A friend posted the following on another forum, & I thought I'd re-post here as there is more solar expertise & experience here. hope that's ok.
Has anyone had this happen on their solar panels before? The squiggly lines across the solar cells. It doesn't look good, but do you know what it is and what causes it?
I have had it suggested that this is a micro short circuit, which sort of makes sense, given it looks vaguely like a lightning strike, but in reality I have no idea.
There is a bit of water on the panels too, so ignore that. I had just washed everything after a trip when I noticed the weird lines.
The panels are about 3 years old. Set up with a gap between roof and panel of about an inch. I've been suspicious of a drop in output but haven't measured it as yet. I think that will be today's job. I was doing a fair amount of driving recently and not relying on the panels so didn't notice it as much as I might if I was camped up. Normally though, the panels will have me fully re-charged by say 10am if in good sunlight. On a couple of days I noticed it was still charging at 11am and through till nearly lunch time, but didn't think much of it as I was running the fridge as a freezer and overnight the battery would have had a lower SOC. Will take a closer look at output today.
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I await with interest what the experts might say, so my comment is just 'thinking out loud', and not telling you something you already know. A short circuit is just that - the short distance between two poles. I can't imagine a short circuit wandering back and forth across wires. Hopefully, it is an issue in the 'glass' surface. Something that from this point forward can be known as 'solar worm'. A worse case might be some sort of fracturing in the base that could separate the circuit.
The wiggly lines are just what they look like, an arc between the grid wires in those modules. If you look real close, you can see the bubble of copper built up each side if the arc line. If the arc repeats too often in the same place, those tiny threads actually get burnt through and module loss starts to become panel output loss. The output voltage open circuit will be the same as the specs on the back of the panel say, but the short circuit current starts to drop off the more damage there is in any module.
The cause, generally poor wiring practices, either panels connected in parallel with under size cable and each panel added in to this under size wire. 6mm auto cable can carry the output of a 150w 12v panel, not 2 or 3 panels all paralleled into the same single run of 6mm auto cable.
The problem starts with the panel getting hot because it can't get all its output through the wire because of a resistance build up, the weakest modules get the hottest in the panel that suffers with the most resistance, generally the panels further down the string. Add a larger capacity panel to the same parallel string and real problems start to emerge.
When the solar controller determines the battery is full or needs to drop to a low voltage such as the step from boost or bulk charge down to float charge. The only way it can do that is to stop accepting any output/input from the solar. The solar array voltage now climbs to open circuit voltage, the hottest modules have the lowest output so therefore the lowest push back against current coming in rather than current going out, so the module becomes a heater and finally an arc runs across the module trying to reduce the current and voltage, a short circuit. This path is now slightly burnt so a carbon track is laid, this makes the path for an arc to travel down easier than the first time, and so the arc continues to burn across the module until it fails.
This is why blocking diodes were included in all earlier built solar panels. When roof top solar started, panels were connected in a single series string to build the voltage and not the current. Bypass diodes remained but the blocking diode became redundant resulting in a cost saving for the panel manufacturer and the buyer being none the wiser.
The arc across the panel is the end result, same thing happens when more than 1 series string is connected into the MPPT controller, the high output from one string reverse flows into the string with a shaded panel, then the same process as mentioned about happens.
T1 Terry
A person may fail many times, they only become a failure when they blame someone else John Burrows
Those who struggle to become a leader, rarely know a clear direction forward for anyone but themselves
well, maybe not from your mate, I'm guessing it isn't what he wanted to hear.
The 60w panels on Tom & Carmel's van have suffered from the electric eels crawling through the modules, that was cause by the people doing the roof replacement deciding all that cabling wasn't required and a 160w panel could be substituted to replace 4 much smaller output panels resulting in turning the 60w panels into heaters, they did not fair well from that abuse. I didn't have enough panels in stock to replace all the crook ones, so just built up sets of 4 panels in series fed into a Victron MPPT controller, the only way I could see to get around the under rate cable problem because it was all under the roof now rather than outside where the problems could addressed. Hiding things so make it look better is not always a good idea ........
T1 Terry
A person may fail many times, they only become a failure when they blame someone else John Burrows
Those who struggle to become a leader, rarely know a clear direction forward for anyone but themselves
Any reason blocking diodes could not be fitted to my friend's panels ? He has two panels on a 4wd one has the 'worm the other OK. Given George's experience 3 years down the track deterioration may be a slow process, so if my friend can access the wiring to beef it up/and/or fit blocking diodes (to both panels or just the affected one?) maybe this could prevent further damage?
