The dataset includes daily values of total solar energy received by a horizontal surface in the Athens area, expressed in MJ/m², covering a 20-year period from 2001 to 2020. The calculations were based on data from the actinometric station of the National Observatory of Athens in Thissio (latitude: 38.972° N, longitude: 23.717° E). For each of the days under consideration, the values of the total incident solar radiation on a horizontal surface were collected at 1-hour intervals, expressed in W/m², where, using an appropriate integration method (the trapez...