One of the worst things about alternative energy is trying to figure out what it's going to cost you. Electricity from the grid is easy: you plug stuff in and get gouged with a bill at the end of the month.
With solar, you buy a few thousand dollars of equipment and get it installed at one point in time. To compare it to grid electricity, you have to estimate how much power it will produce over the lifetime of the system, divided by the number of months. You then have to add in federal and state rebates, mortgage issues and electrical buy back from the grid.
Hence, the Clean Power Estimatorfrom the California Energy Commission. California residents pop in their zip code and a few other facts and it will spit out how much you can save. It seems to favor clean power, but it's not too far off. In my neighborhood, it says a solar system will cost $8,000 but after rebates the total bill comes to $3,780, which is close to what others have estimated. It will cut 1,812 pounds of CO2. It will give estimates for businesses too.
If you're thinking of going solar, give it a run through first to see if it makes sense in your area.