Explanation "Thin object"

[gugel88]

Hi,

I am trying to simulate the loss of shading during to pylons and its open wires. In PV Syst there is an option called "Thin object". I don't really understand the description and function of this option. It says:

"If the shading object is sufficiently thin, its shade will not cover a full cell. Even if it is rather far and produces a

broad semi-shading (due to the sun's diameter), the irradiance loss should be considered as the integral of the

shading figure, and will be the same as the effect of a well delimited thin shading of the same wire.

This is the case of electrical wires above the array, handrails, etc.

In these cases the current in the cell will be reduced by a factor of the order of the wire diameter by respect to the

cell's size. This is the value which should be attributed to the "Thin object" electrical effect ratio parameter.

Then during the simulation, the "Module" loss caused by this thin object will be reduced by the "Thin object ratio".

The reduction is directly taken into account in the loss factor according to modules. "

Could anybody explain that to me?

Is it possible at all to simulate shading losses with PVsyst of open wires with a diameter of about 3cm and a distance of up to 50m to the PV modules?

[André Mermoud]

If the shade was very sharp (shading object very close), only a contribution of 3 cm width would affect the elecrtrical mismatch. The concerned cells are not completely shaded, and the shade contribution will be around 3 cm/15.6 cm, i.e about 20% of the full beam.

Now the apparent diameter of the sun as seen from the earth is 0.54° (Sun's diameter is 1.4 Mkm, sun-earth distance is 150 Mkm).

Therefore the shade of one point at 50 m will be a patch of about 50m * sin(0.54°) = 0.47 m. The shade of this 3 cm wire will be spread over around 50 cm width.

This will cover several cells, and will not produce significant electrical mismatch losses. The shading effect will therefore be limited to the irradiance deficit, i.e. the "Linear shading" corresponding to 3 cm width obstruction.

As a conclusion, at this distance you should use the "Thin object" option for this wire, but with a negligible contribution (1%, i.e. the minimum allowed in the program).

[gugel88]

Ok, that seems plausible to me.

Is there any recommendation how to select the best value for thin object depending on the distance of the wire?

At the pylon there are many wires, but not only at a height of 50m, but also at a height of for example 20m.

Will be the electrical mismatch loss at this height as negligible as with 50m height and should I chose 1%?

Or should I chose 5% or anything else then? Would you say that it is a linear dependence on the distance (if the wire diameter stays the same)?

Thank you.

[lonav]

Hello,

I have a question which I think is related to this post. I have simulated the shading effect of a tracker screw bar at the worst case scenario (meaning the bar tilt which will cast the largest shade on the modules). The bar is not defined as a thin object though.

Now, as for the shadow animation there will be some little shadings and I would expect that to be seen in the "E grid" values, but the outcome is the same as if there were no bars. Is this the consequence of the shading loss being so low (less than 1 W·h) that the program would neglect it?

Thank you.

[André Mermoud]

If you have a little object's shade on a rather big PV array, the shading effect ,ay be very little. You can see it in particular situations with the "Animation" tool.

If the annual shading effect is lower than the resolution of the percentages in your loss diagram, you will obviously not see it.

[Jen H]

To follow up on gugel88's post (copied below), does anybody know of any studies in which either

• the fraction for electrical effect for thin objects is defined or
• the shading loss due to a defined thin object is calculated?

 

Thanks!

 

Is there any recommendation how to select the best value for thin object depending on the distance of the wire?

At the pylon there are many wires, but not only at a height of 50m, but also at a height of for example 20m.

Will be the electrical mismatch loss at this height as negligible as with 50m height and should I chose 1%?

Or should I chose 5% or anything else then? Would you say that it is a linear dependence on the distance (if the wire diameter stays the same)?

[André Mermoud]

There will be a detailed tool for this determination in the next version 6.65.