Author Topic: Anyone with experience with partially shaded panels?  (Read 471 times)

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Offline Sredni

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Anyone with experience with partially shaded panels?
« on: June 26, 2022, 01:08:50 pm »
I am... asking for a friend.

By partially shaded I mean there would be trees on one side of the panels that will cast a shade on a third or even half the panels in the later hours, near sunset (actually, I --- I mean my friend could place panels on both sides of the trees, so one set of panels will be partially shaded in the first hours of the day, while the other set of panels would be partially shaded in the last hours.

I am not as much concerned about the inevitable drop in power produced, as I am in the life of the panels. I have read skimmed through a few papers and... MPPT is not so easy.

Why I-- this friend of mine is considering this complication?
Because he has a naturally sloped part of his land that looks south and that it will lend itself to place the panels at the right (average) angle. Plus, there is room for at least 2.5 times the panels that can be placed on the roof. Plus, there is the possibility to mount them on a pivoted structure that would make them seasonally tiltable to get the right angle each season. Plus, they can be cleaned every time they are dirty.

Are there people, out there, with panels on their roof that get shadow from nearby buildings or tall trees? Or wishfulthinkers like this friend of mine who have their panels on the ground and have experience with partial shading (and potential remedies to avoid shortening the life of panels)?
Do they use multiple MPPT circuits to track the maximum power for each (subset of) panel(s)? Or is not worth the effort, and we better dig some coal, instead?

EDIT: corrected MMPT to MPPT
« Last Edit: June 26, 2022, 01:57:05 pm by Sredni »
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Online bdunham7

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Re: Anyone with experience with partially shaded panels?
« Reply #1 on: June 26, 2022, 01:24:43 pm »
I have an installation where some of the panels are shaded for a few hours in the morning and others for a few hours in the evening.  What is the concern about panel life?  I've not heard of that as an issue.  Mine are 10 years old and haven't had any problems.
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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Offline Sredni

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Re: Anyone with experience with partially shaded panels?
« Reply #2 on: June 26, 2022, 01:28:00 pm »
What I have read so far is that some of the cells in the panels might end up sinking current and degrade with time because of that. I will try to fetch the source - it basically said that not all cells in a panel are protected by diodes (I guess there are clustered in groups). But I am relieved to hear about your experience.
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Offline Jeroen3

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Re: Anyone with experience with partially shaded panels?
« Reply #3 on: June 26, 2022, 01:34:52 pm »
There are several approaches.

1. The MPPT wil scan more often. There are bypass diodes that pass the current when a cell is shaded or defective. (goodwe method)
2. Split the string size to multiple mppt, shaded and unshaded panels. (or based on azimuth and angle)
3. Use optimizers that can bypass panels which are not producing. (solaredge method)
4. Use microinverters. (enphase method, I have this, 3 panels have shade from the building itself until 1pm)

Eventually you can also worry about the panel orientation with regards to in which orientation the cells are put in series.

« Last Edit: June 26, 2022, 01:39:11 pm by Jeroen3 »
 
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Online bdunham7

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Re: Anyone with experience with partially shaded panels?
« Reply #4 on: June 26, 2022, 01:38:34 pm »
What I have read so far is that some of the cells in the panels might end up sinking current and degrade with time because of that. I will try to fetch the source - it basically said that not all cells in a panel are protected by diodes (I guess there are clustered in groups). But I am relieved to hear about your experience.

In a series circuit, the individual cells will block current, not sink it, if they are shaded.  On mine, the 60 cell panels have 3 bypass diodes so 20 cells per diode.  If one and only one cell were completely shaded, it would have to withstand the potential of the other 19 cells.  Since it is just a diode, as long as it has a reverse voltage capability of at least 15 volts or so it should be fine.
« Last Edit: June 26, 2022, 01:57:55 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 Siwastaja

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Re: Anyone with experience with partially shaded panels?
« Reply #5 on: June 26, 2022, 01:42:36 pm »
Bypass diodes take over to prevent panel voltage (or more correctly, substring of the panel, usually one third) going negative (by more than Vf of the diode). Obviously you could assume that bypass diode is rated to carry the current generated by other panels of the same current rating, and last as long as the panels do.
 


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