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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.
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.
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