Passive Solar Home Plans


Efficient use of the sun's energy is not necessarily a modern phenomena. Many centuries ago the Anasazi Indians of Southern Colorado found a way to capture the oblique rays of a winter sun. They simply built their stone houses against the south slope of canyon walls. The remains of their solar dwellings  are still with us today.

During the summer solstice sunset, light shines through a porthole and hits the very corner of a doorway into an eastern room. When the sun sets on the day of the winter solstice, it shines through a different porthole onto the corner of the doorway to the tower. The movement of the sun's rays along the wall is noticeable well before the solstice, so the Anasazi sun priests would have had time to plan their ceremonies. When the light first becomes visible in the room early in April, the Anasazi would have known that it was time to get ready to plant their first crops.


Unfortunately we all can't live at the base of south facing canyon wall so if we live in the South West we might decide to live in an alternative passive solar dwelling called the Adobe. These are houses made from mud bricks that have tremendous heat absorption ability. Solar radiation is absorbed during the day and released gradually during the cold nights.

Passive solar heating is accomplished by collecting and distributing heat from the sun without external mechanical pumping systems. Efficient storage of heat requires separation of  collector from heat storage vaults.. Passive systems are generally  low tech and low price. It may be as simple as a south facing window with fabric roman shades that are drawn in the evening to prevent heat loss or as complex as a solar greenhouse retrofit  with a massive heat sink wall.


 Some people say passive systems are better than active systems because they cost less and use no external energy source. Practical systems make use of both active and passive components. Let us first consider this simple  passive solar greenhouse from the JC Solar Home Kit.


This passive solar greenhouse would be a cozy little place to go on a sunny, cold January day in the North America. As a matter of fact it might even get a  too cozy. In the Plattsburgh NY area I have recorded internal solar greenhouse temperatures over 160 F with daytime outside temperatures less than 20 F.
What happens in the evening? 
Well the outside temperature on a typical January evening in Plattsburgh may easily drop below -20 F.
How about the inside temperature?
Well a simple solar greenhouse like this with no external means of heating  and no heat storage system would loose most of it's heat rapidly. A few hours after sunset the internal temperature would be close to 0 F.
Is it possible to hold onto some of this heat?
Yes. A simple greenhouse heat storage system consists of 55gallon drums filled with water. Water is an excellent inexpensive heat storage medium. Concrete is also good  for storing heat as long as it is insulated from the floor. Covering the glazing after the sun goes down would also help to retain the heat gain of the day.
Sounds a little crude do you have anything a little more house like for a winter shelter?
Sure. How about a cube octahedron solar greenhouse?


Looks like a fun place to visit, but do you have something a little more cubicle?
 How about a conventional square house with a solar greenhouse for a roof?





Now this is beginning to look like a real house though the living area seems a bit confined. How many square feet of living space could I expect from a cubical house like this?
This cubical house is designed to be 16 feet wide and 16 feet long so the combined living space of the first and second floor would be about 500 square feet. The greenhouse attic would add another 100 feet to this estimate, but let's not call this living space because of the extreme  temperature variations expected in the attic.
Ok I got it. Now my question is how do I get this heat out of the attic and into my main living quarters?
A fan would do the trick.
If you use a fan to pump hot air into the house it's no longer passive?
That's right?
What good is it than?
Well It's good because the fan uses less energy to heat your house than an oil burner, and if you must have a passive heated house you could technically have the fan powered by a photovoltaic system. It's good because you are making good use of your roof for heat collection and, it's good because you have separation of collector area from storage area.
Is their anything bad about this heating system that I should know about?
Yes air is a poor heat transport medium. Concrete walls insulated on the outside could be used as a heat sink to moderate the living space temperature, however since air is a poor heat transport  medium would not recommend this system.

What kind of passive solar heating system would you recommend?
Well if you must use a passive system to heat your house I recommend using a solar greenhouse attachment on the ground floor. Light plastic flaps allow hot air to enter your house during the day and prevent the escape of heat at night. A solar greenhouse might look something like this:

It's funny looking. Are you sure this is a greenhouse?
It's funny looking because it's a solar greenhouse. It's designed to maximize heat gain. The angle of the glazing is designed to be perpendicular to the sun's rays at the coldest time of the year. Ultraviolet radiation from the sun is transformed into infrared radiation when it strikes a darkened surface inside the greenhouse. This infrared radiation or heat is trapped behind the glazing. As you know hot air is lighter than cold air so it will rise and be concentrated at the apex of the greenhouse. If we allow this hot air to flow naturally into the house we have a classic passive solar hot air system. 



A better  more aggressive system would  be to pump this hot air into a low concrete lined storage vault. Heat stored in a low location is more valuable since it has a tendency to rise in a cold air environment.

Could I see what this greenhouse might look like attached to a house?
Sure. This is my Model B., an 80 foot long house. The greenhouse is 40 feet long and 12 feet high with a glazing surface of 400 square feet.

What does the back of the house look like?
Notice that the back of the house has few windows . This is done to reduce heat loss where no heat gain is possible.

That's very nice, but do you have anything  a little less grand that would fit on my building lot?
How about Model D? It's a simple inexpensive, easy to build,  and purely passive:


Too radical. Do you have something a bit more attractive and a bit more conventional?
Well I'll try. 
My model C is a  forty foot long two story house with a solar greenhouse on the ground floor. Heat is allowed to flow around the first floor during the day. The first floor acts as a simple heat storage vault. At night this stored heat keeps the bedrooms warm. It looks like this:

Well the roof is more interesting than your model D, but  I'm looking for something more conventional. Do you have some simple passive system without all this solar greenhouse business?
You are a difficult customer, but I am here to please. Check out the model H with the same dome like roof that you liked in the model C.  It is a three story, four bedroom house with  a rear entrance to a two bedroom basement apartment complete with first floor kitchen and living room. The house  is about 40 feet long and 30 feet wide. Instead of  a solar greenhouse it has large  vertical windows facing south that may be insulated in the evening.

Model H

Could I take a peek at the first floor?
I guess.

Notice the area just behind the front windows. This area would be great for hanging plants. The wood stove, in the living room, is surrounded with brick to act as a heat sink. Wood may be stored in either side of the wood stove  compartments to facilitate the storage, heating, and drying  of the logs.

How practical is a house like this? 
Well if you don't mind burning wood to keep warm it is a very practical house. The solar heat gain would be minimal, however..



How about active solar systems? How practical are they?
Let's just say it's easier to separate the heat collection area from the heat storage area with an active solar heating system. You may take a peak at a few  of my active solar heating/solar power house designs if you like.  The modular designs are based on hexagonal frames with cube octahedron roofs. Traditional housings designs could be modified to be solar compatible. I just happen to like this type of structure and feel that it is easily applied to solar application.


passive solar