Backtracking Parameter Management
When using the backtracking strategy in a PVsyst simulation, the backtracking angle used is identical for all trackers in a given orientation. It is computed from a reference tracker width-pitch ratio, called the backtracking GCR. The first step of the backtracking computation is therefore to identify two reference trackers and use them to set the reference backtracking GCR.
PVsyst scenes with tracker arrays
When constructed within PVsyst, the 3D scene is usually composed of tracker arrays.
In this case, the pitch is specified in the array's definition, and there is only one value for the backtracking GCR. If several tracker arrays are defined, using different pitches or different tracker widths, PVsyst will choose the array with the highest width/pitch ratio (backtracking GCR) as reference. All trackers will then operate using the same angle computed from the reference GCR, so that no mutual shadings are ever created.
Independent trackers
When importing a 3D scene designed with other CAD software, trackers are defined as independent tables and not as arrays. Within PVsyst, this is also the case when you fill a zone. In this case, it is necessary to identify a pair of reference trackers to serve as a basis for the full backtracking calculation. This is the objective of the Backtracking Management tool, available in the Tools menu of the 3D editor.
Automatic tracker choice
The Backtracking Management window shows the list of trackers (tables or arrays) and their parameters for each orientation group of your 3D scene. Trackers are listed by decreasing pitch value. By default, the reference backtracking parameters are set to "Automatic": the backtracking GCR corresponds to the highest detected GCR in your 3D scene.
Custom tracker choice
The automatic mode can be deactivated to select another reference tracker for the backtracking angle computation. Trackers with a higher GCR than the chosen backtracking GCR will be highlighted in red, and a warning message will appear. It is important to model the shadings in that case, as these highlighted trackers will likely be shaded. The selected reference tracker will also appear as selected in the scene to help you cross-check your choice.
Manual override
By deselecting the reference pair of trackers, one may also enter custom values. A custom pitch, width, and inactive bands can be defined. These values are only used for the backtracking angle computation and will not override anything in the 3D scene.
In general cases, it is advised to only modify the pitch. In advanced cases, these parameters can be used to emulate specific behaviours:
- Operating with a narrower table (e.g., divided by 2) can be used to emulate half-backtracking behaviour.
- Defining inactive bands on one side or the other of the reference tracker will force different behaviours in the mornings and afternoons. This approach can be useful on tilted terrain.
The validity of any custom definition should be checked by running a shading animation in the 3D scene. Do not forget to enable shading simulation if some of your trackers can be shaded.
