enphase calculation?

I am trying to find the amperage of this enphase array for wire size and breaker size:

system size: 23.25kw
total modules: 93 x 250w modules
inverters per branch: 14,13,14,13,14,13,12
Inverters: enphase 215 micro
Voltage: 3 phase 208v

Here is what I came up with.

(93 modules) x (1.1 max output amps) = 102.3 x 1.25= 127.8

* the 1.1 max output amps I got right off the micro inverter.

And another question: Why couldn't you do the system size of 23,250 / 208v x 1.25?

Thanks in advance!

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: enphase calculation?

    I am not an Enphase expert--But the maximum branch circuit an Enphase can be connected to is 20 amps @ 240 VAC (and probably 208 too).

    20 amps * 0.80 NEC derating / 1.1 amps = 14.5 (14) inverters maximum per 20 amp branch circuit

    The next question is you have 7 strings of inverters and a 208 VAC 3 phase main panel (?).

    If so, most utilities are very picky about their 3 phase loads and Grid Tied installations. Normally, you have to "balance" the solar power across all three phases equally.

    However, there are limits in the balance requirements... For example the utility may allow a maximum of 10 kWatt imbalance (before they charge you extra for the larger than allowed on standard service power imbalance).

    Also, a utility may require some sort of guarantee that if there is a single phase loss, that all phases of the solar power source need to be shut down. That may be a phase loss contactor or Enphase may have phase loss shutdown supported internally with their own hardware (I don't know--I do not install solar power).

    In the end, I am not quite sure of your question... You have 7x 20 amp circuits that need to be evenly split among 3 phase connections (2 strings per phase, and a third orphan that goes somewhere--following utility engineering instructions). At least for a "typical" (as I understand) installation.

    You do need to know about your AC Main Panel and the utility connection. There are "open delta" and (I think) "open Wye" feeds from the utility possible (and probably a dozen others that I have no clue even exist). That may affect how you distribute your strings on the various phases.

    Perhaps one of the installers with three phase and Enphase experience can give you some better information--I am a bit of out my depth here.

    You should be talking with the utility anyway--The will need to analyze their existing equipment and approve your solar install (before it is connected/turned on).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Mdsolar
    Mdsolar Registered Users Posts: 6
    Re: enphase calculation?

    I will also be tapping the line side service and not adding a breaker.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: enphase calculation?
    Mdsolar wrote: »
    I will also be tapping the line side service and not adding a breaker.

    I am not an electrician and don't work for a utility--But a Line Side tap usually requires the addition of a new meter+AC Main panel for connecting your loads (or in this case, the Enphase sources) to the utility network--Without having to add a new drop from the utility access point (pole/transformers/etc.).

    So the "not adding a breaker" does not really make sense to me... You would be adding a meter+main 3 phase breaker (or fuse) service entrance+7 branch circuit 20 amp breakers.

    When dealing with industrial installations--You pretty much cannot take anything for granted. A power engineer may be needed(?).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Mdsolar
    Mdsolar Registered Users Posts: 6
    Re: enphase calculation?

    Coming off the 800 amp mdp we would tap the line side and add a 200 amp Fused Disconnect. Next we would add a 200 amp Non fused Disco outside next to meter. From there we would install a 200 amp sub panel on the roof by the array. This is on top of a gas station.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: enphase calculation?

    Are you bringing down all three legs of the three phase power to the panel?

    Obviously, you know more about this than I do... So I am still a little confused about the details of your question and specifically what you are asking. Is the question regarding the current rating of the 3 phase feed (or split phase feed) to the panel with the Enphase connections?

    In California, there are a whole lot of issues with Solar and Commercial Billing (reservation charges, actual power generated, kVAR charges, etc.) which (many times) makes Solar GT not cost effective--And in some cases, actually raised the electric bills rather than reducing them. As well as questions regarding electrical panels (explosion rating or not) in gasoline stations. All interesting to me--But not anything I have ever worked with/on.

    There are some service stations around my area that have solar panels on the gas pump canopies.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Mdsolar
    Mdsolar Registered Users Posts: 6
    Re: enphase calculation?

    Yea I think California is way different than MD when it comes to solar. And the solar array is on the canopy. The sub panel is on the building roof. The panel will be 3 phase 208. And as far as electrical pipe/switchgear I have brought that to there attention that these might have to be explosion proof fittings and gear.
  • ARTsolar
    ARTsolar Registered Users Posts: 14 ✭✭
    Re: enphase calculation?

    I believe this is the formula you need for calculating your amperage per branch for your three phase system

    215W / 208V X the # of inverters / 1.732 = amperage

    Then multiply by 1.25 to determine your OCPD

    This is a link to the enphase commercial design guide that has this and other useful information laid out in it.

    http://enphase.com/wp-uploads/enphase.com/2011/08/Enphase-Application-Note-Commercial-System-Design-for-M215.pdf
  • Mdsolar
    Mdsolar Registered Users Posts: 6
    Re: enphase calculation?

    Thanks! That's what I was looking for. Anybody know what the 1.732 is you multiply by?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: enphase calculation?

    It is the sqrt(3) conversion factor from total equivalent single phase power/current spread out among the three phases.

    Reading the document link ARTsolar provided--Enphase has a 3 phase cable harness (5 wire, inverter connection connects single phase to each inverter, rotating phases every inverter). So you can put 24 inverter per 20 amp 3 phase branch circuit.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Mdsolar
    Mdsolar Registered Users Posts: 6
    Re: enphase calculation?

    Thank you guys. This def cleared things up for me. I had this system at 127 amps which was way over kill!