advice on solar panel installation

Hi. new here and new to solar panels and could use some help. It seems to be very difficult to find conclusive information on the internet. I am going to install 36 235w panels on my house roof in 4 separate strings of 9. I am trying to figure out what wiring size I need. The panel specs say unipolar 4 mm2 and I don't know what that means. When I search for wire it's all just coming up as 12 awg and 10 awg and such. Also, what is use 2 and do I need it if I am not burying the wire? I was intending to just lay the wire in my mounting rails and come out the end of the rails, into a snorkel and down into the inverter. Also I am having a very difficult time coming up with the MC4 connectors I need. my panels use female for both the - and + and the only places I can find that sells just the female halves wants $3.50 a piece for them which seems crazy to me.

Thanks everyone.

Comments

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: advice on solar panel installation
    different wrote: »
    I am going to install 36 235w panels on my house roof in 4 separate strings of 9.

    Welcome to the forum,

    What brand and model are the panels (that will help me understand the connectors on your panels). What about your combiner box, disconnects, and lightning arrestors? What about your panel frame grounding? You can buy a combiner box that has built in connectors that will accept the MC4 cables from your panels, has a lighting arrestor, has a disconnect.

    Before answering your specific questions it would help to know if this is a grid tied system and where it is located. If the system will be grid tied, you will need permits and inspection. Which version of the NEC must you follow? You may need an arc fault combiner.
    different wrote: »
    I was intending to just lay the wire in my mounting rails and come out the end of the rails, into a snorkel and down into the inverter.

    Is the inverter indoors? If so, your intentions sound dangerous... you don't want to give a path for lightning into your house. Also, 9 panels in series is some high voltage DC... you really should be following code. Even if you're not grid tied and not inspected, your insurance company can deny claims if the system is at fault and not up to code.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: advice on solar panel installation

    Some basic wiring info you'll need to know:

    First, that array comes to 8,460 Watts so what inverter(s) are going to be used?
    Second, the four strings will need to meet in a combiner box with circuit protection like one of these: http://www.solar-electric.com/misomnsoarco4.html
    Third, the panel specifications are key to sizing wiring. It is likely that these 235 Watt panels are around 30 Vmp and 7.8 Imp so an array of 9 x 4 would be 270 Vmp and 31.2 Imp. But don't guess; get the right numbers. That would be pretty low Voltage for most GT inverters which normally run 300+ Volts. It may be better to have three strings of twelve instead.
    Fourth, the distance from the panels to the inverter is very important in determining proper wire size. It not only has to be large enough to carry the maximum current but also to prevent any significant Voltage drop.

    4mm^2 is a metric wire size roughly equivalent to 12 AWG. I have never seen panels with only female MC4 connectors on both positive and negative leads. This would be a very bad thing as they could too easily be hooked up wrong. Check this twice. Consider getting different panels if it is indeed the case.

    Having to buy separate cable ends will be quite a pain as you will also have to buy a crimper to assemble them with. Have a look at our host's selection of MC4 cables and adapters here: http://www.solar-electric.com/incaforsoelp.html

    Laying the wire loose probably will not pass inspection anywhere. If at all possible it should run in conduit. Any 'loose' wiring will have to be secured and be rated for exposure to the elements.
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: advice on solar panel installation

    If you have a inverter that that grounds one side of the array, you can use "USE-2" wire, 10ga, preferably black and white (code requires grounded conductors to be white - although most installers just use black and tape the ends white). USE-2 wire was created for Underground Service Entry use and has great, tough insulation about 4mm total diameter.
    If you have an ungrounded inverter (transformerless type) you are supposed to use PV type wire that is double insulated. Since its ungrounded, neither conductor can be white so usually use black and red although many just use 2 blacks and tape one of them red as red fades to black within a year in the sun anyway. 10ga PV wire is about 6mm fat and I can tell you that your 4 pairs of PV wire won't fit in 3/4" conduit.
    Unless you have the special crimper for MC4, just buy say 100' lengths of "extension cables" with male and female ends from your solar supplier and cut it to get your home run cables.
    Be aware that the solar industry is rife with different connectors. MC was getting snotty about its MC4 type for awhile and many other companies jumped in with either MC4 compatible (slightly different to avoid infringement) or way different. I like Amphenol which can get from Digikey at a good price.
    Don't know your array arrangement, but let me tell you about what we call skip-wiring. When you plug your modules together into strings, plug every other one together - thus skipping one. Go down the row of modules like this, then connect the end two together, then come back down the row connecting the skipped modules and you can end up back just about where you started. Be sure to dress up the wiring with special clips from your supplier to keep the wire from obstructing drainage down your roof. Don't use plastic wire-ties; your solar system will last 40 to 50 years - wire ties won't. If you arrange your array wiring with a little forethought, a lot less home-run wire is needed (less voltage drop too). Generally, you can place a junction box at a convenient spot, run short PV wires to the ends of your skip-wired strings. then transition to THHN wire (cheaper) in the junction box and run EMT conduit to your inverter. You can get all kinds of colors of THHN to keep your 4 pairs of wire from getting confused. I buy rolls of $$$ PV wire rarely now.
    Let us know how it works out for you.
  • differentdifferent Registered Users Posts: 12
    Re: advice on solar panel installation

    Thank you for the replies. I have submitted my plans and specs on everything to the building inspector as well as the utility and have been given the ok for everything and obtained the permit. My system will be grid tie and will be using MX 235 panels that run at 37 volts each. My inverter is a Sunny Boy 8000US which requires voltage to be between 300 and 480. 9 panels should be 333. The panels and racking will be grounded with a 6 awg copper wire running to 8 foot grounding stakes. I am unsure why it would be unsafe for me to lay the pv wire in the rail instead of clipping it to the side with expensive clips. my rails is 1.5 inches wide and 3 inches deep and crosses the panel just 3 inches below the MC4 connector so I could simply lay the wire in the rail and then come back out to the next panel with only 3 inches exposed underneath. I am just unsure how I can run conduits on the roof that will have so many different entry points. Especially since my inverter is going to be on the wall directly below the end of the top rail, so I was thinking I could exit the rail and go right up into a snorkel then down a conduit into the combiner and dc disconnect. The only issue I could see is if the rail somehow got full of water, but even then there would be no connections in there. Do you guys advise against me doing that?

    thank you so much!
  • differentdifferent Registered Users Posts: 12
    Re: advice on solar panel installation

    Also, I was planning on buying a large roll of pv wire and a crimper since my array is quite long and the wires with the connectors on the end already seem very costly. Also I have not been able to find anyone selling them with two female ends. My panels (mx) do indeed have both male ends on them. The Tyco MC4 female ends I got are all - so they only fit into one side. Tyco makes the + female ends as well and they have a red o ring instead of a blue. I don't know exactly how to describe them, but the two different connectors have different key bumps on them so the - cannot be pushed into the + on the panel.

    thanks again
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: advice on solar panel installation

    Wire that is unsecured is wire that can move around. Wire that can move around is wire that can abrade. So if it is not securely fastened there is the possibility of the insulation being damaged over time.

    Check to make sure that 37 Volts on the panels is Vmp not Voc.

    I'd have to see those ends to understand what you mean by the design. It doesn't sound like a good idea to me to have both (-) and (+) the same type of connector.
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: advice on solar panel installation
    different wrote: »
    My system will be grid tie and will be using MX 235 panels that run at 37 volts each. My inverter is a Sunny Boy 8000US which requires voltage to be between 300 and 480. 9 panels should be 333.

    37 is probably Voc - Open Circuit Voltage. The maximum power voltage Vmp is probably around 30. So 30x9 = 270. That is less than recommended for your controller. Furthermore Vmp will further decrease when panels get hot or when it's cloudy. 30x12 = 360 would be much better. Voc will be 37x12=444, which will give you some (rather small) margin for the times when panels are getting cold.
  • BB.BB. Super Moderators, Administrators Posts: 29,523 admin
    Re: advice on solar panel installation

    I would double check the panels and with the panel vendor/mfg.... Having the same sex connectors on + and = panel leads does not make any sense.

    You cannot put the panels in series without using adapters. And it is really easy to swap +/= and ruin a bunch of panels (panels connected reversed are "dead shorts" and will conduct too much current and fry (if the power source--such as 3 other parallel strings of panels is capable of over current).

    I would suggest that you really think twice about getting these panels. Either there was a mfg error, or the mfg has no idea how to properly make solar panels. Or these are for some special use... Something is not right.

    And 4mm2 cable is around 12 awg... That is pretty standard cable for solar panels. Depending on how you wire the panel back to the GT inverter and where you put a combiner box with breakers or fuses--You will need heavier cable from the combiner to the GT inverter... And you may need heavier cable from the array to the combiner if the distances are long (more than a few 10's of feet) to reduce voltage drop.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • differentdifferent Registered Users Posts: 12
    Re: advice on solar panel installation

    so if I simply run 3 strings of 12 instead of 4 strings of 9 that would be better?

    I also don't like that both connectors on the panel are male, but I didn't make them :) This ebay auction is the only place I could find pictures of the two together. if you zoom in the picture then you can see the shafts of the connectors are formed different so as not to fit into the wrong places.

    http://www.ebay.com/itm/Solar-Panel-Power-Cable-Adapter-Tyco-SolarLok-Female-to-MC4-Male-/300662834566?pt=LH_DefaultDomain_0&var=&hash=item4600e6c586
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: advice on solar panel installation
    different wrote: »
    so if I simply run 3 strings of 12 instead of 4 strings of 9 that would be better?

    You need to look at the panel specs first. Do you have a sticker on the back of the panel? Can you post the numbers from there?
    different wrote: »

    The two connectors on this picture are not MC4. Can you post the pictures of the connectors from your panel?
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: advice on solar panel installation
    different wrote: »
    My inverter is a Sunny Boy 8000US
    different wrote: »
    so if I simply run 3 strings of 12 instead of 4 strings of 9 that would be better?

    Does SMA have an online string calculator? If so, try out your configurations and see what it says. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • differentdifferent Registered Users Posts: 12
    Re: advice on solar panel installation
    NorthGuy wrote: »
    You need to look at the panel specs first. Do you have a sticker on the back of the panel? Can you post the numbers from there?



    The two connectors on this picture are not MC4. Can you post the pictures of the connectors from your panel?

    Then perhaps I am mistaken about what Mc4 even means. those connectors are what work on the panels I have.

    the tag on the panel sas Voc: 37Vdc
    Vmpp: 29.8 Vdc
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: advice on solar panel installation
    different wrote: »
    Then perhaps I am mistaken about what Mc4 even means. those connectors are what work on the panels I have.

    The pictures are of SolarLock connectors. I don't know much about them.

    MC4 connectors are different.
  • differentdifferent Registered Users Posts: 12
    Re: advice on solar panel installation
    NorthGuy wrote: »
    The pictures are of SolarLock connectors. I don't know much about them.

    MC4 connectors are different.

    are they compatible?
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: advice on solar panel installation
    different wrote: »
    are they compatible?

    I don't think so. I'm 99% sure they're not. But I don't know much about SolarLocks.
  • differentdifferent Registered Users Posts: 12
    Re: advice on solar panel installation

    Thank you everyone for all the help so far. Would this be the correct wire to run in my application?

    http://www.ebay.com/itm/500-12-AWG-PHOTOVOLTAIC-PV-NOT-USE-2-Solar-Power-Cable-Wire-UL-4703-/271202221658?pt=LH_DefaultDomain_0&hash=item3f24e97e5a

    I intend to buy a crimping tool and make all my wires the right length.

    thanks
  • WayneTPVSWayneTPVS Registered Users Posts: 9
    Re: advice on solar panel installation
    different wrote: »
    Thank you for the replies. I have submitted my plans and specs on everything to the building inspector as well as the utility and have been given the ok for everything and obtained the permit. My system will be grid tie and will be using MX 235 panels that run at 37 volts each. My inverter is a Sunny Boy 8000US which requires voltage to be between 300 and 480. 9 panels should be 333. The panels and racking will be grounded with a 6 awg copper wire running to 8 foot grounding stakes. I am unsure why it would be unsafe for me to lay the pv wire in the rail instead of clipping it to the side with expensive clips. my rails is 1.5 inches wide and 3 inches deep and crosses the panel just 3 inches below the MC4 connector so I could simply lay the wire in the rail and then come back out to the next panel with only 3 inches exposed underneath. I am just unsure how I can run conduits on the roof that will have so many different entry points. Especially since my inverter is going to be on the wall directly below the end of the top rail, so I was thinking I could exit the rail and go right up into a snorkel then down a conduit into the combiner and dc disconnect. The only issue I could see is if the rail somehow got full of water, but even then there would be no connections in there. Do you guys advise against me doing that?

    thank you so much!

    different: Seams you are on the right track but IMO I would follow advise from the board as:
    1. Go with 3 x 12 strings. 9 modules even at VOC will not reach the SB8000US start voltage of 365v
    2. The channel in the racking can be used for wire management, but still must be clipped/secured at intevals from abrassion. the cost of clips far outweighs what an arc fault fire can cost. consult the maufacture instructions
    3. If you are homerunning each string the SB8000us can take upto 4 individual strings and has an integrated DC disco. You will have 6 current carring conductors and the ECG thru the gooseneck. At 8a Isc with derates 12awg or 4mm/2 should be sufficant, but consult local code.
    4. the biggest issue you face is 2 female connectors on the modules. this is wrong/specials that got out the door. the pictured connectors are Tyco Solarlok females keyed +/-, you will need to replace one side on all modules with the neutral male ( in pdf ) to make series connections work.

    http://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Data+Sheet%7F2-1773458-2_SOLARLOK_INSTALLATION_MANUAL%7F0411%7Fpdf%7FEnglish%7FENG_DS_2-1773458-2_SOLARLOK_INSTALLATION_MANUAL_0411.pdf%7F4-1394462-7

    Good luck
    Wayne
  • t00lst00ls Solar Expert Posts: 212 ✭✭✭
    Re: advice on solar panel installation

    I have the 235 watt mx solar panels ... they do in fact use tyco proprietary connectors.... bought mine online somewhere ...I will look up the links and post them if the moderators dont have a problem
  • BB.BB. Super Moderators, Administrators Posts: 29,523 admin
    Re: advice on solar panel installation

    No problem--Posts/links that ask/answer questions are fine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • t00lst00ls Solar Expert Posts: 212 ✭✭✭
    Re: advice on solar panel installation

    never mind...the ebay store where you found pictures.....sells the connectors crimpers and a bunch of other wire tools

    http://stores.ebay.com/Win-Solar-LLC?_trksid=p2047675.l2563

    you just need these to do series connections unless you just want to use the neutral male , but then you need twice as many female connectors
    http://www.ebay.com/itm/Tyco-Solar-Connector-Negative-Female-10-AWG-5-1394462-6-/300857059219?pt=LH_DefaultDomain_0&hash=item460c7a6793

    http://www.ebay.com/itm/Tyco-Solar-Connector-Positive-Female-10-AWG-5-1394462-5-/300561707917?pt=LH_DefaultDomain_0&hash=item45fadfb38d
  • differentdifferent Registered Users Posts: 12
    Re: advice on solar panel installation

    Thanks so much for all the help everyone. I'm getting most stuff figured out now.

    As far as crimpers go, will any of the ones that say MC4 crimper work? Is it worth buying a good one, or will one of the cheap ones work good enough for one job?

    thanks!
  • PhotowhitPhotowhit Solar Expert Posts: 4,996 ✭✭✭✭
    Re: advice on solar panel installation

    I would buy one designed for Tyco connectors, I don't know if Tyco connectors are similar enough to use the MC4 crimper. If I was to buy an MC4 crimper now, I would be sure to get one that compresses the crimp straight up and down and not hinged on one side.

    For other people looking at inexpensive panels, the added cost of 2 cables to interconnect each panel will make the MX panels more expensive than many other inexpensive panels that have pre attached cables for this propose. So looking at the total cost is important.

    There are roof top combiner boxes such as this one. So you can combine your strings on the roof and bring down the combined array.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
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