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<< Click to Display Table of Contents >> Unlimited sheds |
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The orientation "unlimited sheds" is an extension of the "fixed tilted plane" orientation that adds 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.
With this orientation setting, the mutual shading of the rows of tables (or sun-shields) is estimated using a simple geometrical computation, which 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 of rows with an "infinite" length (that is, the calculation doesn't take the edge effects into account).
•One of the main results is the loss of irradiance, i.e., the shading factor is the shaded area fraction of the full array (depends only on the pitch and tilt angle). The result also slightly depends on the number of rows, as the first one is not shaded. This is what we call the "linear" shading.
•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 a range of possible mismatch effects. In general we suppose that the production of a partition (a portion of each row) becomes zero (in terms of the beam component) if the bottom row of cells is fully shaded, and proportional to the shaded fraction of the cells otherwise. This is what we call "partition model" in the near shadings. The same recommendations in terms of partitioning hold.
To use this option, the software requires entering 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.
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" dialog 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 Meteo Computations": you can moreover have a quick weather calculation for your site, and immediately estimate the irradiation losses over the year.