Literary and poetic — you'd see it in song lyrics, poems, and scenic description but rarely in everyday speech, where 太阳 (tàiyáng) 'sun' is the default.
culture
Strongly associated with sunrise/sunset imagery and, in older PRC propaganda songs, was a metaphor for Chairman Mao — e.g. the 1960s anthem '东方红' (Dōngfāng Hóng) 'The East Is Red' calls him a 红太阳 (hóng tàiyáng) 'red sun'.
