Flat on diffuse steps

Method

At each sunlit timestep the plane-of-array irradiance is computed at the tracking rule's rotation and at rotation 0 (1). The tracker lies flat when GHI is at least the GHI threshold and the flat plane's irradiance exceeds the tracking rotation's by at least the gain threshold (2). The defaults are a gain threshold of 0.05 and a GHI threshold of 100 W/m², from pvperf's flat-switch rule. A tilted axis lies in the plane of its axis at rotation 0. A timestep in wind stow keeps the stow position. The irradiance compared is the transposed irradiance before the horizon, near shading and the IAM.

The math

1. Candidates
2. Switch

$$G_{trk} = G_{POA}(\rho),\quad G_{flat} = G_{POA}(0) \tag{1}$$ $$\rho' = \begin{cases} 0 & G_{hor} \ge G_{min} \text{ and } G_{flat} \ge (1 + g)\,G_{trk} \\ \rho & \text{otherwise} \end{cases} \tag{2}$$

where

Symbol	Meaning	Unit
$G_{POA}(\rho)$	the plane-of-array irradiance at rotation $\rho$	W/m²
$\rho$	the tracking rule's rotation	degrees
$\rho'$	the rotation the tracker takes	degrees
$G_{hor}$	the global horizontal irradiance	W/m²
$G_{min}$	the GHI threshold	W/m²
$g$	the gain threshold, a fraction	—

API

array.irradiance_tracking = true, array.irradiance_tracking_method = flat_switch, array.irradiance_tracking_gain, array.irradiance_tracking_min_ghi_wm2

Symbols follow the symbol registry.