Placement of bypass diodes

flynmoose

New Member
A little thread necro here but I am as confused as OP and my confusion comes straight from late Amy Beaudet - The Solar Queen.

In her article on diodes she states:

Most solar panels have bypass diodes built in these days, so you typically won’t have to worry about that anymore. However, if you have multiple solar panels wired together in series, and you consistently have shading on one or more of the solar panels, wiring a bypass diode in parallel across the shaded panel can prevent the current from being forced back through the shaded panel and cause it to heat and lose power. So, it acts the same as the internal bypass diodes, but bypasses the entire panel instead of the individual cells.

So I assume this is what OP was referring to and @Hedges is offering in the previous post as a solution.

I am debating 3S vs 3P with 215watt / 22Voc. I would prefer 3S for wire size and lower transmission loss as a have a fairly long run from where the roof penetration is to where the MPPT will live. But an RV roof is an ever-changing solar surface and parking could easily change shading where one panel is partially or completely shaded while another is not. Seems like a lot of factory systems (ZAMP) only work with 2/3/4P setups - I guess because they build lower voltage PWM chargers? Or maybe because of this very issue - which running each panel in parallel ups the current but eliminates the shading concerns on an RV roof?

Will the J-Box diodes be all I need or should I also look to have full-panel bypass diodes in the event that I have sun/shade mix on my roof?
 
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Hedges

I See Electromagnetic Fields!
If the PV panels data sheet says having a string partially shaded is improper use and voids warranty, then added bypass could be useful. Otherwise I wouldn't worry about it, just rely on what's in the junction box.

If used panels, you could test to make sure diodes are functional.
 

Rogli

New Member
Like this.
But cheaper to just open junction box (if you can) and solder in replacement diodes. Go way oversize so they run cool.
Diodes are only needed if shading happens. But can be important in that case, to avoid damage to shaded cells.

View attachment 51001
Thanks so much. I shall try this. I shall try to post a picture from the junction box which is too cheaply built. Brass sheets instead of copper and diodes quality is poor. I need to solder the replacement diodes and wires coming out of the panel, but that's another issue. I bought a 200w soldering iron for that job.
 

Rogli

New Member
A little thread necro here but I am as confused as OP and my confusion comes straight from late Amy Beaudet - The Solar Queen.

In her article on diodes she states:



So I assume this is what OP was referring to and @Hedges is offering in the previous post as a solution.

I am debating 3S vs 3P with 215watt / 22Voc. I would prefer 3S for wire size and lower transmission loss as a have a fairly long run from where the roof penetration is to where the MPPT will live. But an RV roof is an ever-changing solar surface and parking could easily change shading where one panel is partially or completely shaded while another is not. Seems like a lot of factory systems (ZAMP) only work with 2/3/4P setups - I guess because they build lower voltage PWM chargers? Or maybe because of this very issue - which running each panel in parallel ups the current but eliminates the shading concerns on an RV roof?

Will the J-Box diodes be all I need or should I also look to have full-panel bypass diodes in the event that I have sun/shade mix on my roof?
You exactly got me right. I, too, was discussing this based on YouTube video of Amy. I didn't know she has passed away. May her soul rest in peace, amen. I got the idea that what she meant was adding a bypass diode to bypass an entire solar panel.
Picture shared by Hedges seems to correspond to that idea.

The panels that I have are of very poor quality. Few of them have developed micro cracks in the cells (visible lines). I get two to three amperes less than the rated current in just 2 year of use. Recently bought a 200w soldering iron to solder new diodes (plenty of them in a junction box as someone suggested) and panel positive and negative wires that are loose (I have temporarily used nylon zip-ties). So I have these panels combined in parallel, including the ones with micro cracks and damaged cells, which are connected to the solar charge controller to charge the lead-acid deep cycle tubular battery. I hope the panels with the micro cracks and damaged cells do not cause any problems to the other panels in the parallel, or can they? I individually tested thrm by short-circuiting them to measure the DC amps during sun and they do yield some amps anyhow.
 

sunshine

Solar Addict
I hope the panels with the micro cracks and damaged cells do not cause any problems to the other panels in the parallel, or can they?
You could put a blocking diode on each panel if in parallel.
This was the old text book solution to uneven light on panels in parallel. In practice I found them to be redundant in my 12v setup because the shaded panel always produced enough voltage to prevent any reverse current from the ones in full sun and removed them all
However a blocking diode on only your damaged parallel panels may allay any fears
 

Hedges

I See Electromagnetic Fields!
The panels that I have are of very poor quality. Few of them have developed micro cracks in the cells (visible lines). I get two to three amperes less than the rated current in just 2 year of use.

Instead of trying to make a silk purse out of a sow's ear, can you pick up some better quality used panels?

What brand/model did you find to be so bad?
 

Pappion

Retired Engineer Tech
Bypass diodes installed in the panels have a low reverse voltage rating. I ordered 15A 45V for replacement. Good enough for sections in a panel. Not good enough for entire 48v panel or higher.
bypass diodes
 
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