I have fond memories of eating oranges fresh of the tree in Florida, and lemons fresh off the tree in Sardinia, but as much as I'd like too I can't really move to either location...
So, I would like to grow a well fruiting pair of orange and lemon trees in the greenhouse I'm putting up. From what I've read, for this to work the greenhouse has to be kept heated to a minimum of 7°C to 10°C throughout the winter. To me this seems criminally wasteful of energy to say the least.
It got me thinking about building a "greenhouse within a greenhouse" during the winter, perhaps a free-standing cuboid with sides of rock-wool containing grow lights with local heating,or perhaps having internal clear plastic dual-layer walls to put up in winter around them, with insulation under the concrete base of that section. Either way there would need to be some sort of ventilation; I was thinking of counter-flow heat recovery ventilation, perhaps incorporating a Peltier to make it more compact, with the inefficiency of the Peltier providing the additional heating to hold it above ambient.
The botanic gardens I've visited have always just gone for an egregious waste of energy for their hot-weather sections.
Hope to collect some good thoughts and/or experiences from the hive mind!
Post edited at 21:02