Newbie with a question please.

OK,

So I have a china version 250w grid tie inverter and it is hooked up directly to the breaker box and it works fine, Also, I have 600watts of sloar panels going to a combiner box then going to the inverter.

My question is:

How to I stack the inverters so that I have 2 of them running together into the breaker box.

Do I go on the DC side red to red and black to black so that BOTH inverters recognize the solar panels in the combiner box?

If so, then what do I do with the opssite side? Do each inverter have to go individually to a breaker or do they somehow tie in together?


Thank you

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Newbie with a question please.

    First, get the normal warning out of the way... Installing Grid Tied inverters without UL/NRTL listings, without building permits, and without utility approval is usually against the law in most places. The utility can disconnect your power and the local town/county could red tag your home. Also, many of the newer utility meters may not turn backwards, and some even will turn forward when you are sending power to the grid (i.e., charge you retail rates for generating power). Also, many new meters can report back to the utility that you are generating power. All as part of revenue protection (people wiring meter backwards, etc.).

    The reason for NEC code, NRTL listing services, and licensed electricians/professional engineers/etc. is to reduce the risk of fire/danger in your home.

    And the answer, Grid Tied inverters are synchronized with the grid--So, you would keep adding GT inverters in parallel to your dedicated circuit up to the rating of the circuit breaker:
    • 15 amp breaker * 120 VAC * 0.80 NEC derating = 1,440 watts maximum input from GT inverters on 15 amp circuit
    • 15 amp * 0.80 derating = 12 amps max continuous current on 15 amp branch circuit
    Good luck and be safe.

    -Bill

    PS: Just to add clarification, each GT inverter should have its own array. Usually they will not play together well if you have several GT inverters connected to one solar array. You only parallel their outputs to the home wiring/utility grid (following good design and code requirements).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Newbie with a question please.

    Thank you Bill,

    Yea I am aware of all the legals, My utility company is fully aware that I am on solar (offgrid) and have left several messages with them that I am going ongrid. My meter DOES spin backwards so no prob. there (I watched it as well)

    When you say parallel how exactually do I do that?

    red to red black to black ( on dc side of inverter)?

    and on the other side where the 1st inverter goes to the breaker box what would I do? Run it independiatly to the box as well?
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Newbie with a question please.

    Do not parallel the GT inverters on their DC input side.... They actively control the current and voltage from the solar panel/array (Maximum Power Point Tracking). The algorithms from one inverter doing a I*V test of the array will confuse other attached inverters.

    Just max out the array for each inverter (single array for a single inverter DC input).

    Then simply connect the AC side of the GT inverter to the AC branch circuit (more or less, just like attaching any other loads using L1/L2/Neutral if a 120/240 VAC split phase circuit or just using L1 and Neutral if a 120 VAC branch circuit).

    In your case, if using 600 watt GT inverters on 15 amp 120 VAC circuits, then two inverters in parallel on one 120 VAC 15 amp circuit would be the safe limit (assuming GT inverters meet the NEC/NRTL operating requirements).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Newbie with a question please.

    So then if i understand it correctly.

    I will run each inverter to its OWN SEPERATE array and on the output side they will run separate to the breaker box where they will both be wired into seperate screws in the double pole breaker right? Thanks
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Newbie with a question please.

    Yes, but you could wire 2x 600 watt GT inverters to the same breaker as they both would be under the 15 amp current limit when they are both outputting maximum power.

    You only need separate breakers when you exceed 80% of the rated branch circuit capacity (at 100% of branch capacity, breakers are supposed to eventually trip--minutes to hours or more). 80% is considered the "design" maximum current of a branch circuit. Or, another way of looking at it, you need to design the branch circuit to be 1/0.8 or 1.25x larger than your maximum sustained current.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Newbie with a question please.

    so technically i can run 4 seperate 250w inverters to the 30amp double pole breaker since 2 divided by 30 is 15amp each side so then that would be right right?
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Newbie with a question please.

    Ummm.... First, I assume these are 250 Watt 120 VAC GT Inverters? And you are talking about a 30 Amp 120/240 VAC split phase breaker?

    Second, you need to review the specifications of your GT Inverters. They should tell you the maximum sized circuit that they can be connected to. For example they may say 15 amp @ 120 VAC or 20 amp @ 120 VAC, or 20 amp @240 VAC, etc.

    I would assume that your GT inverters are 120 VAC units and sized for either a 15 amp or 20 amp maximum branch circuit. In the US, NEC normally requires:
    • 15 amp circuit requires 14 awg minimum
    • 20 amp circuit requires 12 awg minimum
    • 30 amp circuit requires 10 awg minimum
    But there are other issues too. Maximum operating temperature, type of insulation, fill factor in conduit, and any local code requirements (the city I grew up in requires 12 AWG wire minimum for all household circuits--an expensive pain in the behind).

    Remember that circuit breakers are part of a layered protection scheme... The circuit breaker is to protect all down stream wiring and attached devices from overheating/fire (reduce the chances of harm/failure).

    If you have a 30 amp breaker, then you need to run a minimum of 10 awg (properly rated) cable from the breaker to all loads/outlets/attachment points. You should not attach, for example, a 14 awg wire from your 30 amp breaker to a 250 watt GT inverter... Yes, the inverter will not overheat the 14 awg wire, but if there is a fault somewhere (or somebody else adds 10 more 250 watt GT inverters), the 30 amp breaker cannot protect the 14 awg wire and you could get a fire.

    Current NEC books/code have sections that list the requirements for Grid Tied Solar PV systems... Also, similar requirements are needed for the DC side of the wiring system too (correctly sized and rated wiring, possibly UV/outdoor rated, and possibly fuses/breakers depending on solar array configuration). There are also DC and AC disconnect requirements (many are locally defined by building departments and utilities).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Newbie with a question please.
    and have left several messages with them that I am going ongrid. My meter DOES spin backwards so no prob. there (I watched it as well)

    Personally,, I don't think "leaving the utility a message" constitutes good practice! The utility "being aware" that you are off grid, does not connote approval of going "grid tie". I think if you do be a bit more involved/proactive getting your grid tie system signed off by the utility and your insurance. You may not care if you have valid insurance, but clearly the utility has a legitimate interest to ensure that your system is safe, since it is now tied to their system, and any potential fault could damage their equipment or injure their workers.

    Icarus
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