You could put a 12v regulator in the line, but... that is massive waste of a 24v panel. Yes, wiring panels together in series will increase your voltage. Either way, you need to put a regulator and fuse in line to prevent overpowering your components on an exceptionally sunny day. Don't forget your diode to prevent power from nuking your solar panels.
I built something similar to this last summer, it's great fun! I wish i could find the original instructions i used, but this is pretty close.http://www.howcast.com/videos/470062-How-to-Make-a-Beer-Can-Cooler-that-Runs-on-Solar-Power