The interest in using solar heat has been increasing over the last two decades and various home designs have been created in an effort to utilize passive solar heating. It is virtually impossible to use passive solar heat in a building that is not specifically designed to take advantage of all the radiant heat from the sun. Even in homes utilizing passive solar home designs, there can be fluctuations in temperature and most lenders will not finance passive solar homes unless they have a back up heating system.
Active solar home designs include mechanical devices. Passive solar home designs have no mechanical components for heating. The heating is dependent exclusively on sunlight and the ability of the materials of the house to absorb and store heat. The earliest examples of passive solar home designs are actually underground homes that were built in the 1970s.
The earth absorbs and stores the radiant heat of the sun. A few feet below the surface, ground temperatures tend to remain the same, within a few degrees, all year long. Underground homes take advantage of the constant temperature below the earth's surface to keep the home warm in the winter and cool during the summer. Caves also have this tendency to remain at fairly constant temperatures year round. New solar home designs take advantage of the same principles as underground homes.
Many different types of materials have been used in passive solar home designs. Straw bales, rubber tires and other materials that absorb heat have been tried. The problem with many of these materials, is while they absorb heat they may not store heat. Passive solar home design requires materials that store heat and release it slowly.
The single most important factor in passive solar home design is that the home face true south in order to take the most advantage of the sun's rays. Many solar homes have large windows facing south to absorb the sunlight and bring it into the home. One of the best building materials for passive solar home designs is concrete, either concrete blocks or poured concrete. Concrete absorbs heat well, but releases it slowly, making it ideal for passive solar home designs.
One difficulty with passive solar home designs is a lack of ventilation. It is necessary for the health of people living in the home to have air exchange, to kept the air fresh and oxygenated. Passive solar designs usually require tight sealing to prevent heat loss. Lack of ventilation can also result in a build up of humidity inside the home and the formation of harmful molds.
Existing homes cannot effectively be converted to passive solar homes. Active solar heating systems cannot provide sufficient heat year round to heat the average American home. Active solar systems also require, in most cases, a large area to store heat, usually in bedrock, or in large blocks of rock.
Passive solar home designs offer hope that at some point, many homes will be minimally dependent on outside energy for heating needs. As the designs improve, so does the efficiency of the home designs. The technology is constantly improving and in the near future it may be possible to live in homes that receive all their heating energy from the sun.