1. What is Passive Solar?
2. Five Elements of Passive Solar Home Design
3. What are the Economic Benefits?
4. Where can I find a Passive Solar Architect?
5. What Incentives are Available?

1. What is Passive Solar?
Passive solar uses the power of sunlight to generate heat for a house or building following the principle that heat moves from warmer materials to cooler ones until there is no longer a temperature difference between the two. Unlike active solar heating systems, passive solar design doesn't involve the use of mechanical and electrical devices, such as pumps, fans, or electrical controls to move the solar heat, instead relying upon strategically designed windows, walls and floors to collect, store and distribute solar energy in the form of heat in the winter and reject solar heat in the summer.

Passive solar design can reduce heat and energy bills significantly, utilizing the sun directly or indirectly to heat, light or cool a home or building. Passive Solar methods include orienting a building east to west, incorporating large south facing windows with adequate overhangs and shading to keep the sun out during the summer months, coupled with a tight building envelope.

2. Five Elements of Passive Solar Home Design
The following five elements constitute a complete passive solar home design. Each performs a separate function, but all five must work together for the design to be successful.

• Aperture (Collector): The large glass (window) area through which sunlight enters the building. Typically, the aperture(s) should face within 30 degrees of true south and should not be shaded by other buildings or trees from 9 a.m. to 3 p.m. each day during the heating season.

• Absorber: The hard, darkened surface of the storage element. This surface—which could be that of a masonry wall, floor, or partition (phase change material), or that of a water container—sits in the direct path of sunlight. Sunlight hits the surface and is absorbed as heat.

• Thermal mass: The materials that retain or store the heat produced by sunlight. The difference between the absorber and thermal mass, although they often form the same wall or floor, is that the absorber is an exposed surface whereas thermal mass is the material below or behind that surface.

• Distribution: The method by which solar heat circulates from the collection and storage points to different areas of the house. A strictly passive design will use the three natural heat transfer modes—conduction, convection, and radiation—exclusively. In some applications, however, fans, ducts, and blowers may help with the distribution of heat through the house.

• Control: Roof overhangs can be used to shade the aperture area during summer months. Other elements that control under- and/or overheating include electronic sensing devices, such as a differential thermostat that signals a fan to turn on; operable vents and dampers that allow or restrict heat flow; low-emissivity blinds; and awnings.

• Direct Gain: Buildings designed for passive solar heating usually have large, south-facing windows. Additionally, materials that absorb and store the sun's heat can be built into the sunlit floors and walls. The floors and walls heat during the day and slowly release heat at night, when the heat is needed most.

• Sunspaces and Trombe Walls: Other passive solar heating design features include sunspaces and trombe walls. A sunspace functions much like a greenhouse and is built on the south side of a building. As sunlight passes through glass or other glazing, it warms the sunspace. Proper ventilation allows the heat to circulate into the building. Conversely, a trombe wall is used to trap heat. As a very thick, south-facing wall, which is painted black, it is constructed of material that absorbs a high amount of heat. A pane of glass or plastic glazing, installed a few inches in front of the wall, helps hold in the heat. The wall heats throughout the day, slowly releasing the collected heat at night as the structure cools.

• Day lighting: Day lighting is a passive solar design principle that uses sunlight to light the interior spaces of a building. Day lighting uses direct, diffuse, or reflected sunlight to provide full or supplemental lighting for building interiors. Artificial lighting accounts for as much as 40% to 50% of the energy consumption in many commercial and institutional buildings, and 10% to 20% of energy consumption in industry.

Day lighting, in combination with energy-efficient lighting can substantially reduce building energy consumption. Day lighting also contributes to more satisfied and productive occupants.

There are many design features that help keep passive solar buildings cool in the summer. For instance, overhangs can be designed to shade windows when the sun is high in the summer. Sunspaces can be closed off from the rest of the building. And a building can be designed to use fresh-air ventilation in the summer.

• Passive Cooling: Passive cooling can be as simple as orienting your windows to take advantage of natural ventilation and creating cross ventilation. For example, the visitor center at Zion National Park incorporates a cooling tower. When natural ventilation is not adequate, water is sprayed on pads at the top of the towers creating a passive evaporative cooler. The cool, dense air "falls" through the tower and exits through the large openings at the bottom of the towers.

3. What are the Economic Benefits?
By utilizing the sun directly or indirectly to heat, light or cool a building, passive solar design can reduce heat and energy bills significantly.

If you are designing a new home, incorporating passive solar design elements can be quite cost-effective or no-cost, depending on the architect with whom you are working.  However, converting to passive solar on an existing building may require an additional cost for the remodel or retrofit.

Consult 2-3 architects or firm for quotes to get the best deal. 

• Utah Chapter of the American Institute of Architects (AIA)

5. What Incentives are available?

A list of available state and federal incentives can be found at:

• Utah State Energy Program
• Database of State Incentives for Renewable Energy and Efficiency

Or, visit our How To section for information on incentives by application, resource and technology.