This chart shows solar insolation in kilowatt-hours per square meter per day in many U.S. locations.  For simplicity, we call this figure "sun-hours per day".  To find average sun-hours per day in your area (line 3), check local weather data, look at the map above or find a city in the table below that has similar weather to your location.  If you want year-round autonomy, use the lowest of the two figures.  If you want only 100% autonomy in summer, use the higher figure.  If you want a utility intertie system, and you have net metering available in your state, use the average figures.