Placement of bypass diodes

Rogli

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Hello mates. I am new here and have some beginner level experience with solar panels. I have asked this question about bypass diodes placement from some installers but they have no idea about it. Apparently, installers do not place bypass diodes in their installations but I heard that bypass diodes can bypass an entire solar module, if it becomes shaded (I am talking about modules connected in series). I attach a picture for your consideration showing 6 solar modules wired in series.

Where the bypass diodes need to be placed and in which direction? Let's assume each panel is 45 volts at 17 amps. It would help in understanding if you can extend this picture by showing the placement of bypass diodes (20 or 30 amps each) and their direction. The goal is to bypass the entire module in the event of partial shading because otherwise it would shut down the whole system. I intend to run load without battery through inverter. I understand that upon clouds, inverter will shut down the load but I want to deal with partial or full shading of a module(s).
 

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mopat

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Bypass diodes are connected in parallel with modules, a photovoltaic cell or panel to shunt the current around it.
1621621369337.png
 

mikefitz

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Almost all solar panels have bypass diodes in the junction box on the back of the panel. Each panel has the cellsbypass3.jpg divided into two or more elements connected in series with a bypass diode across each element.
bypass diode.jpg


Mike
 
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Rogli

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Bypass diodes are connected in parallel with modules, a photovoltaic cell or panel to shunt the current around it.
View attachment 49924
Thanks a lot, and for this illustration. Based on your response, I extended my own illustration of the modules string. Please check and let me know if placement of diodes is ok, and the direction from negative to positive? In final positive line, I illustrated a blocking diode.

I have a question though : since, MC4 connectors are used join the lines, how can I get a diode in between? They do sell MC4 diodes but it's shape / orientation is designed to fit the MC4 terminal attached to the positive wire (line). In other words, they are blocking diodes.
 

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rin67630

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Thanks a lot, and for this illustration. Based on your response, I extended my own illustration of the modules string. Please check and let me know if placement of diodes is ok, and the direction from negative to positive? In final positive line, I illustrated a blocking diode.

I have a question though : since, MC4 connectors are used join the lines, how can I get a diode in between? They do sell MC4 diodes but it's shape / orientation is designed to fit the MC4 terminal attached to the positive wire (line). In other words, they are blocking diodes.
You don't need to add manually bypass diodes if the panels are already equipped (quasi all are!). You need (if ever) only ONE blocking diode per string, not one per panel as shown on your picture.
 

Rogli

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You don't need to add manually bypass diodes if the panels are already equipped (quasi all are!). You need (if ever) only ONE blocking diode per string, not one per panel as shown on your picture.
I understand that about blocking diode per string however goal here is to bypass the entire solar panel (module) in case of shading. Please refer to the picture by mopat in this thread where bypass diodes are shown in addition to the blocking diodes.
 

rin67630

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I understand that about blocking diode per string however goal here is to bypass the entire solar panel (module) in case of shading. Please refer to the picture by mopat in this thread where bypass diodes are shown in addition to the blocking diodes.
Bypass diodes are mainly already built in. They are essential to protect panels cells from reverse voltage in a string when a part of the panel is shaded.
Your attachment picture is wrong.
 

Rogli

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Bypass diodes are mainly already built in. They are essential to protect panels cells from reverse voltage in a string when a part of the panel is shaded.
Your attachment picture is wrong.
I am specifically referring to the color picture shared by the member namef "mopat": is this picture the one you are referring to?


From my understanding, bypass diodes are built in the solar modules: but what I meant is the bypass diodes to bypass entire solar module from a string. Again, the color coded picture shared by mopat clearly demonstrates that.

Note that If I buy solar modules the bypass diodes are inside the junction box but I would like to install further diodes as shown in the picture by mopat.
 

rin67630

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From my understanding, bypass diodes are built in the solar modules: but what I meant is the bypass diodes to bypass entire solar module from a string. Again, the color coded picture shared by mopat clearly demonstrates that.

Note that If I buy solar modules the bypass diodes are inside the junction box but I would like to install further diodes as shown in the picture by mopat.
That is not necessary: the bypass function for the whole panel is ensured by the built in diodes as well.
You could at the very maximum get for a 72V string with a completely shaded panel 35,5 V instead of 35,1V (one Schottky 0.4V forward voltage instead of two) if you add additional bypass diodes... Not worth the cost and effort.
 

mopat

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Your attached white board drawing leaves a lot to be desired. You seem to have drawn diodes connected across two different strings; that is not correct. Most everyone explained bypass diodes are "built-in". Here's a photo:
1621856151165.png

What panels are you (going to) using? Manufacturer & model number = ?

A standard 60 cell PV module is usually built from 3 substrings, each protected by a bypass diode. The 3 substrings are serially connected to each other to form the PV module (as shown in photo).

Bypass diodes are a standard addition to any crystalline PV module. The bypass diodes’ function is to eliminate the hot-spot phenomena which can damage PV cells and even cause fire if the light hitting the surface of the PV cells in a module is not uniform. The bypass diodes are usually placed on sub-strings of the PV module, one diode per up to 20 PV cells. This configuration eliminates the creation of hot-spots and enables the PV modules to operate with high reliability throughout their lifetime.In addition to effectively fulfilling this function, many people believe the bypass diodes are also effective in reducing power loss due to shading in PV installations. This is far from the truth.
 

Rogli

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Thanks. What I heard was that bypass diodes can be placed outside the solar panel as mopet demonstrated in the picture. I am not sure if the picture refers to multiple panels or strings of cells in one panel (or PV module).
What is still not clear is how to mitigate the entire power loss in a string of panels due to shading on a single panel. One panel shading causes entire string to lose power.
That is not necessary: the bypass function for the whole panel is ensured by the built in diodes as well.
You could at the very maximum get for a 72V string with a completely shaded panel 35,5 V instead of 35,1V (one Schottky 0.4V forward voltage instead of two) if you add additional bypass diodes... Not worth the cost and effort.
 

Rogli

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Your attached white board drawing leaves a lot to be desired. You seem to have drawn diodes connected across two different strings; that is not correct. Most everyone explained bypass diodes are "built-in". Here's a photo:
View attachment 50207

What panels are you (going to) using? Manufacturer & model number = ?

A standard 60 cell PV module is usually built from 3 substrings, each protected by a bypass diode. The 3 substrings are serially connected to each other to form the PV module (as shown in photo).

Bypass diodes are a standard addition to any crystalline PV module. The bypass diodes’ function is to eliminate the hot-spot phenomena which can damage PV cells and even cause fire if the light hitting the surface of the PV cells in a module is not uniform. The bypass diodes are usually placed on sub-strings of the PV module, one diode per up to 20 PV cells. This configuration eliminates the creation of hot-spots and enables the PV modules to operate with high reliability throughout their lifetime.In addition to effectively fulfilling this function, many people believe the bypass diodes are also effective in reducing power loss due to shading in PV installations. This is far from the truth.
 

Rogli

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Thanks for your message. I understand the function of bypass diodes inside the panel but I am referring to the picture you earlier posted : are the boxed illustrations strings inside one panel or they are 4 separate solar panels (or PV modules however you may wish to call them)?
If they are solar panels, it seems that each 2 are connected in series (two strings), and then two strings wired in parallel.

Referring now to my picture, the boxes represent 6 solar panels (PV modules). Each panel is 45v 17 amps. These panels are wired in series, thus voltage shall sum up. It is just one string consisting of 6 solar panels wired in series. I understand that each panel has built-in diodes. But the problem occurs when one panel gets shaded partially or fully ; entire string output is lost. To mitigate this, I heard that it is possible to place bypass diodes across the wires joining them. This looks very much like the picture you posted (assuming the boxes are 4 separate solar panels) except that in my picture there is just a single string.

Additional note: I aim to join 6 600 watts panels in series and output wires to inverter in order to run an airconditioner. Inverter is off-grid which works without battery. I aim to run airconditioner without battery during the sun hours. If one panel becomes shaded, inverter would trip and therefore the airconditioner.
 

rin67630

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Thanks. What I heard was that bypass diodes can be placed outside the solar panel as mopet demonstrated in the picture. I am not sure if the picture refers to multiple panels or strings of cells in one panel (or PV module).
What is still not clear is how to mitigate the entire power loss in a string of panels due to shading on a single panel. One panel shading causes entire string to lose power.
No.
The total voltage will be reduced by the voltage of the shaded panel + n times 0.5V.
n being the number of built-in bypass diodes.
If you frequently have shaded panels, you might want to prefer parallel configurations.
 

Rogli

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No.
The total voltage will be reduced by the voltage of the shaded panel + n times 0.5V.
n being the number of built-in bypass diodes.
If you frequently have shaded panels, you might want to prefer parallel configurations.
What I have observed is that the whole system would shut down, if one panel in a string of panels connected in series gets shaded. For this reason, there are micro-inverters instead of just one inverter.
I prefer parallel configuration, but the inverter I have is designed for panels in series. Anyways, I still am now confused about the picture shared by mopat, since you say it is the wrong picture.
 

Hedges

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What I have observed is that the whole system would shut down, if one panel in a string of panels connected in series gets shaded. For this reason, there are micro-inverters instead of just one inverter.
I prefer parallel configuration, but the inverter I have is designed for panels in series. Anyways, I still am now confused about the picture shared by mopat, since you say it is the wrong picture.

Mopat's picture shows correctly connected bypass diodes and reverse-blocking diodes.

Your hand drawn sketch doesn't show how diodes are connected, but quantity and location appears to indicate they would go between panels (which is wrong for bypass diodes), also their orientation is wrong.

PV panels ought to have bypass diodes built in. Usually two or three; all will be in series contributing their voltage drop if all sections of panes are shaded.
If you get zero output with one panel shaded, could be faulty bypass diodes. Some DMM have a "diode check" scale which could be used to test the diodes if you open junction box and have the panel in darkness. Checking the two or three in series might not work with the DMM; you have to know how to set up additional hardware to test it.

If you do need to bypass an entire diode with panels that could be done. You could buy blocking diodes with MC4 connectors and pairs of "Y" connectors, then connect a panel in parallel with a diode. I think the diode polarity (and its connector gender) is already correct for that.
 

Rogli

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Greetings Hedges. You got my concern spot-on. Thanks for understanding.
Seems that the panels I have experienced are poor quality (I got the news of rejected lot panels being sold from China and then resold as fresh stock by some resellers).

If the picture by mopat is correct, then why the bypass diodes are installed outside the panels? Or that is one panel? I am taking it as 4 panels. Please clarify.

In your last paragraph, did you mean bypass an entire panel with diode? I would be so grateful if you please hand sketch a diagram. In near future, I would like to install six 650 watts solar panels wired in series to power an inverter to in-turn power an air-conditioner.
Thank you so much.
 

Hedges

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Like this.
But cheaper to just open junction box (if you can) and solder in replacement diodes. Go way oversize so they run cool.
Diodes are only needed if shading happens. But can be important in that case, to avoid damage to shaded cells.

1622392159873.png
 
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