For when I am not using the garage, I would also black out the garage door and close it onto a pair of 2×4 scraps. This would leave a gap under the door, and the top would be kicked in a bit so there is a gap on top too. The afternoon sun would hit my West facing black garage door which would cause the door to heat up. The hot air would go into the garage, drawing the cold air off of the garage floor. This would effectively be a Trombe Wall.
Although, maybe I could rig up a lock-slot so the door has about 2 inches of travel and run a micro-controller timer to automatically lift the door the 2 inches around noon and shut it at dusk.
Solar Workshop or Studio
Describes how to convert a garage into a delightful solar heated and lighted workshop, studio, sunspace or playroom