...would be determined largely by how well the system is insulated vs. how well it permits lower frequency radiant energy to enter. Your glass, floors and walls will all increase in temperature and glow in IR losing heat from the system. If you perfectly insulate (an unattainable ideal) then the temperature is limited only by the energy in the sunlight that comes in. Anyway, I am certain you can do better than 190 F.

This is something you could try yourself. A greenhouse doesn't have to be any bigger than a "breadbox" with a pane of glass (and a thermometer). Though the smaller you go, the less insulation you will be able to include.