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  • Solar Panels on Boathouse Roof

    Looking for a little guidance!

    I'm planning to install solar panels on my floating boathouse roof at my off-grid cabin. DIY project into a second charge controller of an existing system. 6 panels, roughly 1750W total.

    A couple questions have come up because of this

    1) What should I ground the panel frames to? Into a ground rod in the lake? Should this be bonded to the main cabin ground (probably 100 ft away)

    2) All those articles about electric shock drowning got me thinking. Open Circuit voltage of three panels in series is almost 120V DC. If power from the shore TO the boathouse (AC from the inverter) runs through a GFI, is there something similar for the DC circuit from the panels to the shore. Or am I overthinking?

    Thanks

  • #2
    nautiqueskier,

    If I understand you correctly.....you want to add a few more panels to an existing system at your cabin using an additional charge controller for the new panels connecting to the existing batteries.

    Yes the panels should be grounded close to the panel array. Ground rod in the lake would work fine. Are you in a lightening strike area? If so this wire should be 6 ga. bare copper with no sharp bends. A minimum of 8" or so radaii on any bend as lightening is high frequency and will jump off bends. The other reason to ground here is panel fault, I.e. a shorted wire or panel. Personally I would bond it to the the main ground rod as well. If you are running the DC panel output in buried PVC conduit I would use 6 ga bare coppper buried along side the conduit. This serves as an excellent ground in itself.

    On the issue of DC GFCI's , normally the whole system is protected by one DC GFCI, this requires that battery negative not to be grounded. I do not think that a DC GFCI for the panels only will work properly if the rest of the system is grounded as the DC GFCI will fault. DC GFCI 's are way more complicated than AC ones. It's not at all like an AC GFCI, most consist of ganged DC breakers with a trip breaker...I.e. two DC feed breakers ganged with a 1 amp trip breaker. Both positive and negative cannot be grounded. Read the posts from other posters on this issue.

    I do not use DC GFCI on my systems even though it is built in my controllers.
    It causes issues with monotoring equipment such as an Internet connection for monitoring.

    please do post a bit more info on the type af charge controller used including make, model, batteries, inverter used, and the existing grounding arrangements and maybe a bit on the loads. This will help others to advise the best course to take on this.

    david
    Last edited by Tecnodave; 05-28-2019, 08:45 AM.

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    • #3
      Thanks for the help.

      Yes additional panels to an existing system. The other panels (1200W total) are on the roof of the cabin, again probably 100 feet away from where these new panels are going. The existing panels are grounded separately, 6ga bare copper, need to check but don't believe this ground is bonded to the ground plate used for the rest of the system. And this ground is nowhere near the new panels.

      Charge Controller is two Flexmax 80s
      Inverter is an Outback VFXR3524
      12 2V batteries in series for 24V. Will look up Ah.

      Current solar output averages 2kWh / day in summer. Forested area so don't get sun all day. One of the reasons for panels in new location is to capture sun at different time of day. Working with the landscape, as we're on a hill.

      Loads vary. In the summer, Battery Monitor indicates draw when we're away is on average 1.6kWh / day. When we're there, generator is running extensively for high wattage tools and appliances we have.

      Wouldn't say a lightning strike area, probably have lightning every couple years. Guess it only takes once though.

      I do have a GFPD but even tripped, it wouldn't stop the current from a short at the boathouse near the water, it would just isolate it from the rest of the system.
      Last edited by nautiqueskier; 05-28-2019, 10:47 AM.

      Comment


      • #4
        Does the Flexmax have built in GFCI and AFCI, not sure on that. I'm a Classic User. On my Classic's it would trip the built in GFCI, but not sure on the Flexmax, same folks designed both those controllers. but to be sure listen for a response from a Flexmax user. I'm pretty sure that for the GFCI to correctly detect a fault at the boathouse array you could not ground the array at the boathouse or use bare copper back to the controller location for the GFCI to work correctly all grounds must go back to the common ground point, then trough the GFPD. The problem with that arrangement is that you invite lightening up to your house. I would tend to avoid that.

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        • #5
          I had to think on that for a bit as I do not like how the NEC addresses the issue of DC GFCI. You should be grounding the frames of the panels at the boathouse only to a local ground, run the positive and negative wires to the controller , since both controllers are on the same system the GFPD will shut down the system when a fault occurs at the boathouse. In this case it might be more correct to call the ground wire "a lightening down conductor" . You do pose a though question there.

          I do think that the GFPD will shut down the system, but then again I'm not sure how Outback does their GFCI, I think it is external to the controller

          I would really like to hear more posts on this issue.

          EDIT: This may be where a GFPD or GFCI will not protect you, it shuts down the system but the panels still would have voltage on them. Only the ground rod would.
          Last edited by Tecnodave; 05-28-2019, 12:44 PM.

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          • #6
            Grounding is a sketchy area in the NEC, because it (NEC) does have some practices that seem "dated" or not in good sense.

            If it was my install, I'd do as tecnodave suggested, ground the mounting hardware at the dock, and run the HV-DC in conduit, maybe using UG feeder wire in the conduit, because we all know underground conduit never cracks or leaks.
            Powerfab top of pole PV mount (2) | 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

            Comment


            • #7
              Mike,

              I have seen sealed nitrogen pressurized conduit with pressure guages and monitoring equipment in communications equipment rooms containing data cables in law enforcement networks

              Comment


              • #8
                Originally posted by Tecnodave View Post
                Mike,

                I have seen sealed nitrogen pressurized conduit with pressure guages and monitoring equipment in communications equipment rooms containing data cables in law enforcement networks
                Yep, that's for leak checking. or mostly for the antenna cable conduit. They use a tiny bit of pressure to keep out water (really bad news in antenna or data cables).
                Some antenna hardline cables are pressurized coax, using nitrogen at one or two PSI, to keep the cable dry and lossless. At 50Kw, your loss shows up as melted parts.
                Powerfab top of pole PV mount (2) | 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

                Comment


                • #9
                  Alright I'll ground the frame at the boathouse. Tecnodave, you think not bonded to the cabin ground?

                  And yes, Outback's GFPD is external. Agree in this case think it'd just protect the system. Problem as I see it would only be if there was a short to the panel frame (which would now be grounded to the lake) and a ground fault in the wiring before the GFPD, which could result in current through the water (I think, not sure) and nothing would trip.

                  Thanks for everyone's thoughts on this

                  Comment


                  • #10
                    EDIT.....on reflecting a bit more on this issue.....read next post..

                    Yes I think not bonded at cabin ground. Lightening does funny things, I thing that the GFPD will "see" the short to ground at the dock and shut down the controllers but the voltage will still be flowing through the fault. That would need to be corrected before the GFPD will allow system restart

                    On AC feeding an outbuilding here in California the inspectors will want what I had first suggested bonding both ground rods togather but this is a bit different. I have been asked by inspectors here to bury the uninsulated grounding wire down 24 inches bonding two ground rods. But that was on a house feeding an outbuilding that had been built in thr '30 on concrete rubble. I pretzeled 8 ground rods trying to get one under the POCO meter, first ground rod was 8-9 feet away from meter, second one 15 feet further at outbuildings, big concrete chunks down 3 feet, could not remove. Inspector requested buried ground rods bonded together,
                    Last edited by Tecnodave; 05-30-2019, 09:19 AM.

                    Comment


                    • #11
                      And on rethinking the issue, my first answer is in line with the NEC, ground the panels to a local ground rod, bond that ground rod to the main system ground rod, and run that bond outside the conduit as bare 6 ga solid copper to give any lightening strike a better path to earth and not coupled to the DC output.

                      One of of the issues with the NEC is that it is printed and distributed one way but in the code it states "when in dought , refer to the AHJ" , unfortunately building inspectors are often clueless as to the issues.

                      So yes bond both grounds as that is what the NEC wants, but how does your local AHJ interpert that?

                      in any case the connection has to be at the main ground rod, not at the common neutral or ground connection as in some GFCI or GFPD installations

                      if if there were a short at the array the GFPD should shut down the system and would not allow startup until the fault is cleared.

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