Passive solar is a way of designing a building so that its heat regulation is largely done using the immense free and perpetual energy of the sun. No "active" systems (eg. photovoltaics) that require energy in manufacture and maintenance are generally used - just smart design and smart choice of materials. No matter what happens with the price or availability of conventional energy sources, the passive solar system will carry on functioning. At its most basic passive solar consists of:

ORIENTATION - Lining the building up so that the long side faces as close to true south as possible.
GLAZING RATIOS - Installing the correct amount of window glass on each side of the building.
OVERHANGS - Calculating roof overhangs on the south side so hot summer sun is blocked, but winter sun can fully enter.
THERMAL MASS - Incorporating sufficient high-thermal mass materials to absorb and slowly release solar heat.
INSULATION - Insulating the building envelope to a high standard in order to retain as much of that solar heat gain as possible (and to keep extra heat in the summer from entering).

When it comes to a passive solar greenhouse, however, the design varies a bit from that of a home since you’re catering to plants as well as human occupants. In addition to heat, plants require a great deal of the sun’s actual light. This means you go full out on glazing the south side of the building and apply insulation and thermal mass elsewhere. Some windows on the east side are also helpful to let the morning sun gently warm things. Roof overhangs are less applicable since the plants will need full access to the sunlight in all seasons.

Passive solar greenhouse design makes a whole lot of sense in Alberta’s climate where we get plenty of sunshine to “harvest” heat, yet cool nights and a long season of cold where that heat would otherwise be quickly lost if not stored. Classic “glasshouse” designs have the disadvantage of overheating easily in the summer while losing all that heat rapidly once the sun goes down. In the shoulder and winter seasons these greenhouses need expensive and energy-intensive supplemental heat to maintain growing temperatures, and that heat passes quickly through their low R-value glass or plastic shells.

Groundswell Network’s Passive Solar Greenhouse in Invermere, BC