This post is meant to empower you to know more about your system and expected solar projections using a common website put on by NREL the national renewable energy laboratory. http://pvwatts.nrel.gov/ if you navigate to this website the first thing it wants to know is your location because based on weather data from key stations across the U.S. we can project how much sun light we should expect year round.
Page 1 Just enter your city and state and hit enter.
page 2 This is just letting you know the closest weather station that it will be pulling data from so click the orange arrow at the top right of the screen to proceed. If the website changes over time I am sure there will be some sort of obvious similar process.
Page 3 Enter your solar system size. Example if you have (4) 300watt DC rated panels this is 1,200 watts or 1.2KW so enter 1.2 in the DC system size box.
Leave the Module type as standard
If the array will be on your roof then choose fixed roof mount, if the array will be on the ground choose fixed open rack. This has to do with cooling... the ground mount will have better air flow therefore making the solar panels more efficient because the hotter the solar panel is the less efficient.
Leave system losses as 14%
Tilt... If you are on the ground the standard tilt is a 30 degree tilt, if you are on the roof that varies too much so you will need to find that out for your self
Azimuth... 180 degrees equals due south, 90 degrees equals East, 270 degrees equals west, if you are between that you can use the tape measure tool on google earth and when you measure the north to south exterior of your home that will give you a heading which will be your azimuth.
If you are looking to check the value of solar offset this section is fairly generalized because most utility companies have a tiered system with different rates in the summer from the winter, but for a good generalization you can put something somewhere in the middle of winter and summer to get an idea of energy value.
After filling all of this out just click the orange arrow at the top right to proceed
You will see a monthly projection of what your system should produce in kWh and this is the power in AC being produced from your solar system. The average sun hours per month are listed along with your projected energy value of this solar system.
Hope this empowers someone out there... Knowledge is power as G I Joe says
Solar and Generator Division Coordinator