12.1 Introduction12.2 Steps Required to Produce a NWP Forecast and Grid Resolution12.3 Comparison of Model Configurations for Four Operational Models (ECMWF, NAM, GFS, RAP): Spatial and Temporal Coverage, Deep and Shallow Cumulus, Turbulent Transport, Cloud Fraction, Cloud Overlap, Stratiform Microphysics, Aerosol, Shortwave Radiative Transfer12.4 Possible Sources of Error in Forecasted Irradiance12.5 Present-Day Accuracy of Solar-Irradiance Forecasts12.6 ConclusionsReferences