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Sheds mutual shadings

The unlimited sheds orientation type is an extension of fixed tilted plane with additional geometrical parameters defining the tables arrangement (in regularly arranged rows). This allows the application of a simplified 2D model of mutual shadings based on these parameters. This approach is generally faster than defining a 3D shading scene and can therefore be used for example in more preliminary studies.

Mutual shadings

With this orientation setting, the mutual shading of the tables' rows (or sun-shields) is estimated using a simple geometrical computation. It gives the mutual shading fraction as a function of the Transverse Incidence Angle or "Profile angle". This mutual shading may then be taken into account during the simulation process. These calculations are applicable on all irradiance components, for example on the beam or on the diffuse. The main assumption is that rows have an infinite length (i:e: edge effects are not taken into account).

Linear shadings

One of the main consequence of the mutual shadings is the loss of irradiance. It is directly linked to the shading factor of the shaded area, which mostly depends on the pitch and tilt angle. The result also slightly depends on the number of rows, as the first one is not shaded (i.e: with n rows, mutual shadings only impacts \((n-1)/n\) \% of the rows). This is what we call the "linear" shading.

Electrical shadings

It is also possible to estimate the electrical effect of these shadings. For instance, the current of a string of cells is limited to the current of the weakest cell, i.e., the shaded one. This may impact other unshaded sub-modules, leading to additional mismatch effects. In general we assume the production of a partition (a portion of each row) to be zero (in terms of the beam component) if the bottom row of cells is fully shaded, or proportional to the shaded fraction of the cells otherwise. This is what we call partition model which is described in details in this section.

To take electrical shadings into account, PVsyst requires the number of partitions in the transverse dimension (width) of the table row, as well as the width of one cell. The shading factor effect is then shown as a function of the profile angle.

Please note that with thin film modules with "long" cells of around 10 mm width, the cells should be placed in the transverse dimension of the shed, so that only a little part of each cell is shaded at a time. When the thin film modules are arranged in this way, the electrical effect of shadings is greatly reduced.

Notes

The three parts of the shed tool: Geometrical design, Shading graph and Yearly yield graph, are meant for a better understanding when optimizing a row-based layout.

Please carefully see the limitations when using sheds with near shading scenes.

PVsyst uses the simplified 2D model within several special tools for viewing and optimizing the shed mounting (and also sun-shields). This is implemented in several places in the software:

  • In the Orientation menu via the option unlimited sheds. Similar choices are offered for NS-axis trackers or sun-shields.
  • In Tools / Tables and Graphs of Solar parameters, you can define the geometry, optimize it with the mouse and view the mutual shading effects of your choice on a Height/azimuth diagram.
  • In Tools / Monthly Weather data Computations, you can also have a quick weather calculation for your site, and immediately estimate the mutual shadings irradiation losses over the year.