What is a Passive Solar Greenhouse?
Passive solar buildings are structures designed to meet their heating and cooling requirements simply through their interaction with the sun’s heat. The term “passive” is in contrast to “active” solar like photovoltaic or solar thermal systems which require conventional energy in their functioning. With passive solar, heat from the sun is collected, stored and distributed without any additional energy inputs - it’s all in the materials and design. This makes it cost-effective and highly sustainable. Key elements include proper building orientation, thermal mass, glazing ratios, optimal insulation, and calculated roof overhangs.
A passive solar greenhouse is an ideal solution to season extension in a cold climate since it allows the sun’s heat to penetrate its south face while the rest of the building is well-insulated to retain that heat overnight and into the cooler months. Thermal mass integrated throughout the greenhouse absorbs the solar warmth, storing it for slow release once the sun goes down and reducing the risk of overheating during the day. Nighttime heat loss can be further reduced by drawing thermal blinds over the glazed south-facing wall.
A strictly passive system can be complemented by an active “climate battery”, also called annualized geo solar (AGS). This system uses fans to pump excess heat from the greenhouse to the well-insulated ground beneath it to be drawn back out when the building drops below a threshold temperature. The power needed to move air in this way can be provided by photovoltaics or other renewable sources.
For anyone interested in designing and constructing their own passive solar greenhouse we highly recommend the Passive Solar Greenhouse Design Course over at smallfarmacademy.com