You need to ask,What is the capacitor supposed to do for the panel ?What is the industry ?A
+1. The question is completely incomplete; it's roughly equivalent to "how much water should I add to a recipe". What are you actually trying to do? Why do you think a capacitor is needed at all?
Power factor correction possibly? <rubs crystal ball>
Possibly. (Magic 8-Ball says "Ask again later.")
You're probably going to fail on this one, as you've not managed to ask a meaningful question about whatever it is... L