John and Alice Carpenter spent a good portion of their
monthly income to heat their two-story colonial-style house last winter. They took steps
to eliminate drafts and block up leaks, but their energy bill was still high. John and
Alice considered installing an active solar system, but the cost was too high and it would
take years before they saw any payoff. Then they heard about passive solar techniques from
Solar energy is often perceived as being the alternative energy source of the future.
In fact, a simple and less expensive form of it, passive solar energy, has been in use for
Solar energy systems don't have to be complicated or expensive to do an effective job
of conserving energy. Passive solar systems, unlike active ones, require no significant
mechanical equipment and operate without any external power. Instead, they rely on natural
heat movement through convection, conduction and radiation.
No matter what type of passive system you install, each includes the same elements
which must all work together for the system to be successful. The most obvious component
is the collector, a large glass (or plastic) area that sunlight passes through. Next is
the absorber, a dark surface that sunlight strikes after it passes through the collector.
Now that you've collected heat, you must distribute it. This is accomplished using natural
methods of heat transfer, though some "hybrid" systems use fans, ducts, and
blowers to boost air movement. Lastly, you must have a control, or heat regulation device,
which helps prevent overheating in summer and heat loss during sunless periods. Also, your
passive system may include heat storage in the form of materials that absorb and hold heat
well, such as masonry or water.
One of the most important steps in a passive solar installation is orientation, or the
positioning of your house in relation to its environment. For the most effective use of
passive solar techniques, your house should face due south.
The Greeks realized this and used passive solar successfully to heat and cool their
homes. They learned to build their homes to take advantage of the sun's energy when wood
became scarce. They believed that exposure to the sun was healthy and building their homes
facing south was best.
A typical Greek house had a south-facing portico similar to a covered porch, where the
sun could enter during the winter and be kept out during the hot summer when it was high
overhead. Earthen floors and adobe walls absorbed much of the solar heat and a low wall
was also constructed between the pillars to keep out drafts. Unfortunately, they had no
glass, so they had to rely on a completely passive system, letting their architectural
design and the sun do all the work.
The Romans not only copied the Greeks but advanced their ideas by designing buildings
for different climates. They used clear window coverings such as glass to enhance the
solar effect. The most innovative use of solar energy was in the public baths of ancient
Rome. The Baths of Caracalla, one of the largest, held over 2000 at a time. The hot baths,
or caldarium, faced the winter sunset to get as much solar heat as possible. The whole
south wall of the bath house was glazed with glass. These giant windows trapped so much
heat by late afternoon that bathers would "broil" from it.
The Romans, like the Greeks, thought solar heat to be healthier than artificial heat.
Doctors considered the sun therapeutic for many ailments. Solar architecture became such a
part of Roman life that sun rights guarantees were were written into Roman law.
A passive solar house uses no mechanical devices, such as motors, pumps, or fans to
distribute heat. A well- designed solar home functions in harmony with the local sun and
weather conditions, with spaces and components arranged so that heat transfer is primarily
by natural convection and radiation. The result is an efficient and livable building,
with side benefits of increased brightness and more comfortable surroundings. To make the
house even more energy efficient, it can be partially buried and constructed of thick
adobe. A top tier of windows can heat the rear of the house, while stone walls behind
large windows provide heat for the front.
A sunspace is a partially or totally glazed room that is added to the south-facing wall
of a house. Unlike a conventional greenhouse, a sunspace is well caulked and
weather-stripped, and includes materials for storing solar heat.
Solar heat is collected through the sunspace windows, which are angled equal to the
latitude plus 15 degrees (any tilt in the range of 45-60 degrees works well for most
locations). It's then absorbed and stored by masonry or water-filled containers that can
be positioned and sized in a variety of ways. These include a masonry wall separating the
sunspace from the main building, 55-gallon drums inside the sunspace, and potting
beds. Also, a water wall can take the place of the masonry wall, or a rock storage bed can
be added either below the sunspace or in the adjoining basement of the main house.
According to recent studies, well designed sunspaces can provide up to 60 percent of
your home's heating requirements during the winter. This percentage varies depending on
the square footage of the sunspace glazing. local climate, and the heating requirements of
There are over 100,000 passive solar homes throughout the country. Not all were
custom-built; many are part of vast subdivisions in California and New Mexico. However,
just as many can be found in cold northern states like Wisconsin. They take all forms from
log cabins to townhouses. Some are even pre-fab units made in a factory and shipped to the
By combining age-old passive solar technology with today's "smart" houses,
the most effective means of conserving energy can be had.