PVsyst 8 settings

Method

PVsyst 8.1.5's second search sometimes ends after one step although the next step gains. These settings reproduce that. The rule is fitted to PVsyst's hourly output. PVsyst does not document it. Every step is scored as in the best plane angle method except the second step of the second search (1). That step loses the share of its beam and circumsolar that rows of unlimited trackers would shade at a ground cover ratio of cos 45° (3, 4). The ratio is cos 45° whatever the pitch of the array. The shading is computed for a beam that crosses the axis at the angle θ (2). With the sun on the side the axis points to, θ is the start rotation. On an axis toward the south that is a sun south of east. With the sun on the other side, θ is the true-tracking rotation when backtracking moved the start, and nothing is removed otherwise. A start on a rotation stop does not count as moved. With the sun on the axis side, the factor drops below 1 once the start is steeper than 45.03°. A factor above 1 removes nothing from a positive beam and circumsolar. It makes a negative circumsolar more negative. The Perez circumsolar term is negative under some overcast skies. The rotation kept is the evaluated rotation with the highest score. The second step counts with its reduced score. The rule was fitted on three PVsyst 8.1.5 runs of one single-axis tracker field with backtracking. One run is the field as built, one has the rows 100 m apart and one has weather without beam. These runs have 3,160 hours where the second search ran alone and could climb two steps or more. On 3,058 of them the rule gives PVsyst's outcome. A fourth run without backtracking checks the rule too. Over the four runs the rotation equals PVsyst's on 16,466 of 17,600 sunlit hours. With the full climb it equals PVsyst's on 15,409.

The math

1. Second step
2. Beam angle
3. Unshaded fraction
4. Score of the second step

$$\varphi_2 = \min\left(\varphi_{max},\ \varphi_T + 2\,\Delta\right) \tag{1}$$ $$\theta = \begin{cases} \varphi_T & s_y > 0 \\ \theta_T & s_y \le 0,\ \text{backtracking on},\ \varphi_T \ne \theta_T,\ \varphi_T \notin \{\varphi_{min}, \varphi_{max}\} \end{cases} \tag{2}$$ $$m = \begin{cases} \dfrac{\cos\theta}{g\,\cos(\varphi_2 - \theta)} & \theta \text{ set by (2)} \\ 1 & \text{otherwise} \end{cases},\quad g = \cos 45^\circ \tag{3}$$ $$G'(\varphi_2) = G(\varphi_2) - \max\left(0,\ \left(B(\varphi_2) + C(\varphi_2)\right)(1 - m)\right) \tag{4}$$

where

Symbol	Meaning	Unit
$\varphi_2$	the rotation of the second step of the second search, in PVsyst's sign	degrees
$\varphi_T$	the tracking rule's rotation, where both searches start	degrees
$\Delta$	the step of the searches: 1	degrees
$\varphi_{min}, \varphi_{max}$	the rotation stops	degrees
$\theta$	the angle across the axis of the beam the shading is computed for	degrees
$\theta_T$	the true-tracking rotation, which faces the sun without backtracking or stops	degrees
$s_y$	the component of the sun's direction along the tracker axis, positive on the side the axis points to	—
$m$	the unshaded fraction of the rows for the beam at $\theta$	—
$g$	the ground cover ratio of that shading: cos 45° = 0.7071	—
$G'(\varphi_2)$	the score of the second step	W/m²
$G(\varphi)$	the irradiance the best plane angle method compares at rotation $\varphi$	W/m²
$B(\varphi_2), C(\varphi_2)$	the beam and the circumsolar on the plane at $\varphi_2$	W/m²

API

array.irradiance_tracking_search = pvsyst_8

Symbols follow the symbol registry.