For the quickest way to estimate your solar energy production, simply look at the below insolation map, locate your city and then multiply the corresponding (kwh per kw per yr) production number by 80%. Why 80%? Because there is about a 20% efficiency loss in most solar systems.

This will tell you how many kWhs per Kw of energy your system should generate over a year.

Of course, this calculation assumes that your solar system is not affected by shading or other physical factors that would limit its expected production.