The use of Diodes

[Mikem3]

Knowing nothing about Solar Cells, except that they heat up
and drag down the output if any cells get shaded, I put on my
thinking cap and decided that a diode for each cell would prevent
this happening, I hope, so I bought a load of diodes, but I think
that I have made a mistake, 110 of these diodes are rated at
6 amps 600 volts, normally I would think that the voltage means
maximum limit, but I feel that this might be a wrong assumption.

Do any of you know enough about diodes to give me some good
advice.

Please.

Mike.

 

[AE4KR]

Most commercially manufactured solar panels have diodes built-in to protect against back-feeding and shading issues.

There are a few applications where external diodes could be useful. If you're using parallel batteries which each have their own BMS and/or thermal shutdowns, diodes could be used to isolate them from each other to prevent big surges if their BMSs decide to join or leave the bank with big voltage differences, for example. (But you'd probably want a much bigger diode.)

The most important voltage rating on a diode is PIV, or peak inverse voltage. That's the voltage at which back-feeding the diode will cause it to fail.

Current ratings can be continuous or momentary.

Using a common silicon diode will result in a voltage drop of .65 - .7 volts. That means at 6 amps, it will have to dissipate about 4.2 watts of heat. Be sure to plan for this in your system.

 

[Mikem3]

Thank you AE4KR, these are all common or garden diodes, so you
reckon that they are fine?

Mike.

 

[mikefitz]

Hi Mike from Croydon.
Not too sure how you Intended to use the diodes but with a solar panel, the cells are interconnected in such a way it would be difficult/ impossible to access each cell to make a connection.
All solar panels have bypass diodes installed on the panel to reduce the effect of shading. The panel will have the cells arranged is series groups, two or more groups depending on the size of panel. There is a bypass diodes in parallel with each group of cells.
So your thinking is good, but the panel manufacturer has included the diodes in the design.

The panels do not have blocking diodes In series , the solar controller has built in circuits that prevent back feed.

Mike

 

[Bud Martin]

Knowing nothing about Solar Cells, except that they heat up
and drag down the output if any cells get shaded, I put on my
thinking cap and decided that a diode for each cell would prevent
this happening, I hope, so I bought a load of diodes, but I think
that I have made a mistake, 110 of these diodes are rated at
6 amps 600 volts, normally I would think that the voltage means
maximum limit, but I feel that this might be a wrong assumption.

Do any of you know enough about diodes to give me some good
advice.

Please.

Mike.

Are you talking about putting in diode in parallel in parallel of each cell in the solar panel? Panel with 72 cells will need 72 diode, but how are you going to get to each cell on the panel assembly.
Panel these days has bypass diode for each string in the panel.

Bypass Diodes | PVEducation

www.pveducation.org

 

[Mikem3]

Thank you mikefitz, I am a real novice, but trying to build a solar
set-up from scratch, so I am learning swiftly, and each suggestion
from you experienced people are a real help.

Mike.

 

[Mikem3]

Are you talking about putting in diode in parallel in parallel of each cell in the solar panel? Panel with 72 cells will need 72 diode, but how are you going to get to each cell on the panel assembly.
Panel these days has bypass diode for each string in the panel.

I am not sure, Bud Martin,at the end of each set, I am looking at adding a diode
between the cells and the bus cable to the batteries.

I really am learning.

Mike.

 

[Bud Martin]

I am not sure, Bud Martin,at the end of each set, I am looking at adding a diode
between the cells and the bus cable to the batteries.

I really am learning.

Mike.

May be you are talking about Blocking diode.
Draw out the diagram showing where you are planning to put the diode.

What is Blocking Diode and Bypass Diode in Solar Panel Junction Box?

Bypass Diode and Blocking Diode Working used for Solar Panel Protection in Shaded Condition. What are inside a Solar Panel Junction Box. Working of Blocking Diode. Working of a Bypass Diode.

www.electricaltechnology.org

 

[AE4KR]

Thank you AE4KR, these are all common or garden diodes, so you
reckon that they are fine?

Mike, I think we're all struggling to understand what problem the diodes would address, and where you'd plan to install them. So far, it sounds as if they'd be redundant to the diodes already in the panels.

EDIT: Ahhh...building your own panels from individual cells. Got it.

Using an individual diode for each cell would not work, because it will drop the output of each cell by .65 volts. That's about what individual silicon cells produce. There would be nothing left.

It would be more reasonable to figure out what you want the panel's output voltage to be, use strings of individual cells in series to get that voltage, then use one diode at the point the string is parallel-connected to other strings. You'll need to add one more cell than anticipated to cover the voltage drop in the diode. On an individual string, PIV of 600 volts and Imax of 6 amps should be plenty, unless you're creating very long series strings.

 

[mikefitz]

Building a panel from individual cells in an interesting concept, in the same category as wearing hair shirts or building perpetual motion machines.
If your solar cell has a specification with a maximum current lower than 6 amps then you could use the diodes.
I guess with shading the volt drops will result in too low a output voltage to be of any use, unless you have lots of cells in series.

Mike

 

[Mikem3]

Thank you all once again, as far a solar goes, I really am a novice!

Bud Martin, that is the best site that I have seen so far, the basics
and methods of building solar, seems to be a deep secret, to me
it is.

AE4KR, your observations are also helpful, I had no idea that a diode
would use all the voltage.

mikefitz, you could be right about the Hair Shirts, etc., but I have plenty
of time to try things, I don't know about the cells yet, I bought them as
they were the highest rated according to the site, they are 383 watts each,
I was looking for 6 volts, but never got an answer to the question, I won't
know what the voltage is until I put some wires on a panel.

Mike.

 

[Don B. Cilly]

A Schottky diode usually has a much lower forward voltage drop.
-

 

[mikefitz]

383 watts per solar cell is not possible.
A single solar cell generates about 0.6 volts. The current will depend on the size of the cell , perhaps around 5 amps for a large cell.
Perhaps a link to the cells you have would help the discussion.

Mike

 

[efficientPV]

Bypass diodes should normally be not more than 45V PIV. There are specific diodes designed for this purpose and going over 45V will increase the forward voltage of the diode greatly increasing heat. As a bonus, these low voltage diodes easily short out in the event of a near lightning strike saving the cells from damage.

 

[Mikem3]

Thanks again for all the great help, some I don't yet understand,
but I will soon.

Mikefitz, below is a picture of the front and the back of cells that
I have, I also include the link to where they came from, Aliexpress,
which is a branch of Alibaba.
Site where purchase was made.

Mike.

 

[Don B. Cilly]

The purpose of the exercise still not being very clear... are you going to make some sort of sculpture/film-prop/robot-shirt out of them? you must realise that economically at least, it make no sense? Even without counting labour... if you plan to use them to charge batteries...

-

 

[Bud Martin]

Thanks again for all the great help, some I don't yet understand,
but I will soon.

Mikefitz, below is a picture of the front and the back of cells that
I have, I also include the link to where they came from, Aliexpress,
which is a branch of Alibaba.
Site where purchase was made.

Mike.

View attachment 88682

According to your link, each one of that piece is rated at 4.79W.

 

[Mikem3]

I don't understand Bud Martin, I just had a look again, I can assure you
that, that 4.79W was not there when bought that cells.

I keep learning and spending stupidly.

I based my build idea on a report that MIT had a better design than that
on a roof, it is a zigzag tower, I only had the shape of the cell layout, but
no circuit, I thought that I could work that out!

Thanks to your suggestions, I can, hopefully come up with something, I
thank you all for your replies and advice, if you think of how I can achieve
any success, please tell me, I will be grateful for your guidance and will make
sure whose idea it was, along the way.

Mike.

 

[Bud Martin]

I don't understand Bud Martin, I just had a look again, I can assure you
that, that 4.79W was not there when bought that cells.

I keep learning and spending stupidly.

I based my build idea on a report that MIT had a better design than that
on a roof, it is a zigzag tower, I only had the shape of the cell layout, but
no circuit, I thought that I could work that out!

Thanks to your suggestions, I can, hopefully come up with something, I
thank you all for your replies and advice, if you think of how I can achieve
any success, please tell me, I will be grateful for your guidance and will make
sure whose idea it was, along the way.

Mike.

They sell the 383W kit which has 80pc of that cell to create 385W PV panel that you have to wire them together. Read the description.

 

[robby]

Okay I am confused!
So the idea is to take a single cell that is producing .5V and run it through a Diode which in best case will drop that voltage by .4V
So your panel will only produce about 20% of it's original power??
Am I missing something?