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Here is a fantastic tool we are so fortunate to have at hand in New Zealand. It is called SOLARVIEW and is produced by NIWA. This an excellent tool for providing a early assessment of the Solar value of a particular section when you are searching for that perfect place to build your Earthship or Passive Solar Home.
So how does it work?
You simply input the street address of the section you are looking at and it will give you the Latitude and Longitude that Solarview needs. Then simple press the ‘Create solar view’.

History of Passive Solar Heating - excellent with lots of picture; history and science


Introduction to Solar Energy

The sun's energy arrives on earth in the primary form of heat and light. Other aspects of solar radiation are less easily perceived and their detection often requires sophisticated equipment. All solar radiation travels through space in waves, and it is the length of these waves (the shortest is less than a millionth of an inch, the longest more than a thousand yards) by which all solar radiation is classified. The aggregate of all radiation aspects of the sun is called the solar spectrum.
There are two important facets about the solar spectrum.
1. While the sun emits radiation in all wavelengths, it is the short wavelength radiation that accounts for the majority of energy in the solar spectrum. For example, the portion of the spectrum perceived as the visible light is a relatively small segment compared to the variety of spectrum wavelengths, yet accounts for 46 percent of the energy radiating from the sun. Another 49 percent, that which is perceived as heat, is derived from the infrared band of the spectrum.
2. The proportion of different wavelengths in the solar spectrum does not change and therefore the energy output of the sun remains constant. A measurement of this phenomena is known as the Solar Constant, defined as the amount of heat energy delivered by solar radiation to a square foot of material set perpendicular to the sun’s rays for one hour at the outer edge of the earth’s atmosphere. The Solar Constant measurement is about 429.2 BTU’s with minimal changes over the year. The energy measured as the Solar Constant is not a measure of the amount of solar energy that actually reaches the earth’s surface, since as much as 35 percent of all the solar radiation intercepted by the earth and its surrounding atmosphere is reflected back into space. Additionally, water vapor and atmospheric gases absorb another 15 percent. As a global average only about 35-40 percent of the solar radiation entering the atmosphere actually reaches the earth’s surface.
As a practical matter, global averages are of little interest. The essential point is that the atmosphere impacts on the amount of solar energy that actually reaches the earth’s surface - the more atmosphere solar radiation has to move through, the more is lost on the way. In this regard, two celestial events – the daily rotation of the earth and its seasonal tilt of the earth's axis – are important in determining the length of atmosphere through which the sun’s rays must pass before striking any particular location on the globe (Fig. 1).
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Figure 1. The amount of solar energy reaching the earth's surface is determined by the amount of atmosphere through which it must pass.
These events set the upper limit amount of solar energy that can reach the surface of the earth at any location on any day of the year.
One of the conditions for accurately measuring the Solar Constant requires the intercepting surface to be perpendicular to the sun’s rays. Since solar radiation travels in parallel rays, the perpendicular position identifies the maximum density of rays striking a surface. Any deviation from perpendicular reduces the radiation density and the amount of energy intercepted. This is best illustrated in Fig. 2.
external image fig2.gifFigure 2. These illustrations demonstrate how energy density is determined by the angle of incidence. The amount of light emitted by the flashlight is the same in both illustrations but it is spread over a larger area (right) when the light is tilted away from its original perpendicular position (left).
The angle created by incoming radiation and a line perpendicular to an intercepting surface is called the angle of incidence. Table 1 illustrates that a fairly large increase in the angle of incidence results in only a modest reduction in intercepted radiation.
When sunlight strikes a surface it is reflected, transmitted or absorbed, in any combination depending on the texture, color and clarity of the surface. All completely opaque surfaces both reflect and absorb radiation but do so in different ways. For example, a rough surface such as stucco reflects sunlight in a scattered fashion while a smooth, glossy surface reflects uniformly and at an angle equal to the angle of incidence. The wavelengths of solar radiation that are reflected are determined by the color of the surface material. A red stucco surface, for example, will scatter (diffuse) wavelengths in the red band of the spectrum and absorb all others (Fig. 3), while a white glossy surface will reflect all wavelengths in the visible spectrum at an angle equal and opposite to the angle of incidence.

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Figure 3. Color is perceived when visible light is reflected from a surface. Red surfaces reflect red wavelengths and absorb all others.

Conversely, a rough black surface absorbs all wavelengths in the visible spectrum, while the transparent surface of window glass allows nearly all radiation to pass through it with comparatively little reflection or absorption, and without deflecting it from its parallel lines of travel. Translucent materials also transmit radiation but scatter the rays as they pass. It should be noted that relatively few materials are excellent reflectors, transmitters, or absorbers of the sun’s rays.
Sunlight, in the form of short wave solar radiation, exhibits a transformation from solar energy to heat energy when impacting a material (absorption). The temperatures of a white surface and a black surface exposed the same direct sunlight is a simple demonstration of this conversion. The temperature of the black surface is higher because it is absorbing more solar energy. As solar energy is absorbed at the surface of a material it stimulates movement of the molecules in the material. Molecular movement is measured in terms of heat – the greater the movement, the greater the heat. Since the color black absorbs more of the spectrum than the color white, it will in turn be hotter (more molecular excitement) than white.
As a material absorbs radiation and molecular movement continues to accelerate, the heat energy is redistributed through the material due to the natural phenomenon of maintaining equilibrium. This occurs when stimulated molecules, vibrating at a faster rate, impact adjacent molecules vibrating at a slower rate, thereby dissipating and "spreading the wealth". In this way, heat is conducted away from the source of energy as the material seeks to distribute the energy evenly throughout its mass. The rate at which energy flows or is conducted though a material depends on the density of the material and conduction, the rate at which molecules are capable of receiving and passing on energy. Gases are poor conductors; metals are comparatively good conductors; and less dense materials containing tiny air pockets and voids conduct heat at a much slower rate.
Heat transfer from a solid material to a fluid medium (liquid or air) occurs by radiation (infrared). It is a continuation distributed molecular "bumping" between a solid material and a transfer medium (air or liquid). The added dimension of using fluids is they can move across a hot solid surface, allowing molecules of the fluid to become agitated (heat), then move away from the heat source, and t be replaced by new, unheated molecules. This process of fluid movement is called natural convection when the movement is unaided by machinery (i.e. hot air rises), and forced convection if the process is aided by a pump or fan.
The process occurs naturally as the molecules of a fluid begin to vibrate when heat is applied, and then becomes less dense (lighter) than the surrounding unheated fluid. The lighter heated molecules rise at a rate determined by the amount of heat applied. Boiling water is a good example of heated molecules near the burner rising quickly to the surface to the point of surface disruption (boiling). Steam generated by the process is simply water molecules whose vibration rate is violent enough to allow them to break from of the water surface.
Birds that seem to hang in the air without beating their wings are evidence of the power of natural convection. On clear sunny mornings, air at the surface of the ground (especially dark surfaces) is heated rapidly and rises in columns with enough force to suspend the bird overhead and even push it upward. The reverse of this process occurs as convected molecules get further from the heat source of heat, give up their energy (slower molecular excitement), and fall. Conduction and convection can be thought of as processes by which solar energy can be both transported and stored.
The principle of solar energy absorption was discussed in terms of two surfaces exposed to the sun. Conduction was then discussed to show how absorbed solar energy moves through a material, always in a direction away from the source of heat to attain equilibrium. NOTE: Any molecular movement is continually generating heat in the form of radiant energy. Unlike solar energy, radiant energy is limited to infrared radiation emitted from a material at low temperatures. The extent to which a material emits thermal energy depends both on the temperature of the material and nature of its surface. Polished metal surfaces are poor emitters and poor absorbers of thermal energy. Again, as with solar radiation, the amount of thermal energy a surface will intercept depends on the angle of the incoming radiation.
Glass has the special characteristic of transmitting nearly all solar radiation that it intercepts (which moves through it) and is less transparent to most thermal radiation. The temperature build-up in a closed car on a sunny but cold day is evidence of this characteristic. Solar energy passes through the windows is absorbed by interior materials, and reradiated into the interior space in the form of thermal energy (heat) which is unable to pass back through the glass to the outside. This has become known as the greenhouse effect.
All materials can store heat to some degree. The ability of a material to do so is called its specific heat – the amount of heat, measured in BTU’s for a given mass, a material can hold when its temperature is raised one degree Fahrenheit. As an indicator of a material's value as a heat storage medium in solar heating of spaces, the specific heat of a material is not very useful. The usefulness of a material in such an application is determined by its heat capacity, a measurement of the specific heat of a material multiplied by its density. The higher the heat capacity, the more effective the material is for heating and cooling.
Finally, a good storage medium material must absorb heat when it is available, and give I t up when it is needed, and it must be a relatively good heat conductor. In Table 1 the comparative specific heat and heat capacity measurements for a variety of materials is given, and it shows there is no perfect storage medium in terms of volume, storage capacity, and conductivity.
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Table 1. Specific heat and heat capacity of various surfaces.

Passive Solar Heating
by Judy Fosdick

Tierra Concrete Homes
Last updated: 06-17-2010

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Passive solar heating is just one strategy in a group of design approaches collectively called passive solar design. When combined properly, these strategies can contribute to the heating, cooling, and daylighting of nearly any building.
Passive solar heating in particular makes use of the building components to collect, store, and distribute solar heat gains to reduce the demand for space heating. It does not require the use of mechanical equipment because the heat flow is by natural means (radiation, convection, and conductance) and the thermal storage is in the structure itself. Also, passive solar heating strategies provide opportunities for daylighting and views to the outdoor through well-positioned windows.
It is best to incorporate passive solar heating into a building during the initial design. The whole building approach evaluates it in the context of building envelope design (particularly for windows), daylighting, and heating and cooling systems. Window design, especially glazing choices, is a critical factor for determining the effectiveness of passive solar heating. Passive solar systems do not have a high initial cost or long-term payback period, both of which are common with many active solar heating systems.
In heating climates, large south-facing windows are used, as these have the most exposure to the sun in all seasons. Although passive solar heating systems do not require mechanical equipment for operation, this does not mean that fans or blowers may not, or should not, be used to assist the natural flow of thermal energy. The passive systems assisted by mechanical devices are referred to as "hybrid" heating systems.
Passive solar systems utilize basic concepts incorporated into the architectural design of the building. They usually consist of: buildings with rectangular floor plans, elongated on an east-west axis; a glazed south-facing wall; a thermal storage media exposed to the solar radiation which penetrates the south-facing glazing; overhangs or other shading devices which sufficiently shade the south-facing glazing from the summer sun; and windows on the east and west walls, and preferably none on the north walls.


Passive Solar Design

The most important characteristic of passive solar design is that it is holistic (it relies on the integration of a building's architecture, materials selection, and mechanical systems to reduce heating and cooling loads). It takes into consideration local climate conditions, such as temperature, solar radiation and wind, to create climate-responsive, energy conserving structures that can be powered with renewable energy sources. Some benefits of passive solar designed buildings include:
  • Increased User Comfort: Properly designed, passive solar buildings are bright and sunny and in tune with the nuances of climate and nature. Mass reduces temperature swings and produces a high degree of temperature stability and thermal comfort.
  • Increased User Productivity: Delightful places to live and work, passive solar buildings can contribute to increased satisfaction and productivity.
  • Reduced Emissions: By relying on solar energy, a renewable, non-polluting energy source, passive solar design does not generate greenhouse gases and slows fossil fuel depletion.
For small, skin-load dominated buildings in cold and temperate climates, passive solar design often involves using solar energy to provide space heating. For other kinds of structures, such as internal-load dominated buildings in warm climates, responsible passive solar design is more likely to emphasize cooling avoidance using shading devices, high performance glazing and daylighting.
In a skin-load dominated structure, energy consumption is primarily dictated by the influence of the exterior climate on a building's envelope, or "skin." Examples of typical skin-load dominated buildings include barracks and other low-rise housing, small warehouses, or small retail facilities. By contrast, internal-load dominated buildings such as schools, offices, or large retail complexes often consume the majority of their energy to provide interior lighting and to provide cooling to counteract the heat given off by people, plug-loads (such as computers), fixtures, and other internal sources. Such buildings can require cooling year-round. Note, however, that less solar radiation enters a well-shaded south window in the summer than a similarly shaded window on the north, east, or west side of the building.
Depending on climate, the passive solar design of skin-load dominated buildings might include:
  • orienting more windows to the south,
  • shading to avoid summer sun,
  • incorporating thermally massive construction materials,
  • providing properly sized and installed insulation and,
  • downsizing HVAC equipment.
Depending on climate, the passive solar design of internal-load dominated buildings might include:
  • daylighting work spaces with properly oriented and controlled windows,
  • specifying high-performance glazing that reduce heat gain while admitting visible light,
  • selecting high-efficiency HVAC systems and,
  • incorporating adequate shading devices.
The following information focuses primarily on the Passive Solar Heating of skin-load dominated structures in temperate and cold climates.
Diagrams of 3 passive solar heating systems. The first passive solar heating system is direct gain. Direct gain is the most common passive solar system in residential applications. Direct gain inculdes south glazing, floor mass, wall mass, and clorestory. The second is sunspaces. Sunspaces provide useful passive solar heating and also provide a valuable amenity to homes. The third is the thermal storage wall. A thermal storage wall is an effective passive solar system, especially to provide nighttime heating.
Diagrams of 3 passive solar heating systems. The first passive solar heating system is direct gain. Direct gain is the most common passive solar system in residential applications. Direct gain inculdes south glazing, floor mass, wall mass, and clorestory. The second is sunspaces. Sunspaces provide useful passive solar heating and also provide a valuable amenity to homes. The third is the thermal storage wall. A thermal storage wall is an effective passive solar system, especially to provide nighttime heating.

Passive Solar Heating Fundamentals

Typically, Passive Solar Heating involves:
  • the collection of solar energy through properly-oriented, south-facing windows,
  • the storage of this energy in "thermal mass," comprised of building materials with high heat capacity such as concrete slabs, brick walls, or tile floors, and
  • the natural distribution of the stored solar energy back to the living space, when required, through the mechanisms of natural convection and radiation,
  • window specifications to allow higher solar heat gain coefficient in south glazing.
Modest levels of passive solar heating, also called sun-tempering, can reduce building auxiliary heating requirements from 5% to 25% at little or no incremental first cost and should be implemented for all small buildings in temperate and cold climates. More aggressive passive solar heated buildings can reduce heating energy use by from 25 to 75% compared to a typical structure while remaining cost-effective on a life-cycle basis. This approach should be considered for many small buildings in temperate and cold climates.
The idea of passive solar heating is simple, but applying it effectively requires attention to the details of design and construction. There are four generic passive solar heating approaches: sun-tempered, direct gain, indirect gain, and isolated gain.
  1. Sun-tempering is achieved through modest increases in south-facing windows. A tract builder's house typically has about one quarter of its windows on each façade with a south glass equal to about 3% the house's total floor area. Depending on the climate, a sun-tempered house or barracks might increase this percentage to between 5 and 7%. In this case, no thermal mass needs to be added to the basic design (the "free mass" of gypsum wallboard and furnishings is sufficient to store the additional solar heat.)
  2. Direct gain is the most basic form of passive solar heating. Sunlight admitted through south-facing glazing (in the Northern hemisphere) enters the space to be heated, and is stored in a thermal mass incorporated into the floor or interior walls. Depending on climate, the total direct gain glass should not exceed about 12% of the house's floor area. Beyond that, problems with glare or fading of fabrics are likely to occur, and it becomes more difficult to provide enough thermal mass for year-round comfort.
  3. An indirect gain passive solar heating system (also called a trombe wall or a thermal storage wall) is a south-facing glazed wall, usually built of heavy masonry, but sometimes using containers of water or phase change materials. Sunlight is absorbed into the wall and it heats up slowly during the day. Then as it cools gradually during the night, it releases its stored heat over a relatively long period of time indirectly into the space.
  4. Isolated gain, or sunspace, passive heating collects the sunlight in an area that can be closed off from the rest of the building. The doors or windows between the sunspace and the building are opened during the day to circulate collected heat, and then closed at night, allowing the temperature in the sunspace to drop. Small circulating fans may also be used to move heat into adjacent rooms.
  5. Exterior concrete walls insulated on the outside to protect the concrete from weather are now available. The concrete should be exposed on the inside to exchange heat with the room air.
It is important to incorporate adequate thermal mass in buildings that attempt to achieve a high percentage of passive solar heating.
  1. When possible, the area of thermal mass should be six times the area of the accompanying glazing. Somewhat less thermal mass is necessary in a climate with foggy or rainy winters.
  2. Place the mass effectively by ensuring that it is directly heated by the sun or is spread in thin layers throughout rooms in which there is a large quantity of solar collection.
  3. The color of the mass surface is less important than originally thought; "natural" colors (e.g. colors in the 0.5 to 0.7 absorption range) are quite effective.
  4. Thermal storage may be incorporated in floors or walls consisting of concrete, masonry, or tile. Generally, walls should remain light colored to reflect light and enhance the space.
Sizing of glass areas, insulation values, shading, and mass will depend on climate. Higher solar savings contributions will require greater amounts of glazing and mass. Be aware that the relationship between glass area and mass is not linear. For example, a doubling of glass area may require a tripling of effective thermal mass.)

Design of Passive Solar Heated Buildings

The following are general recommendations that should be followed in the design of passive solar heated buildings.
  1. Passive solar heating will tend to work best, and be most economical, in climates with clear skies during the winter heating season and where alternative heating sources are relatively expensive.
  2. Use passive solar heating strategies only when they are appropriate. Passive solar heating works better in smaller buildings where the envelope design controls the energy demand.
  3. Careful attention should be paid to constructing a durable, energy-conserving building envelope.
  4. Address orientation issues during site planning. To the maximum extent possible, reduce east and west glass and protect openings from prevailing winter winds.
  5. Specify an air-tight seal around windows, doors, and electrical outlets on exterior walls. Employ entry vestibules; and keep any ductwork within the insulated envelope of the house to ensure thermal integrity. Consider requiring blower-door tests of model homes to demonstration air-tightness and minimal duct losses.
  6. Specify windows and glazing that have low thermal transmittance values (U values) while admitting adequate levels of incoming solar radiation (higher Solar Heat Gain Coefficient). Data sources such as the National Fenestration Rating Council "Certified Products Directory" should be consulted for tested performance values. The amount of glazing will depend on building type and climate.
  7. Ensure that the south glass in a passive solar building does not contribute to increased summer cooling. In many areas, shading in summer is just as critical as admitting solar gain in winter. Use your summer (B) and winter (A) sun angles to calculate optimum overhang design.
  8. Avoid overheating. In hot climates, buildings with large glass areas can overheat. Be sure to minimize east- and west-facing windows and size shading devices properly. For large buildings with high internal heat gains, passive solar heat gain is a liability, because it increases cooling costs more than the amount saved in space heating.
  9. Design for natural ventilation in summer with operable windows designed for cross ventilation. Ceiling fans or heat recovery ventilators offer additional air movement. In climates with large diurnal temperature swings, opening windows at night will release heat to the cool night air and closing the windows on hot days will keep the building cool naturally.
  10. Provide natural light to every room. Some of the most attractive passive solar heated buildings incorporate elements of both direct and indirect gain. This can provide each space a quality of light suitable to its function.
  11. If possible, elongate the building along the east-west axis to maximize the south-facing elevation and the number of south-facing windows that can be incorporated.
  12. Plan active living or working areas on the south and less frequently used spaces, such as storage and bathrooms, on the north. Keep south-facing windows to within 20° of either side of true south.
  13. Improve building performance by employing either high-performance, low-e glazing or nighttime, moveable insulation to reduce heat loss from glass at night.
  14. Locate obstructions, such as landscaping or fences, so that full exposure to the sun is available to south windows from 9 A.M. to 3 P.M. for maximum solar gain in winter.
  15. Include overhangs or other devices, such as trellises or deciduous trees, for shading in summer.
  16. Reduce air infiltration and provide adequate insulation levels in walls, roofs, and floors. As a starting point for determining appropriate insulation levels, check minimum levels in the CABO Model Energy Code.
  17. Select an auxiliary HVAC system that complements the passive solar heating effect. Resist the urge to oversize the system by applying "rules of thumb."
  18. Make sure there is adequate quantity of thermal mass. In passive solar heated buildings with high solar contributions, it can be difficult to provide adequate quantities of effective thermal mass.
  19. Design to avoid sun glare. Room and furniture layouts need to be planned to avoid glare from the sun on equipment such as computers and televisions.
Drawings of passive solar heating strategies: subdivision layouts and south overhang. Short east-west cul-de-sacs tied into north-south collectors is a good street pattern for solar access.
Drawings of passive solar heating strategies: subdivision layouts and south overhang. Short east-west cul-de-sacs tied into north-south collectors is a good street pattern for solar access.


Among the primary types of buildings that can benefit from the application of passive solar heating principles are:
  • barracks and other low-rise housing in temperate and cold climates (locations that experience above 2,000 degree days annually),
  • small PX facilities (less than 10,000 square feet),
  • warehouses, and
  • maintenance facilities.

Case Study

McKay Center - University of Wisconsin Arboretum, Madison, WI





Products and Systems

Building Envelope Design Guide: Cast-in-Place Concrete Wall Systems, Masonry Wall Systems

Federal Green Construction Guide for Specifiers:


  • Designing Low-Energy Buildings with Energy-10 Software Integrating Daylighting, Energy Efficient Equipment, and Passive Solar Design in Commercial Institutional and Residential Buildings available from SBIC.
  • E Source Electronic Encyclopedia Rocky Mountain Institute. Available from E Source (see especially Chapter 5: Space Heating)