I was discussing our proposed green house with Barb. I am suggesting a heat storage in the ground system. More complex, but much more energy efficient. What with the possible mini ice age as a result of global warming, this is looking to be a wise investment.
Say if you have a link, I’d like to see that, to show Hubby.
Back in the latter 60's and early 70's, there was a couple , both of whom were in their 80's name Helen and Scott Nearing, whodeveloped in NH an 'in ground"/bermed greenhouse
that they grew their own crops for over 10 1/2 months of the year.
It was a glass greenhouse, using old storm windows and native stone, which might have been painted black, as a solar storage and collection system.
Given that they were native New Hampshirites, you might find some of their books in the local library; they even taught classes on how to build earth bermed greenhouses.
I believe that they then expanded their greenhouse collection system to include 55 gallon, black plastic barrels to act as solar collection and solar mass retention.
Since they precede Google, that search engine is of little benefit in finding title or location of their books.
As I recall, the key concepts were southerly exposure to catch "maximum winter solar direction" , the use of vapor barrier, and comfortable plant table height and width.
All given, due consideration for the ages.