Solar Panel Connector "Boxes"

[WStayton]

Hi All!

  I'm in a bit of a quandry, here . . .

  I have ordered and paid for eighteen each 200 wattt, 24 volt nominal, panels that I will wire in six groups of three each in series, and then the six series-groups in parallel to the Midnite Solar MPPT Charge Controller CLASSIC 150.

  What exactly do I need for the "combiner" boxes,  do I then need a separate box to feed the six separate circuits into to combine them, yet again, before feeding them to the solar controller?

  When you google "solar combiner boxes" you get a plethora of choices and I am confused as to what is required.

  I suppose I should start with my electrical code inspector, but this solar stuff is all new to him, so he is inclined to let me do pretty much whatever I want to with minimal interferance from him - so he's really not much help, except to have somebody electrically knowledgeable to roll ideas by.  <grin>

  I checked with NYSEG, the local grid suplier and they said that they couldn't really advise me, except to send theri inspector by and have him decide whether or not what I want ed to do was acceptable to NYSEG, but that a "consult" for some purpose other than the final certification of the installation incurred a $200 charge, just for the inspector to set his feet on the property!  I declined!  <grin>

  Also, what do I need with regard to lightening arrestor's?   Is one each on the top of the whole mess enough, or do I need one on each corner, or yet some other configuration??

  Midnight Solar makes a relatively new lightening arrestor that SEEMS to be the latest and greatest, so that is what I am proposing to use, unless sombody has a better idea!

  I also see everywhere on the Xantrex documentation to ONLY use ONE ground rod and to ground everything to that one rod.  I understand not wanting to have "ground loops" but if I have a disconnect for the incoming line. something that I am going to insist on, I THINK that I am going to have to have at least TWO ground rods to keep everything separate - one for the incoming service and one for the solar/house set-up, no?  How do I make the Xantrex happy with that?  I WILL be happy when everything is cut loose from the line, but when they are hooked togather, so I can sell power to NYSEG, in the summer, there will absolutely be two ground rods in the system . . .

   So what does everybody think?  How many and what make of connector boxes?  How many lightening arrestors?  How to deal with the one/two ground rod problem???

  Responses are hereby solicited!  <grin>

Regardz,

Wayne Stayton

[mike90045]

Combiner boxes simply take the power leads fro PV's, and combine them in parallel.

They also have a fuse or ckt bkr  for each series string, so a fault does not cause too much damage.

They have a buss bar to tie your inputs together, and allow for connecting the #6 cable for the run to the battery charger.  Don't try to wirenut 3 #14s to a single #6 - it don't work well ! (for very long)

So, it's a J box, large enough for fuses or breakers, some short buss bars, and some knockouts.   Midnight has some very nice ones.

[WStayton]

mike90045

  So I need something like the "Midnite Solar MNPV6 PV Combiner" to tie my six string of three each solar panels all together, but do I also need a separate "combiner/uniter" box of some sort to tie the three panels in each string into a series?  As in six each combiner/uniter's, or just one big one and lots of lead extensions?

  And, they sell lead "extensions: for the solar panels, which only have about a 1 meter pigtail, AIR, do I need one of those for each panel to lead them to their "combiner" box, to get 72 volts DC???

  I was not impressed by the "extension-leads", they look about as weather tight to me as a sieve!  How do you keep the juctions between the panel pigtail and the lead extension from getting shorted out???  Do you use shrink tubing with a big gob of RTV inside of it before shrinking, or what???

  My electrical experience is all with domestic-type 120/240 and, for that, you try to have EVERY junction contained inside of some sort of enclosure - do you still try to do that with solar photo-electric DC???

  I'm like a three year old - I've got more questions than you can shake a stick at!  <grin>

  Thanx for the input, so far, Mike!

Regardz,

Wayne Stayton

[Tom Reed]

You need 1 - 6 circuit combiner box, but you might want to go with an 8 circuit in case you want to add more panels in the future.

On my system I got 50' extension leads which were then cut in half to give 25' pos. and neg. leads to a couple of J boxes under the roof. From the J boxes 10 ga. thhn wire was run through the wall down to basement where the combiner box is. My combiner has a breaker for each string, there are 7 on my system. The breakers are also handy for checking the performance of each string. Just switch on 1 string at a time, around noon, and read the charge controller to see how much power it puts out.

Those connections are pretty heavy duty and rubber/edpm sealed, mine haven't been a problem. They were just plugged together during the install with no additional prep.

[mike90045]

The MC connectors are rated for UV and weather (rain, ice) exposure.  Never cut the PV panel cable, you will void the warranty!

Buy the extension cables, and cut them.   You may want to buy the unlocking tool for the MC connector (there is MC3 and MC4, 2 different tools and cables, MC4 being newer).  Without the tool, you cannot separate the cables.  Also, be sure there is no amps flowing in the cable, the connectors are not rated for 300V disconnects, they will arc and fry if the panels are lit or the fuse is in.

[DanG]

http://www.dehn-usa.com/dehn-Application-Guides-pubcid1.html#guide

The above link has a lot of good points for lightning safety if you read around (ignore) their proprietary device hype. In particular the 'rolling ball' zone of protection/vulnerabilities is good food for thought.

Some say the mechanical structures should be incorporated into the overall system ground with just one grounding point but I see evidence otherwise. I have used panels that took a lightning hit at some point in their life, not an automatic fatal event - bleached some of the deep blue off the wafers when the framework-roof mount led the strike into the attic wiring that played merry 'ell with the household appliances & electronics. When protecting the mounts and framework, etc., the SHORTEST POSSIBLE path to an earth ground will save that sort of grief - I removed those used panels & their entire system off their roof and the installers led the metal conduit on a path convenient for them and the grid-tie panels so had that ground lines were eight or twelve feet longer than the attic lights just eight inches under the PV mounting brackets.

For every lightning strike there are thousands of static leaders reaching up from the earth and only one or a small local group win the competition - I've seen my modem cable leaking blue hissing-buzzing static across a window sill to the aluminum siding right before a strike - having some other place be more desirable is a good start - but not to include the neighbors houses or any area that is likely to be inhabited, adding cables and a lightning rod to a distant tree that the cattle gather under could lead to liabilities and full freezers for all the relatives.

Looking at the telephone installers bag of tricks is a good start - like having the DC output line coiled a few turns before it enters any structure, forcing the DC line to make a ninety-degree bend at close proximity at a robust earth grounded point, using drip loops (even shallow droops) to keep water from following conductors to any box or structure entry point, and as a last line of defense having a self-sacrificing lightning arrestor where conductors enter a structure and/or before conductors reach charging-inverter panels. Remember lightning arrestors have a finite life, they fatigue over time, reading some specs its 40 or 50 distant spikes, 3 or 5 moderately close hits or the one direct hit before they are useless... and nearly impossible to tell what they have seen, so a periodic change out schedule would be good if we remember & can afford it...

Its such a complicated argument over codes and industry best-practices pretty much every aspect of the system needs to be reviewed, ie: when burying plastic conduit should a solid conductor ground be laid bare in the conduit trench to keep the internal circuit wires from getting blown out when the surge ignores the 600V insulation, air gap and PVC conduit when it seeks earth ground?  I don't have a clue but thats how I did it.

Just keep asking questions, no question is the dumb question

[LowGear]

Thank goodness for DanG.  Here's my not stupid question.  mike90045 linked this battery cabling site and it really twisted my little gray cells somewhat.  I'm curious if it applies to solar panels as it does to batteries.

http://www.smartgauge.co.uk/batt_con.html

Casey

[DanG]

Yes but only minutely, the lowest voltage or amperage panel will limit the others, one panel outputs 27.56 and another 27.54 in parallel we will only harvest 27.54 volts (summing the current) and/or if in series with one 6 amp output and one 6.05 amps we only harvest 6 amps (summing the voltage).

What the battery interconnect "ideal" details show is over time input/output numbers skew, drift, slide, avalanche, collapse and such & so on since it is the CHEMICAL process getting limited or nudged in different directions by conductor path and connector choices.

Solar panels use an ATOMIC-level process that degrades only billionths as much over the same time period so when using factory matched panels with their internal diodes intact and decent matching wiring the closest thing would be the serial/parallel thing listed above but that is beyond our control at the factory.

Mixing panels of different sizes and outputs is its own thing, but two factory identical panels should produce exactly what each did on day one day in and day out no matter which connects first to a buss bar, etc...

[Tom Reed]

Interesting how the linked article talks about how important proper wiring is especially with high end batteries. Well the best way to go if you're going to spend the $ for high end batteries is to create a single series string of large AH cells instead of lots of smaller batteries paralleled. You'll spend less time bent over a battery bank filling cells with distilled water too.

[WStayton]

DanG:

  You said " . . . two factory identical panels should produce exactly what each did on day one day in and day out . . ."

  If this is true, why do manufacturers guarantee their panels to produce something like 80% of rated output after ten years, then?

  It was my understanding that solar panels gradually degraded in performance from their initial level to some lower level over a period of time and that, then, they were stable in output thereafter.  Is this another thing I've gotten wrong???

  Geesh, this stuff keeps getting more and more complicated for something that was SUPPOSED to be simple - just put them in the sun and sollect the electricity indeed! <grin>

Regardz,

Wayne Stayton

[Tom Reed]

If it were easy everyone would be doing it. It is far, far easier now than it was even in the '90's.

[DanG]

Golly.

Day in and day out isn't the 'same' as 'year in and year out', is it now?

Warranty...
90% at ten years,
80% at 20/25 years,
then past warranty...
perhaps 70% at 50 years (no one knows yet) and you want we should complain?

How many inverter - charger - home pc's - teevees - stereos - shop tools will still be 100% and in use after 10 or 25 years?

[WStayton]

DanG:

You said: "How many inverter - charger - home pc's - teevees - stereos - shop tools will still be 100% and in use after 10 or 25 years?"

  Yea, but the guys selling those things USUALLY don't say  " . . . two factory identical (insert item) should produce exactly what each did on day one day in and day out . . ."

   When you say "day-in-day-out" without qualification, I take it to mean FOREVER, unless you put some limitation on the statement - otherwise the statement is worthless. I could have something that is time stable for five days but loses 50%  of its performance over the first six months of use, and I could say, as you did, that its performance is constant "day in day out".  Would you NOT be mislead by that statement???

  If it degrades over time, its performance is NOT constant "day-in-day-out" but rather degrades over time. PERIOD!!!

  I have this all white swan I would like to sell you - well, he does have a FEW black feathers, but he is REALLY all white!!!  Come on, is he white or isn't he???  Do Photo electric panels degrade over time or don't they??

  I take issue with people who try to squirm through small holes and not really say what the truth is.

  Sorry, but that's the way I see it!

Regardz,

Wayne Stayton

[Carlb]

Wayne wrote,
Do Photo electric panels degrade over time or don't they?Huh?"


Answer,
Yes, everything degrades over time just look in the mirror

[Thob]

Wayne wrote,
Yes, everything degrades over time just look in the mirror

Yep, my mirror gets a little worse every day!