Okay, so what they do is install the panels on your house for "free" (or some rough approximation thereof). They claim the Federal (and perhaps state?) tax credits on your behalf, and then "lease" the panels back to you. I believe you pay a set monthly fee and are also responsible for your electric bill, though of course the system is sized so as to minimize the bill that you pay the utility. They also maintain the system (cleaning, repairing broken parts, etc).

The advantage, of course, is the 0/low upfront costs.

Whether or not this model works for the roof tile system is another question entirely. Of course, the bill would be much larger, but the tax credit might be larger as well.

I'm not sure how they handle a circumstance in which your income causes your tax credit to be phased out. Likely there's fine print where you have to pony up extra money.