All-Sky Imager: A New Instrument for the Estimation of Solar Irradiance, Cloudiness and Aerosol Optical Properties

Abstract

Aerosols and clouds are the most important constituents in the atmosphere that attenuate the incoming solar radiation. Under clear skies, aerosols become the dominant factor that affect the intensity of solar irradiance reaching the ground with the variability in direct normal irradiance (DNI) being more important than the one induced in global horizontal irradiance (GHI). For cloudy skies, the spatial and temporal variability of clouds is a challenging issue on solar irradiance resource and forecasting. In recent years, all-sky imagers are used for the detection of aerosol optical properties, cloud coverage, type and velocity in a bouquet of applications including meteorological observations and solar energy control systems. The developed algorithms can provide also sufficient information about the reconstruction the three-dimensional nature of clouds, the real-time resource and short-time (0–30 min) forecast of solar irradiance. In this study, a brief overview of the current bouquet of methodologies—named as “Sky Analyzer”—developed in the Laboratory of Atmospheric Physics, University of Patras for all-sky camera applications in meteorology and solar energy forecasting is presented.