A new study conducted by DOE’s National Renewable Energy Laboratory (NREL) documents how solar looks as an investment in various regions across the U.S. While the study intentionally omits and state or federal incentives, it does reveal some of the factors that allow homeowners to save more and faster than others, given the same panel type. The study used a software called the System Advisory Model (SAM) to analyze simple payback period in Phoenix, Tampa, Boston, Kansas City, and Seattle. Overall, the study did find that Boston averaged the quickest returns, whereas Seattle had the potential for the longest payback. According to the analysis, the driving factors behind how cost effective rooftop solar is are: Local electricity price, utility tariff for purchasing excess electricity generated at the house, solar resource at the site and panel orientation and Installed cost of the PV panels. While state and local incentives also play a major role, as they do in the Carolinas, it appears customers have the greatest potential for savings when they have high electricity cost (Boston ~ $0.21/watt), high buyback rates, especially relative to electricity price(Boston ~$0.19/watt), the availability of solar, and of course the average cost of solar. This study does not account for (but does acknowledge) other variables that change within a region, such as orientation, shading, and roof pitch. These can play as large a role as any other factor in the feasibility of a solar project. All more the reason to do your own research, and to seek out consulting rom solar companies with positive reviews.