I looked for that article we were talking about, regarding fracturing cells for greater output. I found lots of articles on how fracturing can reduce output, but not the one for which I am looking. I did find a patent for manufacturing cracked cells to increase output.
Patent for fracturing cells. Link
Here are my observations on the subject. I test my panels with an ammeter instead of a voltmeter. A tiny section of a broken cell will give the same voltage as a full cell. Testing with an ammeter, I feel, gives a better indication of the power capacity AND gives a bit of a stress test. That assumes finding a sunny day here in the alleged Sunshine State.
Virtually all of my 34 watt, 6 volt panels have one or more cracked cells, at least in the later pallets. This worried me, at first, but I have come to embrace them and have enjoyed studying them. These tiles have much thicker glass than you find in standard modules. That allows a great diversity in crack modes without breaking the glass. The cracks that concern me the least are longitudinal ones across the fine silver traces between two main bus bars. There is no degradation at if the tiny silver wires are intact. If they are broken, the current still flows to the nearest bus bar. Outside of the main area, A crack with broken wires would eliminate a small amount of current from reaching a bus bar.
The ones that really concern me are the ones made by someone really serious about destroying a panel. These cracks fan out over the entire cell, looking like lightning bolts or, perhaps, a fern. The cell ends up in lots of pieces with the potential that several of those fine lines will fail, drastically reducing output. Given the choice, I choose the panels with the simpler cracks.
That being said, label-rated short circuit current should be around 7.5 amps, if I remember correctly. In practice, I have observed as much as 9 amps on these modules with multiple cracked cells. With such variation, I feel it is probably important to sort the panels for similar outputs, even as simply as Hi, Medium and Low, to maximize the overall production of power.
Have any failed? Hard to say, because I run in strings of 21 and they have bypass diodes. I do know that I had 2 with the edge delamination problem and their diodes were bad. 3 foot jumper cables allowed me to bypass those and continue operation with the rest of the string.
Some of the tiles were received with the glass smashed. That usually resulted from screws being left in the tile above. There were also some piles that were simply stacked too high and cases of probable malice. Not surprisingly, cells were damaged, too, when the glass was smashed. Usually, these modules work! I have one on the solar shed that has broken glass from a tree strike after installation. I tried to seal it with some of that miracle AS-SEEN-ON-TV clear sealant. It did not stay clear more than a few days and ultimately crumbled off. It turns out, though that the sheet of sticky plastic between the glass and cells maintained a seal and the tile with the broken glass still has good output, though in Phase 3, it is not presently connected.
This is not to say that all cell fractures are benign or beneficial. You’ll recall the panel I blasted with the shotgun. That did not really affect that module, but then it was already somewhat handicapped by having been bent and bowed by Tom’s front end loader getting “just a little too close.” (Right. Basic laws of physics indicate that two things can’t occupy the same space at the same time, for every action there is a reaction, and while matter can neither be created or destroyed it can be smashed to bits.)
While I am still a bit shaky on the physics of less-than-perfect solar cells, I am fully aware that my lights are on because around 350 previously discarded panels are keeping my batteries charged! If they work, use them, but please don’t take a hammer to them! Or a tractor.
By: Neal Collier
