Shading according to defined module location

[maranden]

Hi,

I am currently writing a master thesis analyzing the actual and forecasted power production of solar power systems in Norway.

Working out the prognosis I use PVsyst.

I wonder if the simulations conducted with shadings according to module layout takes into account the height of the module above ground.

In my work, the modules at one site are located 5 meters above ground on a building, however, I am unsure if the simulation takes this into account.

The horizon I have defined has obstacles in a sun elevation angle 6 - 11.5 degrees, measured according to ground level.

However, having defined the module layout and specified the module location 5 meters above ground, the obstacle height is 30 - 50% overestimated.

This mostly will effect the yield in the winter months, where sun is scarce in the north.

None the less, my thesis aims at giving accurate information as to the discrepancy between forecasted yield in PVsyst and actual production.

If the program takes this into account, then it's all good. On the contrary, I will have to redefine my horizon.

As far as I've looked, no answer has been found for this question.

I chose to contact you before defining horizons for other sites and hope that the answer might also help others.

Sincerely, Martin Andersen

[Bruno Wittmer]

Dear Martin,

the horizon shadings are supposed to be at 'infinite' distance, which has two consequences:

- The angle under which the sun gets shaded is always the same, irrespective of the height above ground. This is why the horizon line is defined as a series of solar height angles as function of the azimuth

- As a direct consequence, for a given sun height, the shading is either completly on or off for the entire installation.

This approach works well with far away hills and mountains.

If you have shading obstacles that are close enough to the installation, so that the height at which the modules are mounted makes a difference, then you have to model them as a 3D objects in the 'Near shadings'.

Make sure to include only objects that can actually cast shadows on your PV modules, since the near shadings consume much more CPU time during the simulation than the simplified horizon shadings.

Best regards,

Bruno Wittmer

[maranden]

To this post I have a follow up question;

Is it so that the level of the horizon corresponds to the Z value 0 in the near shading 3D scene construction?

Or is the curvature of the earth taken into account?

Meaning: do we assume sun height 0 degrees and the Z value 0 to be the same in the modelling?

When making the 3D model, does my placement of objects in the Z direction have any influence on the shading, or is only the relative placement of objects important?

Just wondering if the same result will be given if object 1 is at Z = 0 and object 2 is at Z = -5 or if object 1 is at Z = 5 and object 2 at Z = 0.

Best regards, Martin

[Bruno Wittmer]

Dear Martin,

the sun height, which is at the input of the shading calculations, depends only on the date and time, and of course the geographical coordinates of the site. It is expressed as an angle, which is the same at all points of your shading scene. This means, that we treat the sun beams as a perfectly parallel bundle of rays, which is a fairly accurate approximation of real conditions.

So the answer to your question is, that only relative placement of the objects with respect to each other is relevant.