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<< Click to Display Table of Contents >> Near shadings Limitations |
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See also: Shadings - General and PV Planes.
You can now define up to 8 different orientations, and the shading calculations are performed quite independently for each one (one shading factor table, one diffuse and albedo integral for each orientation).
Therefore there is no limitation anymore about the orientation differences.
A 3D shadings scene may now be constructed with every kind of orientation, even the seasonal tilt adjustment.
There were several orientations situations in PVsyst for which the 3D shading calculations was either approximate, or impossible.
As the shading calculation table cannot be "doubled" (in the present state of the program), the configurations with several orientations cannot be calculated accurately. This concerns:
- The Seasonal Tilt Adjustment: the shading factor is established relatively to the plane orientation. The table cannot be valid for the summer and winter situations at the same time. Therefore near shadings are forbidden.
- The Heterogeneous (double orientation): in this situation two independent incident irradiance calculations (for both plane orientations) are made during each step of the simulation. This would normally involve two different shading factors, one for each irradiance component, which is not supported yet. However the program allows calculation (approximated) if the orientation difference between both planes is not too different (the difference limit is fixed at 25°, adjustable in the "Hidden Parameters"). In this case it applies the same shading factor - calculated for plane #1, see below - to both planes.
- The sheds with sloped bases (sheds perpendicular to a 2-sided roof) are a particular case of the double-orientation situation. Here the 3D shading calculation is of particular importance due to the mutual shadowing of the sheds. But in this situation the global orientation differences will not be very marked, so that we fall in the approximated case mentioned above.
NB: For 2 different plane orientations, the shading factor is "globally" correctly calculated when the sun is shining on both planes, but it is not quite correct to apply it identically on both irradiance components. Moreover in the present algorithm the shading factor calculation is of course not performed when the sun is behind the plane; and for this limitation the plane #1 is taken as reference... This will be improved for a next version.
For tracking planes, the plane situation is well determined for any sun orientation, so that the beam Shading Factor may be computed without ambiguity at each time. But the diffuse shading factor - which results of a yearly average related to a given plane orientation - is not yet correct. PVsyst computes diffuse shading factor for 5 typical orientations (or 4x3 with 2-axis tracking) and uses the appropriate value at each time step.