Interaction of orientation and near shadings entries

[deblynn]

Hello,

The text below is copied exactly from the help file in version 6.25. I would like to verify a few of the points :

1. Is it still true that if you develop a 3D sheds model, you should use fixed tilted plane in the orientation tab?

2. However, for a tracking array, from what I am reading, a 3D model should always be used? And then should the orientation tab also specify tracking?

3. Is it still true that the orientation tab does not include electrical cell effects for sheds? I thought that is what the electrical effect dialog is for....

4. Is it still true that near shading should only be used for up to 50 sheds? Or has that limitation been removed by more recent upgrades, so long as one can wait a few minutes while it runs...

Thanks,

-Debbie

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Near shadings and sheds

In PVsyst detailed simulation, the mutual shading of sheds (or sun-shields) can be computed in two different ways:

- By defining them in the "Orientation" parameters option. You have here to define general parameters of sheds (width, tilt, pitch, etc.) valid for the whole PV system, and the simplified computation is assumed to be "linear" (without electrical cells effects) and for unlimited length (that is, neglecting edge effects on both extremities of the sheds).

- By explicitely defining a PV plane as sheds in the "Near shading" scene. In this case the computation accounts for shed edges, and a module partition can be defined.

Please note that these two options should not be used at the same time, as the shadings will be accounted for two times !!!

Definition by the "Orientation" parameter shed option

This option is most suited when you have a field of numerous and little sheds (for example "one-module" wide sheds), sufficiently long as you can neglect the edge effects.

Nevertheless, if you have to combine such an array with other surrounding shading obstacles in a near shading scene, you should define the basic array in the near shading scene as an horizontal plane, covering the sheds base extent (i.e. the whole area used for installing the sheds, on which the surrounding shadings will apply).

This way the mutual shadings will be taken into account by the “plane orientation” shed algorithms, while the surrounding shadings will apply on the basis plane. This is of course an approximation, but the only way when the sheds are so numerous that the near shading complexity and calculation times become prohibitive.

Shed definition in the Near Shading scene

The "Near shading" shed construction should only be used when the number of sheds is less than, say, fifty sheds. The computing time and complexity of the shading factor calculation grows with the square of the number of elements.

When you define sheds in the 3D scene, you have to choose a fixed tilted plane (not sheds) in the "Orientation" parameters, with the real values of tilt and azimuth of one shed. .

[deblynn]

So I developed a backtracking single axis tracking array with the details specified in both the orientation tab, and the near shadings dialog.

When I ran the shading table, all values came up as zero (for beam, diffuse, and albedo).

However, when I ran the model, there were several changes to the results, compared to the model with backtracking defined only in orientation.

1) Near shadings, irradiance loss was added (1.6%)

2) Far Shadings / Horizon loss decreased

3) IAM factor increased

Is this what should be happening?

Thanks!

-Debbie

[André Mermoud]

This is indeed a very old text in the help, which has not been updated for the new developments. Sorry.

 

1. Is it still true that if you develop a 3D sheds model, you should use fixed tilted plane in the orientation tab?

The statement is rather that you should not use "Unlimited sheds". You can use fixed or several orientations.

 

2. However, for a tracking array, from what I am reading, a 3D model should always be used? And then should the orientation tab also specify tracking?

Yes it should be used,for taking the mutual shadings of trackers into account in any case. With backtracking, it is necessary for the calculation of the mutual shadings on the diffuse part, even if there is no loss on the beam component (table with null everywhere). See How is calculated the Shading Loss on diffuse with tracking systems ?

 

3. Is it still true that the orientation tab does not include electrical cell effects for sheds? I thought that is what the electrical effect dialog is for....

Since a very long time (but I can't remember when), there is a generic calculation of the electrical losses in the "Unlimited sheds": as soon as the bottom cell is shaded the string becomes inactive. You have to define the number of strings in width in the row.

 

4. Is it still true that near shading should only be used for up to 50 sheds? Or has that limitation been removed by more recent upgrades, so long as one can wait a few minutes while it runs...

There is no formal limitation on the number of sheds. If you define too much in the 3D tool, the calculation time may become prohibitive (see our FAQ With my big power plant the calculation time becomes prohibitive)

There were already a significant optimization with the version 6, we are working on further ones.

 

When I ran the shading table, all values came up as zero (for beam, diffuse, and albedo).

For beam component, the zero shading factor is by definition of the Backtracking mode. The shading factor on diffuse or albedo calculated from this table of moving orientations are not relevant (PVsyst should not show them). The shading for diffuse has to be computed for each position of the trackers, using a shading factor table calculated for a fixed plane at this orientation. This is done for some positions, and interpolated.

 

However, when I ran the model, there were several changes to the results, compared to the model with backtracking defined only in orientation.

1) Near shadings, irradiance loss was added (1.6%)

2) Far Shadings / Horizon loss decreased

3) IAM factor increased

When using backtracking, the plane orientation is no more optimal in backtracking situation: the shadings for beam component disappear, but not the shadings for diffuse and albedo.

As the yield is less for very low sun's heights, the relative horizon loss may indeed be lower.

The IAM increases as in backtracking situation the sun has an increased incidence angle.