The Solar Radiation feature depends on the geographic location and weather station specified for the project. This can be set using the Location Weather and Site dialog. Click Analyze tab 
Project Location panel 
Location. You can also access this dialog from the Sun Settings dialog and the ViewCube Set Location drop-down. You must be signed in to Autodesk Online Services to access the Location Weather and Site dialog.
Unless otherwise changed, the project location is set to the latitude and longitude of a major city specified by your locale specific version of Vasari.
You can define Location using an Internet Mapping Service. The Project Address can be entered as a place name or more accurately as a Latitude and Longitude, if it is known. The eight closest weather stations are listed.
Once the Location is set, the weather data available from a station closest to the chosen location is automatically loaded. You need an active internet connection to do this.