Newbie question - cracks in solar panel glass

[Intheswamp]

Sorry, I'm not highly educated on solar panels but looking at Youtube the other day I stumbled upon this one where a guy goes over several different problems that can befall PV panels. I thought the guy did a good job of explaining several things. It might help. https://www.youtube.com/watch?v=Rw8XuB0BSVI

[WayneG]

Impossible to walk on and even if you could I'd expect the cracks to be on the outside. It's too spread across the panel for it to be a kids ball etc and again the cracks are internal. Hoping someone has also come across this problem.

[J.P.M.]

Hi All
I have 2 Jaycar ZM9059 150W 12V Panels, of which one of them has the snail trail cracks, I have asked Jaycar for comment. The one beside it is fine. Has anybody else had this problem. It appears at this stage not to be effecting the performance.

Image2-Panel.jpg

Sure looks to me like some vertical loading was applied, especially if adjacent panels are not exhibiting the same cracking. Maybe some D.F. tried to walk on it. Are the cracks localized about like a footprint might be ? Or, perhaps something impacted like a football ?

I note that a lot/most of the cracks are at 45 deg. to the major axes. If there are more localized cracks, that may indicate induced stresses, perhaps from differential thermal expansion, wind loading or combinations of other external loading(s).

[WayneG]

I can assure you the scratches are not on the outside of the panel.

[Mike90250]

Those look like scratches. Snail trails are fatter and not usually as straight. But it's not right for sure.

[WayneG]

Hi All
I have 2 Jaycar ZM9059 150W 12V Panels, of which one of them has the snail trail cracks, I have asked Jaycar for comment. The one beside it is fine. Has anybody else had this problem. It appears at this stage not to be effecting the performance.

Image2-Panel.jpg

[emartin00]

I don't think there is ever a good reason to risk micro or macro cracking a panel by walking on it. just because it does not break that day, does not mean it's OK to do.

I agree 100%, that's why I was asking the OP if he did. While it may no appear to do damage, it does in the long run.

[Mike90250]

I'm going to ask the obvious. Do you happen to walk on the panels when you clean them?

I don't think there is ever a good reason to risk micro or macro cracking a panel by walking on it. just because it does not break that day, does not mean it's OK to do.

[J.P.M.]

Years ago in college we did experiments using optical stress analysis. A brittle lacquer spray would be applied to a test object and they we would stress it. The cracks in the lacquer would line up with the calculated peak stress lines and if I remember correctly the spacing between the cracks were proportional to the stress.I also think it lined up with the dreaded Mohrs circle which was graphical way of avoiding vector analysis of stress when slide rules ruled the world. Luckily my freshmen engineering class was the first one where everyone was required to have calculator and slide rules were banned from use in classes.

Did similar and at the time said "so what ??". The wisdom and elegance of the method dawned on me slowly as I progressed. Eventually, I came to the opinion Mohr's circle was a better teaching tool than using it as a design tool. That was reinforced to me the first time I saw interferometry flicks for some failure analysis I got involved in a couple of years after graduation, and saw the max. displacement/stress for a section did indeed line up At 45 deg. just like a Mohr's circle would show, and the load cells and strain gages would confirm.

Interferometry and is a great analysis tool, but I'm still a fan of understanding Mohr's circle as a way to get the most out of such newer methods.

FWIW, we could use calculators unless the lesson being taught involved how to analyze a situation, or the Prof. was real old school. Generally calculators were allowed for exams, but usually all homework required showing calcs. until grad school. Toughest undergrad exams I had were from a prof who taught a course in in engineering mathematics. His exams were always open book and the answers would be given and be deceptively simple like "pi", "e", 0,1,-1, etc. The student would then need to explain and show w/calcs with why the answer was what it was. Worst answer I recall - because everyone bitched loudly about it - was (e^pi)/10 involving the probability dist. of failures in a production process. Nobody got that one. Big PITA.

Back on topic.

[emartin00]

I'm going to ask the obvious. Do you happen to walk on the panels when you clean them?

[peakbagger]

Years ago in college we did experiments using optical stress analysis. A brittle lacquer spray would be applied to a test object and they we would stress it. The cracks in the lacquer would line up with the calculated peak stress lines and if I remember correctly the spacing between the cracks were proportional to the stress.I also think it lined up with the dreaded Mohrs circle which was graphical way of avoiding vector analysis of stress when slide rules ruled the world. Luckily my freshmen engineering class was the first one where everyone was required to have calculator and slide rules were banned from use in classes.

[J.P.M.]

I guess these are snail trails from what I can find online?

I thought that might be a possibility as well, but after your flicks and seeing the telltale 45 deg. shear stress pattern to what look like but may not be cracks, I moved that down my list of possibilities.

Still, and after thinking about it more overnight, I suppose it's possible - maybe even likely - that the first and most common location of delamination(s) may occur along lines of max. shear stress caused by slight and/or occasional panel/array movement or settling over time.

[littleharbor]

Looks like an issue with the encapsulant delaminating from the cell, especially due to the skipped nature of the flaw. There might have been some contaminant on the cell surface which is causing the release. I doubt this is going to cause any production issues if it doesn't spread in any substantial way. In my opinion there are no cracks in the glass.

[J.P.M.]

Ojk, I had another look and littleharbor is correct. It is not the glass, it is underneath, so I guess these are the microcracks? Until you get down real close it looks like in the glass, sorry about misleading. What is the prognosis if I have these? Pics attached. Looks like I didn't do a good job washing either, I'll have another pass at it now.

Well, the cracks appear to have the not quite smoking gun but quite likely indicator of failure due to a shear stress. That type of failure occurs at 45 deg., the point of max. shear stress. The question becomes the source of the stress, frame movement or thermally induced, or both, or other things, all perhaps in combination.

To me it looks like the glazing cracks may have initiated on the underside of the glazing and the encapsulant is following the same line. I'd think that the glazing is more brittle than the encapsulant and when the glazing gets a micro crack that would perhaps not otherwise be noticeable, the encapsulant accentuates the visibility. I kind of don't think the encapsulant would do what's being observed on its own without some local instigating condition such as a glazing microcrack.

Perhaps the cracks are not "feelable" on the surface in the same fashion a windshield crack may not be detectable from the vehicle interior side. If so, my guess is the panels will continue to function, but once a glazing crack allows moisture of other stuff in/behind the glazing, that panel will begin to fail and cause the string it's on to lose most or eventually all production capability.

[scrptdr]

I guess these are snail trails from what I can find online?