The Weather Underground site (wunderground.com) has a tool you can use to evaluate the solar potential for your location. While it does not account for the specifics of your roof, or potential shading issues, it does give you a perspective on the solar energy available in a relative context.
Click the image or here to go to the calculator page. The seasonal variations become quite clear, if you live closer to the equator there will be much less variance of course. Here in the northern latitudes the variance requires that we plan the size of our solar installations thoughtfully. Solar thermal system need to be designed so they do not over produce in the summer - or a heat dump mechanism needs to be considered. And solar power systems can be designed to overproduce in the summer so that a grid-tied system can “bank” energy credits under a Net Metering contract with the utility, and use those credits in the winter.