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Shades, MPPT, PWM, serial, parallel and ideal solar setup

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  • Shades, MPPT, PWM, serial, parallel and ideal solar setup

    Hello Gents,

    I reaching to you because I need your insights to make an enlighten decision about the best solar system design for my use case.

    I read a lot of posts about MPPT and PWM controllers and I believe I have a good understanding of the pros and cons of each technology. My goal is not to starts another post about MPPT and PWM controllers but rather to try to find the optimal design that will allow me to deal with shading.

    We are typically camping from early June to late September and the temperature during that period varies from 5 to 30C. The power budget is ~50 Ah/day with (weather factor included) roughly 2.5 hours to recharge the batteries bank thus suggesting a solar array that can provide something like 25 Amps.

    The batteries bank, according to my power budget, should provide 3 days of sunless autonomy with a DoD of 50%. I guess that the bank should be roughly around 83% Dod each day.

    The panels layout is a single row on the awning's side near the front of the trailer to maximize their chances to be exposed to sunlight. The opposite side and the back of the trailer are typically closer to trees. I'm also planning to tilt the panels so their backs will be as the same level as the AC cover's top in a attempt to minimize the risk of having the AC casting shades on them and improve exposure to sunlight. Those precautions obviously won't not be enough to prevent shading but a guy has to start somewhere. roof model.jpg

    I will be using a junction box on the roof in order to ease wiring the panels in series or parallel and to have a single pair of wires going down to the batteries bank. I would also like to keep the wire to the battery bank as small as possible to ease fishing them around.

    The components I'm considering for that project are:
    • A set of monocrystalline solar panels either:
    • three 12v 160W
    • four 12v 100W
    • A 12v batteries bank composed of 2 xCrown CR-330 6 volts batteries in series.
    • A Bogart Engineering Trimetric 2030 battery monitor
    • A charge controller either:
    • Bogart Engineering SC2030 (30 Amps) linked to the Trimeric 2030
    • Morningstar PS-MPPT-40 (40 Amps)

    My previous readings involving shading issues would either suggest:
    • To wire the panels in parallel and use a PWM charge controller
    • To wire the panels in series, benefiting from the panels' bypass diodes, and use a MPPT controller

    I must admit that the MPPT from a technical point of view is very appealing, regardless if the 12 volts panels were to be in series or parallel just by the fact that the bulk charge period can benefit, even if its not always optimal, from a current boost.

    I also saw the Gone with the Wynns : Sailboat Solar Power - Series vs. Parallel & Shading video: https://youtu.be/1qD3mN8VotQ, in which I believe they are making use of an Outback Flexmax MPPT charge controller, and end up recommending to wire the solar array in parallel.

    This brings me to my question, lets say we vent the MPPT vs PWM economical factor and only focus on harvesting as much power as possible from a solar array that will be knowned to be exposed to varying shading conditions.

    What would your experience recognize as the best setup to deal with the potential shading caused by the surrounding trees.

    Would it be:
    • To wire the panels in parallel and use the PWM controller
    • To wire the panels in series and use the MPPT controller
    • To wire the panels in parallel and use the MPPT controller

    Thank you

    Marc
    Last edited by marc.turcotte.qc; 04-13-2017, 08:53 PM.

  • #2
    PWM or MPPT has nothing to do with your question (shade or no shade). PWM is completely antiquated and way to expensive to even consider on a system larger than 200 watts on a 12 volt battery. It would be extremely foolish to even consider PWM.
    Last edited by Sunking; 04-13-2017, 09:25 PM.
    MSEE, PE

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    • #3
      Originally posted by marc.turcotte.qc View Post
      ... The power budget is ~50 Ah/day with (weather factor included) roughly 2.5 hours to recharge the batteries bank thus suggesting a solar array that can provide something like 25 Amps.
      ....

      The components I'm considering for that project are:
      • A set of monocrystalline solar panels either:
      • three 12v 160W
      • four 12v 100W

      ...
      3 * 160W + 4 * 100 = 880 watts of panels

      880 / 18V = 48.8A into a PWM controller

      880 / 14V = 73.3A out of a MPPT controller

      Your 40A controller is to small and both will supply well over your daily power budget of ~50AH with moderate shading problems.

      WWW

      Comment


      • #4
        Originally posted by Wy_White_Wolf View Post

        3 * 160W + 4 * 100 = 880 watts of panels

        880 / 18V = 48.8A into a PWM controller

        880 / 14V = 73.3A out of a MPPT controller

        Your 40A controller is to small and both will supply well over your daily power budget of ~50AH with moderate shading problems.

        WWW
        I think he's doing either set of panels, not both.

        Since the panels are not far away from the charge controller, I vote parallel with MPPT. I made a series of videos testing shading with parallel vs series, parallel won by a long shot.
        Solar Queen
        altE Store

        Comment


        • #5
          Hello again,

          Solar Queen is right, I'll use 3 or 4 panels, depending on what I learn from this discussion.

          I'm very interested in watching your videos Solar Queen. Could you give me a link where I could find them ?

          Everything I read or saw so far, indicate that I very easy to shutdown a whole panel is you shade the right cell; typically a corner one.

          The sun rotates around the trailer during the day changing the shades cast by the trees so, my initial thoughts were that I can increase the odds of having some power supplied to the charge controller if I use more smaller panels to generate the nominal power necessary to charge the batteries bank.

          The one thing that prevent me for taking a decision is, would panels (with internal bypass diodes) wired in series be as effective as panels wired in parallel when partially shaded ?

          That would be nice to have them wired in series to reduce the wires gauge but I'm more concerned to make sure that the solar array will provide me some power than reducing the wires gauge.

          Marc

          Comment


          • #6
            Originally posted by marc.turcotte.qc View Post
            Hello again,

            Solar Queen is right, I'll use 3 or 4 panels, depending on what I learn from this discussion.

            I'm very interested in watching your videos Solar Queen. Could you give me a link where I could find them ?
            The moderators have asked me not to include links. You can just search on YouTube for "How to Wire Shaded Solar Panels". You'll see my smiling face.
            Solar Queen
            altE Store

            Comment


            • #7
              My compliments to you my Queen.

              Your videos are very well made and very instructive. I will definitively go parallel with an MPPT controller.

              I have one remaining issue to clarify.

              The solar array need to provide 400W and would prefer to install 3 panels instead of 4 to ease the installation effort but....

              Are 160W panels built with 3 strings in parallel instead of 2 ? This would allow them to provide an additional current path internally.

              If not, I guess I would be better of using four 100W panels instead of three 160W thus having the additional "current path" provided by an extra wire toward the controller.

              Do you have any thoughts on this ?

              Marc

              Comment


              • #8
                Don;t use a prime number of panels. Get 2, 200W panels .
                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
                  Hello Mike,

                  I don't have any panel at this time. The ones I'll buy will have the same characteristics and be from the same manufacturer.

                  Could you be more specific about why using an odd number of panels could be a problem when wiring them in parallel ?

                  Marc

                  Comment


                  • #10
                    Originally posted by marc.turcotte.qc View Post
                    Hello Mike,

                    I don't have any panel at this time. The ones I'll buy will have the same characteristics and be from the same manufacturer.

                    Could you be more specific about why using an odd number of panels could be a problem when wiring them in parallel ?

                    Marc
                    An odd or worse prime number of panels overall is bad because you cannot divide it up into an smaller grouping of panels.
                    Say you have three. You can only connect all three in series or all three in parallel. But if you have four you have the added option of two strings of two each.

                    A worst case would be something like 17 panels. Either all in series (too high a voltage) or all in parallel (too many wires, too much current).
                    You would be better off keeping one panel as a spare and running two strings of eight.
                    SunnyBoy 3000 US, 18 BP Solar 175B panels.

                    Comment

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