The left part of this block computes the sky brightness using a simplified inverse Perez computation, which are then used for a more detailed inverse Perez computation. For details see section 8.3.1.10 of [1]. For a validation see Figure 8.9 of [1].
The model assumes that each sensor is placed on a vertical wall and that the sensors are rotated multiples of 90 degrees with respect to each other.
The parameters rho can be used to set the ground reflectivity
corresponding to each of the measured solar irradiation inputs.
The parameter delta is the shift of the south sensor compared to south in the west rotational direction.
Furthermore, the longitude and latitude have to be set.
[1] F. Jorissen. (2018) Toolchain for optimal control and design of energy systems in buildings. PhD thesis, Arenberg Doctoral School, KU Leuven.