Electrical shading losses in versions 7.3.X

[Michele Oliosi]

Quote

Shadings, module layout: Improved the evaluation of the electrical effect of shadings on the bottom cell for submodules or partitions

Minor version 7.3 has introduced a new way to compute the electrical effect of shadings, whenever only the cell at the bottom of the modules or submodules is shaded.

The goal of the update is to better represent the actual behavior of these electrical effects: if one gradually shades the cells the are at the bottom of a module or submodule row, the electrical shading loss should quickly increase linearly until a plateau is reached (they are at their maximum value) once the full cell width is shaded.

Compared with version 7.2.21 this tends to decrease the electrical shading losses. However the discrepancies have been more marked in certain cases.

In practice:

• In the "module layout" mode: the new bottom cell evaluation is performed for each submodule independently. This is the most accurate way to model this effect in PVsyst, and we are confident that update 7.3 has improved the overall accuracy of the evaluation.
• In the "according to strings" mode (fast and slow): the bottom cell evaluation happens globally for the whole scene. An average shadow height is evaluated and compared to the width of the bottom cell. This approach has been extensively tested in regular setups, and should be more accurate than 7.2.21 for regular arrays with many rows, on a single orientation.
  However, this approach tends to underestimate the electrical shading effects as soon as irregularities are added, e.g. other shading objects, being on a complex topography, or using different orientations. This unfortunate effect has been discovered recently and a correction is being studied. The new behavior can be circumvented, see below.
• When using the "unlimited" orientations, with electrical effect activated: this situation is ideally regular, we therefore expect that new corrections yield a more accurate result (see caveat just below).

A less common error affects projects using the unlimited orientations and half-cut modules in landscape. At the moment the bottom cell evaluation is incorrect for this case. We recommend using version 7.2.21 for this specific case.

Workaround for the "according to strings" mode:

To revert to a behaviour that mimics version 7.2.21, users can modify the parameter "3D elec. shading: Fraction of bottom cell for no shading" to 0 %.

Note that in certain cases, the behaviour of 7.2.21 cannot be replicated. This is for example the case whenever shades cover only a very small fraction of the area, or with thin shadings.

The second parameter in the screenshot can also help mimic version 7.2.21 for the "module layout" case. We however consider the new calculation better than the previous.

[Haus]

Hi Michele,

I have done a 3D simulation (slightly hilly terrain plus overhead line (poles and wires)) with the PVSyst Version 7.2.21.

Now I did the same simulation with Version 7.3.2 but the electrical losses increases from about -1,5% to -2,5%. I didn't changed anything.

Could this change be caused by the the new way to  calculate the electrical effect?

Hope you can help me in this case. If you need anything please let me know.

Regards

[Michele Oliosi]

@Haus

Yes I believe it is due to this new calculation. The overhead poles and wires probably cause very little shadings overall. Some of these situations were neglected in version 7.2.21, and are not neglected in version 7.3.2 anymore.

I would suggest trying to change the advanced parameter controllling the cell width to 0, as in the screenshot above, and then making sure that the thin shading fraction is low enough. However depending on the original amount of shadings I believe the electrical shadings may increase even more. If you can let us know the results that would be very valuable.

If the discrepancies are too high, I would invite you to send us your project at support@pvsyst.com (exported via the main window > File > Export project), this is the best way for us to check in details on a case by case basis.

[Haus]

Hi Michele,

I changed the advanced parameter controlling the cell width to 0, but nothing changed.

The fraction for electrical effect is 25% for the HV cable (assumed cable diameter 10cm and distance to array about 50m.

I would send you the zip file to support@pvsyst.com.

Looking forward to you feedback.

Regards

 

 

[Michele Oliosi]

The behaviour above will be retained for all 7.3 patches, including the latest one 7.3.4. As mentioned we are working on an overhaul but it will be made avaiable in a new sub-version: PVsyst 7.4.