IMBY (in my back yard) is a tool that can calculate how much electricity you can create through solar or wind power. The online tool was created by The National Renewable Energy Lab and is really easy to use.
First you input your address, then you indicate whether you want solar or wind power. You then draw the area on the map of your house were you want the system and then it calculates based on the area you selected what type of system you need etc. Below is the info the tool gave for my mother's house is Irvine, CA assuming a solar system. This is a really neat idea that allows you to determine what you may need without having to sign a contract. I suggest you take it for a test spin. It's free! (you can click on the image to get a closer view)