Passive Systems


The most direct way to use the energy of the sun is to design buildings to allow as much sunlight to come into as much of the building, reducing the need for electric lighting. Windows, skylights, and light tubes can all bring free sunlight into your home or business.

Light tubes act as skylights with a slight difference. A skylight lets light in through a glazed opening (an opening covered with framed glass or other clear material) in the ceiling directly above the room being lit. A light tube uses a similar glazed opening on the roof, but it allows sunlight to be delivered to a room not directly beneath the glazed opening. Light tubes are flexible tubes lined with highly reflective foil that run from the roof glazing to the ceiling of the room. Light tubes are used when people don’t want a skylight opening on the roof on the front of the house or when pipes or other elements in an attic space make construction of a traditional skylight impossible.

Several studies have found that using more natural daylight not only reduces utility bills, but also improves people’s dispositions and reduces absenteeism, definite benefits to both families and employers. When increasing the amount of natural light entering a building, be careful to use quality products and ensure proper installation of the glazing. The location, size and type of window materials are also important considerations and relate to other aspects of passive use of solar energy.

Passive Solar Building Design

Passive solar building design is a combination of energy-efficient design features: proper use of daylighting, landscaping, and thermal mass; and correct orientation of the building so that the long dimension of the structure runs as close to east-to-west as possible. Keeping the long side of the building facing within 15 degrees of due south not only allows maximum heat gain during the winter, it helps avoid heat gain in the summer.

Since this page intends to provide an overview of most solar energy technologies, we won’t go into great detail on passive solar building design at this time. However, remember these things:

  • Because of reduced utility costs, a well-designed and well-built passive solar building may cost a little bit more to build, but it costs a lot less to own over several years than a seemingly less-expensive conventional building.
  • Passive solar buildings do not have to look "strange." They can be built out of the same materials as those used in conventional buildings. A rule of thumb is that the window area on the south side of a solar building should equal about 10 percent of the floor area. On a solar building, the designer places more of the windows on the south side and fewer windows on the other sides.
  • Sometimes existing buildings can be retrofitted to become fairly effective users of passive solar energy. When considering such a project, develop a list of possible passive solar and energy-efficiency changes to the building. Then weigh each change based on criteria including cost, payback, visual appeal, and local building codes before making your decision.

The book Passive Solar Design Strategies: Guidelines for Home Building, developed by the Sustainable Buildings Industry Council (SBIC), is an excellent resource for further study of passive solar design techniques. It provides a good introduction to a software package called "BuilderGuide, Energy Analysis Software for Homebuilders," which was developed by the U.S. Department of Energy's National Renewable Energy Laboratory. SBIC also has developed an advanced energy simulation program for commercial buildings called "Energy-10." Information on these programs and training in their use can be obtained through the Division of Energy

North Carolina State University’s Solar Center web site carries a significant amount of basic information on solar building design. This page contains numerous fact sheets dealing with a wide variety of passive and active solar system information. On the same site, you can find information on how to obtain several different solar home plans, some for free, to get an idea of the variety of good passive solar home designs.

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