Grid tied microinverter bypass for emergency situations

Discussion in 'Off Grid Living' started by CaseIGL, May 24, 2013.

  1. CaseIGL

    CaseIGL Monkey

    Hi all,

    I just had a solar system installed on my home and I've been loving it so far. I don't have enough panels to cover all of my normal usage but it's cutting into my power bill pretty nicely.

    The system I had installed consists of microinverters on the roof that convert the DC from the panels to AC and then it joins into our home wiring at the breaker panel. There is no battery component to the solar install, although I was tempted for preparedness reasons. Doing so increases costs $8-12k and just doesn't make sense financially when that money could go towards other preps.

    I have my own homemade battery bank and inverters that I plug into transfer switches so I can run critical loads for 8-12 hours off batteries alone. I also have a portable generator that I can use to recharge this bank of batteries during the day. It works pretty well, but in a longer term outage I'd like to be able to tap into the solar panels as well, since fuel may be a concern.

    My "idea" is to create a temporary wiring bypass for my panels for use only during emergencies. I can unhook the panels from the microinverters very easily, they have twist lock MC4 connectors. My thinking is that I can hook up 4-6 of my easiest to reach panels on my roof to a junction box that lies on the roof and then run one nice sized cable from my roof to the garage and have a solar charge controller attached to my battery bank.

    Each panel pumps out around 150-225 watts (max 240). Being able to have 1kW of power all day would certainly help in a bad situation. I have a lot more panels but getting to the wiring would be more hassle than it would be worth unless it was looking really long term.

    I've been looking at prices on connectors and wiring and it looks like I can get all the supplies I would need for under $1000. I don't need a really fancy charge controller since it would be emergency use only. In fact it might be smart to have two cheaper ones, even. Obviously the goal is to have the materials on hand and ideally tested before something really bad were to happen. I'm thinking I would build, construct and test with the 4-6 panels in mind but have additional components to do more later.

    Just wondering if anyone else has done this? I need to dig in and figure safe wire gauge and the best way to wire the panels at the box (in series, parallel etc).
  2. BTPost

    BTPost Stumpy Old Fart,Deadman Walking, Snow Monkey Moderator

    I would look at getting in between the Panels and the MicroInverters, with a set of electrical TAPs, that would feed directly to a Diode Isolated, Combiner Box, up on the roof, as a Permanent Installation, rather than having to climb up there, and reconfigure things, each time you need to have Solar Charging for your Battery Bank. Then use some BIG wires to bring the output of the Diode Isolated, Combiner Box, down to the Battery Bank, and do so at the Highest Voltage, you can configure the Solar Panels, to deliver. Then you can use a QUALITY MPPT Charge Controller, (Outback Power Systems MX or FM Series) to charge whatever Battery Bank Buss voltage you might have at the time. The Outback stuff can be configured to charge any Battery Buss Voltage, you need. If you want the MicroInverters to feed the AC Buss, you just need to throw the AC Breaker, ON, in your Main AC Panel ,where they connect in, and if you want solar to the Battery Bank, you throw the AC Breaker, Off, and throw the DC Breaker ON, to the Input to the OutBack MPPT CC, and it will then put all the solar Power coming down the DC Feed, right into the Battery Bank. NO climbing, do hassles, and NO BS... Just two Breakers that are Mutually Exclusive ON, or OFF.
    Remember... Ohms Law E I2/R... so you want the highest DC voltage you can configure on the DC Wires coming off the Roof, as Higher voltage means Lower AMPs, for the same Power Level, and the Resistance of the Wires is fixed, by the wire size, so Higher Voltage means Less LOSS, in Heating the wires. Electrical Engineering 101... @TnAndy, @ghrit
  3. CaseIGL

    CaseIGL Monkey

    Thanks BT. Unfortunately I think I'm already past that point since I would have to take down a significant number of panels in order to gain access to all the wiring that's in place already. Honestly I see this as more of a once or twice in a lifetime type need. I'm talking a major earthquake or other disaster that results in power being down for weeks. I don't lose power enough to have invested the money to do it the right way, which your plan most certainly is!

    I guess I feel like I'd sleep better at night knowing I have a workable plan (however wonky) to leverage some of the power on my roof in that "bad" scenario (however remote the possibility actually is). Once something happens it'll be too late to have the stuff on hand. Outages of more than eight hours are rare here to begin with, so even in bigger event that was a few days long I wouldn't feel the need to get up on the roof. Only if it's clearly a broader disaster.
  4. ghrit

    ghrit Bad company Administrator Founding Member

    OK, I'll buy that. One takes the gamble, tho', that the once happens while you are nimble enough to climb up there and that you weren't injured in the event. Now is the time to do it right the (second) time. YMMV, uv cuss.
  5. CaseIGL

    CaseIGL Monkey

    Good point. I'm thinking as long as the complicated parts are already done there will be someone nimble enough around to get up there even if I'm not. I'm nimble enough to set it up in the first place, but that's not a bad idea thinking about someone else handling it. Putting some color coding on the wires when I put things together could go a long way towards having my son or someone else do the roof part. Red to red, yellow to yellow, etc!
  6. TnAndy

    TnAndy Senior Member Founding Member

    Some issues I see:

    1. MC4 connectors aren't twist lock....they are plug in and lock. You need a special tool to unlock them. The previous MC3 connectors could be pulled apart with no tools. Also, you DO NOT want to connect or disconnect under load, you may get a real arc doing this. I'm surprised you can get to ANY of the connections, since most of the time they are tucked well up under the panel at the microinverter.

    2. Your panel voltage will be a real issue. Probably they are a voltage a cheap charge controller can't handle.....most likely your panels are in the 30 something volt range.

    In the "olden days", you bought 17-18v panels for a 12v based system, and charge controllers we 12v based. You will probably have to buy a decent ( read that as NOT cheap ) MPPT charge controller to drop your panel voltage down to something your battery bank can use.

    I don't think there IS a cheap and easy solution to what you want to do.

    My system is a "hybrid hybrid" ahahahaaaaa.....the first 30 panels run to 3 Outback charge controllers, a battery bank, and a pair of grid tie grid tie inverters that produce true 240vAC. Now the sweet thing about Outback GTFX series inverters is when the grid goes down, the grid contact open ( stopping flow to the grid, in compliance with UL 1741 standards on "islanding" ), but ANOTHER set of contacts close, and you get the power where you want a transfer switch.

    OK, my NEXT set of 10 panels ( to be followed by 10 more in a few weeks ), I used the Enphase microinverters like you have, and tied them directly to the grid....going strictly for reduction of power bill. Of course, like you, if the grid goes down, there goes about 1/4 of my power production.....which I've finally gotten up to around 800-900kw/hrs/month.

    SO, my work-around is this, should the grid go down and not look like it's coming back for a LONG time. I'll disconnect the wiring from the Enphase 10, and route it to the off grid contact side of the Outback inverter....fooling the Enphase inverters into "thinking" they ARE still grid tied....and thus they would run ( Actually tried this with one panel and inverter as a works, even though Enphase says it won't and nobody will recommend it...I understand....they are C-T-A )
    Cruisin Sloth and BTPost like this.
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