Solstices occur four times per year: during summer, fall, winter, and spring.

Solstices occurs two times per year during summer and winter.

Explanation:

An even that occurs when the Sun reach its core of north or south excursion that is more associated to the celestial equator is called as Solstice.  

This event happens twice per year. One occurs around the of the June month and the other occurs at of the December month. Both the occurrences of the equinoxes and the occurrences of the solstices determines the year's seasons.  

When it occurs in the June month it is known as “June Solstice” and when it occurs in the December month, it is known as “December Solstice”.