I will get the forumla for you, but i am not familiar with these solar panels except in Drip in Sprinkler, however I too thought such things long time back to know more about Solar power and their load facilities during night and sunny days.
I am pasting this answer, but hoping someone will give better answer for you.
In a direct current, 1 amp at 110 volts equals 110 watts,
whereas 1 amp at 220 volts equals 220 watts.
but what could be 1 amp of 12volts in watts? I think 12 watts would be for 12volts.