Back in my 'hippy-dippey/bell bottoms days', there was Scott and Helen Nearing who used a solar greenhouse to grow crops in Vermont for 10 1/2 months of the year.
They were both in their early 80's, but both very active, and taught sustainable glass berm greenhouse construction, and I thought they established an educational foundation.
The ideal setting for the greenhouse was partially subterranean(built into a hillside), facing south, south east (SSE)direction to catch the maximum amount of winter sunlight.
They used a stone & concrete floor, several 55 gallon plastic barrels (painted black), and natural stone wall behind the barrels as a heat sink, and heat storage.
If they could grow crops in winter in Vermont, I imagine that anyone could use the same techniques to grow crops in more hospitable conditions.
Anyone with funds and space sure could. Unfortunately that is not what we are faced with.
We have some books with those subterrainean methods. Unfortunately, we also have a house with concrete patios across the entire front and back of the house. The back is southerly west orientation.
There is no way to turn the greenhouse we have into such a type like that either. At this time, we do not have funds to build that type, though we do begin to plan and save.
Till then we are stuck with what we have and whatever modifications that can practically and economically be made.
We have a sun room attached to the house with a concrete floor and no method to heat, except running an electric heater, which would be cost prohibitive-the green house is not insulated.