14 kw ground mount solar adding 3 kw roof solar.

Cooker1967Cooker1967 Registered Users Posts: 12 ✭✭
I have 14 kw solar going into four 15 amp breakers at the ground mount. from there the # 4 wire goes 30 ft to a solar main disconnect with 200 amp round fuses L1 and L2.  From the disconnect it has a line tap before the 200 amp main house disconect.  My question is can I put a 100 amp breaker box before the solar disconnect and put the ground mount on a 80 amp breaker (four 15 amp breakers. 15 x 4 = 60. 60 x  1.25= 75) and the new 3 kw on a 15 amp breaker?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 28,993 admin
    I think I need to understand your setup better--And some better information about voltage/current/deratings/hardware/etc.

    I am guessing, but the 15 amp breakers should already have been derated by 1.25? You would not need to do it again with the 80 amp breaker (as long as the wiring supports 80 amps branch circuit, there is usually no reason not to use the larger breaker).

    It also appears that your Vmp-array is something over ~233 volts. Hi voltage DC rated circuit breakers are relatively uncommon and (can be) expensive....

    And the solar charge controllers that are rated for such high current/voltage--Not common for residential size systems.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • littleharbor2littleharbor2 Solar Expert Posts: 1,282 ✭✭✭✭
    Midnite Solar does have 300 volt rated DC breakers

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • Cooker1967Cooker1967 Registered Users Posts: 12 ✭✭
    Thanks for taking the time to respond.
    Going into the four 15 amp breakers at the ground mount is ac power, so everything going into the new 100 amp breaker box is also ac power.  The inverters on the panel's do the DC to ac conversion.  The thing I do not understand is the ac breaker size I need going to the  new 100 amp panel,  the new 3kw is a 15 amp per the manufacturer the other breaker I just added them up which was four breakers = 60 amps total  x  1. 25 = 75 amps closest breaker size is 80 amps. I would like to put a 15 amp breaker in there but I don't think it works that way. 
  • BB.BB. Super Moderators, Administrators Posts: 28,993 admin
    Is this a grid tied system (panels to gt inverters to solar sub-panel to actually main panel)?

    240 vac (Texas?) (120/240 vac split phase?).

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cooker1967Cooker1967 Registered Users Posts: 12 ✭✭
    Grid tied.  Line tapped between maim house shut-off and 200 amp main sub panal, no shut off in house 120/240. So it goes utility in, meter, main house shut off, line tap from ground mount, and then to house. 
  • Cooker1967Cooker1967 Registered Users Posts: 12 ✭✭
    edited December 2018 #7
    Another option would be to run the 3kw New systen to the inside main sub panal with a 20 amp breaker but then I would have to add another single breaker, breaker box coming off the inverters, and disconect. 
  • Cooker1967Cooker1967 Registered Users Posts: 12 ✭✭
    And yes the great state of Texas. 
  • BB.BB. Super Moderators, Administrators Posts: 28,993 admin
    Have you measured your "high noon" current (cool/clear day) for the 15 amp branch circuits? And what is the output current rating of the GT inverter(s)?

    15 amp branch circuit seems a bit on the small side... Something closer to 20 amps (or more) may be a better idea (next time?).

    More or less, for solar/continuous current flow circuits--I would suggestion the NEC 1.25 derating for branch circuits:
    • 15 amp circuit * 1/1.25 = 12 amps max continuous current recommended
    • 15 amp GT inverter output * 1.25 NEC derate = 18.75 amps ~ 20 amp branch circuit recommended
    More or less, US/North American breakers are generally rated to not trip at below 80 % ( 0.80 = 1/1.25) of rated current... And are supposed to trip (minutes to hours) at >= 100% of rated current flow.

    If you are line tapped before the main panel... You need some good information from somebody very familiar with the NEC (or your local equivalent) code.

    In general, the cabling needs to be sized to be equal to, or greater than, the breakers... If you have a 200 Amp main breaker/disconnect, then you need a 200 Amp rated branch circuit to both the main house panel, and the solar sub-panel/main panel/first breaker (i.e., if you have just after the main breaker at 200 Amps, then connect to a second panel/breaker of 80 amps, then what follows down stream can be 80 amp rated cable.

    And the tap where you connect utility drop/main panel/solar panel needs to be rated for the total current of both the main panel service and the solar panel (i.e., if you have 200 Amp house panel + 80 amp solar sub-panel = 280 amps).

    In combined solar+main single panel, you are allowed to be 1.20x the rated current of the panel (i.e., a 200 amp panel * 1.20 = 240 Amps "total" load + GT solar)....

    Probably need a simple line drawing with cable AWG and "boxes" + GT solar inverter ratings to give a good answer to your question...

    And probably somebody with more NEC/code experience than I...

    Also, have you checked with your Utility? In many areas, GT systems over ~10 kWatt can have different requirements and rate plans...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cooker1967Cooker1967 Registered Users Posts: 12 ✭✭
    Just checked the amps coming from the breaker box and it's 21.4 amps at 5550 w.
    Maximum number of inverters per string is 7 and I have 5 inverters x 4 strings =14kw, per apsystems data sheet for yc600  
  • Cooker1967Cooker1967 Registered Users Posts: 12 ✭✭
    When I pulled the cover off the wire mgt box to check for amps I have 10 Guage from the inverters to the breaker box and 6 gauge from the breaker box to the cut-off switch don't know where I was getting 4 Guage from. 
  • Cooker1967Cooker1967 Registered Users Posts: 12 ✭✭
    OK so I have decided to not  touch any part of the 14 kw system.  I would have to run 30 ft of 1 inch conduit underground with three runs of #4 wire and pull all the old stuff out which would all void my install warranty.  Not worth it.
    I have decided to install a 100 amp sub panal on the adjacent wall as my 200 amp main panal which has one double space left.  The new 3kw solar will then feed into that.
    Any ideas or potential code violations that anyone can think of? 
  • BB.BB. Super Moderators, Administrators Posts: 28,993 admin
    Only thing to be careful of--You need to install the solar breaker pair at the opposite end of of the bus bars from the utility connection. (assuming a 200 amp rated box with 200 amp utility feed/main breaker).

    This is to prevent the bus bar in the main panel from carrying any more than 200 Amps anywhere on the bus bar.

    One question... Are you going to need any more breaker slots in the main panel (for tools, electric car, etc.)? At some point, you may want to look into adding on to your main panel.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cooker1967Cooker1967 Registered Users Posts: 12 ✭✭
    I have a electric car hooked up to my main 200 amp house panal which was my last slot.  What I'm thinking is pull that 50 amp breaker and use that position for the 100 breaker for the sub panal.  The only thing I will use the sub panal for is the car at 50 amp breaker (only draws 35 amps) and a 20 amp breaker for the 3 kw solar.  I looked up the specs on the two new micro inverters and each inverter has four  panal which I'm hooking up a 8 panals to two micro inverters, but you can hook up to four micro inverters to a string. The new sub panal will have #4 copper. 
  • Cooker1967Cooker1967 Registered Users Posts: 12 ✭✭
    That 50 amp breaker is on the bottom right second from the bottom. 
  • BB.BB. Super Moderators, Administrators Posts: 28,993 admin
    What will the sub panel be rated at (50+20=70 Amps minimum)?

    What insulation type will be the 4 AWG cable? Roughly, depending on insulation rated ~70 to 95 amps...

    And check with your local code jockeys... Some folks may have issues with mixing solar+load breakers in a single sub-panel.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cooker1967Cooker1967 Registered Users Posts: 12 ✭✭
    I was going to put a 100 amp 6 12 panal

  • Cooker1967Cooker1967 Registered Users Posts: 12 ✭✭
    Thanks BB. I WILL 
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