Passive & Active Solar – What’s the Difference?

 Active Solar, Passive Solar, Solar Greenhouse, Sustainable  Comments Off on Passive & Active Solar – What’s the Difference?
Feb 072016

Passive solar heating is a name that refers to sunshine streaming through south-facing windows on winter days when the sun is low in the sky. If the long side of the house faces south and is not shaded, and the windows are large, a substantial portion of the home’s winter daytime heating may be supplied by the passive solar gain effect.

Passive solar is so called because solar heating directly through south windows in winter does not need any mechanical devices – electric fans or pumps – to deliver the solar warmth into the house space.

Of course, larger south windows will deliver more sunshine to the home’s interior rooms. As larger windows are deployed, two problems arise that need attention. First, in a well-insulated conventional home, larger south windows will cause the rooms to overheat. Second, during long cold winter nights these large double-glass windows will lose a substantial amount of heat to the outdoors.

Passive Solar Homes
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However, these situations have practical solutions. The problem of daytime overheating can be mitigated by adding thermal mass  – earth materials, concrete, or large containers of water – to the interior spaces or solar greenhouse areas. And the problem of nighttime heat loss may be mitigated by adding moveable nighttime insulation to the large window areas. Both of these solutions cost money and they involve aesthetic and architectural concerns.

Thermal Mass
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Active solar heating is a term that refers to the use of electric pumps or fans to move the sun’s heat to the interior of the home or building. The sun’s heat is collected by solar heating panels mounted on the roof or on the ground, then transferred to a thermal storage tank of water or to a thick radiant concrete floor slab. This is achieved by circulating liquid or air heat-transfer fluids from the collectors through copper pipes or air ducts to thermal storage. In air systems large bins of potato-size rocks have also been used to store solar heat for later delivery to the heated spaces in the home.

Active solar heating systems fulfill the four system functions of:

  1. solar heat collection
  2. transport of heated water (or air) to the interior of the home
  3. storage of the solar heat, and
  4. distribution of the solar heat on demand to areas that need it



These solar thermal collector panels (used to gather the sun’s heat) are typically 4’ x 8’ insulated flat boxes with a single glass cover and a blackened copper tube and fin absorber plate inside.

Active solar heating systems are popular for heating domestic hot water as well as for space heating. The many possible configurations of active solar installations require a skilled designer to size and integrate all the components – collectors, pipes, pumps, tanks, automatic controls – into a smooth, efficient, reliable, and durable home heating system. To achieve optimal performance and cost, a skilled installer trained in solar system options and behavior is also required. Solar training classes, solar home workshops and ebooks are available at or for more in depth information.