Don't feel frustrated if you get a little confused by the phrases passive solar energy and active solar energy. The terms have been tossed around rather loosely, especially in connection with houses and in the advertisements of builders.
Passive solar energy has been around since the time caves were heated and cooled by their location in relation to the rays of the sun, a concept we know as orientation. Combine orientation with the kinds of materials used for building houses and the harnessing of the sun's energy and you have a simple explanation of passive solar energy. Mention such things as roof collectors, fans, pumps, heat-exchange units, thermal products, controls and sophisticated technological equipment and you are talking about active solar energy.
In most cases, passive solar energy in a house may not be quite as effective as active solar energy, but it can be surprisingly functional and inexpensive, especially if the passive ideas are incorporated into the house during the planning and construction stages.
In an active system, the reliance is on technology that is somewhat independent of the building. Items related to this technology can always be added later.
Single-family houses with passive-solar-energy features are gaining popularity in subdivisions. This type of design formerly employed glass over special walls to store heat, but now contractors are putting up glass-enclosed solar rooms to be used for living purposes as well as for heat reservoirs.
In one such housing project in a Denver suburb, a builder has been using thermal-energy storage panels made by the Dow Chemical Co. These panels store heat from direct sunlight, then release it after the sun sets.