Panel Hot spot

Cooch · Member

Panel Hot spot

denmonkey · Senior Member

I don't believe Ive seen that on any of my panels. Most of my stuff is ex house install stuff, so they've been in the sun for some time

What makes you call them a hotspot and have you seen info on them before ?
Is this the same panel in both pics ?

has the input changed as far as you're aware ?

sorry no info, just lots of questions :)

cheers Brett

dogbox · Guru

could that be moisture

Peter_n_Margaret · Guru

I have never seen it, but have heard about it often. I think this is a common failure mode of cheap panels.
Terry would be better to comment.
Cheers,
Peter

Cooch · Member

Same panel in both pics, just a closer view. Im only guessing its a hotspot - it seems to be internal resistance as the silver conductor rails(?) look like they are burned from over current or shorting. Still seems to charge the batteries ok but im concerned it might lead to bigger problems.

T1 Terry · Guru

I've seen quite a few 12v panels with hot spots as well, even Kyocera branded panels, so cheap Chinese isn't necessarily the problem.

The problem generally results from panels strings in series where quite high voltages are generated but the panel does not have a blocking diode installed and the bypass diodes have failed.

These are cheap roof top solar panels and these are real hot spots

-- Edited by T1 Terry on Thursday 1st of August 2019 02:22:40 PM

Mamil · Senior Member

From my experience in the solar industry, hotspots are due to short circuits in parts of the cell, resulting in excess current flow. This in turn causes localised heating and breakdown of that part of the cell, and/or the bus bar that serves that section of the panel. Causes are varied, but include micro-fractures in the cells from manufacture, point impacts during transport, installation or use, or penetration of moisture from underneath.

The discoloration in your picture is a bit unusual because of it's position right on the edge of a cell, which is not the usual place for hotspots to form in my experience. Have you checked under the panel at that point to see if anything has pressed up on the underside and penetrated the white backing sheet? That would be the first thing to check.

Other than that the best way to diagnose these things is a thermal image, as that'll tell you if it's just discoloration of the backing material, or really is a hotspot - see my example below. That's how we find issues in the field, but I appreciate not everyone has a thermal imager in their toolkit!

As a general point, the industry promise of solar systems having a lifespan of 25 years is proving to be wildly optimistic. However, in general we find the panels are the most reliable part of the system, it's more commonly things like isolators, junction boxes, connectors, inverters that fail, but we've also had our fair share of panels fail - both cheapie and from high end brands. The only difference is that the high end manufacturers are still around to honour their warranties whereas the cheapie brands have long since taken the money and run!

IMG_20190409_131054 (600x800).jpg

IMG_20190409_131110 (800x600).jpg

-- Edited by Mamil on Thursday 1st of August 2019 07:07:25 PM

T1 Terry · Guru

Hi Mamil, back in the '70's and 80's they fitted blocking diodes as well as bypass diodes in just about all panels, Solarex was a well known brand back then. Some where along the line they determined blocking diodes were not needed and I'm wondering if this is the point where the solar panel failures started to show up.
I think the reasoning was the solar output would always have some where to go, so the bypass diodes stopped current being forced through a shaded or poor performing panel due to high resistance joints. The idea falls down when grid connect systems shut down because the grid failed leaving the panels to open circuit voltage and battery connected systems do the same thing when the controller senses the battery is fully charged.
My interpretation of what happens at this point. This high open circuit voltage strains an already vulnerable panel turning it into a heater, as shown in your thermal imagining, resulting in grid joint failure and arcing eventually burning the hole through the panel. With blocking diodes installed, the only current seen across that panel is the current the panel itself can produce rather than the total current available from the series or parallel connected array.

Does that hypothesis fit in with what you see in the solar industry? Or do you have an alternate theory as to what causes these failures?

T1 Terry

Mamil · Senior Member

Terry, my understanding is that hot spots have a number of causes, including shading/soiling, material imperfections, microcracks in the cells from manufacture or mechanical damage, badly soldered joints, water ingress etc. As I understand your theory the diodes may help to lessen the time it takes these to develop into a complete failure by reducing the voltage passed through the site of the defect, but not solve the underlying problem or prevent reduced performance and eventual failure of that panel. As soon as we detect a hot spot on a panel it is replaced, no question. In a large system with thousands of panels, occasional hot spots and the associated performance degradation until the faulty panels are replaced is negligible, and it is treated as just an ongoing maintenance exercise, but I understand on a small system of only one or two panels the discovery of a hot spot can be more worrying!

T1 Terry · Guru

Not so much the voltage but the total watts passing through the bad junction. The crook spot has increased resistance causing a spot to turn into a high powered hot spot with the output of all the other panels also being fed into that bad joint. The fault becomes greater and allows even more resistance and therefore more localised heat. This keeps growing until the fault becomes so great the supply available can no longer create a circuit across the fault area and the heating stops.
f blocking diodes are fitted, the only current available is what the panel can produce, with a fault already present in the panel, that total current is a rather small figure. It would still show up on thermal imaging but it would not be hot enough to start the burning seen in the burn through panels.

T1 Terry

Cooch · Member

Thanks Guys, i'll be checking the underside of the panel for sure however it seems the verdict is the panel is beginning to fail and ought to be replaced.