Do I need blocking diodes?

[ddxv]

I will have 3 strings of 4 panels.

1 string has a total voltage of 138.84V (link) and 2 older strings have a voltage of 146V.

Likely all three will come together in a combiner box. Either in a DIY style or maybe something more presentable like this:

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There is expected shadows/shade in the mornings, likely sunrise until 3hrs after sunrise with non after that.

Do I need to use a blocking diode?

 

[timselectric]

Do I need to use a blocking diode?

No
The VOC will still be enough to stop reverse flow.

 

[chrisski]

In general blocking diodes are not needed.

This is what I did with a 2p setup, no blocking diodes. Left is unshaded, middle is one panel barely shaded, right is one panel 50% shaded. I don’t see how a blocking diode would help that. The shaded panel is not bringing down production in either example.



The combiner you linked has no diodes, but you could add one.

In theory you have about a 5% loss from the mismatched panels.

 

[sunsurfer]

This is what I did with a 2p setup, no blocking diodes. Left is unshaded, middle is one panel barely shaded, right is one panel 50% shaded. I don’t see how a blocking diode would help that. The shaded panel is not bringing down production in either example.

That is a great test. Thanks.

 

[chrisski]

That is a great test. Thanks.

Here’s the whole thread.

 

[ddxv]

In general blocking diodes are not needed.

This is what I did with a 2p setup, no blocking diodes. Left is unshaded, middle is one panel barely shaded, right is one panel 50% shaded. I don’t see how a blocking diode would help that. The shaded panel is not bringing down production in either example.

View attachment 226781

The combiner you linked has no diodes, but you could add one.

In theory you have about a 5% loss from the mismatched panels.

That's awesome thank you!!

 

[sunshine_eggo]

No
The VOC will still be enough to stop reverse flow.

Exactly this.

To expound a bit, it is important that the Voc of the lower voltage string be higher than the Vmp of the higher string.

I use a mental number of 10%. Any disparity in parallel string Vmp will yield a % penalty roughly equal to the Vmp % disparity.