Using Y connector to connect grid tie and charger controller

Burt
Burt Registered Users Posts: 2
in Off Grid Solar & Battery Systems #1
I have 6 solar panels connected to Enphase M215 inverters. When the grid power goes down, I want to switch the panels over to charge the battery bank. I was wondering if I could connect a Y to the MC4 on the back of the panels and run 10 gauge wires to a charger controller.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Using Y connector to connect grid tie and charger controller

    I don't see any practical/easy/safe way to do that. The Enphase do not lend themselves well to temporary solar panel rewiring (you can sometimes do that with "central" GT inverters because you have to bring the DC array wiring down to the GT inverter anyway. So it is possible to match a charge controller and some switches to the DC array (disconnect the GT inverter).

    Your only choices are to 1) setup an Off Grid Inverter designed to be "back driven" (AC direct connect) to the GT inverter output (it turns out that AC off grid inverters can be bi-directional and you can actually pump power from a GT inverter "backwards" through the Off Grid inverter and actually recharge your battery bank). Or 2) setup an entirely separate Off Grid Array and Off Grid inverter system + Battery bank + Solar charge controller.

    # 1) will work but requires some more technical discussions. # 2) is usually easier and a better system overall (and may be cheaper)... However it does leave you with "dead solar panels" during a power outage.

    There are other options, but they all will take a fair amount of work and cost you money (such as strip out the Enphase inverters and install a "hybrid" battery based inverter system that can do both Grid Tied and Off Grid power--Or there is a new SMA inverter that can run GT or provide "some" AC power when the sun is up for limited AC backup power (no backup battery bank needed).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Using Y connector to connect grid tie and charger controller

    Welcome to the forum.

    There may be an issue with having the two MPPT type inputs tied together all the time; the electronics on one may "fool" the other due to leakage across components and cause it to pick a wrong power point.

    What's more I'm sure we've discussed this before around here but can't seem to find that thread. I don't recall if anyone actually went ahead and tried it to see if the interference was severe enough to be troublesome.

    Best case is to break the connection from one unit to the other entirely. Second best would be to have the charge controller disconnected when the Enphase is working, as the CC will try to be active all the time with battery on its output and PV on its input. If you disconnect the PV from it then its electronics can't interfere with the micro-inverter's. Then when the grid goes down the GTI should also shut down entirely and so its input components shouldn't cause trouble with the charge controller.

    Er, was that clear enough?

    A couple of other things: you would only be able to have one panel on the controller with a constant connection otherwise the input of all the micro-inverters would be coupled and you don't want that; they aren't meant to work that way (a dozen GTI's + one charge controller all coupled on input? Not likely successful). If you separate them you can couple all the panel outputs only when needed to power the controller.

    Also, be sure the battery-based inverter does not have it's AC out connected to the micro-inverter(s) unless it is specifically set-up for AC coupling, in which case you would not need to tap the PV to provide charging.

    In fact using an inverter like the Sunny Island and just AC coupling the GTI output to it would be the shortest route to success, but expensive and somewhat complex (SI is about $5,000 and there is Voltage incompatibility as it is 120 VAC and the Enphase is 240 - but it could be done).

    There: confused enough yet? :p
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