Operational method for deriving high resolution direct normal irradiance from satellite data

Ground-based measurements of solar beam irradiance are expensive and rarely available especially in the sunbelt countries, the favourable regions for concentrating solar energy techniques. A method based on satellite data is presented that calculates hourly solar direct normal irradiance for large regions and for many years with high spatial resolution independently from ground measurements. The attenuation of solar irradiance due to scattering and absorption in the cloud-free atmosphere is calculated by a clear-sky broadband parameterisation model. It uses ozone optical depth from the Total Ozone Mapping Spectrometer, aerosol optical depth from the Global Aerosol Climatology Project and water vapour from the reanalysis of the National Centers for Environmental Prediction. Attenuation due to clouds is taken into account by a cloud index that is derived from the infrared and the visible channel of the geostationary Meteosat weather satellites. As clouds have the strongest impact on beam irradiance at ground, the resolution of the cloud parameterisation dominates the overall spatial and temporal resolution. The presented algorithm provides hourly data of direct normal irradiance related to the nominal 5 ·5 km2 resolution of Meteosat. 2003 Elsevier Ltd. All rights reserved.