A completely passive greenhouse is a tough experiment for most gardeners.
Air circulation is one of the most important aspects to greenhouse climate control. It is more important than most people realize. Every greenhouse needs to have a circulating fan moving air at all times. Although the idea is basic, the principle is critical. Plants need fresh air for a healthy root system and a constant flow of air prevents pockets of warm or cool air staying in corners. It will regulate temperatures and increase efficiency in the greenhouse. This will also prevent mold from forming on walls or plant containers as condensation is less likely to settle especially in a structure like ours that is so well sealed for inclement weather.
If you live in an area with constant moving air and you have incorporated extra side vents, louvres and possibly an extra door for pass-through air, then it may be possible to have a passive greenhouse.
Alternatively, you can look into a solar powered circulating fans although we do not have any personal experience with them at this point.