With high penetration of PV generation in power grid distribution systems, solar irradiance fluctuations introduced by moving clouds may lead to variations in voltage and power flow in the grid and may affect the stability of the grid system. Predicting the characteristics of the fluctuations requires a mathematical approach, such as the combination of a statistical tool and wavelet analysis. The instantaneous clearness index is a parameter on which the Wavelet analysis is applied, and which is decomposed into components of different scales, corresponding to their persistence. These components are examined to evaluate the magnitude and the persistence of the various fluctuations of the solar radiation. The method presented in the present article can offer a valuable tool for the estimation of power flow as induced by solar radiation fluctuations. (C) 2013 Elsevier Ltd. All rights reserved.