The confusion in "Unlimited sheds" in fixed and "Horiz. axis, unlimited trackers" in terms of the sun position

[bkn]

Hello guys,

I find it a bit confusing when in comes to selecting "Field type" in "Orientation" box especially about the notion of "unlimited ~"

In PVsyst help, the following explanation presents:

(http://files.pvsyst.com/help/orientation.htm)

Unlimited sheds: To be used when the sheds are very long with respect to their width. If the sheds are too short as one cannot neglect the edge effects, you should define sheds in the "Near shadings" CAO option instead.

And, "Horiz. axis, unlimited trackers" is not explained in this chapter.

Here are my questions:

1. How "unlimited sheds" in fixed and "Horiz. axis, unlimited trackers" hold the sun position? As an example, how am I supposed to know the rod of the tracker is aligned to N-S direction or W-S direction in "Horiz. axis, unlimite trackers" ? how to vary the simulation between the rod aligned to N-S or W-S using in "Horiz. axis, unlimited trackers"?

2. I tried to google and could not find the definition of "the edge effect" indicated above "Unlimited sheds". I just saw "cloudy edge effect" but it seems that the edge effect input by PVsyst sounds different. What is the meaning of "edge effect" in PVsyst simulation?

3. What would be the major difference the selection of "Horiz. axis, unlimited trackers" vs "Tracking tilted or horiz. N-S axis"? What I mean, which case would be the exact case of using each "Field type"? What I found is that it only difference comes from "the edge effect" seemingly.

Thanks in advance,

[André Mermoud]

Some answers to your questions.

1. - I don't understand well your doubts.

The fixed sheds are obviously usually aligned East-West, i.e. facing the south. Except when you are using domes.

The single axis trackers have always an axis orientation close to N/S, for tracking the sunrise and sunset "sun's height" positions.

An axis oriented E/W would only track the height of the sun on the horizon. It is not useable with PV systems.

2. - The "Edge effects"

When you have 2 narrow tables one behind the other, in the morning or the evening a part of the shade is falling on the ground instead of the table behind.

We don't have this situation in "unlimited sheds".

3. - Difference between "Unlimited trackers" and "Tracker arrays" defined in the 3D scene.

The "Unlimited trackers" shades calculation (from tracker to tracker) is a 2-dimentional analytic calculation.

The "Trackers arrays" defined in the 3D scene use the full 3D calculation of the mutual shadings from the sun's position. It is a much more complex calculation, taking the real sizes of the tables into account ("edge effects").

Now each of these very different calculations are using not quite perfect models, it is normal that there are some little discrepancies.