I have just been asked a question which I was sure I knew the answer to, but you never know :-) .... one is always open to learning :-)

I have a north facing roof, with no trees or obstructions creating shade, on which I have 3 strings - 2 of the strings consists of 8 x 375w panels (total of 16 x 375w panels) and a 3rd string of 8 x 545w panels.

The roof area does not allow for all the panels to be installed in Portrait which means that 2 panels in the 3rd string had to be installed Landscape orientation - see picture provided.

The question is if anyone sees any issues with this - mounting a number of panels in a string as portrait and others landscape?

Note: I cannot split the 2 Landscape panels out into another string as the startup voltage requires more than the 2 panels can produce and there is no space for any additional panels to be added.

PS: If you ask Google AI the question it comes back with:

Yes, you can mount solar panels in the same string with both portrait and landscape orientations, but it is not recommended because it can lead to inefficiencies and potential performance issues. Mixing orientations within a single string can cause power losses, especially if there is partial shading, because the different panel layouts can affect how bypass diodes work. For optimal performance, it is best to dedicate each string to a single orientation. 

Mindful that I mentioned there is no shading or obstructions and all panels are facing North - does anyone have any thoughts/input as to this being a real issue or am I good with the way it is?

In the spirit of learning, any thoughts or input is always appreciated

Thanks

If there is no trees that can cast shadows, how can the orientation make a difference? it is not as if the panel knows it is horizontal or vertical :)

I think your panels will work exactly the same in either orientation or mixed.

Yes. For this particular case the different orientation of 2 panels in the string of 8 does not matter. Will work the same.

Some additional info:

• Based on how half-cut panels are wired internally and given the fact that the most of the objects generate vertical shadows (poles, trees, chimneys etc.), the best orientation of panels for areas with occasional shadows casted by nearby objects is portrait.

• For the areas where shadows are generated only by the sun hitting the horizon or hiding behind nearby buildings, the best orientation is landscape. This way, the horizontal shadow will turn-off each loop of cells individually. In portrait, horizontal shadow would turn-off whole lower half of the half-cut panel. Same applies to ground-mounted PV plants with multiple rows of panels, where the front rows will generate horizontal shading.

• On the other hand, portrait orientation has a significantly lower cost of construction and mounting hardware, which outweights potential benefits of landscape orientation in the most cases. Therefore, landscape is being widely used for the flat roofs only, where the space between the rows is the most precious resource. Here, portrait would cast long shades and would been prone to wind damage.