The equation will return a “zero” every 12 hours. For example, today mine returned zero at about 11:20am and will again at 11:20pm, when the sun is on on the other side of the Earth:
You need to put a Condition after the trigger in your automation so that it only triggers in daylight. In my case, I just include a condition that says the trigger is only valid after sunrise and before sunset. This is my UI Condition which follows the Trigger:
You could just put a condition that says it can’t trigger before 07:00 or after 18:00 - or something similar
That condition is probably redundant on mine because I also have a condition that says if my solar PV is producing below a set amount of power, (ie it’s not sunny) leave the blind open. Clearly there’s not much power being produced at 11:20pm.