Do solar panels ever fail because of shading?

[littleharbor2]

modern solar panels are so well made (I believe) compared to earlier panels from ten plus years ago, and I can't find any reports of panels failing anywhere, when I search on Google, but perhaps I'm doing it wrong.

There are lots of 40+ year old panels still out there working fine. The encapsulation process is virtually the same as some of the earliest panels. While efficiency has improved yielding higher power output the module building process hasn't changed a whole lot.

 

[efficientPV]

What are the failure statistics? My original post asked if anybody here had had a solar panel fail because of shading, nobody has said yes so far. What does "This" mean, in your sentence "This is some vindication of what I have said for years"?
Why is full or near bypass bad for cells, when, as long as the bypass diodes are working, the cells aren't taking the current?

Why would you think the cells don't have any current going thru them. They do and the weaker ones or disproportionately shaded overheat. It is easy to see with a FLIR camera. Everyone here just sees a panel failure as just bad luck.

 

[Substrate]

Back to square one. The bypass diodes and panel engineering is such that when the cells are chosen, even under shaded conditions, both the cells and diodes *should* be designed to handle that reverse-biased condition.

Another way to look at it is that by making it the consumers fault, the seller can pawn off cheap-ass panels that weren't designed or manufactured well, knowing that the consumer knows jack-squat about good panel engineering.

 

[SenileOldGit]

Why would you think the cells don't have any current going thru them. They do and the weaker ones or disproportionately shaded overheat. It is easy to see with a FLIR camera. Everyone here just sees a panel failure as just bad luck.

I would think the cells don't have any current going thru them (when shaded) because the diodes offer the path of least resistance, thus the current goes through the bypass diodes - which is the whole point of them. Are you suggesting something different happens?

 

[wattmatters]

I would think the cells don't have any current going thru them (when shaded) because the diodes offer the path of least resistance, thus the current goes through the bypass diodes - which is the whole point of them. Are you suggesting something different happens?

A bypass diode only bypasses a string of cells, not individual cells. So imagine one cell in a string being shaded while others are in full sun, like particularly bad bird dropping, or some lichen growth.

By and large transient / soft* shading isn't that big of a deal. Hard shading which impacts individual cells for long periods isn't good for them.

* by soft I mean dappled light as opposed to hard shading like that caused by lichen, or a large bird-dropping or a stuck leaf, or particularly poorly placed objects (it might be the panels are poorly placed) such as roof vents/stink pipes which can cast hard shade on just a few cells.

 

[rancher1913]

forgive my ignorance but dont all panels get shaded everyday at night

 

[curiouscarbon]

forgive my ignorance but dont all panels get shaded everyday at night

uneven shading seems to be the root of one problem. at night the panel of course evenly shaded. but during day, something like backwash of energy can apparently heat up small parts of the panel and long term result in something going sideways

 

[RCinFLA]

uneven shading seems to be the root of one problem. at night the panel of course evenly shaded. but during day, something like backwash of energy can apparently heat up small parts of the panel and long term result in something going sideways

It also doesn't hurt much in morning or late afternoon when illumination level current drops quite a bit so there will be much lower current flowing through bypass diode. Partial shading in morning or late afternoon is almost a given but luckily the current is low.

Somewhere in my hard drives I think I have a report done by a German university that evaluated several hundred used panels. For the full population they had about 4% bad bypass diodes. There were about 40 or 50 panels that had info tags claiming they were installed in a location where there was some near mid-day sun partial shading due buildings, trees, or antenna tower. This group had 50% of the panels having bad bypass diodes.

The failure rate doesn't surprise me, but it is very dependent on panel build quality. Tab power device packaged diodes with some amount of diode heat sinking makes a world of difference from a low-cost panel with two cheap parallel axial leaded pellet diodes soldered together.

I have seen cheap panels with axial leaded diodes just SMD soldered in that had solder melted from the bypass diode heating so they just fell off their connecting point. An axial leaded diode enclosed in a small junction box can get up to about 220 degs C in bypass mode at full sun illumination on a hot day.

There is a lot of semiconductor company failure rate data on reliability versus diode temperature. Above 150 degs C the average time to failure drops several orders magnitude. At about 220 degs C it is in the order of a thousand hours of MTBF versus a million hours at 100 degs C.

 

[SenileOldGit]

When was the report done by the German university? I think the date is extremely important when it comes to my question, because I'm only concerned about panels that have been made in the past five years. We could be talking about 15 year old technology in that report, which doesn't apply to today's panels.

 

[JCSchwarb]

I have been reading up about bypass diodes, and I noticed that the guarantee for my Canadian Solar panels states that they mustn't be in shade for more than 100 hours, or something like that, and I have a large tree that is currently shading my panels for several hours of the day, which I am going to have severely cut back - but has anybody here ever had a panel fail because of shading? I presume that first the bypass diode(s) have to fail, which would then force the electricity from the unshaded panels to go through the solar cells in the shaded panel itself, thus causing excess heat in the solar cells?
I presume that as soon as a bypass diode fails, you would see a marked drop in the output of your string, because that panel really will 'bring the other panels down' to its level - I wonder how long a panel can last when a bypass diode (or all three bypass diodes) have failed, and it's in shade? Have any tests been done of this? It should be pretty easy, buy a £200 panel, or a secondhand one that isn't too old, and remove the bypass diodes, put it into a string, and see what happens to it.

I am really surprised to read about this. Does this mean daily tree shade can affect this?

 

[curiouscarbon]

I am really surprised to read about this. Does this mean daily tree shade can affect this?

yes.

as discussed above, when the sun is shining brightly and a tree casts a hard shadow, it means the bypass diodes can activate and heat up quite a bit, depending on how the shade falls on the panel. the heat results in the premature failure of the protective diode. once it fails, the cells will begin to degrade more quickly with shading that has hard edges.

200 hours with 2 hours of partial shading per day (hard shadow from trees) implies the panel warranty would expire after 100 days or 0.3 years

kind regards

 

[wattmatters]

200 hours with 2 hours of partial shading per day (hard shadow from trees) implies the panel warranty would expire after 100 days or 0.3 years

Don't know about elsewhere but here in Australia no manufacture's warranty can usurp obligations under Australian Consumer Law. And such a warranty would. Goods must be reasonably durable and fit for purpose.

Four months is not reasonably durable nor fit for purpose for solar PV panels. The installer is first and foremost responsible for upholding these obligations, but if they are no longer around then the obligation falls directly onto the manufacturer.

Which why installers here generally don't like using crap panels or inverters, and especially don't like dealing with manufacturers who don't stand behind their products. Because while the installer may remedy the fault for the consumer, they still need to recover that loss from the manufacturer.

The phoenix company installers are the ones to watch out for, they will use crap products and leave you high and dry if/when something goes wrong.

 

[curiouscarbon]

to be honest.

if a company said their solar panel warranty was void after 200 hours of hard shading in sunlight,

i would laugh and plainly state that priorities are out of order.

specify a diode with current capacity to mitigate heat failure.

 

[RCinFLA]

forgive my ignorance but dont all panels get shaded everyday at night

At night, you don't have sun illumination on other series cells that drives the shaded PV cell into high reverse bias voltage.

Typically, no more than 20-25 cells in series for each bypass diode. Usually, a long row pair in panels so bypass diode can be in junction box at one end of panel. This limits max reverse bias to about 10-12 vdc. Six row panel means three bypass diodes in junction box.


All PV cells have some shunt defects. This creates their shunt resistance. A cell can have a few bad defects or a lot of small defects to have the same shunt resistance. Problem is when reverse biased due to shading the few bad defects get very hot spots in the cell.

A quality manufacturer examines cells under reverse bias with an IR camera to detect hot spots.


There was a guy on Youtube recently bragging he removed all the bypass diodes in his panels and they work fine. That might be true if he never has any strong shading at mid-day. It is also true he may end up burning down his house. This was pretty common about 15-20 years ago when panels cost more and a lot of DIY'er built their own panels from 'eBay' cells. The DIY'er had no knowledge of PV cell shunt defects and what bypass diodes are for.


Under normal illuminated forward current conditions, a shunt defect is subjected up to about 0.6v due to cell voltage. Under shading, with no bypass diodes, the shunt defect can be exposed up to near full voltage of series array in reverse bias.

If you are lucky, the defect only melts a hole in the plastic backing of panel allowing humidity intrusion.

 

[JCSchwarb]

yes.

as discussed above, when the sun is shining brightly and a tree casts a hard shadow, it means the bypass diodes can activate and heat up quite a bit, depending on how the shade falls on the panel. the heat results in the premature failure of the protective diode. once it fails, the cells will begin to degrade more quickly with shading that has hard edges.

200 hours with 2 hours of partial shading per day (hard shadow from trees) implies the panel warranty would expire after 100 days or 0.3 years

kind regards

This is insane, I see so many neighborhoods that have lots of shade from trees, panels on different parts of the roof - this manufacturer seems to be making panels for solar farms only and not for typical residential.

 

[pollenface]

Hopefully there's no shade in the boxes they come packed in

 

[JCSchwarb]

Hopefully there's no shade in the boxes they come packed in

ROFL! I live in what I call El Scorcho Florida where any bit of shade is much appreciated by everything from cars to plants to people. My deck gets so hot it can’t be walked on without getting 3rd degree burns, so I figured a bit of shade on the panels to knock the edge off would be a good thing, lol.

 

[RCinFLA]

Unless tree shading is very close to array, there will be light diffusion and shaded cells can produce enough current to prevent bypass diodes from kicking in.

Primary issue is cheap bypass diodes that get cooked when there is high bypass current during extreme lighting illumination contrast between full illumination and shaded regions.

 

[pollenface]

My deck gets so hot it can’t be walked on without getting 3rd degree burns

I hate getting 3rd degree burns

 

[SenileOldGit]

yes.

as discussed above, when the sun is shining brightly and a tree casts a hard shadow, it means the bypass diodes can activate and heat up quite a bit, depending on how the shade falls on the panel. the heat results in the premature failure of the protective diode. once it fails, the cells will begin to degrade more quickly with shading that has hard edges.

200 hours with 2 hours of partial shading per day (hard shadow from trees) implies the panel warranty would expire after 100 days or 0.3 years

kind regards

You say that "the heat results in the premature failure of the protective diode". I think it's far (FAR) more likely that the heat CAN result in failure (not necessarily 'premature') of the diode. I asked on this forum if anybody has had a solar panel made in the last five years fail, nobody had one. I can't find ANY evidence of solar panels that are under five years old (i.e. that have bypass diodes) failing, on Google, I searched for hours. I was really worried about shading when I first got my solar panels, because I read the Canadian Solar manual and I was trying to buy optimisers for my panels, but I'm glad I didn't bother.