Micro inverter install - is it really that simple?

DonM
DonM Registered Users Posts: 4
in PV Installers Forum - NEC, Wiring, Installation #1
I am looking at installing a system using Enphase M215 inverters. Looking at their installation sheets, it appears to be just wiring their cable to a 2 pole 20 breaker in the main panel. Is it really that simple? Other then NEC & other building code issues, is there no other requirements for equipment to grid-tie into PG&E?

Don M
Mariposa, CA
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #2
    Re: Micro inverter install - is it really that simple?
    DonM wrote: »
    I am looking at installing a system using Enphase M215 inverters. Looking at their installation sheets, it appears to be just wiring their cable to a 2 pole 20 breaker in the main panel. Is it really that simple? Other then NEC & other building code issues, is there no other requirements for equipment to grid-tie into PG&E?

    Don M
    Mariposa, CA
    Well, of course you have the paperwork issue to deal with - interconnect agreement and whatever permits you need, but yes, microinverter systems are electrically very simple to implement. Up to a point in size you just daisy chain the inverters and connect the last one in line to a breaker in your service panel. For larger systems you'll either need to have an AC combiner or multiple backfed breakers in your service panel (depending on the whim of your AHJ) up to the 120% rule.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #3
    Re: Micro inverter install - is it really that simple?

    usually they will want a separate disconnect for the solar back-feed that is external to the panel and may want separate meter as well but all that should be available from PG&E and you AHJ. Each AHJ may have differing requirements for the AC run off the roof.
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  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    #4
    Re: Micro inverter install - is it really that simple?

    solar_dave is correct, there may be some requirements for AC disconnects. Your AHJ may require one on the roof.

    PG&E's requirement is as follows.
    -If your meter is accessible to their linemen from outside the property 24/7, no disconnect required.
    -If the meter is not accessible, you have two options
    a) install a disconnect that is accessible 24/7
    b) provide a key to whatever doors and/or gates block access to the meter. They will put the key in a lockbox on your property (like realtors do), and their linemen will be able to open the lockbox (with a key).

    The only other thing that you might not consider to be "really that simple" is bringing your grounding electrode system up to code and making the irreversible splice between it and your solar GEC. But there are no other equipment requirements.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #5
    Re: Micro inverter install - is it really that simple?

    Also there is mounting restrictions in my locale. One must provide a 3 foot clearance to the peak of the roof line for the fire department to be able to vent the roof in case of fire. Also my AHJ requires an engineers sign off for the added roof load (showing the calculations) and the electrical drawings. Now my AHJ seems to be some of the toughest around, in fact the structural inspector came and inspected the mounting to confirm it was as drawn. The electrical inspector red tagged my system twice before approving it, mostly for ground connection issues (pretty much kind of silly stuff like the electrician put 2 wires in a single grounding lug and one box didn't have a grounding lug bar installed, just a single screw).
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  • DonM
    DonM Registered Users Posts: 4
    #6
    Re: Micro inverter install - is it really that simple?

    Sorry - AHJ??? Don't know that acronym. This is Mariposa County - near Yosemite - and things are pretty behind the times and loose as far as the county building department goes.

    Meter is accessable at side of road. System will be ground mounted and connected to a 100A (just in case) sub-panel at the mounting location. I'm thinking 3 strings of 17 (250 - 270W ) panels ought to about cover 75% +/- of our 1K KWH/Month needs. New construction (first occupied 1 year ago) of my own design and only part time (50 - 60%) occupancy for another 2 years plus we are still building out the outside - like added a spa in August, so it is a little hard to get the true demand but it is looking at between 800 - 1200 KWH per month.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #7
    Re: Micro inverter install - is it really that simple?
    DonM wrote: »
    Sorry - AHJ??? Don't know that acronym.


    Since the names (and location within the local, county or state government structure) for the group that does the inspections and permits and enforces the relevant codes varies from place to place, we just say "Agency Having Jurisidiction" or AHJ. You figure out who that is for you. :-)
    SMA SB 3000, old BP panels.
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  • DonM
    DonM Registered Users Posts: 4
    #8
    Re: Micro inverter install - is it really that simple?
    inetdog wrote: »
    Since the names (and location within the local, county or state government structure) for the group that does the inspections and permits and enforces the relevant codes varies from place to place, we just say "Agency Having Jurisidiction" or AHJ. You figure out who that is for you. :-)
    Thanks - I knew it had to be someting like that - I just couldn't put the words to the letters. Judging by the issues I had building the house - they should be the least of my problems. A friend has already permitted (after construction) the ground support structure for 2 similar sized systems (using SMA and a string of panels) on his property and I'm just going to copy his application for the structural part and modify the electrical as needed. It's all the same inspector for the most part... usually the head of the department. Nice guy.
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  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    #9
    Re: Micro inverter install - is it really that simple?
    DonM wrote: »
    I'm thinking 3 strings of 17 (250 - 270W ) panels ought to about cover 75% +/- of our 1K KWH/Month needs.... it is a little hard to get the true demand but it is looking at between 800 - 1200 KWH per month.

    A rough estimate is that 51 panels at only 250 watts will produce almost 140% of your stated need. Unless you have very poor performance due to lots of shading. I think you could probably go with two circuits of 17 (or less) and add more later if you find it's not enough.

    Do you know about PV Watts? http://rredc.nrel.gov/solar/calculators/pvwatts/version1/
    I suggest using it to estimate if your system sizing is in the right ballpark.
    System will be ground mounted and connected to a 100A (just in case) sub-panel at the mounting location.

    A 100A subpanel is actually going to be about the bare minimum "AC combiner" for the size system you have in mind.
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  • DonM
    DonM Registered Users Posts: 4
    #10
    Re: Micro inverter install - is it really that simple?
    jaggedben wrote: »
    A rough estimate is that 51 panels at only 250 watts will produce almost 140% of your stated need. Unless you have very poor performance due to lots of shading. I think you could probably go with two circuits of 17 (or less) and add more later if you find it's not enough.

    That's my plan - but I am going to build the support structure for 51.

    Do you know about PV Watts? http://rredc.nrel.gov/solar/calculators/pvwatts/version1/
    I suggest using it to estimate if your system sizing is in the right ballpark.



    A 100A subpanel is actually going to be about the bare minimum "AC combiner" for the size system you have in mind.

    Thank's - I'll check it out - and I just happen to have a 100 panel hanging around.
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