, and not feasible if the weather is cold, according to what I am understanding, the voltage will rise.

 

[Justin Laureltec]

18 on the (4) 100 watt panels and 18.2 on the suitcase

...okay, so for the purposes of calculation, I'm figuring a max of 9A per panel (and the suitcase has 2?) so I figure 18A @ 18.2v @50' and come up with 8AWG being perfectly fine, but don't go lighter than that... sooooo basically, right back where we started
On the other end, between your SCC and your battery, you'll need heavier gauge depending on the distance from SCC to battery, since the SCC is putting out higher amperage at lower voltage, which requires heavier cable. But your panel-to-SCC wiring is all good at 8.

 

[Santa]

Guys and/or Ladies, this thread has become a little complex for me here. I am not stupid, but sometimes I am ignorant and need to study things when life isn't hitting me over the head with other things like my bathroom flood twice from the neighbors and the many complications after (I am dealing with now). I am trying to figure this out AND I WILL. Thank you for helping and your input, each and every one.

 

[JeepHammer]

FYI, Combining panels in parrallel that way can be dangerous when the panel count goes over 3 or so. The reason is if any panel develops a problem, it can be back-fed the combined current from all the other parrallel panels, which can have more total current than the wire and panel can handle, posing a fire risk. That's why combiner boxes always individually fuse or circuit breaker each string.

With all due respect,
That's not correct.

Parallel panels won't have an issue with a damaged/defective panel,
The parallel wiring simply skips the defective panel.

Current, following the path of least resistance, will simply avoid any resistance that could cause a fire.

The traces in a solar panel will be the first to go, being panels *Usually* have 10-12 Ga wire.
Once a pan trace opens (which can't start a fire) the circuit to that panel is dead, open since this is DC, not AC, there is no 'Live' wire left to start a fire.

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Wouldn't the panels' blocking diodes protect against this?

As long as they're working properly, but I don't like betting on electronic devices proper operation for fire prevention, a fuse or circuit breaker is much safer. If you've ever had a personal encounter with a fire, you'd take every precaution as well.

Facts First,
Fuses, Breakers, Diodes have SPECIFIC functions.

Less & less panels are coming with blocking diodes.
Blocking diodes are 100% effective in stopping back feeding and 100% reliable when used within tolerance.

Using the WRONG component for the job is the builders fault 100% of the time.

The panels in a COMBINED parallel string CAN NOT back feed each other, it's impossible.
DC circuits REQUIRE a completed circuit, both positive and negative.
Like charging a 48 volt battery as 2 each 24 volt batteries,
4 each 12 volt batteries,
8 each 6 volt batteries,
Any single panel in parallel WILL NOT accept current from the other panels.

The only way a panel can do ANY damage is *IF* it becomes a 'Load', at which time a trace will burn and open the circuit entirely...

--------

*MY* (personal) usage/method.
TEST EVERYTHING, EVERY TIME.
*YOU* don't know what the manufacturer did unless you inspect & test.

Know the difference...
A phenolic (plastic) diodes used in combiner boxes & panels will BLOW OUT, break/burn, open the circuit, when overpowered.
It's a makeshift 'Fuse' of sorts.
A steel case diode will not.

The ONLY way to kill a diode is over volt, or over amp.
Common Diodes *Usually* come with 150 to 300 volt limit,
The amperage limit is what you seriously need to watch.

Charge controllers have input diodes that do the blocking.
This is so when the sun goes down the batteries don't heat the panels, blocking battery current from reaching panels, which would defeat the purpose of a charge controller...

Adding extra diodes at panels or combiner boxes with diodes simply drops the voltage production from the panels to batteries.
Every diode in the line will drop the line voltage between .2 and 1 volt.
You can tell how good of diodes were used by checking the voltage drop through the diode,
Cheap diodes will drop about a volt (line losses), the better diodes will drop voltage .2-.3 volts.
The more diodes you add, the more inefficient your system becomes, line losses stack up.

When parallel panel wires come into a combiner box, the panel wires are 12 or 10 Ga, while the wire FROM combiner to charge controller MUST carry the combined power of the panels...
See above, separate completed SOURCE circuits CAN NOT back feed each other, unless the panels becomes a 'Load' not 'Source'...

--------------

Notice size of main (combined) lines on left, and right in image below.
Both are 'Parallel', two different ways to wire Parallel...

 

[Santa]

Okay, I've read back... the panels on the roof are roughly 18.2v, 5.5A, so in parallel they're fine all the way to 12AWG.

The suitcase is a little funky... does it have an SCC built-in, or is it just the panels? If it has an SCC built-in, then it's stepping down the voltage/up the amperage, in which case you're back to using 2AWG at 50'. If it's just the panels out 25' away, then you're still high-voltage low-amperage, in which case you're good to stay at anything heavier than 12AWG going to the SCC, then of course heavier gauge from the SCC to the battery.

RE; Suitcase panel: I would LOVE to directly answer your question of "does it (suitcase panel) have an SCC built-in, or is it just the panels" but cannot. Originally, about 2012, I bought an "all-in-one" along with the suitcase panel. The battery/all-in-one was since stolen. I still have the suitcase. This was my introduction into solar/backup power. I don't know or understand what they used as a charge controller. I tried to ask them (Lion) about it, but never got an answer. Is there something on the back of the panel that can answer this?

 

[Justin Laureltec]

RE; Suitcase panel: I would LOVE to directly answer your question of "does it" (suitcase panel) have an SCC built-in, or is it just the panels" Originally, about 2012, I bought an "all-in-one" along with this suitcase panel. The battery/all-in-one was since stolen. I still have the suitcase panel. This was my introduction into solar/backup power. I don't know or understand what they used as a charge controller. I tried to ask them (Lion) abouty it, but never got an answer. Is there something on the back of the panel that can answer this? I hope that made sense.

Hmmmmm interesting... well I will make a logical guess that the SCC was in the "battery/all in one" unit, because since the cabling between the SCC and the battery needs to be heavier-gauge to handle the higher amps at lower voltage, it always makes sense to mount the SCC as close to the battery as possible. So you're probably fine.
An easy(ish) way to test this would be to pull out the suitcase in the sun and use a voltmeter at the cable leads... if you read between 12 and 14vDC, the SCC is in the suitcase. If you read 16-22 or so, the suitcase is just panels and the SCC was in the all-in-one unit that's now gone.

 

[MisterSandals]

Yes. There is a limit of 30 amps on this SCC.

Wow, with the panels in parallel as we've been discussing, 29amps is right up there! It would run hot if your 5 panels produced that much power.

What are the maximum input volts of this SCC?

I ask this because if you were to hook up your panels in series, or even a combination of series and parallel, then your amps become very manageable (and wire sizes very reasonable).

Santa don't be discouraged, you are in excellent hands, especially with the minds that have joined in today! I know I've learned a LOT!

 

[Justin Laureltec]

With all due respect,
That's not correct.

With likewise due respect @JeepHammer , given that solar panel manufacturers themselves state that, indeed, you must individually fuse more than 2 parallel-connected panels, I suggest that your understanding of how a failed panel acts is incorrect. A failed panel (depending on how it failed, obviously) can indeed act as a load, thus the importance of individual fusing of parallel panels... which is further backed up by the layout of every reputable commercially-available combiner box in existence.

Windy Nation, for instance, says here:

"Commercially made solar panels over 50 watts have 10 gauge wires capable of handling up to 30 amps of current flow. If you connect these panels in series, there will be no increase in current flow so fusing is not required for this string. This is not the case when you have panels connected in parallel, as when connected in parallel the system current is additive. For instance if you have 4 panels each capable of up to 15 amps, then a short in one panel can draw all 60 amps towards that short-circuited panel. This will cause the wires leading to that panel to far exceed 30 amps causing that wire-pair to potentially catch fire. In the case of panels in parallel, a 30-amp fuse is required for each panel. If your panels are smaller than 50 watts, and use only 12 gauge wires, and 20 amp fuses are required."

Eaton (as in, Eaton Cooper Bussman) says here:

"Depending on the desired PV system capacity, there may be several PV strings connected in parallel to achieve higher amperage and subsequently more power. Systems that have less than three PV strings will not generate enough fault current (short-circuit) to damage the PV modules, conductors or downstream equipment, and do not present a safety hazard, provided the conductor is correctly sized based on local codes and installation requirements. When three or more PV strings are connected in parallel, a PV fuse on each PV string will protect the PV modules and conductors from overcurrent faults and help minimize any safety hazards.The PV fuse will also isolate the faulted PV string so the balance of the PV system can continue to generate electricity. "

BRE says here:

"In a PV array formed from a number of strings, fault conditions can give rise to fault currents flowing though the d.c. system. Two key problems need addressing – overloaded string cables and significant module reverse currents, both of which can present a considerable fire risk. Fault analysis shows that the maximum fault current flowing in a string cable to be (N -1) x Isc. A system of three or fewer strings cannot generate sufficient fault currents to present hazardous module reverse currents. Hence with three or fewer strings, fuses can be omitted providing that string cables are suitably rated. Such a method does not clear the fault, but simply prevents a fire risk from overloaded cables. The installation of string fuses can provide protection against fault currents in all other cases. While some fault combinations are less likely than others, in order to provide full protection of all cables and modules – string fuses are required in both the positive and negative legs of the string cabling. (See section 2.1.5)."

I can provide more references if necessary, or you can search for yourself, but I think the point is clear - a complete understanding of how these systems work leads one to the inescapable conclusion that a faulted panel can indeed cause a fire, and it's well worth the small investment of an inline fuse to protect against that. I've personally seen a failed panel burn a hole in itself (and can provide a photo of that if it would be helpful), so I cannot possibly overstate how very important it is to follow safety protocol when working with PV arrays.

 

[JeepHammer]

So, jumping from back feeding and diodes to fusing?
Which is why I started with component FUNCTION in the first place...

As described, and shown in the image, and laid out in text...
A properly functioning panel, simply shaded, will NOT become a 'Load'.
A seriously DAMAGED panel *Could* become a Load in PARALLEL where it has access to full, combined AMPERAGE.

I have seen damaged panels scorch, carbon up, cook,
Never, not once seen one catch fire and burn, not even when struck by lightening...
I'm not aware of anything flammable in better quality (I think you called them "Reputable Manufacturers".

Diode losses at the panel,
A diode stops ANY back feeding, period...
Any panel damage CAN NOT be 'BACK FED' no matter how much amperage is in the combined line.
The circuit is one way, period.

And again, I'll point out when the diode is properly sized for the panel (Max Amp Rating) ANY over amp attempt at 'Back Feeding' from combined main lines, and the diode pops, opening the circuit just like a fuse.
While I have no objections at all to adding fuses to panels at all, a fuse isn't a one way blocking in diode...
And that brings us back around to CHECK/TEST/VERIFY EVERYTHING...

3, 5, 6, 8, 10, etc amp diodes are common, it's just too easy to size the diode to the panel,
A good time to fuse the panel also if you feel it's needed.
And I'll point out the diode,
First bocks ANY back feeding,
Second, sized correctly blows out BEFORE the wiring can melt/catch fire,
The blow out works just like fuse, opening the circuit.

In my opinion, since you are there anyway, adding a 5¢ fuse is pretty cheap insurance,
But I'm not driven to demand anyone to do this any specific way...

In Parallel, a diode at each panel drops line voltage a total of 1/2 to 1 volt TOTAL,
Acceptable losses...

-------

Series wiring, ONE diode per SERIES.
Where the SERIES hits the combiner, a diode, each diode drops total voltage 1/2 to 1 volt, acceptable losses.

One diode per panel will drop voltage AT EACH PANEL about 1/2 to 1 volt PER PANEL.
That's 1/2 to 1 volt PER PANEL,unacceptable losses for me, but folks can do what they want.

The same with One Fuse per Series string, since either the diode or fuse will open the circuit ENTIRELY,
Making any 'Potential' energy the string can produce to ZERO,
Open circuit means no danger.

There is MUCH LESS Amperage in a Series string, and amperage is what heats cables and starts fires.

-----------

Now, I've been doing this a LONG TIME, and I understand it fully...
I separate Series & Parallel and build for each, there is no 'Universal' way to do the wiring, just like components need to be sized specifically for the string/panel being used...

While common diodes, and fuses come in all different sizes, and are cheap,
The panel manufacturers have no idea in the world what *YOU* are going to do...

A common phenolic diode looks like this, and it's quite small.
As you can see they come in a number of Amperage limits so they can be sized specifically to the application.
At 6¢ to 35¢ each, no one has an excuse NOT to size diodes to the panels/application being used.

Now, when I'm wiring panels, I do something a little different,
I use a diode that fits in a fuse block.
When you do this about 25 years you learn that a fuse block makes a good combiner box,
With easy find, quick change components...
It also allows you to change configuration, expand in minutes WITHOUT being proprietary, not a slave to changing everything every time you want to make a change, add panels.
Lower cost than proprietary, and you aren't a slave to some company that charges 6 times the price for half the capability...

A quick change diode, runs about $1.50 each in bulk...

A quick change fuse,

A quick change fuse block, from small and indoor, even single string/single panel...

To big enough for any strings I know about, and waterproof...
With or without LED indicator that tell you what fuse/diode failed.

From under $5 topping out about $35, pretty affordable for your panel string combiners/panel protection.

-----------

Do things how ever you want to,
Dismiss ideas and take them off the table,
It doesn't make those ideas any less valid or workable.

 

[Justin Laureltec]

So, jumping from back feeding and diodes to fusing?
Which is why I started with component FUNCTION in the first place...

...um... wasn't jumping from anything... your long response above started with a comment from another user about fusing.
And all the above is great. My point is, you said "The panels in a COMBINED parallel string CAN NOT back feed each other, it's impossible. " which is not true at all and in fact very dangerous to believe, so I hope you'll reconsider your wording and stances without feeling the need to write another book.
If not, eh. More power to you, I suppose.

 

[JeepHammer]

...um... wasn't jumping from anything... your long response above started with a comment from another user about fusing.
And all the above is great. My point is, you said "The panels in a COMBINED parallel string CAN NOT back feed each other, it's impossible. " which is not true at all and in fact very dangerous to believe, so I hope you'll reconsider your wording and stances without feeling the need to write another book.
If not, eh. More power to you, I suppose.

Again, no disrespect, but 'Writing A Book' is how you convey the complete picture.
An 'Idea' can come through in a short video,
An education comes from text books, detailed writing and defining the issues, which isn't a 'Short' subject...

The OP asked a question about Series/Parallel,
Not a 'What If, Worst Case, 15 things go wrong at once scenario" to confuse her basic question, and asked me to have a look...

Now that the issue is further confused I'll now make a diagram explaining the difference in diode, fuse use.
That shouldn't take up more than about 3 MORE hours...

 

[Santa]

Sorry, I took a nap and am catching up=thank you for your time and information!

 

[Justin Laureltec]

That shouldn't take up more than about 3 MORE hours...

Whatever floats your boat, friend.

 

[Santa]

Oh come on. Please allow others to give their opinions and info without criticism. How are we going to learn otherwise?

 

[Justin Laureltec]

Oh come on. Please allow others to give their opinions and info without criticism. How are we going to learn otherwise?

I concur, really, I just feel that matters of safety should not be taken lightly, and all safety mandates state that three or more parallel panels or strings of panels must be individually fused.
There are ways around this, that's a fact... My opinion is that it's simpler and safer to just do it rather than engineering a way around it.