I think a combo of thermal mass storage and heat transfer is needed, to counter heat loss to the external glass. If the air doesn't get too cold, then warm soil/roots can keep plants alive in 1 or maybe 2 zones colder areas. But beyond that I'd suggest moving air through a warmed mass to keep it from getting too cold, along with blankets or some method to limit heat loss from the glass too.
I have the book "The Forest Garden Greenhouse":
https://www.goodreads.com/book/show/26251273-the-forest-garden-greenhouse and it goes into a variety of steps they take to grow plants that need a higher USDA zone to survive their cold winters. They tend to manage a 4-5 zone shift, growing say zone 9-10 plants in zone 4. They bury air tubes several feet deep under the greenhouse, insulate the soil under it from the external soil, and then run fans to pump hot air through the soil to keep it cooler in the summer and then when the temps drop to run the air through at night to keep the air at say 40F. When the soil gets cooled off too much, then they need to supplement heat and do that using a sauna that's attached to the north wall of one of the greenhouses, and they leave the door into the greenhouse open.
They also design the greenhouse so that the north wall has thermal mass to be heated by low winter sun but is shaded from high summer sun. They also use stone retaining walls that are shaded by climbing plants in the summer but exposed during the winter to absorb heat. I would think that a
solar panel and battery to power a fan that turns on only when the temperature is outside a certain temp range, meaning it is on if the temp is below say 45F or above 90F, near the top, but is off between 45-90F.
.png)
1
