|Fig. 1: Elements of a passive solar design. (Source: Wikimedia Commons)|
A key factor in building homes with minimal environmental impact is energy efficiency. A passive solar home is a home in which heat is captured from the sun and stored for future use. This can be coupled with the use of a solar thermal system, which also utilizes the sun's energy to generate energy, to generate effective, minimal cost, environmental friendly energy.  The passive solar design can be used to mainly heat the open spaces in a home whereas solar thermal technology is used to heat water and run other utilities like a cooling system. It is a common misconception that this system fails in the summer, the relationship between these two low- impact systems does well in dealing with the difficulties that a summer period can present.  This is possible because the passive solar design can be used to reject solar heat and the solar thermal system can run cooling systems to maintain a comfortable living environment within the home. Also, using trees, shading, and overhangs can greatly improve summer time temperature maintenance. Seemingly unrealistic, a home of this character can be a full year option if it meets a few qualifications. See figure 1 for an illustrated picture of a passive solar home.
For an obvious reason, a portion of the south side of your house must face the sun-unobstructed. Without a wide-open view of the sun, your home cannot get the necessary solar energy need to perform all the tasks it must complete to run a conventional home. Using one of three methods (direct gain, indirect gain, isolated gain) a passive home collects thermal energy as the sun rises on the south side.  This heat is stored in structures strategically placed in different parts of the home. In order carry the process to completion in the most efficient way possible, the home must ensure that a few design elements are adequate.  First, the distribution mechanisms of the house must be optimized to ensure the heat can flow freely and get to every corner of the home. Once the heat is stored it can be distributed in many ways such as: fans, convection, conduction, and radiation. Next, the capacity of storage of the objects that hold the heat must be maximized. Things such as concrete, stone, and tile are very effective in absorbing heat in the summer and repelling it in the winter.  Finally, and maybe most importantly, having optimal windows for this structure is key. Windows that face south and have some shade to avoid overheating are paramount in having a successful passive solar home. 
Where your home is can change some of the requirements of a passive solar home as well as a solar thermal system. If a home is in a place that doesn't receive a lot of sun, a passive solar home will need another system to supplement the heating of a home because it wouldn't be able to provide adequate heat to the entire home.  A passive solar home also faces a challenge in providing comfort in cooler mornings. The sun hasn't risen and the objects have disseminated all their stored energy.  This is another time when a passive solar home may need a supplemental system to maintain comfort for those within the house.
Though there are many technical difficulties in setting up a passive home, it can be a viable option in terms of providing a conventional living environment. It can achieve this not only at a similar cost, but at a much smaller energy consumption rate. Using proper guidelines and design techniques, a passive solar home can efficiently capture, or repel, solar energy, and use it to create whatever environment a homeowner would desire.
© Bryce Marion. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Passive Solar Design," U.S. Office of Energy Efficiency and Renewable Energy, DOE/GO102000-0790, December 2000.
 J. Kachadorian, The Passive Solar House: Using Solar Design to Cool and Heat Your Home (Chelsea Green Publishing, 2006).