Author Topic: Solar panel shading  (Read 479 times)

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Offline asdasd296

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Solar panel shading
« on: April 20, 2021, 03:37:13 pm »
Hello

I have searched this topic lot on internet and there seems to be lot of miss leading information in my opinion.

Statement is when one solar panel is shaded or gets bird poo then that will drag whole system down. This in reality is not happening.
Reason is that there is at least one, most probably 3 by-pass diodes in solar panel junction box.
by-pass diodes will by-pass the shaded solar panel and system performance is decreased only by one panel.

I have tested this on my solar installation witch is 5,8 kWp system with 5 kW central inverter. I covered one solar panel with piece of card board and system output decreased around one panel output power.

what is really case in here? is that miss leading information only marketing for micro inverters or what?
 

Offline CatalinaWOW

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Re: Solar panel shading
« Reply #1 on: April 20, 2021, 03:55:10 pm »
Perhaps it is just ancient knowledge, passed down without checking or updating.  Bypass diodes weren't always a thing in solar panels.

Never think first of evil.  Incompetence is far more common.  Even though evil is not rare.
 

Offline fourtytwo42

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Re: Solar panel shading
« Reply #2 on: April 20, 2021, 04:26:43 pm »
Unfortunately as you have discovered lot's of information on the internet is rubbish. When it comes to things like solar all sorts of "experts" creep out of the woodwork who have no idea what they are talking about.

As you point out most commonly used large solar panels of 60 cells or above are divided into sub-strings with shading diodes, depending upon the amount of the panel shaded it will still operate to a limited extent, insofar as the whole system is concerned a few panels shaded will not cause system failure in a properly designed system (the inverter should tolerate a wide input voltage range).

Micro inverters do little except reduce system MTBF & increase costs.
 

Online bdunham7

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Re: Solar panel shading
« Reply #3 on: April 20, 2021, 04:41:14 pm »
I can't speak for others nor the claims they make, and without knowing when they made those claims and to what specific systems and panels they were referring to, you can't fairly evaluate or criticize them.

As far as shading goes, if shading did not have a demonstrable impact on solar production, SolarEdge would not have a reason to exist since their product does nothing but deal with uneven panel production.  Can you cite a recent, reasonably credible source that makes the claim that shading one one cell or one panel will 'shut down' a string system?

Now as for what actually happens and why shading might be an issue, lets take an example of a 10 panel string with 5 panels in full sunlight and 5 evenly shaded so that they get 50% sunlight.  What outputs would you expect for a string inverter versus a SolarEdge or Enphase system, assuming the panels have bypass diodes?  Which are you most likely to encounter in a real-world situation--partial shading of part of an array during part of the day or one random panel being 100% shaded by cardboard?

A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline asdasd296

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Re: Solar panel shading
« Reply #4 on: April 20, 2021, 05:25:47 pm »

Can you cite a recent, reasonably credible source that makes the claim that shading one one cell or one panel will 'shut down' a string system?

EEVblog recent video in time 23:50.


Now as for what actually happens and why shading might be an issue, lets take an example of a 10 panel string with 5 panels in full sunlight and 5 evenly shaded so that they get 50% sunlight.  What outputs would you expect for a string inverter versus a SolarEdge or Enphase system, assuming the panels have bypass diodes?  Which are you most likely to encounter in a real-world situation--partial shading of part of an array during part of the day or one random panel being 100% shaded by cardboard?


Yes in many situations SolarEdge or Enphase system will produce more energy overtime I don't deny that.
 

Online bdunham7

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Re: Solar panel shading
« Reply #5 on: April 20, 2021, 05:52:33 pm »
I said "credible source".   :-DD

Yes, that comment appears to not be fully supported by evidence, but it was just a comment during a video on another topic, so possibly not fully thought through.  Perhaps a correction is in order.  One shaded panel in a plain string should simply result in a 3-5 volt drop (3 diodes) in whatever the remaining panels produce, which isn't a big drag.  OTOH, he did have a chart showing a steep dropoff, so perhaps his bypass diodes have burned out on the panel that gets shaded a lot.  They do have to conduct a lot of current during a shading event.
« Last Edit: April 20, 2021, 05:54:16 pm by bdunham7 »
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline Marco

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Re: Solar panel shading
« Reply #6 on: April 20, 2021, 07:52:25 pm »
Statement is when one solar panel is shaded or gets bird poo then that will drag whole system down.
Google seems to have no problem to have their first page of answers to solar panels and shade be accurate, so the statement is hardly common.
« Last Edit: April 20, 2021, 07:55:48 pm by Marco »
 

Online bdunham7

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Re: Solar panel shading
« Reply #7 on: April 21, 2021, 07:53:48 pm »
Or in some instances perhaps the theory that the blocking diodes should mostly alleviate shading issues isn't correct.  I hadn't considered that the MPPT might not track correctly on some inverters.

https://www.eevblog.com/forum/blog/eevblog-1386-295w-inverter-vs-370w-solar-panel-wtf/msg3554145/#msg3554145
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 


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