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  • #16
    Originally posted by sensij View Post

    Opinions vary, but I would let your actual consumption be the strongest factor in sizing your system. If you are confident that 4x T105RE's have enough storage to meet your needs, the 30 A mppt CC is a good match to them. Oversizing the array will not hurt your system, and provides some insurance against several consecutive days of cloudy weather that the Kid sizing tool doesn't consider. "Clipping" at 800 W is not a problem if you don't *need* the energy that is being clipped, and generally speaking, the only days you will experience that clipping are the kind of ideal solar days in which your battery will be easily charged anyway. On those days, even with a 40 A CC, that power would get clipped anyway because the battery will be in absorb and not taking the maximum power the array can generate.

    You will be glad to have that extra power on less ideal days.
    That's kind of what I was thinking when I sized this system figuring between shade and cloudy days, there would be times of the year when having an oversized solar array would be advantageous. Knowing the Kid would clip the power and protect batteries. Thanks for another perspective.

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    • #17
      Originally posted by sensij View Post

      No, if you go with 3 panels, you have to put them in parallel, and the Vmp for 60 cell panels in parallel is too low to support a 24 V bank (and you need fuses, heavier wire to carry more current, etc).

      2x2 is fine with the 30 A controller, really.
      Ignore that. It's nonsense.

      If you use the KID controller 3 or your panels in series is your best option. With 2 x 2 is less power than 3 in series with the KID controller. If you look at the Power Graph the Kid Controller maximum operating efficiency on a 24 volt battery is 90 to 100 Volts Vmp. Your panels Vmp is 31 volt and 3 in series is 93 volts which is perfect and will allow the KID to pump the full 30 amps into a 24 volt battery operating at 28.7 volts If you were to place them in a 2 x 2 as suggested would put Vmp at 62 volts, and that limits max current to less than 30 amps. Not what you want. Again check the power graphs on page 49 of the manual.

      FWIW you can put the panels in parallel and it would work, poorly, but would require larger wire, combiner, fuses, and again limit current to less than 30 amps operating at 31 volts which is bare minimum voltage on a 24 volt battery. So if you want to use the fourth panel with a current booster for a water well pump is a good plan with the Kid Controller. The kid Panel with 3 of your panels wired in series is perfect match up with the controller. Do not use 4 of your panels wired 2S2P as you essentially will have less power than using 3 of the panels. Again look at the charts and graphs to verify.

      I do not recommend it, but where you are located you can wire all 4 in series because it never drops below 9 degree C and that is probable colder than reality in St Croix. At 124 volt Vmp would drop current down to 26 amps maximum or 750 watts cap. Not something I would recommend, but it could be done. Essentially you throw one panel away.

      Now if you want to throw away 25% of you power and daily production, do what Sensij says. 40 amps on T-105's is a bit high but not detrimental. It just means your batteries would use a bit more water.

      Another option you might consider is US Battery which is Trojans major competitor. In the 6-volt golf cart size category you can get up to 300 AH. Otherwise above 300 AH you have to move up to a L16 BCI group size. Both Trojan and US Battery make L16's which refers to the physical dimensions. US Battery is slightly less expensive in the USA and a quality product. Consider it because with your location, if you use T-105's you end up throwing most of the available production away. Example if charged by noon, all power stops and not utilized unless you turn something on to use power from the panels. Batteries are like a bucket. Once filled up with water, you cannot add more. Anything you try to add just spills on the ground and lost forever. 4 x T-105's can yield up to roughly 1.1 Kwh/day useage with a maximum discharge to 50% of 2.7 Kwh. Your panels in your area can generate 4.5 Kwh per day of usable energy.
      Last edited by Sunking; 12-18-2017, 05:17 PM.
      MSEE, PE

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      • #18
        Originally posted by Sunking View Post
        Ignore that. It's nonsense.

        If you use the KID controller 3 panels in series is your best option. If you look at the Power Graph the Kid Controller maximum operating efficiency on a 24 volt battery is 90 to 100 Volts Vmp. You panels Vmp arer 31 volt and 3 in series is 93 volts which i sperfect and will allow the KID to pump the full 30 amps into a 24 volt battery. If you were to place 2 x 2 as suggested would put Vmp at 62 volts, and that limits max current to less than 30 amps. Not what you want. Again check the power graphs on page 49 of the manual.

        Yes, thanks for the correction, 3 in series is ok here.
        ​​​​​​
        The graphs on page 49 show 30 A max output on a 24 V system for any PV voltage less than 100 V. They aren't true efficiency curves (which would show higher efficiency with the PV voltage closer to the battery voltage, if the Kid performs like most other high quality mppt controllers)
        Last edited by sensij; 12-18-2017, 05:16 PM.
        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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        • #19
          Sunking, please don't create conflict where there is none. I am always glad when someone finds and corrects an error in what I've posted, although I'd be happier if I didn't make those errors.

          We disagree on the behavior of over-paneled systems. So be it. We can each describe what we think a well-designed system looks like it, and the people reading can use their own critical thinking ability to decide what they think will be right in their situation. There is no need for personal attacks.
          CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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          • #20
            Ok, so basically I have one panel too many. I guess I will just use the three and try to find another use for the fourth one.

            One thing I have a question on Sunking, you mentioned: "So if you want to use the fourth panel with a current booster for a water well pump is a good plan with the Kid Controller"

            Can you explain this a little more? Do you mean to use all 4 panels together but use the output of the CC to power the well pump? And what do you mean by current booster?

            I have also seen a Blue Solar 35A charge controller. https://www.victronenergy.com/solar-...rtsolar-150-35 Could this be a happy medium? I realize no matter what I will charge these batteries up really fast using 4 panels and therefore just waste their capabilities once charged. I have a well, so I'd liek to use their excess capacity in some way.

            Unfortunately I already purchased the T-105RE batteries. I considered the US battery but read I believe Sunking's recommendation to use the RE batteries with the thicker plates. Also the place I ordered them from had free pickup so my Dad pickled them up for me in FL and shipped them down.

            Once again, I really appreciate all the advice!

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            • #21
              Originally posted by tang tonic View Post
              Ok, so basically I have one panel too many. I guess I will just use the three and try to find another use for the fourth one.
              If you have all 4 already, I'd suggest that you perform your own experiment to see what works best for you. Using all 4 in a 2x2 system will give you more power during most hours of the day, and more energy overall. Just compare how the system behaves with three in series vs using all four 2x2. See which configuration gets your charge controller hotter, or which one gets you into float sooner. Undersizing the PV array is the number one mistake people make when building systems, and an inability to recognize the benefits of over-paneling is part of the problem.

              You designed a good system for yourself. I would not let this thread cause you to second guess the decisions you made until you have actual results that suggest something isn't performing as expected.
              Last edited by sensij; 12-18-2017, 05:58 PM.
              CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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              • #22
                Thanks sensij, sounds like a good approach.

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