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Off The Grid

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Passive solar: interior thermal mass

Thermal mass on the interior of the building is able to store heat or cold, and then slowly release it back out to the surrounding air. Heat from a sunny winter day as well as the coolness of a summer night can be retained inside the insulated shell of the exterior walls if the building incorporates adequate thermal mass. Thermal mass is needed to prevent daytime overheating of the structure and to stabilize its ambient temperatures through nights and periods of cloudy weather.  The more mass is available, the more stable the interior temperature.  Also, the more directly the winter sun hits the mass, the higher the solar heat gain.

Floors can provide a good source of mass. Concrete, brick, flagstone, or other masonry materials work especially well.  Any of these can be layered over with cork — an organic material that insulates well, and has the advantage of creating a softer surface underfoot.  Earth floors can be used, but do not perform as well.  Insulating beneath the floor helps to return the heat gains to the interior of the building more quickly.  Interior walls and houses are often framed with wood, but if built out of masonry materials such as rock or adobe, these can provide excellent mass, especially those interior walls hit directly by the sun. Concrete poured between studs is a quick way to add mass. (more…)

Passive solar: insulated exterior shell

The better the insulation in the

  • walls,
  • roof,
  • foundation,
  • floors,
  • doors,
  • and windows,

(the shell of the house), the slower the leakage rate of heat or cold from the inside of the house to the outside, and vice versa.  To be more specific, heat always flows from the higher temperature to the lower temperature — so we don’t say that the cold escapes the house during hot summer days, but the hot flows to the house. Often it is initial cost considerations that determine the amount of insulation that gets added to a structure.  Even when the rest of the house as well insulated, it is often difficult (or even impossible) to insulate doors and windows to the same degree.  Therefore, these can cause one of the biggest heat loss or heat gain areas in a house.  A super-insulated, well-sealed structure with few or no openings would be extremely energy — efficient in that it would effectively conserve whatever heat or cold is inside the building. (more…)

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. (more…)

History of Solar Energy Usage

We often think that modern societies were the first to use solar energy. Not true! Early cave dwellers preferred caves that had openings facing southeasterly that allowed the morning sun to warm them up without overheating in the warm months.  Native Americans in the Southwest oriented their pueblo dwellings.  So the low winter sun would keep the buildings by direct solar radiation, cliffs and overhangs blocked the sun during the summer months, helping to keep the dwellings cooler when the sun was high in the sky.

The ancient Greeks, with a climate that was sunny almost year-round, built their houses to take advantage of the sun’s rays during the moderately cool winters and to avoid the sun’s heat during the summer.  Modern excavations of many classic Greek cities show that individual homes were oriented towards the South and entire cities were planned to allow equal access to the winter sun.  It is interesting to note that by 500 B.C., when the Greeks had almost completely deforested their whole country and needed to find a reliable alternative fuel source, they chose solar energy. (more…)

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