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Safe to rewire old system to higher voltage?

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  • Safe to rewire old system to higher voltage?

    I'm changing an old system from off-grid to grid-tied. The solar array had been wired in 10 parallel strings of 4 panels each, to feed fairly low voltage (82 Voc) to a charge controller for a 48v battery bank. To feed the new SMA sunnyboy 3.0 i need higher voltage. I'm all set to rewire into 2 strings of 20 panels each (410 Voc), and it just occurred to me that the panels may not be safe at that higher voltage. Without thinking about it i suppose that i'd been assuming that a system voltage up to 600v would be fine, but I don't know if that's true of these old panels.

    The panels are Photocomm, Inc Power Value PV-65 modules. I have a spec sheet that lists OC and MP voltages and current ratings, but there is no mention of max system voltage. The company doesn't appear to be around anymore. Should i be concerned about wiring these panels into 410v strings?

  • #2
    I'd be concerned. Older panels will be in poorer shape than new, some dirt, moisture and your voltage spec starts going down.
    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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    • #3
      Originally posted by TroySmith80 View Post
      Should i be concerned about wiring these panels into 410v strings?
      Possible. From the model number sounds like they are 65 watt panels made for 12 volt batteries (18 volts Vmp). They were never intended to be used for grid tied applications which can go as high as 1000 volts.

      Another issue you might run into, especially if you have to pull a permit and pass inspection, or if the POCO inspects the system before they connect you can fail the installation if they do not see a UL-1703 certification sticker.
      Last edited by Sunking; 04-08-2018, 12:33 AM.
      MSEE, PE

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      • #4
        No permits or inspections where i live, pretty sure the POCO (i assume that means power company) won't care either. This house is actually part of a sub-grid with several backfeeding systems on the same service drop. It'll just be adding a little more backfeed to a system that already has a lot of it. So really i'm just concerned with making sure it's a reasonably safe thing to do.

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        • #5
          Well, good news. I got some help on the roof and someone was able to read a label that stated max system voltage at 600v! Posting for resolution and future reference for anyone else searching, photocomm pv-65e panels (at least the ones we have) are rated for 600v.

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          • #6
            We also checked out wire condition and other aspects, things looked a little weathered, but still very much intact and confidence inspiring.

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