Thorns in rotation

Is it a dps increase to add it into my rotation on appropriate bosses? And if it is, should I only be doing it in solar?
It is sometimes a raid dps increase but a personal dps loss. On fights where it is single target but the tank gets a damage buff(or the enemy gets a debuff) like a spark tank on Ryo or a hatchling tank on Alys your thorns will do a stupid amount of damage.

You don't need to cast it in solar because you are casting it on another player. At that point thorns is a buff on them and uses their AP or SP for its damage and their damage modifiers and counts as their damage.