Passive solar energy use

Passive solar technology is simply a set of techniques for using sunlight for useful energy without the use of any active mechanical systems.  These methods convert sunlight into usable heat (passive solar heating — hot water, warm air, and heat stored in thermal mass), cause air-movement for ventilation, and store heat for future use.  Passive cooling is the use of the same design principles to reduce summer cooling requirements.

Solar design (also called solar architecture) requires a basic understanding of how the sun moves in the sky over the year, and how this movement affects the sunlight that reaches a specific location at different times in the summer in the Northern Hemisphere.  The sun rises as well as sets to the north of the east-west line, and is high overhead at noon.  In the winter, the sun is much lower at noon and rises and sets at points that are further to the south.  It is possible by taking advantage of those changes to build a house that is naturally cool in the summer and warm in the winter.

The key to solar design is proper solar orientation.  Ideally a house should face true South rather than magnetic South, but a house that is within 15° east or west of true South will still collect 90% of the available sun.  Any good compass, manual, or map will help determine true South for a given location.  Using the North Star to represent the wall opposite true South also works and gives the most reliable direction you can. If the house is rectangular align the longer side of the rectangle with the east-west axis.

Here are a few of the most popular building and design techniques for maximizing passive solar efficiency:

  • insulated exterior shell, to minimize heat loss, and to utilize all the internal heat sources,
  • interior thermal mass, to maximize the amount of heat stored within the house and reduce the temperature variations during the day,
  • insulated glass, to let sunshine and solar energy in, and keep the heat in as well,
  • solar overhangs, to reduce the unnecessary heat gain in warm season.

Those concepts will be explained in details in the future posts.


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