Get yourself a volt meter while you are there.
Simply hook up the leads from the volt meter to the solar panel leads and move it around to get the maximum voltage output.
As the solar panel gets more direct sunlight, it puts out more voltage.
That’s it.
References :
http://www.radioshack.com/search/index.jsp?kwCatId=&kw=solar%20cell&origkw=solar%20cell&sr=1
http://www.realgoods.com
References :