LTSpice solar panel, trouble with bypass diodes

Thread Starter

Gustn07

Joined Feb 22, 2024
5
So, I'm currently trying to simulate a solar panel (datasheet is in attachments) in LTSpice. I posted the screenshots below of my schematics I drew and also put the LTSpice file in attachment. Now the simulation works great without the bypass diodes, but when I implement these bypass diodes the results are much lower. The bypass diodes are just normal diodes but when I use zener diodes the results are even worse, no matter what parameters I give. The parameters of the zener diodes used in the picture are: average forward current = 20A and the breakdown voltage is 30V. I'm no expert with these bypass diodes, so is there anyone who can help me with this problem?

without bypass diodes:
1712494637902.png

with bypass diodes:
1712494790134.png

with zener diodes as bypass diodes:
1712495137895.png

Kind regards

August
 

Attachments

crutschow

Joined Mar 14, 2008
34,706
The bypass diodes are shunting the current to ground and you are seeing the forward voltage drop of the three in series.
What is their supposed purpose?
 

Thread Starter

Gustn07

Joined Feb 22, 2024
5
When a solar panel is partially shaded or obstructed the shaded cells produce less electricity than the unshaded cells. This happens because shaded cells create a reverse bias across the shaded portion, essentially acting as loads rather than generators. In a solar panel, cells are typically connected in series to achieve the desired voltage output. When some cells are shaded or otherwise not producing electricity, the output of the entire string drops significantly, as the current produced by the unshaded cells is limited by the shaded ones. So here comes the bypass diode in play. The bypass diode is connected in parallel with each solar cell or a group of cells within the panel. When a cell or portion of the panel is shaded, the bypass diode provides a low-resistance path for the current to flow, effectively bypassing the shaded portion. This allows the current generated by the unshaded cells to continue flowing without being significantly affected by the shaded cells.
 

ericgibbs

Joined Jan 29, 2010
19,024
The bypass diode is connected in parallel with each solar cell or a group of cells within the panel. When a cell or portion of the panel is shaded, the bypass diode provides a low-resistance path for the current to flow, effectively bypassing the shaded portion. This allows the current generated by the unshaded cells to continue flowing without being significantly affected by the shaded cells.
Hi G7,
Can you say where you got this information regarding a parallel diode across a panel.?
E
 

ericgibbs

Joined Jan 29, 2010
19,024
Hi G7,
Your modified sim shows that each panel group has an output of ~14v, so your forward biased bypass diodes will be conducting/shorting to 0V, when the panel is NOT shaded.

EEG57_ 1614.png
 

Thread Starter

Gustn07

Joined Feb 22, 2024
5
But what is the purpose of the three series diodes (D12, D13, and D14) to ground in your sim?
These should represent the bypass diodes. So if the first cells are shaded, the current should run through the diode that is parallell to those cells. My apologies if my image is not clear because of the diodes. These shouldn't be ideal diodes I think because they should have a breakdown voltage so thats something I need to change but I just don't know how. If you have any more questions let me know.
 

eetech00

Joined Jun 8, 2013
4,013
I believe the diodes are basically "steering" diodes and don't have to be zener diodes. Probably can be shockley diodes of appropriate current carrying capacity.
 

Thread Starter

Gustn07

Joined Feb 22, 2024
5
Sorry, but I see no need for those three diodes in you circuit.
Those are what is limiting the voltage.
They shouldn't be removed but instead need to be replaced with something that recreates a bypass diodes. This is necessary because I want to simulate the power curve with different shades. The problem is that I don't know wich kind of diodes I need to replace them with.
 
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