Upgrading Panel For solar

Batikikik
Batikikik Solar Expert Posts: 141 ✭✭✭✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
Have you ever guys install soalr system with 100amp main ???
And what is the importance of upgrading main from 100 to 200 amp??
I have seen a lot of installation with 100amp panelboard, but I have never done it myself.
Your opinions and suggestions ?
Thank you
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Comments

  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #2
    Re: Upgrading Panel For solar

    The importance is the NEC rule that allows you to connect feed breakers of up to 120% of the panel's rating.

    So, if you have a 100a rated main panel, with a 100a main disconnect breaker from the utility - the most you can add from the solar would another 20a breaker.

    But that breaker has to be rated 125% of the load it services, so the max solar you can actually feed into a 100a panel with a 100a utility disconnect breaker and a 20a solar disconnect breaker would be 16a.
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  • Batikikik
    Batikikik Solar Expert Posts: 141 ✭✭✭✭✭
    #3
    Re: Upgrading Panel For solar

    It means you can install array not more than 2 strings ?
    lets say 2 strings of 13panels , total26 each I short circuit is 7.62A
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  • Batikikik
    Batikikik Solar Expert Posts: 141 ✭✭✭✭✭
    #4
    Re: Upgrading Panel For solar

    SUNNY BOY SB6000US user guide shows me that I have to put 50A breaker.
    But if I have 2 strings of 13 and output current rating is 7,62A*2=15,3 It means I can put 15,3*1.25=20A Breaker ....
    So which way is right ?
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #5
    Re: Upgrading Panel For solar

    It means that the maximum amperage you can feed into a 100a panel that has a 100a utility breaker is 16a of AC (FROM the inverter).
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #6
    Re: Upgrading Panel For solar

    No, this based on the AC circuit capacity

    240 vac x 16 amp = 3,480 watts inverter output maximum.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #7
    Re: Upgrading Panel For solar
    Batikikik wrote: »
    SUNNY BOY SB6000US user guide shows me that I have to put 50A breaker.

    For a panel rated at 200a, the 120% rule would allow you to install a feed breaker from the solar of UP TO 40a.

    To legally put in a 50a breaker, you would either have to upgrade the panel, or remove the 200a utillity breaker and replace it with something smaller - say 180a.

    For a 100a panel - to add a 50a breaker for feed in from inverter, you would have to downgrade the utility feed breaker to a 50a.
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  • Batikikik
    Batikikik Solar Expert Posts: 141 ✭✭✭✭✭
    #8
    Re: Upgrading Panel For solar

    I always do upgrading 100amp panel before install any solar system , because I am sure even you can install and hook solar to 100amp panel is not good. Much better for solar system has 200amp main
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  • Batikikik
    Batikikik Solar Expert Posts: 141 ✭✭✭✭✭
    #9
    Re: Upgrading Panel For solar

    In Sunny Boy inverter guide it tells maximum output current for SB6000us is 25 AMP..
    But tthis rating is max ,how can you determine without measurement actually current output?
    thank you
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #10
    Re: Upgrading Panel For solar

    The two limits are Inverter's current limit and the second is the limit of the ability of the solar panels to produce electricity...

    Problem is that solar panels do not have an accurate power limit... If I was being real code type person... 1.25 NEC derating factor and 1.25 solar derating factor used by NEC for solar arrays (and that is Isc, which is 10% or so over Imp). That is 1.56x rated power or only loading solar panels to 64% of circuit rating * another ~90% which gives us ~58% of circuit rating for solar panel's "soft" power/current limit...

    Then you can get into the fact that Inverters are "constant power" devices... Is the service around 240-250 VAC, or is the service voltage closer to 220 VAC (very rough back of the envelope calculation):
    • 16 amp (of 20 amp service) * 220 VAC * 1/1.25 solar derating * 0.90 Isc derating = 2,534 watts of solar panels
    So, for a 20 amp circuit, would NEC deratings get you down to ~2.5 kW of solar panels to meet the intent of NEC for current limits (that are below the GT Inverter's Listed "hard" current limits)?

    -Bill :confused: B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #11
    Re: Upgrading Panel For solar
    Batikikik wrote: »
    In Sunny Boy inverter guide it tells maximum output current for SB6000us is 25 AMP..
    But tthis rating is max ,how can you determine without measurement actually current output?
    thank you
    It doesn't matter.

    If you really want to install a smaller breaker than the inverter calls for, you have to very carefully measure what you expect your max current to be - and be prepared to explain to the inspector why you are undersizing the breaker.

    100A panel/main breaker is fine if you aren't installing more than 3840W AC of PV. Using STC DC ratings you'd be good for well over 4000W STC of PV.

    Example: Enphase M190 inverters each will push 0.8A 240V max. 20 of them will push 16A max. You can use 230W STC panels without issue with the inverters - there are even a couple 250W panels you could use if you really wanted - that would get you 5kW of PV on the roof on a 100A panel without any issues.

    Would a larger panel be "better"? Sure - but panel upgrades can be costly so why do it if the existing panel is sufficient?
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  • Batikikik
    Batikikik Solar Expert Posts: 141 ✭✭✭✭✭
    #12
    Re: Upgrading Panel For solar

    drees I am gonna use 26 panels each 225watt and one inverter sb6000us
    And I do upgrading of panel , because i think 5850W requires 200amp panel.
    Inverter input is 15,2A(2 strings) inverter output max is 25 A(but it is max it is not actually the rating) .what do you thing ??
    I think only way to know is measuring with tool , because I tried to do it with formula
    As an inverter is transformer I tried this foruma Iinput*Uinput=Ioutput*Uoutput
    But it doesnot work , so only way is to measure
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #13
    Re: Upgrading Panel For solar

    I am not quite following your last post... Solar power is so variable--You cannot use "marketing/nominal" ratings as "safety" points... Only the current limit of the inverter and those of breakers/fuses are accurate enough to use without adding huge derating fudge factors for solar PV system energy.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #14
    Re: Upgrading Panel For solar

    If the inverter max output is 25A, I believe you are stuck and have to protect it with a 35A breaker at minimum. The spec sheet indicates that a 50A breaker is the maximum OCD device rating. I suspect that most installs end up using a 40A breaker for these inverters as that is the next commonly available OCD device above 125% of 25A (35A breaker are not common).

    There is no way you'd get away with a 20A breaker on this inverter with 5.8kW of panels hooked up to it. The breaker would likely trip nearly every day.

    Panel size doesn't matter - NEC simply states that when backfeeding PV the total size of the OCD devices feeding the main panel may not exceed 120% of the panels rating - bigger panels just make it easier to meet this requirement.

    If you have a 100A panel and install a 40A PV backfeed breaker - then you'd have to downsize the main breaker to 80A to be legal. Yes - a 200A panel makes it a lot easier if you are going to install anything more than 20A of PV.


    It sounds like you are trying to do these installs for a business - but it also sounds like you have had little training in the basics of PV installation and electrical work - are you sure you know what you are doing?
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  • Batikikik
    Batikikik Solar Expert Posts: 141 ✭✭✭✭✭
    #15
    Re: Upgrading Panel For solar

    Yes. thank you for posts
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