Quantifying the occurrence and duration of power fluctuations introduced by photovoltaic systems

In moderate climates short time fluctuations in solar irradiance and their impact on the distribution grid will become an important issue with regard to future large scale application of embedded photovoltaic systems. Several related and important studies from the past are recalled. The approach that is presented here uses the method of time scale decomposition of the solar irradiance and derived quantities in order to determine the power content of fluctuations depending on their characteristic persistence. Pseudo random time series of solar irradiance, based on measured values of instantaneous clearness index are applied as input data. Power flow calculations are carried out in order to assess the impact of fluctuating solar irradiance on the grid voltage. The 'fluctuation power index' is defined as a measure for the average frequency of occurrence of fluctuations of a specific persistence. A typical scenario is simulated and the results are interpreted.