Speaking of useful online tools, I should mention also a solar array modelling service, provided by RoofRay on their homepage. They use Google Maps and various other information to help you estimate the solar potential of your home or business before taking the financial plunge to invest in solar energy.
Using the site’s modelling tools, you can evaluate how much solar energy your home could capture and how that would affect your monthly bills based on past weather conditions, current electricity bills, the slope of your house, as well as how many panels your roof can hold.
With Google Maps you can calculate the square footage of your roof and build virtual panels. Then RoofRay estimates the output potential of the roof, costs of installation, and ROI. Another section shows existing installations that have already been completed by other people, including specifics of the roof used and total peak power.
Of course, RoofRay does not replace solar experts, but undoubtedly could answer some of your basic questions, and generally it is a quite interesting online service that deserves our attention.