Iso-shadings diagram

[Lunatic09]

I've tried to simulate vertically installed bifacial PV system(Tilt : 90 degree, Azimuth :0 degree).

I have a few questions about iso-shading diagram(attached image file)

1. Why there is each persentage(1%, 5%, 10%, 20% and 40%) of shading losses? and what does it mean? 

2. Is the shading loss mixed direct shading and diffuse shading? if it mixed, is there way to seperate the direct and diffuse shadings ?

[Michele Oliosi]

Hi,  the iso shading diagram is exactly what the name says, it displays the sky positions that produce the same shading factor as a continuous lines.
These iso-shading lines are akin to isolines on a map, which show you the points at a given altitude.

In general you can read the lines as follows: take the 40% line: as long as the sun is positioned at a sky position below that line, there will be at least 40% of shaded surfaces.

The iso-shading diagram just shows the direct shading factor. The diffuse one is computed separately.

On a separate note, I have never seen an iso shading diagram like yours. Please make sure that all the objects in the 3D scene are well defined and do not intersect each other. Also make sure that all PV surfaces have the correct orientation.

[Lunatic09]

Thank you for your response.

I simulated vertically installed bifacical pv system without any shading objects.

 

[Simulation Conditions]

PV module tilt : 90˚  / azimuth 90˚ (Faced west side) / shed distacne 100m (for eliminate interference between modules)

Even if there is no shading objects around PV modules, there is shading loss around 10~20˚ Azimuth.

Could you explain me why those losses occures?

[Michele Oliosi]

Ah yes, if you see the shading factor table

you will notice that the 90° height is always 1, because the sun shines on the side of the table, which is considered full shading. The iso-shading diagram was aimed at interrow shading, so it does not handle this case well. You can disregard the shading lines in the isoshading diagram.