New Grid-Tie install 16.7kw help

DesertRatDesertRat Registered Users Posts: 25 ✭✭

New to forum and have a couple of questions:
 I have (22) JASolar 370 (1500vdc) panels.  Panels have QC 4.10-35 connectors. JASolar also makes a 370 (600vdc) which uses the     common MC4 connectors.   I can purchase the QC 4 connectors but have MC4's on hand.  Can these be mixed or is it better to keep the connectors the same?

Next question is I have 2 SMA 7.7 inverters.  Electrical plan shows a combiner box (seeAttched) with 2 40a breakers.  Been looking at Midnite Solar boxes but not sure which to get.  Can anyone help me out?  Thanks


  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    Generally, the solar panel warranties are only valid if they are not modified (changing connectors, drilling "non-approved" holes, etc.).

    And you have to be careful, there versions of connectors that have similar names, and look the same, but they do not mate reliably when intermixed.

    On the other side, solar panels are pretty cheap these days ($0.50 per Watt vs $10.00 per Watt 15 years ago)... Eating the warranty costs if a panel "goes bad" may not be that painful (and for a period of time, the warranties were longer than the life of the solar panel companies).

    There are "Combiner Boxes" that are used with (typically) 3 or more parallel solar panel strings--They use fuses or circuit breakers to protect a shorted solar panel from being feed too much current by the other parallel strings--And causing a fire. These fuses/breakers have to be rated for (up to) 600 VDC (depends on the series connected panels).

    The 2x 40 amp "combiner" in your drawing is just a standard 120/240 VAC split phase XX slot sub-panel with isolated neutral (from your local electrical supplier or home improvement store). You would not use a "solar combiner" for this.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DesertRatDesertRat Registered Users Posts: 25 ✭✭

    Thanks for your reply.  To be safe I'll buy the QC4 connectors and go to the local home improvement store for the electrical box.
  • DesertRatDesertRat Registered Users Posts: 25 ✭✭
    Bill,  I replied too quickly without giving thought to your reply.  All my electrical items will be outdoor as my electrical panel is on outside of house ( attached photo).  So what type of combiner do I need.  

  • solar_davesolar_dave Solar Expert Posts: 2,397 ✭✭✭✭

    This is my 12.5 Kw setup with dual inverters. the center is the DC disconnect and the AC combiner is on the right with a breaker for each inverter.  Try to use hard conduit out here in AZ, the Flex stuff just died after a couple years.  If you can mount the expensive inverters behind a locked gate that would be a good idea.

    This is the solar meter and required in my area master AC disconnect (with a faded approval sticker.)  You can see why I hate the flex stuff, cracked plastic connector.  The lock is the utilities and was a PITA to repair. The disconnect feeds a single  breaker in the main panel.  

    My DC combiner is in the attic using a weather head and I can't find a picture of that, but it basically fuses each of 8 strings separately. The original installer idiots used 4 8 amp fuses and 4 10 amp fuses,  PITA to diagnose after about 3 years of service when the 8 amp fuses started to give up.

    With that big a system you better check out the back feed requirements for you existing panel, I had to install all new service feed from transformer and upgrade the entrance to 400amp with dual 200 amp breaker panels to get the added "load" into the system.  I didn't holler much because I new I would need to add another 125 amp sub in my man cave building. (hehe fly on the lense).  

  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Here's the MidnightSolar box I used for 6 breaker locations

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • DesertRatDesertRat Registered Users Posts: 25 ✭✭

    You have a nice clean install. 

    I have 400 amp entrance service.  Requested that when house was built in 2010.  The inverters and combiner box would be mounted under the solar array.  The only thing on the house wall would be the required ac disconnect.  

    As I am on 10 acres (Nv) with no fence, security/theft is an issue I am looking into.  Does midnite solar make a combiner box with 2-4 breakers?  Thanks

  • solar_davesolar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    edited May 2020 #8
    Hmmm I would think the best location for the inverters would be on the east or north walls,  The direct afternoon sun is hard on the electronics and I am sure the roof is even hotter. Ours are all on the east facing side, for the electronics I would have preferred north but that is the street side.

     Looks like the 4 gang Midnite box is a single output.  You might check with this sites sponsor and perhaps there is a 4 into 2 string combiner. I think I saw a 3 gang one on their site.

  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    I would be very concerned about using a Midnite Solar combiner box...

    The requirements for 120/240 VAC Boxes/Sub Panels from "Home Depot" should be quite different electrical design/breakers used vs that for solar combiners.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DesertRatDesertRat Registered Users Posts: 25 ✭✭
  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    edited May 2020 #11
    Yes, that should work. 1x double pole (240 VAC breaker for each 40 GT inverter input (two total breaker sets).

    Some folks have strong feelings on Home Depot vs other brands of electrical boxes and breakers (one being better than another). 

    I do not have enough experience to make a good recommendation one way or another. Hopefully, others where will thelp)

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,630 ✭✭✭✭✭
    edited May 2020 #12
      Security from humans and critters out in the desert. Both really important.

     Home Depot has about everything that is out there for AC V. You just need to know what to order, and what not to.
     Square D from Schneider and you can't go wrong. HD often has to order the specified equipment and that is where people get into trouble.
     They want it now and end up buying what is on the shelf.
     DC BOS from the store here or any good solar supplier is a good choice.
    "we go where power lines don't" Sierra Nevada mountain area
    E-mail [email protected]

  • DesertRatDesertRat Registered Users Posts: 25 ✭✭
    Bill and Dave,

    Thanks for the info. and going to HD now.  
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