Flicker from PV Systems

This paper reviews the issue of flicker produced by photovoltaic systems. A brief introduction is given to flicker and the basic mechanism by which flicker can be produced by clouds passing over a PV array. Flicker can also be produced by the control actions of PV inverters but that mechanism is not considered in this paper. The properties of clouds relevant to PV flicker are discussed, including the fact that clouds transmit some sunlight through them, that they travel across the Earth's surface at a finite speed and that there is an area of partial shading surrounding a cloud. These produce a ramp rather than a step change in output of a PV system and this effect on flicker is described by the flicker shape factor.