Enphase and a Generator

FatawanFatawan Solar Expert Posts: 71 ✭✭✭

Hello all-- I am an old member who installed my first system back in 2011. I am building a new house and planning my solar install. I already have 36 330W LG panels with integrated Enphase microinverters(bought pre-tariff). These will be installed on a standing seam metal roof. I had the walkthrough with my electrician today, and, to his credit, he said he had no experience integrating solar into his installs.The house will have a whole-house Kohler generator (~20kW). How should the transfer switch and Enphase output be wired to completely lock out the panels during a power outage? I keep reading about connecting on the utility side of the transfer switch on my side of meter, but what exactly does that entail? I'd like to describe the setup exactly to the electrician(or at least feign knowledge when I describe it). He and I drew out the setup but he really didn't have a solution that he could implement. Just to add another variable, I was planning to run the wiring from the roof down conduit to a Midnite Solar combiner box/disconnect switch.

Thanks for your input

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,625 admin

    The typical method would be to wire the Enphase output "upstream" amd the transfer switch (on the utility side) to the utility side main panel. The downstream side of the transfer switch is connected to a sub panel with all of your "protected loads" you want the genset to run...

    Or, you need to create a main panel (directly connected to your meter/utility service)--This is your "unprotected" breaker panel and may have only a few connections (meter power in, Enphase AC in at the "bottom of the panel" (other side of bus away from main breaker), and a "branch circuit" out to your transfer switch.

    And wire the output of the transfer switch to a sub-panel which will power all of your protected loads (or will look very much like a main panel if you are powering all of the branch circuits in your home).

    Remember that the first "main panel" connected to the meter has to be large enough to manage your 11,880 Watt array's AC output... Roughly:

    • 36 panels * 330 Watts per panel = 11,880 Watts
    • 11,880 Watts / 240 VAC = 49.5 amps of AC current
    • 49.5 Amps of continuous current * 1.25 NEC derating = 61.2 amps

    (note: you need to figure out the exact rating of your 36 Enphase units and they will probably be divided among 3x 20 amp branch circuits for 60 amps total or possibly 4--You need to check).

    If you have a 200 Amp main panel and 60 amps of solar, then the main panel will need a reduced main breaker (1.2x Main Panel rating to support solar branch circuits):

    • 200 Amp main panel * 1.2 solar 'uprate' = 240 Amp max in panel
    • 240 Amp rating - 60 amp solar = 180 Amp main breaker rating for panel (to utilty meter)

    You might want to think about wiring up a generator transfer switch "bypass switch" of some sort. Allows you to bypass the generator auto transfer switch (for service) and bypass to supply utility power directly to your protected load panel.

    This can be done with regular breakers and a generator interlock kit:

    https://duckduckgo.com/?q=generator+interlock+kit&atb=v122-1__&iax=images&ia=images&iai=http%3A%2F%2Fi.ebayimg.com%2Fimages%2Fi%2F172244594942-0-1%2Fs-l1000.jpg

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,799 ✭✭✭✭✭

    Wire the panels to the uitlity side of the generator transfer switch, not the generator side.

    Your electrician should know what that means

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • FatawanFatawan Solar Expert Posts: 71 ✭✭✭

    Bill--Thank you for the detailed explanation. I will forward that on to the electrician

    Mike--I have told him that, but he was having trouble coming up with exactly how to implement it.

  • BB.BB. Super Moderators, Administrators Posts: 30,625 admin

    More or less, you will probably end up with two main panels (and the associated expenses)... One connected to the meter (utility power). The second connected to the transfer switch AC output for the balance of your "protected" AC loads... Probably no way around that.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • garciajj74garciajj74 Registered Users Posts: 5 ✭✭
    Installing a generator myself soon But in my case I have the feed for the solar panels going through an 80 amp contactor so that they shut down at night. The Enphase micro inverters use power at night. In my case close to 4 Amps. So I installed a contactor controlled off a timer so the system shutsdown at night and restarts in the morning. I will run a sensing line from the emergency side of the Transfer switch and use a relay to open the contactor when the generator is running. 
  • BB.BB. Super Moderators, Administrators Posts: 30,625 admin
    Enphase should not use more than a 0.050 Watts (manual link) at night:

    https://www.solar-electric.com/lib/wind-sun/IQ7-7plus-7X-Micro-Manual.pdf (manual page 32, 50 mWatt night/tare losses)

    4 amps * 240 Volts = 960 Watts...

    That is pretty close to what an electric room heater consumes (900-1500 Watts or so).

    A typical relay based contractor may draw around 6 Watts, or ~100+ micro inverters should be drawing (0.050 Watts)

    I would wonder if something else is going on... How did you measure the 4 amp draw?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • garciajj74garciajj74 Registered Users Posts: 5 ✭✭
    I measured the amperage on the feed from the solar panels and on the utility side of my breaker panel. 
  • garciajj74garciajj74 Registered Users Posts: 5 ✭✭
    When I opened the solar panel breaker the Amperage I was reading on that phase would drop off of the utility phase as well.  It didn't make sense to me either that the panels were drawing so much at night.
  • BB.BB. Super Moderators, Administrators Posts: 30,625 admin
    In general, these should be connected to a double pole (ganged) 240 volt breaker.

    Was the one you cycled a single pole/120 VAC breaker? That would be the "wrong one" (usually).

    It is also possible there is something else connected (other load like HVAC or similar)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • garciajj74garciajj74 Registered Users Posts: 5 ✭✭
    It was a double Pole breaker. And I am a 100% sure that there is no additional loading on that circuit. I'm not sure if this makes a difference but 27 of my micro inverters  are of the older Enphase M215 and 10 micro inverters  are of the newer IQ7.
  • garciajj74garciajj74 Registered Users Posts: 5 ✭✭
    I live in New York and the way it is wired is directly from the solar panels it goes into a subpanel which in turn goes into a production meter then out to a fused disconnect then back in to the main panel. In my case when it comes back in from the fused disconnect I have it going to my contactor then back into the main panel.
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