The Map Controller shows annual Global Horizontal Irradiance (GHI) and Direct Normal Irradiance (DNI). The map is derived from Vaisala’s solar dataset: the first comprehensive, contiguous, and high-resolution solar dataset with global coverage. The map images show the annual mean GHI or DNI based on 10+ year means from 1997/1999 – 2018 from the Vaisala 1.0 solar algorithm. The dataset is based on actual, half-hourly, high-resolution visible satellite imagery observations via the broadband visible wavelength channel at a 2 arc-minute resolution. 

The color overlay on the map allows you to compare different regions using the color scale located on the left side of the Annual Mean Irradiance Tools. "Warm" colors like brown and orange indicate higher irradiance. "Cool" colors like purple and blue indicate lower irradiance. You can select different overlays based on the particular type of irradiance you are interested in: GHI or DNI.