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Nickus de Vos avatar image
Nickus de Vos asked

Solar panel work in parallel but not in series string

Hi all

I'm trying to help out a friend with a solar panel issue, it's 4x 100W 18V panels.


One of the panels doesn't seam to work in a series string, however it works just fine when connected to the controller on its own, going over 17V around 4A, my conditions wasn't perfect.


The other 3 panels work just fine, I can string them in series, but as soon as I add the 4th one the string doesn't work, I even tried to swop it around to give it another position in the string. I also tried it just with a string of 2 panels but still nothing.


All these tests were done on my Smartsolar 100/20 and I know the controller is good, since I have similar size panels which works as expected.


What can be wrong with this panel, can it be something simple like a fuse or something and is it easy to fix? I never opened a solar panel before.


Nick

Solar Panel
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4 Answers
russ-tanner avatar image
russ-tanner answered ·

try hooking the panels one at a time and check the output voltages. You may have a bad panel.

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Nickus de Vos avatar image Nickus de Vos commented ·

Hi

As I said I did check the panel on its own and the voltage was around 17V, the other 3 panels also checked on their own showed around the same voltage which is fine considering my poor sun conditions while testing.

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Kevin Windrem avatar image
Kevin Windrem answered ·

When panels are connected in series a shaded panel may not support the current the other panels are trying to produce. This can cause the voltage on the shaded panel to reverse. To prevent this, "bypass diodes" are placed across the panel (or sub-strings with the panel).

The panel you are having problems with may have bad diodes. With the panels in series, measure the voltage across the suspect panel. If it is backwards this indicates bad or missing bypass diodes. Don't leave the panel in this state because a reverse voltage on the panel can damage it.

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Nickus de Vos avatar image Nickus de Vos commented ·

Ok I didn't check the voltage with a multimeter, I'll do that tomorrow.

But if the voltage is backwards as you describe and the diodes are bad, won't the panel then also show issues when connected in parallel to the controller?

If the voltage is backwards then surely the Easysolar won't detect the panel at all and in my case it did?

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Kevin Windrem avatar image Kevin Windrem Nickus de Vos commented ·

You won't see a revered voltage in parallel or by itself. It's only in series that the current from other panels can reverse bias a panel that isn't producing as much as the others.

In parallel, a shaded panel will have less current to contribute. By itself, the panel's voltage will drop but won't reverse.

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wkirby avatar image
wkirby answered ·

I have another theory for you to investigate.
I think the rogue panel has a bad connector on it. I have seen this happen before.
The connector mates well with the connectors on the cable leading to the charge controller when connected on its own, but it is not making a good connection with the connectors of neighbouring solar panels.

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svtti123 avatar image svtti123 commented ·

I have to agree I have had this happen as you describe.

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Nickus de Vos avatar image Nickus de Vos commented ·

I'll check it out as a possibility thanks, all connectors used in the system is MC4.

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michelg avatar image
michelg answered ·

Hi, it could be an issue with a dead diode, or simply that part of the wiring has not been correctly welded, and the current is not flowing through it.

I had such issue in one of my panels.

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