The Solar Atlas is a joint initiative of Latvia, Lithuania, Poland and Estonia. Radiation maps are based on satellite data provided by EUMETSAT CM SAF SARAH data set for period 1991-2014. Read more from EUMETSAT web page
Comparison of satelliite data with ground-based observations of radiation data from Latvia, Lithuania and Estonia show that the average monthly solar surface irradiance and direct irradiance values of satellite data are somewhat lower (6-9 W/m2) than those measured in meteorological stations. The difference in direct normalised irradiance is 13-18 W/m2.