Passive Solar is a method of building design that uses structural elements to heat and cool a building without the use of “mechanical” or “electrical” equipment. For example, the windows, walls and floors are designed so that they collect, store, and distribute solar energy in the form of heat in winter and reject solar heat in the summer.
Passive solar design techniques incorporated into architecture decrease the amount of energy needed for lighting, heating, cooling, and other loads. (Dunlop, 20) Buildings designed for passive solar heating usually have large, south-facing windows.
Materials that absorb and store the sun's heat can be built into the sunlit floors and walls. The floors and walls will then heat up during the day and slowly release heat at night, when the heat is needed most. This passive solar design feature is called direct gain. (NREL, Passive Solar) Solar heating systems that do not use a “collector” to absorb the sun’s energy.