Learning Processes to Predict the Hourly Global, Direct, and Diffuse Solar Irradiance from Daily Global Radiation with Artificial Neural Networks

Table 4

Correlation of different parameters to (HDI)_D.

Variables	Correlation to (HDI)D
Mean temperature (TD)	0.520
Sunshine duration (SD)	0.927
Declination angle (δ)	0.65
Relative humidity (HrD)	−0.669
Wind speed (WSD)	0.687
Global solar radiation (GD)	0.940
Daylight hours (DH)	0.558
Extraterrestrial radiation (ERD)	0.556
Sunshine fraction (SF)	0.865