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September 2, 2021

What Is Passive Solar Energy?

  • icon SOLAR

What is the difference between active and passive solar energy? Most people associate solar energy with photovoltaic panels and electricity.

  • Active solar energy requires numerous pieces of equipment to generate, transmit, and deliver power. But none of these are needed for passive solar heating and cooling.
  • Passive solar energy refers to design and materials that collect heat from the sun and store them in existing building elements. This is known as a structure’s thermal mass.


How Is Passive Solar Design Achieved?

Homes can benefit from passive solar energy with a few design basics. There are five of these in total, which can provide highly efficient heating and cooling.

  • Aperture: An area of large windows or other glass for solar energy to be collected. Ideally, windows should be within 30 degrees of true south. Shading can limit the amount of energy that comes in during cooler months, so windows must be in direct sunlight from 9:00 a.m. to 3:00 p.m. to deliver heat effectively.
  • Absorbing Surface: Any exposed surface that is in the direct path of sunlight. A masonry wall, water container, or the floor can absorb heat from the light that hits it.
  • Thermal Mass: Material below or behind an absorber that retains or stores heat. Brick, concrete, tile, or stone store heat well. Drywall can achieve this if your home is well-insulated and located in a moderate climate.
  • Distribution Method: Solar heat must be distributed from collection/storage points to living spaces. Conduction, convection, and radiation can be relied upon in a strictly passive design. However, ducts, fans, and blowers can be installed to regulate head distribution.
  • Control Elements: A roof overhang can be used to provide shade in strategic areas. You could also install awnings, insulating shutters, or low-emissivity blinds as well as electronic sensing systems. A differential thermostat is one example, it can automatically turn on a fan when needed.


How Does Passive Solar Energy and Work with HVAC?

Passive solar heating systems capture heat from the sun within the building. That heat is released when sunlight isn’t available. A direct gain design allows sunlight in through south-facing windows while floors and walls absorb and store heat. The thermal mass releases heat into the home during the night with 60% to 70% of the sun’s energy used. Water-filled containers may be installed within the living space, if the structure can support them (per cubic foot, water stores 2x as much heat as masonry).

Indirect gain works by placing the thermal mass between the sun and living space; sunlight is then transferred via conduction. Using 30% to 45% of the sun’s energy that strikes the glass, indirect gain can be achieved with a Trombe wall. A dark-colored masonry wall placed 1 inch or less behind south facing glass absorbs solar heat, which then radiates into the interior. By late afternoon or early evening, solar heat has migrated to the interior surface of the wall. Heat starts radiating into the room when the indoor temperature falls and reaches a lower level than that of the surface.

Passive solar cooling systems use non-mechanical ventilation to reduce unwanted heat gain. It is accomplished through shading by overhangs, awnings, or trees. Ventilation can help cool the thermal mass at night so it can absorb heat once again the next day. Natural ventilation such as an open window is a great source of passive cooling; with wing walls, you can draw in air through windows situated perpendicular to the breeze.

Contact Sunworks

Both active and passive solar energy can help make your home more energy efficient. If you’re thinking of investing in a solar system for your home, Sunworks can manage your entire solar project, from permitting and design to construction and operation. Call 866-600-6800 to learn more and discuss the details of your project.

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