When did China set 24 solar terms a year?

As early as the Spring and Autumn Period, four solar terms were set, namely, mid-spring, mid-summer, mid-autumn and mid-winter. By the Qin and Han Dynasties, the 24 solar terms had been completely established. In BC 104, the taichu calendar written by Deng Ping officially set 24 solar terms in the calendar, and defined the astronomical position of the 24 solar terms.