Take a look here:
Mango in central Italy: an experiment.
(shamelessy self promoting
).
If you carefully plan everything you can get about 18F higher (during night) inside your structure, just with sun heating everything (no bills, no blackout).
But of course, the perfetct greenhouse is the one that suits your needs.
(also keep in mind that my structure has to stay up for several months, and so it isn't very quickly to put on and down).
Hope this can be useful.