This always depends on how much electricity you use in your home, and where your house is located. The average American household uses 600 Kilowatt-hours of electricity per month. However, an energy efficient home may use only half that.
In a sunny climate, a 2 kilowatt PV system can produce 300 kilowatt-hours of electricity per month. (To generate 2 kilowatts of power you need about 240 square feet of solar panels.) Therefore, the first step in planning a solar system is reducing electricity consumption. It is always more cost-effective to invest in energy efficiency than to install a larger PV system. Planning, mindfulness and some initial investment can result in a dramatic reduction in electricity use, without sacrificing the comforts to which we've become accustomed.
The first and most important step to take is recording your monthly electrical usage, and finding the average kilowatt hours used.