Solar garden boxes, or something

Solar garden boxes, or something

On Easter weekend my family and I visited historic Williamsburg, VA; wherein Virginia it can still be pretty chilly. The leaves were just barely starting to show on the trees at the time. There was a garden that was sporting these sorta "solar boxes" for want of a better term, wooden plywood things with lids that were fashioned from, what looked like, average pane glass windows, hinged and mounted on an angle to aim south. At the time I was struggling at home just to get some seeds to germinate in my bay window indoors, while these anacronist throwbacks had full heads of lettuce growing outdoors in March! I recently had some windows replaced in my home and saved them specifically to this end and was looking for information about these things - really anything I can find - a formal label, anything. Google has returned very little about solar box gardening, etc. They were such a low-tech option for wintering plants that I didn't think to ask one of the curators at the time, and what with the fam there and running about, each with their own agenda it never happened. Now, I know how to build most anything out of scrap but I'm not fond of re-engineering things that, obviously, have been working for centuries. Does anyone here in the LJ garden have a clue for me? Does anyone even know what I'm talking about?
our 2 japanese maples

our 2 japanese maples

Container garden success!

Container garden success!

Tulip

Tulip

Some quick tips

Some quick tips

Raising Existing Beds

Raising Existing Beds

Angel wing Begonia

Angel wing Begonia