I use a garage as a shop. I insulated the walls and ceiling and put 4-year
UV greenhouse polyethylene film over the outside of the south garage door,
which makes for great light and heat when the door is open. I'd like it
to open and close automatically to store solar heat in the slab floor,
except when nobody's home.
Garage door openers are fairly inexpensive, and safe and powerful and
versatile (some people use them to haul boats out of the water :-), and
it's easy to add more foamboard insulation to the doors. It's odd we don't
see more of them used for automatic "movable insulation" in solar heating
systems. I've only heard of one application like that, for a homeless
shelter in Washington state.
The film is attached to the frame with spring wire extrusions and taped
to a PVC pipe so it can roll up for storage under the eave in summertime.