How to choose a Solar Panel
MUCH more information will give you a much better answer

Find average daily insolation by month from  Gaisma

Watt hours max per day != Watts rate max x sunshine hours from Gaisma.

If storing in a battery and retrieving the average wWattage you can run continually  ~~=

Watts = Panel_peak_Watts x Sunshine hours per day / k  

k is a mimimum of about 30 and can be 60+.
 Depends on how well you match panel to battery etc.

What are you operating?
 what Wattage?
 What location?
 More ...?

Olin says black side up.
 Sometimes its pretty blue side up :-)
 Depends on technology used in cells.