The characterization of the solar radiation variability is a
fundamental step before prediction and is crucial to transform
an intermittent source of energy into a stable one. As solar
irradiance result from a nonlinear and non-stationary process,
we use a multifractal approach based on the Hilbert-Huang
Transform (HHT) consisting of an empirical mode
decomposition (EMD) followed by a spectral analysis. In this
paper, we will briefly introduce the HHT data analysis method.
Such a recent adaptive data analysis method has been applied to
Reunion Island global solar radiation time series of
measurements with a sampling rate of 1/60 Hz over six years.
Through the EMD, daily global solar radiation data were
decomposed into several intrinsic mode functions (IMF). For
each IMF, we estimate the amplitude, instantaneous frequency
and Hilbert spectrum for the original data. From the
comparison of Hilbert Spectrum and Fourier Spectrum, we find
the calculated solar radiation power spectrum follows a power
law behavior close to the Kolmogorov law. The method
described in this paper provides an amplitude frequency
representation of the global solar radiation sequences resulting
in a probability density function and a scaling coefficient. The
multifractal approach allows to extract parameters connected to
the multifractal properties of the global solar radiation.