Passive Solar Energy

      Since the dawn of time, life on Earth has relied on the Sun for
energy. It provides us with light, heat, and even nourishment for
growth. It is only recently that technology has seduced us away from
the sun, promising electrical light available whenever we want, and
plenty of heat, from those supplies of fossil fuels that will supposedly
 never be consumed. However, we know that those fuel sources will run out
eventually, and relying upon them has us working against Nature,
instead of with it. Utilizing Solar Energy is one of the easiest
changes we can make, which will also have a profound effect on the
rest of our precious resources.
     Passive Solar refers to the use of the Sun's energy for heating a
structure, or a water supply. In the simplest of terms, it is allowing
sunlight into the house, through windows, to warm it. Passive Solar
systems consist of three parts: Collection, Storage, and Distribution,
which all work together to take the energy into the home, and spread
it out to be used when and where it is needed.
     Collection is basically the intake of sunlight into the home.
This is done through energy-efficient windows, which face the Sun as
it travels its arc across the sky. In order for the collection process
to be most efficient, planning is crucial at this point. Obviously, if
none of your windows ever face the Sun, it will be hard to collect the
light and energy. That is why site selection and planning are so
important. 
     As a general rule of thumb, a south-facing window will get good
sunlight most of the day long. Of course, there are many factors which
will affect this. The time of year, and the Earth's axial tilt,
radically change the arc of the Sun's path relative to your location.
Therefore, you must plan a different angle to catch more of the winter
sun, when you will need it most, and account for a different angle for
the summer sun, which you may want to shade out. Trees and
obstructions are also important considerations. A building will block
out light all year long, whereas a deciduous tree will be bare in the
winter, thereby allowing in the light you want, while providing the
necessary shade in the Summer. These are just some considerations that
must be made in planning your site for the collection of the Solar
Energy.
     After collecting the energy, it needs to be stored within the
house, to be used later. To do this, large, dense structures called
Thermal Masses are built into the frame of the house. These are
usually built in the forms of floors or walls, and are the structures
that the sunlight hits when it shines through the windows. Brick,
concrete, and stone are all good materials for the storage of solar
heat, as they are all dense, and capable of storing up the heat slowly
during the day, and then slowly releasing it back into the house at
night.
     Finally, after the Sun has gone down, the stored energy is
distributed throughout the house. In the simplest of systems, it just
radiates back out from the Thermal Mass into the rooms. More complex
systems use convection currents, based on the ideas of hot air rising,
and cool air settling, to distribute the air.
     There are three main types of passive Solar systems: direct gain,
indirect gain, and isolated gain. These designs are based upon the
different methods used in the Collection, Storage, and Distribution of
the energy.    Direct gain is the most straightforward method, and basically
consists of laying out the house so that the sun shines through the
windows and heats the Thermal Masses. This may sound deceptively
simple, however, as there must be a delicate balance within the amount
of space and the energy collected. For example, you can easily
overheat in the summer if you don't plan some shading. You must also
carefully plan the locations and sizes of the Thermal Masses.
     Indirect Gain utilizes a storage system immediately inside the
window to collect the sunlight. This system can be either a solid
wall, called a Trombe wall, or a system of water vessels. Since the
storage mass is immediately absorbing the sunlight, it captures more
of the energy, but it also blocks the window from light and external
views, so this system must be carefully planned as well.
     Isolated Gain concerns the addition of a sunspace, which is quite
often a greenhouse, on the south side, or sun side, of the house. This
sunspace is walled in with mostly glass, so it absorbs lots of
sunlight, which then is stored in the floor and walls, and slowly
diffused throughout the rest of the house. Since it is not directly a
part of the house, the house is more protected from temperature
fluctuations. This method is often used in conjunction with another
method.
     Passive Solar methods can also be used to heat water for
household use. Passive water systems use large tanks or panels to
expose the water to the Sun, and then use natural forces like gravity
and convection currents to distribute the hot water, so no pumps are
used. One method, Thermosiphoning, involves the tendency of hot water
to rise, and cool water to sink, which therefore creates a siphoning
effect, drawing hot water out of the tank into use, and cool water
back into the tank to be heated. These passive water heating systems
are usually very simple, and once installed, often require little
effort to maintain, since they have very few mechanical parts, and
rely instead on the forces of Nature.
     There are many easy ways to incorporate Passive Solar Energy into
our homes, even as simply as being aware of which windows face south,
and therefore the Sun. Old, single-paned windows let a lot more heat
escape than they retain, whereas newer, double-paned insulated windows
will make a big difference in the temperature, and the amount of
supplementary heat needed. Shading of trees, buildings, and even
internal furniture can all lead to less sunlight being absorbed, and
therefore being available for distribution later.  In planning a new
home, something as simple as the direction of its orientation can
literally make a world of difference in your heating efficiency. It is
possible to build a comfortable, attractive, and livable home in
harmony with the Sun, and make things a lot easier on the Earth as
well, by not wasting other precious resources. Let us all work withNature, 
not against it! 


Information Resources
While I am listing many written and Internet sources of information,
if you are in the Raleigh, NC area, I highly recommend visiting the NC
Solar Center, which is open during business hours during the week, and
1-5 pm on Sundays. They can be contacted at (919) 515-3480 or 1-800-
33-NCSUN (in NC only).
Their mailing address is:
NC SOLAR CENTER
Box 7401Raleigh, NC 27695-7401
The staff there will happily answer any questions you might have, and
they have an extensive reference library, of which I have highlighted
some particularly relevant selections below. I highly recommend that
the Solar House be your first stop on your quest for the sun...

Other Written Sources:

AIA Research Co. Solar Dwelling Design Concepts. Washington, DC:    
     US Dept. of Housing and Urban Development, 1976.
     70's perspective of the Government's point of view
     dealing with Passive Solar Energy

Anderson, Bruce, Ed. The Fuel Savers. CA:  Morning Sun Press,1991    
     Simple, basic initial Solar for Beginners

Campbell-Howe, R., Wilkins-Crowder, B., Eds. Conference    
     Proceedings, National Passive Solar Conference. CO:   
     American Solar Energy Society, 1997.
     Latest up-to-date information on Passive Solar 

Crowley, John, Zimmerman, L. Zaurie. Practical Passive Solar    
     Design. NY:McGraw Hill, 1984.  
    Basic principles through final case studies

Crowther, Richard L. Affordable Passive Solar Homes. CO:    
     SciTech Publishing Co,1984.
     Good, basic pre-design and design ideas and plans

Freeman, Mark. The Solar Home. PA: Stackpole, 1994    
     Designing and building your home in harmony with Passive
     Solar Principles.


NBA Tectonics. A Study of Passive Solar Housing Estate Layout.    
     London: Dept. of Energy, 1988.
     Larger scale community solar-oriented layout

NC Energy Extension Service. Passive Solar Construction Concepts.    
     NC:NC Energy Division, NC Dept. of Commerce (no date)
     Very detailed and in-depth technical information

NC Solar Center. Directory of Solar and Renewable Energy     
     Resources in NC. NC:NC Solar Center, 1997     
     Extensive resource list of people, companies and products



Online Resources
 
 The NC Solar Center,  an excellent beginning point...

  Real Goods  An excellent source for products and literature

  Local NC  solar page, up in Boone, lots of links

 
 extensive online bookstore,  searchable by subject

 
 Alternative Energy Engineering more active than passive solar,  but still good 
information.

 
 Eco-Topia ECO-friendly technologies page,  with passive solar links
 
 
 Sustainable Building Sourcebookmore 
technically-oriented, lots of excellent information

 
 Jade Mountain Sustainable living company,  source -products and 
literature.

 
 Learn about the government's dealings with Solar. 

  
Suncharts  excellent page detailing the sunchart, which 
is the first
     step in site planning.

  Source  for various products used in Solar systems.

  Earth Integrated Passive Solar Direct Gain Heating Tells why using 
alternative energy methods are necessary
     for the Earth's future, and describes an excellent case
     study. A good site to check out.

 
 El Paso Solar Energy Association Passive Solar water heating, with a LOT 
of other good links.

  California Solar See the commercial side of Passive Solar.

  Joiners' Quarterly Good links to Solar, and other 
eco-friendly construction 
     and planning sites.