Analysing short-time irradiance fluctuations by their characteristic time scales

In moderate climates short time fluctuations in solar irradiance and their impact on the distribution grids become an important issue with regard to future large scale application of embedded photovoltaic systems. The approach that is presented here uses the method of time-scale decomposition of the solar irradiance in order to determine the power content of fluctuations according to their amplitude, characteristic time of persistence, and frequency of occurrence. The ´fluctuation power index´ and ´fluctuation energy index´ are defined as a measure for the occurrence of fluctuations of a particular persistence on an annual basis. Based on values for the squared fluctuation index for Belgium, it is indicated how a suitable strategy for storage and voltage control can be determined.