How Does Solar Heating Work? Active and Passive Systems to Heat Your Home

Humans have always used the freely available energy from the sun for heat and warmth. In this modern age, advances in materials and systems have made solar home heating more efficient and more accessible to home owners. Solar energy can be harvested, stored and released and can help reduce residential home heating costs.

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How Does Solar Heating Work?

Solar heating uses the sun's energy to provide heat for a home, and can even provide hot water as well. As opposed to photovoltaic cells, no electricity is generated. A typical solar heating system consists of a solar collector that captures the sun's ray to heat air, water or some other heat-carrying fluid and transports it to somewhere useful, such as a room.

There are two types of solar heating systems: active and passive systems. An active system requires energy to pump fluid through the system. Heated fluid from the exposed solar panel is then pumped to a storage container for later use. A passive system does not require any energy to move the heat-carrying fluid through the system. It instead relies on the natural convection flow of hot and cold fluids for the transfer of heat. Below are examples of each.

Passive Solar Heating - Convection Heating

These solar power systems take advantage of the fact that warm air rises and cooler air sinks. A solar heater has a large surface area exposed to the sun and heats the air above a darkened panel. The warm air rises and exits the unit while drawing in cool air from the bottom. Air circulation continues as long as the sun shines.

For these systems, special attention must be made to the following:

  • A sunny location should be chosen with few obstacles or shadows.
  • The panels should be as directly oriented to the sun.
  • The surface of the solar collector should be dark and heat absorbent, not reflective.
  • The ambient air temperature should not be extremely cold or the amount of solar energy may not be sufficient to provide a comfortable room temperature.

Passive Solar Heating - Radiant Heat Transfer

Radiant heat describes the transfer from heat from a hot surface to a cooler one. Properly placed windows allow sunlight into the home to heat up rooms. This additional heating can supplement a primary heating system. In the northern locations, an overhanging awning will block the high summer sun from adding heat to the room while allowing the rays in from a low winter sun.

Active Solar Heating

Active solar heating use pumps to move heated liquid from a solar collector to more useful area. Unlike passive heating which relies on the slow movement of convection currents, pumps and thermostats can control the distribution of heat in a faster manner.

These collectors should have a larger surface area than a passive system since the solar energy is continuously being removed by the moving liquid. The larger amounts of heat transfer means that the energy can be stored in an insulated tank for later use. The heated liquid can then be circulated through radiators around the home when the sun sets and the air temperature drops.

For these systems, special attention must be made to the following:

  • The location should be in full sunlight with few obstructions and shadows.
  • The roof should be designed to accommodate the extra weight of the pipes.
  • The solar panels should have a large surface area to collect the solar energy.
  • The solar collector can have better performance if a mechanical system is used to continuously orient the panels directly at sun.
  • The tank must be insulated to retain as much heat as possible.

Passive versus Active Solar Heaters

Passive solar heating systems do not emit any greenhouse gases and require little operating or maintenance costs but do need to be planned and designed properly to maximize solar heating. Your location's latitude must be taken into account. Active solar heating systems require energy to pump a fluid through the system but the collected heat can be stored for later use when the sun sets. Either system can provide a comfortable household environment but should always supplement another heating system that will operate when the sun is not shining.