I would also wonder about the durability of the panels; when something needs to be amortized over 20-30 years to be cost-effective, it had better last more than 20-30 years. If the replacement cycle is such that they only break even, it's much less of a hassle to just buy power from the electric company.

Of course, with the efficiency of solar panels doubling about every 10-15 years, given time this will eventually be very cost-effective.