Author Topic: Solar panel diode confusion  (Read 1972 times)

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Offline andrewlaphamTopic starter

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Solar panel diode confusion
« on: September 15, 2019, 07:24:26 am »
Hey guys can someone explain the purpose of this diode? Im guessing its not to block the flow of current from the battery to the panel otherwise it would be the other way around. Is it some sort of rectifier? 835740-0
 

Offline fourfathom

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Re: Solar panel diode confusion
« Reply #1 on: September 15, 2019, 07:34:32 am »
This is most likely a "bypass diode", used to let a series string of panels continue to operate (at a lower voltage) when one of the panels is shaded.  Without this diode, the shaded panel would present a high impedance and prevent current from flowing in the string.  Here's a link to an explanation: https://www.electronics-tutorials.ws/diode/bypass-diodes.html
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Offline andrewlaphamTopic starter

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Re: Solar panel diode confusion
« Reply #2 on: September 15, 2019, 08:48:49 am »
Ahh ok. I have two of these panels in parallel but need to add a blocking diode would it make sense to just flip the exsisting diodes?   
 

Offline andrewlaphamTopic starter

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Re: Solar panel diode confusion
« Reply #3 on: September 15, 2019, 09:00:26 am »
Just had a look and its a schotty 1n5819
 

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Re: Solar panel diode confusion
« Reply #4 on: September 15, 2019, 09:06:16 am »
It is wired in series so it is a blocking diode. A bypass diode would connect to both leads from the cell array.
 
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Offline andrewlaphamTopic starter

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Re: Solar panel diode confusion
« Reply #5 on: September 15, 2019, 09:46:04 am »
but if its s blocking diode isn't it facing the wrong way?
the picture i posted has the configuration i assumed it should be in but the fact that the diode is flipped is still a mystery to me.
 

Offline fourfathom

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Re: Solar panel diode confusion
« Reply #6 on: September 15, 2019, 03:41:56 pm »
It is wired in series so it is a blocking diode. A bypass diode would connect to both leads from the cell array.
Is it wired in series? Looks parallel to me, although it's not completely  obvious. You could repurpose this diode as a  series blocking diode but this may not be necessary, especially with such a low-power panel.   It will depend on your charge  controller.
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Offline thedoc298

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Re: Solar panel diode confusion
« Reply #7 on: September 15, 2019, 11:56:40 pm »
I don't know what that box is or it's usage, but the diode would function as a reverse polarity diode.
 

Offline boB

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Re: Solar panel diode confusion
« Reply #8 on: September 16, 2019, 12:02:02 am »

The diode is what fourfathom said it was for.   Shading of the panel when it is in series with other modules.

A small diode works here because the PV module is very small (5 watts ?)

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Re: Solar panel diode confusion
« Reply #9 on: September 16, 2019, 01:14:59 am »
Looks like series to me.

 

Offline boB

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Re: Solar panel diode confusion
« Reply #10 on: September 16, 2019, 01:26:56 am »
If it is series, then it would most likely so be that the battery is not discharged as much by the panel over night.

PV modules are very leaky that way so the diode can help that.

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Re: Solar panel diode confusion
« Reply #11 on: September 16, 2019, 01:35:42 am »
Is this panel sold for some specific use like battery charging?

Small panels intended for direct connection to a lead acid battery will typically have a series diode to prevent discharge of the battery. Panels intended for use with a charge controller or inverter will typically have a parallel diode or no diode.
 
 
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Offline fourfathom

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Re: Solar panel diode confusion
« Reply #12 on: September 16, 2019, 03:11:57 am »
Looks like series to me.

Yes, looking at your annotations you appear to be right (and I was wrong).  It is a series diode, and is there to prevent a dark panel from draining the battery.  A good controller won't let this happen anyway, but with a cheap controller or a direct battery connection the diode is probably a good idea.

I tested some of my 100W panels and they actually didn't leak significantly until the reverse voltage exceeded the panel Voc (open-circuit voltage).  Other panels may be more leaky than mine were.
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Offline andrewlaphamTopic starter

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Re: Solar panel diode confusion
« Reply #13 on: September 16, 2019, 10:38:16 am »
Looks like series to me.



jesus that picture really cleared everything up for me, i thought the diode was facing the wrong way and it was wreaking my head. haha, thanks
 


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