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  • #16
    Originally posted by SunEagle View Post
    Either that or he typed in the wrong quantity.

    I think he meant to say 8 x 12volt 200Ah batteries. Which would require some parallel wiring. So I suggested 8 x 6v 420Ah batteries wired in series. Cleaner installation as far as I'm concerned.

    He needs to have a good battery system to meet his needs, especially since he purchased that Outback Hybrid inverter/charging system for around $4000.
    Yes, you are correct! It was a typo, quantity was 8. I haven't purchased the batteries yet so I will defiantly look at the 6V. This is a test system for me. I have had a passion for solar power for a couple of years now. I am a commercial roofing contractor who does military work so I'm trying to incorporate solar into my company. Multiple roofing manufacturer's I'm bonded with are starting to produce PV roofing products. I have been looking into getting a certification from US Solar. They have classes in Fort Lauderdale, FL.

    I had intentions of wiring the batteries in series.

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    • #17
      Originally posted by Krazy1 View Post
      Yes, you are correct! It was a typo, quantity was 8. I haven't purchased the batteries yet so I will defiantly look at the 6V. This is a test system for me. I have had a passion for solar power for a couple of years now. I am a commercial roofing contractor who does military work so I'm trying to incorporate solar into my company. Multiple roofing manufacturer's I'm bonded with are starting to produce PV roofing products. I have been looking into getting a certification from US Solar. They have classes in Fort Lauderdale, FL.

      I had intentions of wiring the batteries in series.
      Like I stated. First you determine you daily watt hour need is. Then you can size your battery system.

      Once you have calculated an Ah rating of your system try to purchase a battery as close as possible with the Ah rating at a voltage less than 12 (2, 4 or 6). You will not find high (400) Ah rated 12volt batteries because they will be too big and heavy. You can find really high (up to 1500) Ah rated batteries in 2, 4 and 6v versions which allows you to build big battery system yet have them all wired in series.

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      • #18
        For a test system, don't bother with short lived sealed AGM batteries, they cost a lot, and while "testing" your first battery bank often gets murdered.
        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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        • #19
          I am having trouble understanding the value of a combiner box in this application. These look like little more than a terminal strip inside of a nema box ? (cost but little value ?)

          It isn't at all obvious to me that 3 strings of 2 panels in series will necessarily have the same voltage, or do they just float up to the same level from the panel converter ?

          If they all get the same sunlight, maybe the strings are similar, but that is not obvious to me.

          Thanks

          Harry

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          • #20
            Originally posted by harryn View Post
            I am having trouble understanding the value of a combiner box in this application. These look like little more than a terminal strip inside of a nema box ? (cost but little value ?)

            It isn't at all obvious to me that 3 strings of 2 panels in series will necessarily have the same voltage, or do they just float up to the same level from the panel converter ?

            If they all get the same sunlight, maybe the strings are similar, but that is not obvious to me.

            Thanks

            Harry
            Similar panels (or sets of panels) wired in parallel to a combiner box getting the same amount of sunlight will also generate the approximately the same voltage.

            A combiner box does more then connect all of the panels strings. It also allows you to install over-current protection for each string. This is code requirement once you exceed 2 panels or 2 strings in parallel. Go to a third string and you now need fuses or breakers.

            Here is a picture of my combiner box. It was designed for 5 panels in parallel going to a PWM charge controller. I have 4 panels wired to it in these pictures.

            PV Combiner box.jpgBehind PV panels.jpg

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            • #21
              Originally posted by harryn View Post
              I am having trouble understanding the value of a combiner box in this application. These look like little more than a terminal strip inside of a nema box ? (cost but little value ?)

              It isn't at all obvious to me that 3 strings of 2 panels in series will necessarily have the same voltage, or do they just float up to the same level from the panel converter ?

              If they all get the same sunlight, maybe the strings are similar, but that is not obvious to me.

              Thanks

              Harry
              All panels have to be matched so they all have the same voltage and currents. The combiner is required to have each strin with its ow fuse, and the feeder with a fuse device.
              MSEE, PE

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              • #22
                Thanks - that makes sense.

                Suppose 1 panel is producing less power than the other 3, just as an example 10% less. How does this work out in the real world ?

                Does the panel voltage just float up to match the other ones in the combiner (with less current) or is it more complicated than that ?

                I ask because I see grid optimizers on the market which appear to be directed at this challenge, and other shade related aspects.

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                • #23
                  Originally posted by harryn View Post
                  Thanks - that makes sense.

                  Suppose 1 panel is producing less power than the other 3, just as an example 10% less. How does this work out in the real world ?

                  Does the panel voltage just float up to match the other ones in the combiner (with less current) or is it more complicated than that ?

                  I ask because I see grid optimizers on the market which appear to be directed at this challenge, and other shade related aspects.
                  As long as two panels in series are matched in current (Imp) within 5% or two panels in parallel are matched within 5% for Vmp you will not have to worry about mismatch losses. Beyond that, you need to do the calculations to see what you are losing and whether it is acceptable.

                  Yes, a good MPPT circuit will pick a voltage below Vmp of the high string and above Vmp of the low string. Both will have less than ideal output, but better than either alone.

                  A poorly designed MPPT circuit can pick a very poor operating point and essentially ignore one string completely.
                  SunnyBoy 3000 US, 18 BP Solar 175B panels.

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