Leasing the sun

There may be many such firms but I've been hearing radio commercials for a company called "Solar City." The business model is to provide rooftop photovoltaic systems at little or no initial cost. Solar City maintains ownership of the system and leases it to the home or business owner. The claim is that the total cost to the owner (lease payment plus paying for the much smaller amount of electricity used) is less than the electric bill prior to installing the system. They have a javascript application in which you install such information as your typical electric bill, your zip code (then followed by actually pointing to your house on a map), your roof slope and direction, and your electricity provider. It then returns a 15 year projection of savings, with a graphical representation of lease payments, electric bills, and the electric bills that would have been paid. There's an estimated rate of increase built in. The result of my initial inquiry looks like this:

Note that, at the outset, I can save $4.00/month. Not a lot. But I used my current electric energy usage. What if I significantly increase my usage by the purchase of a Nissan Leaf? In my post on the subject I estimated that I'd need to utilize about 17.5 kilowatt hours per day to charge the Leaf. Now, of course, I'd be charging it during the daytime rather than at night so the system would need to be sized for my use other than the Leaf plus the 17.5 kilowatt hours per day, a total I'd estimate at about 66 kilowatt hours per day. Though the javascript application doesn't allow one to play with such fine points as what can be run during the day and during the night and the system doesn't allow for storage, adding the Leaf makes a difference:

Ah, $7/month, now we're getting somewhere. Of course, the Leaf is also busily saving me money. Further, it's better to have $7/month than not to have it and I could save a few bucks more by replacing my wife's car with a Leaf. Or not.

Now, in principle, I've eliminated a large portion of my carbon footprint (moreso if I can coerce persuade my wife as well). If I could really do so, and if the solar system replaced 90% of of my household electricity and all of the energy use of mine and my wife's cars, using the information used in preparing this post and this post I can estimate that as much as 25% of my family's carbon footprint could be eliminated. This is well under the 95% that would appear to be required, but it's better than replacing incandescent bulbs with compact florescent bulbs. After appropriate due diligence, I may do so.