Near shadings procedure

Near shading calculations necessitate the reconstitution of the exact geometry of the PV field and its environment, in the 3D-space.

You have first to build the global scene of the PV system by assembling parametrized elements (PV fields, shading obstacles, buildings, trees) which can be adapted from template shapes.

Assembly is done in a global perspective or plane view. Once this scene has been well established you can visualise shadows produced for any sun position or time-of-the-year. You can also run an animation of the shadow evolution over a given day.

During simulation, the calculation of the shading factor for each hour would spend too much computing time. Therefore the programme establishes a table of shading factors as function of the sun's height and azimuth. During simulation, the hourly shading factor can be calculated very fast by interpolation.

The iso-shading curves are a powerful information tool, which superimpose an estimate of the shading factor on a sun's path height/azimuth diagram, allowing to estimate at a glance the shading effects according to the season and time-of-day.

The shading factor is applied to the beam component. The program has also to calculate the shading factor for the diffuse component (as well as for the albedo), which is independent of the sun position and therefore constant over the year.

Simulation results include shading loss calculations for Beam, Diffuse and Global irradiation components.

It is to be noted that the real effect of partial shading on the electrical production of the PV field is non-linear, and depends on the interconnections between the modules. The program gives the possibility of partitioning the field into rectangles, each of which supposed to represent a string of modules in series, and calculates another shading factor according to module cabling. Although not perfect, this second approach should give an upper limit for the real shading loss evaluation.