As nobody has replied, i found the answer in one of the old topics of this forums, but cannot get the sun to appear in game while there's light in the map.
You first have to have the sun enabled in the automatic lighting menu. Then you have to position the sun so it is visible in the dome, which is also in the menu.
DarkFalcoZ wrote:You first have to have the sun enabled in the automatic lighting menu. Then you have to position the sun so it is visible in the dome, which is also in the menu.