Also, currently solar roofing can be a bit of a tax-code hack (depending on where you live). If you buy a new roof, and then put solar panels on top, only the panels get green-energy tax benefits, but if the roof is the panels, then the total cost of the roof is used for calculating your tax benefits.
Larger installs will usually hit caps on the benefits before this matters, but smaller installs in places with high caps can collect more.
[edit] Reading other comments, it's apparently also a permit-hack, as panels need to be permitted separately from the roof (and in HOAs may be subject to board approval).
Can't speak to other states, but Florida state law specifically overrides HOAs when it relates to solar panels on your roof. They are inhibited from preventing you from installing solar on your roof.
Larger installs will usually hit caps on the benefits before this matters, but smaller installs in places with high caps can collect more.
[edit] Reading other comments, it's apparently also a permit-hack, as panels need to be permitted separately from the roof (and in HOAs may be subject to board approval).