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Thin object shading


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Hello,

I find the topic around thin objects rather tricky to understand and would like to know if I'm correct in my assumptions, and then I have a question.

  1. When I create an Elementary shading object in the 3D construction tool, I have the option to make it a Thin object if that is the case (let's say it's a cable), then I must give a % value next to it, which I assume is the "Thin object ratio" described in the Helpfile. The way I understand it, the value to give here is always the ratio between the object's width and the width of a cell in the module (13% in the example). 
    Quote

    Whatever the distance of the thin object, the total shade on the array  (i.e. lack of irradiance) is always the same. We can check with this calculation that the shade integral is always the same (20 mm / 156 mm) whatever the sun position or the object's distance.

     

  2. Then, thanks to the Thin objects shading analysis tool, I can determine the electrical losses, as a percentage, due to my thin object's shading. If I want to make a simulation, with the "according to module strings" method for my near shadings, then I would use the value found in the previous tool as my "Fraction for electrical effect". Correct ? (8.6% in the example)

So overall, after simulation, I will have a decrease of irradiance, associated with the "Thin object ratio", and also some electrical losses, associated with the shaded strings and the "Fraction for electrical effect" that I gave. Right?

Thanks for clarifying the above points if I'm mistaken.

Now, how do I proceed though if I have a cable, but also a tree, and I want to simulate my near shadings with the "according to module strings" method. What value of "Fraction for electrical effect" do I give in this case? 

Thanks so much in advance

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The thin objects in your scene will have the box checked labeling them as a thin object, and the trees will not. The software will calculate shading from cables as a thin object, and trees with the according to strings setting.

As for what % to use, different folks will provide different answers. It is dependent on the technology, the nature of the tree shading, how modules are installed relative to the shading, etc. Typically it will be between 70% and 100% for according to strings. Most of the time I am modeling with 100% so as not to underestimate shading losses.

Edited by dtarin
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The "Thin object" feature is related to the electrical mismarch losses, i.e. the repartition of the shades on the PV modules (or more exactly cells).

It doesn't affect the "Linear" shading loss, which is a deficit of irradiance, and is calculated in the same way as other shades. 

The percentage specified here corresponds indeed to the "Fraction for electrical effects" of the main shadings dialog. This value is the same for all "Thin objects" of your 3D scene.  The best way of evaluating this fraction is given by the specific tool  "This objects shading analysis".

During the simulation, the "Linear shading loss" due to irradiance deficit will be the same.  But for calculating the "electrical mismatch loss", PVsyst will evaluate the loss due to the "string rectangles", and apply  the "Fraction for electrical losses" of the thin object to the shading rectangles affected by the thin object.

This calculation "According to module strings" in indeed an approximation. It is mainly applicable to regular systems for mutual shadings from one row to the next one. It is not realy applicable to other shading objects. This the reason of the parameter "Fraction for electrical shadings".

We don't have any mean of determining the "Fraction for electrical shadings" in a general case. The only realistic calculation is the Module Layout tool. However this tool doesn't manage thin objects. 

 

 

 

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I understand what you're saying.

I'm still confused though as to why there are two different values to give:

  • When we create an Elementary shading object, and tick "Thin object", we have to give a value (still unclear to me what this value is)image.png.347f8f6f8d261beb017ab5d5e7735c00.png

 

  • In the Near Shadings main dialog, the "Fraction for electrical effect", which I perfectly understand, but then what's the purpose of the previous value?image.png.bdea2ddc9ca7ce5d46403e0208295ab7.png
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The thin object shading percentage is a modifier to the electrical shading factor generated by thin objects. Basically if thin objects cause a near shading factor F, the simulation will instead use 40% of F in the simulation (just as what happens with the global "Fraction for electrical effect).
Once you define at least one thin object, you will be able to adapt both the main "Fraction for electrical effect" which is applied to all objects except thin objects, and the one for thin objects that is applied to the factor caused by thin objects only.

 

image.png.86e2bc78a81d5df8e44ceeeddb18dac0.png

 

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