Active band width

Method

The width the controller works with is the collector width plus the inactive band on the upper edge of the row, the edge away from the sun, plus one centimetre of margin (1). The shadow of the row toward the sun may cover the inactive band on the lower edge of the next row without loss, so that band is left out. On a tracker the top band is the band on the edge that is up while the plane faces east, the west edge on a north–south axis, and the bottom band is the band on the other edge. The top band therefore counts while the plane faces east and the bottom band while it faces west. The rotation follows the backtracking equation with this width over the pitch in place of the ground cover ratio (2, 3), and it is then held within the rotation stops of the Racking tab. In a scene whose near shading is the shading-factor table or direct projection, the trackers are the scene's devices, which carry no inactive band, so the width is the collector width plus the centimetre of margin, as PVsyst takes it for the trackers of a 3D scene. On the infinite-row models the band counts.

The math

1. Backtracking width
2. Width over the pitch
3. Rotation

$$W_{bt,i} = W + b_i + 0.01\ \text{m} \tag{1}$$ $$\text{GCR}_{bt} = \min\!\left(1,\ \frac{W_{bt,i}}{P}\right) \tag{2}$$ $$\psi_c = \arccos\!\left(\min\!\left(1,\ \frac{\cos\rho_0}{\text{GCR}_{bt}}\right)\right),\qquad \rho = \operatorname{sign}(\rho_0)\,\max(0,\ |\rho_0| - \psi_c) \tag{3}$$

where

Symbol	Meaning	Unit
$W_{bt,i}$	the backtracking width at timestep $i$	m
$W$	the collector width	m
$b_i$	the inactive band on the upper edge at timestep $i$: the top band while the plane faces east, the bottom band while it faces west, in m; 0 for the trackers of a scene shaded by the shading-factor table or direct projection	—
$\text{GCR}_{bt}$	the ratio of the backtracking width to the pitch	—
$P$	the row pitch, the distance between the rows	m
$\psi_c$	the correction angle at which the shadow just clears the next row	degrees
$\rho_0$	the rotation that would point the plane at the sun	degrees
$\rho$	the rotation the tracker takes, before the rotation stops	degrees

References

1. PVsyst 8 help, Tracking systems and backtracking
2. Analysis of PVsyst 8.1.5 outputs shows this convention in its results.

API

array.backtracking_width_method = active_band

Symbols follow the symbol registry.