It is difficult to determine the right one, or the optimal size for greenhouses. Its size and form are rather a function of the purpose and architectural solution of the building, especially his southern party, and not a priori of the planned heat balance. This balance can be preliminarily calculated only after at least the architectural concept has been completed..

For the designer-architect, the angle of inclination of the glazing is important. For passive systems, direct radiation is the most important. So, external glazing should be designed at this angle, to make the sun's rays, in the period when the assumed profits are to be the highest, fell at right angles to the windows. The greater or less the angle of incidence of sunlight on the glazing, the greater the number of reflected rays. If the angle of incidence of sunlight on the glazing is less than 45°, the number of reflected rays is greater than the number of rays absorbed. This is important for the formation of the southern part of the house.

Passive systems are often complemented by fixed or movable headlamps, which increase the amount of radiation falling on the collector, and which are also reflected in the southern façade. These are planes covered with reflective materials, fixed or movable, also used as night insulation of window openings.

Examples of southern façade with reflective planes: a) arch house. S. Baera in Corrales, N state. Mexico (UNITED STATES),b) holiday home from 1979., Arch. R. Shannon, c) house in the department of Vendeen (half. France) 47°N with 1978 r., Arch. P. Boisseau