Ok ok... So our kitchen windowsill is facing south as well. Just for some reason the way it is angled it doesn't get a lot of sunlight on the windowsill itself. You'll need to watch during the day and make a note on how much sun comes through your windows and where it is landing in the house.

Also a note about the south facing windows. They may work a lot better in the winter when the sun is more angled to the south (for the northern hemisphere). In the middle of summer you may find that the sun is far enough overhead during the day that it's not sending a lot of light through those windows and one on the east or west would work better for catching the morning/afternoon sunlight. Hey, I'm trying to figure it out myself - so let me know what you find works best for you. 🙂