The first thing to understand about passive solar is that it doesn't have anything to do with solar panels, photovoltaic cells, or any other technology. The whole idea is to build and situation your home in such a way as to harness a maximum amount of the sun's energy in the winter, while blocking the sun's rays from heating your home in the summer. And you do it all simply by understanding how the Sun moves where you live.

How Does Passive Solar Work?

There are three main elements that make a passive solar home different from a conventional home: South-facing windows; a ledge of a certain length and angle above those windows; and a mass-wall. The ledge above the windows is short enough and placed at such an angle as to allow the winter sun to shine in and fill the mass wall (or thermal wall) with heat during the day, which is released as the house cools at night. But the path of the sun is at a higher angle during the summer, allowing the ledge to block the sun from directly shining into the house. The mass wall stays cool, as does the house.

Ever feel like your house is hotter at night during the day? Does it get down-right stuffy in the Summer? Does it feel hotter inside than it does outside? That's because the walls and floors of your home have been collecting heat from the sun all day, which has been shining in your windows in the middle of summer. At night, due to a process called convection (http://theory.uwinnipeg.ca/mod_tech/node76.html ) the heat stored within the walls and floors is released into the air, thus heating the room and making it hotter inside your house than it is outside. If you have this problem, you do what most of us do and turn on your air conditioner and/or fans. This is hard on the environment and increasingly devastating to your pocketbook. And it's all because the people who built your house didn't understand building concepts that people around the world understood thousands of years ago ? you work WITH the earth; not against it.

The paragraph below is used with permission from John Schaeffer and Real Goods, a solar panel installation company working in Colorado and California: http://www.realgoodssolar.com . It was taken from the Real Goods Solar Living Sourcebook: http://www.gaiam.com/retail/product/21-0530 :

The angle of the sun from the horizon changes throughout the year. In the summer, the Sun angle (also known as altitude angle) is greatest. That is to say, the sun cuts a high arc through the sky. In the winter the altitude angle is lowest. The Sun cuts a low arc through the sky. The angle changes every day. On June 21, the longest day of the year, the Sun angle is greatest. On December 21, the shortest day of the year, the sun angle is lowest.

Thus, the eves on your passive solar home act as an automatic on-off switch for your passive heating / cooling system. It turns the Sun power's effect on your home off for most of the day in the Summer, but leaves it on for most of the day during the Winter.

Here is simple picture by the Northeast Sustainable Energy Association (NESEA) that will solidify the concept of passive solar home design: http://www.nesea.org/images/overhang.gif . Get it now?

With the exception of adding a slight overhang above South-facing windows, there isn't much you can do about turning your existing home into a passive solar house without major, expensive renovations. But next time you buy a home, before moving into one of those add-water monopoly houses in the new subdivision, think about how inefficient their designs are. Most of the time you'll see that the South-facing windows are either hidden from the sun by the house next to you, or two few, which would cause your home to be cold in the Winter and require more energy from the furnace to heat. Or you may notice that the south-facing windows are in full view of the Sun, but there is no ledge above the area, thus allowing the Sun to heat up your home like an oven during the summer.

The ledge, window and mass wall are probably the three most important concepts of a passive solar home. But it goes well beyond that. For instance, knowing that heat rises, there are ways to control the flow of air throughout your house so as to take full advantage of cooler air in the summer and warmer air during the winter. All it takes is a few well-placed vents that can be switched open or closed depending on the time of the year. If people demand this kind of forethought from their builders we would require only a fraction of the fossil fuels being used to cool and heat our homes. If you combine passive solar design with a few solar panels, this often results in the power company paying YOU each month for the extra energy you're sending back into the grid. Everybody wins with passive solar home designs.

Here are a few more resources if you're interested in passive solar:

http://www.gaiam.com/retail/product/80372

http://www.solarliving.org/workshops/

http://www.colorado.gov/energy/renewables/passive-solar-design.asp

http://www.nesea.org/buildings/passive.html

http://www.realgoodssolar.com/solar/ecs/main/ArticlesVideo.html