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  • Shutting down solar panels

    I have to replace a damage connector on one of my solar panels . These are on a grid tied 5kw system
    i am thinking of covering all of the panels with black plastic to remove the DC power
    Will this work?
    Thanks for any help

  • #2
    No it won't work. For one thing just the light hitting the back side will be enough to
    maintain full system voltage. My own clamp on meter measurements of panels facing
    AWAY from the sun reveal current of some 10% of capacity. Opening any live connector
    will create a damaging and dangerous arc.

    Don't think that anything practical can 100% block the sun.

    Do your work in complete darkness, which is one reason there are so may 120VAC light
    outlets attached to my arrays. Bruce Roe

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    • #3
      Hi Bruce how does the tech guys repair these systems surely they dont wait until the middle of the night.

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      • #4
        Originally posted by bcroe View Post
        No it won't work. For one thing just the light hitting the back side will be enough to
        maintain full system voltage. My own clamp on meter measurements of panels facing
        AWAY from the sun reveal current of some 10% of capacity. Opening any live connector
        will create a damaging and dangerous arc.

        Don't think that anything practical can 100% block the sun.

        Do your work in complete darkness, which is one reason there are so may 120VAC light
        outlets attached to my arrays. Bruce Roe
        When my house was tented last winter, I turned off the array prior to tenting for personnel safety. After everyone was off the roof but before the house was gassed, I fired the system up and got no volt or current.

        I don't know how much voltage potential would be created by covering the front side of a panel but not covering the back side of a panel, but I'd agree it would probably be not be wise to chance it.

        As for facing panels away from the sun, of course you'll get output, and 10 % seems like a pretty likely number given that diffuse light which under clear skies can usually amount to somewhere between 10% and maybe up to 17 % of the measurable GHI, with about 1/3 to 1/2 or more of that diffuse irradiance coming from points other than from the general direction of the sun, that is, from all over the sky, not only from the direction of the sun. Matter of fact, under full cloud conditions, irradiance will come about equally from all directions under the sky hemisphere, and from what I've measured over the last 40+ years, it'll usually or often, at least to a 1st approx., be about 10 % or so of a full sun, pretty much regardless of the direction the measuring device or panel is pointing in.

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        • #5
          The daylight repair procedure is probably too dangerous for me to recommend to someone
          who needs to ask. Also puts equipment at extra risk. I don't know what the tech guys do
          and will not be endorsing whatever it is.

          A LOT of wiring work has been done here under the lights. Bruce Roe

          Comment


          • #6
            To do a daylight repair, as i understand it, you disconnect the AC. That forces the inverter into nearly brain dead shutdown. Then you use the DC disconnect at the inverter . Now no current flows, and MC4 can be opened. BUT you still have +400VDC in the wire to bite you. 400V will jump more of a gap than 240V. Lineman Gloves, a safety observer (to pull your ass off the roof if you get bit) and after the panels are disconnected into 90V strings, you can start troubleshooting the pieces, but don't measure amps, because you will arc burn the MC4's

            But most homeowners and non-solar electricians should /will not attempt this with +400VDC string inverters
            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

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            • #7
              Hold on but doesn't shutting down the power at the breaker box cut the arc completely? Surly a system of this scale will have a 'master' breaker box where all the panels form up into a single arc. So even if you're dealing with a small segment of the grid, you shouldn't be able to form a complete circuit if those panels have to form an arc through the master breaker switch. Or am I missing something here?

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              • #8
                Correction: I imagine a system like this in the manner one would a river with various orders and tributaries combining into a single primary conduit or wire. For each inverter you must have a single negative and positive electrode, which would form a complete circuit between it and every panel in the grid. With a breaker switch you disrupt that circuit, making it impossible to complete an arc... unless you tamper with the grid and form a circuit along a different string of panels.

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                • #9
                  Originally posted by Agincourt View Post
                  Correction: I imagine a system like this in the manner one would a river with various orders and tributaries combining into a single primary conduit or wire. For each inverter you must have a single negative and positive electrode, which would form a complete circuit between it and every panel in the grid. With a breaker switch you disrupt that circuit, making it impossible to complete an arc... unless you tamper with the grid and form a circuit along a different string of panels.
                  I do not believe the issue is on the AC or Grid side of the system but the DC voltage generated by the solar panels to the inverter. Even if you disconnect the AC side you still have voltage present on the DC side wires. Making contact with any of the DC wires while the panels are in the sun could result in an electrical shock. The higher voltage from a large series wired string may get to 600VDC which would be very dangerous.

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                  • #10
                    Who said anything about the AC side? I was referring to a breaker switch for the panels... or does no such thing usually exist for a system of this magnitude? All solar panels have to form a circuit which gets routed to a DC/AC inverter, therefore there should be a breaker switch which interrupts this DC circuit. Unless I'm missing something here this seems pretty straight forward. What happens to solar voltaic energy when it doesn't have anywhere to go? Or are there no switches that exist to safely break a >600VDC circuit?

                    Comment


                    • #11
                      Originally posted by Agincourt View Post
                      Who said anything about the AC side? I was referring to a breaker switch for the panels... or does no such thing usually exist for a system of this magnitude? All solar panels have to form a circuit which gets routed to a DC/AC inverter, therefore there should be a breaker switch which interrupts this DC circuit. Unless I'm missing something here this seems pretty straight forward. What happens to solar voltaic energy when it doesn't have anywhere to go? Or are there no switches that exist to safely break a >600VDC circuit?
                      Usually there is a DC switch at the inverter which will disconnect all DC voltage coming from the panels. The problem is that the wires between the solar panels and that switch will still be energized while the sun is up. That is why the NEC added the code to de-energize all DC wiring to within 10 feet of the panels so that no one came in contact with the DC voltage near the inverter.

                      There are both circuit breakers and disconnect switches that are rated up to 600V DC where they are designed to mitigate any flash when the circuit is opened. Sometimes it is worth installing them at each panel so that the voltage being disconnected is much lower than the entire string. It all depends on the accessibility to open those switches when needed.

                      Comment


                      • #12
                        Originally posted by Agincourt View Post
                        Who said anything about the AC side? I was referring to a breaker switch for the panels... or does no such thing usually exist for a system of this magnitude? All solar panels have to form a circuit which gets routed to a DC/AC inverter, therefore there should be a breaker switch which interrupts this DC circuit. Unless I'm missing something here this seems pretty straight forward. What happens to solar voltaic energy when it doesn't have anywhere to go? Or are there no switches that exist to safely break a >600VDC circuit?
                        To safely break a 500VDC circuit, you FIRST need to break the AC circuit, so that current in the HV DC is at a minimum. This helps preserve the life of the contacts and your life.

                        Not understand how this stuff works, kills people. 500VDC at 3A will ruin your day.

                        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

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