Recognition of Irradiance Transitions Caused by Moving Clouds Harmful to the Operation of PV Systems

Abstract

Edges of shadows of moving clouds cause fast irradiance transitions which can be harmful for the operation of photovoltaic (PV) systems and electrical grids. They can lead to situations where the grid inverter is not able to follow the global maximum power point causing extra losses and fluctuations to the power fed to the electric grid. Partial shading of PV generators also causes mismatch losses. In this paper, a method has been presented to recognize irradiance transitions, falls and rises, caused by the shadows of moving clouds from measured irradiance data. The time of occurrence, shading strength, duration etc. of recognized irradiance transitions have been analysed. It has been found that the duration of irradiance transitions varies a lot from couple seconds up to few minutes and that the average duration of irradiance rises is longer than of falls. In addition, shading strengths of transitions varies greatly and can be up to 90 %. The highest transition rates took place around noon and there can be over 900 transitions in one day.