A solar greenhouse works by letting in solar radiation and trapping the energy from that radiation to increase and maintain the internal temperature above that of the temperature outside - see greenhouse effect for details.

The most basic aspects of greenhouse design are: first, to thermodynamically isolate the system to stop convection and conduction from equalizing the temperature with the ambient temperature; and second, to provide a covering that is transparent to incoming solar radiation to provide the heat source for the greenhouse. After these two basics have been established, a covering material is chosen which will absorb some of the outgoing IR and radiate a portion of it back into the greenhouse environment to reduce radiative energy loss to the sky from the amount that the ambient environment experiences.

The use of insulation and more infrared-absorbent glazing enhances the effect by reducing heat loss by conduction and IR radiation. The soil mass at the base of the greenhouse acts to absorb a portion of the available heat during the solar period of the day for later use as a night time radiant heat source. Installations of subterranean air circulation tubing can be designed to enhance the soil mass heat absorption potential. With proper subterranean design, [1] underground air circulation tubing can absorb most of the daytime solar gain directly into this soil mass to provide air cooling, prevent overheating and serve as an additional heat source at night.

Also the addition of heat storage materials with high heat capacity, such as containers of water or bins of sand and rock absorb heat energy during the day to help prevent greenhouse overheating, and release that energy to maintain the internal temperature during cooling periods, such as during the night.

Practical applications

The modern development of new plastic surfaces and glazings for greenhouses has permitted construction of greenhouses which selectively control the transmittance of both incoming solar radiation wavelengths and outgoing thermal IR wavelengths. The new materials also provide insulation to reduce conductive loss through the glazing in order to better control the growing environment.[2] The research starts with the blocking of convective heat loss as a given in an isolated system and works toward improving IR absorption and insulation to further reduce radiative and conductive energy loss.

Gardeners sometimes use a "greenhouse-in-a-greenhouse" technique, in which they lay additional IR absorbent plastic sheeting inside a greenhouse in order to provide additional warmth in an isolated area to plants or water pipes.

Another practical application of the greenhouse effect is in the creation of solar cookers.

Cite: Wikipedia