When solar energy is discussed, most people get visions of roofs with shiny panels on them. In truth, passive solar is a vital energy source in modern day structures.

Passive Solar

Step outside on a hot and sunny summer day, and you'll feel the power of solar heat and light. Today, many buildings are designed to take advantage of this natural resource through the use of passive solar heating and lighting.

The south side of a building always receives the most sunlight in the United States. Therefore, 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.

Other passive solar heating design features include sunspaces and trombe walls. A sunspace is much like a greenhouse and is built on the south side of a building. As sunlight passes through glass or other glazing, it warms the sunspace. Proper ventilation allows the heat to circulate into the building. On the other hand, a trombe wall is a very thick, south-facing wall, which is painted black and made of a material that absorbs a lot of heat. A pane of glass or plastic glazing, installed a few inches in front of the wall, helps hold in the heat. The wall heats up slowly during the day. Then as it cools gradually during the night, it gives off its heat inside the building.

Many of the passive solar heating design features also provide lighting during the day. Day lighting is simply the use of natural sunlight to brighten up a building's interior. To lighten up north-facing rooms and upper levels, a clerestory [a row of windows near the peak of the roof] is often used along with an open floor plan inside that allows the light to bounce throughout the building.


Of course, too much passive solar heating and lighting can be a problem during the hot summer months. Fortunately, there are many design features that help keep passive solar buildings cool in the summer. For instance, overhangs can be designed to shade windows when the sun is high in the summer. Sunspaces can be closed off from the rest of the building. And a building can be designed to use fresh-air ventilation in the summer.

Mankind has been using passive solar as a heating source for thousands of years. Next time you see a historical or ancient structure, look for passive solar features. The passive solar aspects will immediately be obvious once you know what to look for.