A network of sky imagers for spatial solar irradiance assessment

Abstract

A network of seven low-cost hemispheric sky-imaging cameras has been installed in the Los Angeles basin. This network of cameras provides wide sky coverage to perform spatial solar irradiance assessments. An Image to Irradiance algorithm (I2I) is proposed to simultaneously derive high-resolution diffuse, direct and global solar irradiance from sky images. Spatial interpolation using the Kriging method is used to derive the irradiance field for the whole basin area. The relatively inexpensive network of cameras can provide spatially resolved GHI that is more accurate than GHI derived from GOES-west satellite images provided by the Cooperative Institute for Meteorological Satellite Studies (CIMSS) when the distance to the nearest site is less than 40 km. This work successfully demonstrates that, with minor trade-off in accuracy, solar irradiance monitoring can be achieved using off-the-shelf cameras in the absence of radiometers.