Solar Panels = what is the difference?

[Newcastle George]

My son, Guy, has given me 4 panels, one of which I am about to use as a replacement for a faulty one on the bus. Can someone explain the difference between the two connections on the rear of the panels as shown below.

Bus panel

100_6846 (Custom).JPG

Donated panel

100_6848 (Custom).JPG

George

[jon_d]

The bus panel has the lid taken off and is showing the bypass diodes.

[Newcastle George]

I realise that Jon but does the other contain miniature bypass diodes as it is half the size? I can't remove the cover.

George

[T1 Terry]

Cable on the left of screen, the end where there is no strip on the diode, is negative. The panel has three series groups of modules, each linked to the next via the diodes. The easiest path for the current to flow is through a series section that is generating current because the voltage on the banded side of the diode will be higher than the non banded side, sort of an electrical one way valve with spring pressure and head pressure holding it in the closed position.
If the series section is not generating current, then the voltage on the banded side of the diode will be very close to the voltage on the non banded side. The series circuit through the non active solar modules becomes a resistor of a higher value than the resistance through the diode, so the diode passes the current onto the next series string and so on. The diode is now similar to the one way valve in the open position, the "electrical" pressure is enough to overcome the "spring" pressure and push the valve open and it will remain open until the pressure reduces to below the "spring" pressure .......

Current flow and electron flow still does my head in sometimes, but I'm fairly confident I got the diode flow direction correct .....

T1 Terry

[jon_d]

Are you sure George?

They look the same size to me.

george.jpg

Regardless, the new panel has bypass diodes which is what you need. So, it doesn't matter about the old panel because you're not going 'backwards'.


Further to Terry's info.
Bypass diodes stop sections of the solar panel overheating if the panel is partly shaded.
The current flows though the diode instead of though the shaded section.

[T1 Terry]

Are you sure George?

They look the same size to me.
george.jpg

Regardless, the new panel has bypass diodes which is what you need. So, it doesn't matter about the old panel because you're not going 'backwards'.


Further to Terry's info.
Bypass diodes stop sections of the solar panel overheating if the panel is partly shaded.
The current flows though the diode instead of though the shaded section.

Got myself into all sorts of strife with a Qld uni professor on another forum about the need for blocking diodes to stop one string feeding back into a shaded string where multiple series strings were paralleled into a controller solar input ..... Even showing the thermal imaging and burnt out panels wouldn't shift his opinion that I didn't know what I was talking about .... I wasn't an EE or a professor after all

T1 Terry

[jon_d]

Yep. Blocking diodes and bypass diodes are different.

Blocking diodes stop a parallel string from feeding into another parallel string. The feeding occurs when one string is of a lower voltage and the bypass diodes (or cells) of that string conduct.

It's not immediately apparent because a good MPPT will sweep the range and find the highest power point which by default minimizes the back flow.

I only discovered mine when I noticed that the amp meter on a string was showing negative current in very low light conditions and the charger was "off"

[Newcastle George]

Jon, they look the same size because they are cropped photos. The one showing the diodes is the stuffed panel, the other is the one I intend replacing it with. As the other 3 panels on the bus are the same as the stuffed one do I have a problem?

George

[jon_d]

oOes the label say it has bypass diodes fitted?

[T1 Terry]

The question is becoming confusing George, do you need to know the difference between the two panels, or do you need to know if the replacement panel that you have given zero specs for will do the same job as the panel being replaced that you have also given zero specs for .......

Are the panels connected in series or parallel to the controller?

T1 Terry