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  • Broken or Separated Tabbing wires on DIY panels

    Hello Forum! I am experiencing a recurrent shorting or separating tabbing wires on my homemade panels and cannot figure out how to solve it. My situation and panels are unique and require some explanation and background information. I live in a remote area in the foothills of the Sierrra Madre mountains in the Sonoran Desert in Mexico. The climate here is hot and extremely dry to extremely hot and very humid with torrential rains in the summer months,and very little or no rain the rest of the year.. Temperatures here can and do reach 45 to 48 degrees with 85% humidity. In spite of the desert climate, annual rainfall can be 100 cms. My power system is a hybrid solar with 2 wind generators, rated at 1600 and 500watts,respectively. It is a 12v off-grid system with 48 panels of approximately 100 watts each charging a NiFe battery bank of 10 1.5v 1200AH batteries. The panels are fixed mounted at 27degrees and receive full sun from 7;30AM until 4PM in winter and currently and in summer from 6:15AM until 6PM.
    Because of my remoteness materials for constructing my panels come from all over the world, are shipped to the US usually and brought in by car. Importation costs have ruled out factory-built panels. This due to a 16% duty plus a mountain of paperwork and other fees and "propinas." Also, items like PV glass, aluminum framing and copper cable have necessitated creativity due to their extremely high cost or to just not being available at any cost.
    With this background I started to build my off-grid system five years ago, first studying and reading as much as I could find on the internet and in books. Fortunately I have a background in Electricity and Electronics, and experience as an electronic technician, Even so, I confess having made probably every error imaginable in designing and building my panels and system. My first battery bank was built on 38 deep-cycle marine batteries which though they worked only lasted 36 months. That was when I invested in CIYI NiFe batteries and imported them driectly from China.
    My first panels used plywood backing and aluminum frames with standard glass---most of the glass shattered with strong sun here, The cells were glued with silicone caulk to the plywood. The weather destroyed the plywood by causing it to de-laminate, and ripple. I then changed from plywood to masonite, which withstood the humidity and heat much better and used a marine epoxy paint to encapsulate the cells on to the backing, sealing both. Nevertheless. in spite of the panels seemingly on a self-destruct cycle, they did work! I was producing over a KW net power.
    However, I wanted more sustainable panels, and so I invested in EVA to encapsulate the cells. After some learning curve disasters, and a changing of technique and heat guns, I was producing a better panel, but I learned that EVA never completely cures hard, and that the next days in service would reheat/melt the EVA again so the cells would slide or move sideways sliding one over the next in line and causing shorts. It was also at this time I noticed the first burning out or breaking of the tabbing wires between cells. My conclusion was that the sliding was causing the tabbing wires to break. I also concluded the EVA just kept melting, and then hardening as it cooled. It was then I started to look for a glass substitute as well.
    Again, a lot more research and study. I finally started to investigate poly-carbonates. Up to this point there were no poly-carbonate materials that were strong enough with higher temperature qualities available here. About 2 years ago I came across a clear poly-carbonate 4x8 sheet 6mm thick that has a honeycomb-like structure produced by Bayer called Makrolon. It had 800F melting point, was more transparent than glass, ten times stronger than glass, cut-able with a knife or power saw. It also has a 10 year warranty and has had very good reviews for applications in skylights, greenhouses, and restaurant porches. Makrolon also weighs 1/20th that of glass. Although not cheap, much less costly than glass and more importantly available here.
    I tried a couple of sheets cutting them to a 1meter square. and followed the example on the Internet of a sandwich with Makrolon, EVA, cells,EVA. It once again had the same problem of sliding and shorting out the cells from the sun reheating the EVA every day. I also was experiencing a gravity problem that along with the sliding the cells would starting to fall down, de-laminating from the panel. My next modification was to put a backing sheet, so I then had Makrolon, EVA, cells,EVA, Makrolon and this sandwich in a frame of galvanized sheet metal with an additional cross-brace. This produced a lightweight solar panel, but I still had the sliding problem, so I returned to the silicone caulk/glue and replaced the EVA that had been between the backing sheet and cells with the silicone window caulk. This stopped the strings and individual cells from moving or sliding. However, here was where the problem of the Broken or separated Tabbing wires occurred. This break or separation only occurs between cells, may be only one tab or two or all three tabs. It usually occurs between the middle cells in a given string of 6 cells, never in the ends at the bus connection. It can happen in one string or two or in all 6 strings. It is completely random. Polarity has been checked, there are no shorts, or crossed wires. All panels have 2 diodes correctly in place. A close examination of the panel does not show evidence of overheating or melting. The tabbing wire has just separated in the middle between cells. It appears almost as if cut. The cells have not moved or slid or shifted, There is no sign of the cells having been strained. In all cases this happens weeks or months after installation and having produced an average of 4 to 5 amperes per panel.
    Obviously, this is frustrating and I would appreciate any help the community could give me in solving this.

  • #2
    You have been very industrious, having actually produced 1KW from DIY panels. There is a long
    list of problems, making anything that will last for years. I tried mounting cells on non glass, which
    worked for a bit. But as soon as strong sun hit, the difference in co efficient of expansion between the
    materials started cracking cells, visible and actually audible. I suspect your arrangement has such
    a problem.

    I concluded that only cells on glass, with an approved encapsulant, could survive heat and moisture.
    These produced a quite heavy panel. With the cost of these materials, I concluded only large grid
    tie style panels were economical, practical, and long lived. 16 such panels might replace all of yours
    and out perform yours in every way. good luck, Bruce Roe

    Comment


    • #3
      Yes, bcroe, I agree glass is better. The problem is availability. The glass is horribly overpriced, making them non-cost-effective in this part of Mexico. It is actually cheaper and faster to import panels directly from China. Even with glass, there is still the cracking/exploding problem fro the heat. You can bake bread on my panels; they get that hot. One of the advantages of the Makrolon is that the honeycomb design actual directs air through the panel. I am thinking at this point the problem with the tabbing wire breaking or bursting may have to do with the capacity of how many amperes can flow through them at the panel temps and production of the cells, I have noted that when the ambient temps rise above 28C there is a noticeable dropoff in both voltage and current when temps hit 40C or higher with about a 35% loss. With the lead acid batteries I first had installed the losses were at 50% and higher. I an-m pondering changing or rather building the next panels with thicker heavier gauge ribbon between the cells and see if this makes the difference. There has to be some kind of strain on the tabbing wire that is both extreme and beyond the capacity of the wire. I originally was using a 1.8mm / .16mm that was sold on ebay as 2mm/ .2mm. That was just bad. I now am using 2.54mm/ .76mm Ulbrich wire. But, the problem continues.

      Comment


      • #4
        When you apply the tab wire to the cells, and then jump to the next cell, leave a little slack in the wire, sometimes called a Z fold, to allow the wire to flex and move a bit instead of being torn apart,
        another possibility is to mount each cell only on a penny sized "dot" of silicone seal, and leave the cell "floating"
        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


        • #5
          Thank you, MIKE. i have left some space about 3/16" between cells, but have not left as you suggest expansion space. I have noted that sometimes there is a natural "z" bend occurring. I will make the "z" more apparent on the next build. I am already using the penny-sized silicone seal to float the cells and this was a definite improvement over the EVA on the underside. I will try the z bend and report the results.

          Comment


          • #6
            The Z might work for you; not for me because my encapsulant will form around and through it. Bruce Roe

            Comment


            • #7
              Originally posted by bcroe View Post
              The Z might work for you; not for me because my encapsulant will form around and through it. Bruce Roe
              Even if encapsulated, the Z bends reduce stress as it's not a "rigid" beam held in tension on the cell solder stripe.
              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


              • #8
                Originally posted by Mike90250 View Post

                Even if encapsulated, the Z bends reduce stress as it's not a "rigid" beam held in tension on the cell solder stripe.
                Not so much, because my encapsulant around the Z will tend to make it rigid and unable to flex. No air in there. Bruce Roe

                Comment

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