Sunrooms of our luminary get first-class backing (7)
I believe the answer is:
'sunrooms' is the definition.
(I've seen this in another clue)
'luminary get first-class backing' is the wordplay.
'luminary' becomes 'solar' (I can't explain this - if you can you should believe this answer much more).
'get' says to put letters next to each other.
'first class' becomes 'ai' (As - top quality).
'backing' is a reversal indicator.
'ai' written backwards gives 'ia'.
'of our' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for solaria that I've seen before include "Places to get bronze", "tanneries?", "tanning rooms".)