The Solar Power House Blog

The efficiency and reliability of solar home heating systems and collectors has steadily increased while costs have dropped dramatically since the early 1970s.  They have reached the point of providing an environmentally green, cost-effect and sustainable alternative or supplement to fossil fuel home heating in many parts of the world. These more cost-effective solar heating systems, and improved materials and technologies used in them are making it increasingly possible for average homeowners to reduce their utility bills and to help in improving our environment.  These are very encouraging solar energy facts.

Solar home heating is one of the central applications of the solar power house in which the thermal energy of the sun in the form of heat is used either directly to heat the house interior or transferred into some kind of storage facility.  Liquid and air are two mediums of thermal energy heat transfer and storage.

Solar Home Heating Systems 

 A solar home heating system will be a passive or active system, or some combination of the two.  Passive systems are usually simpler and less costly than active systems, but their applications are largely limited to new home construction.

Passive Solar Space Heating  

Passive solar heating utilizes the thermal energy of the sun through design features, such as large south-facing windows with appropriately dimensioned window or roof overhangs.  They may also incorporate storage mediums such as masonry floors or walls, or water in tanks which absorb heat during the day and release it at night when it is needed most.

Passive solar home heating systems are usually one of the following three designs:

1. Direct gain, which is the simplest, stores and slowly releases heat energy collected from the sun shining directly into the house and warming materials such as masonry or water stored in a tank.
2. Indirect gain, which is similar to direct gain, uses the same heat storage materials. However, the main difference is that these materials are located between the sun and living space (typically the wall).
3. Isolated gain collects solar energy remote from the location of the primary living area in a collector or a sunroom attached to a house, and then the warmer air naturally flows into the primary living area of the house.

Active Solar Space Heating

As in passive solar home heating, active solar heating systems can also use either liquid or air as the heat-transfer medium.  Both liquid and air active solar home heating systems utilize solar panels (collectors) to absorb and collect solar thermal radiation as heat, then transfer the solar heat directly to the interior space or to a heat storage container, from which the heat is distributed.  However, unlike passive systems, active systems use electric fans or pumps and controller components to transfer and distribute this solar heat. 

Although both air and liquid active systems can have a heat storage component, liquid systems are most often used when one is included.   However, active air-based solar home heating systems can employ an air-to-water heat exchanger to supply heat to the domestic hot water system.  But, for both solar heating system types, some sort of backup heating system is usually included to provide heat when there is an absence or deficiency of solar energy heat availability and the heat storage component is depleted.

Also worthy of note is the fact that air collectors are less efficient than liquid collectors because air conducts heat much less readily than liquid does. Accordingly, since less heat is transferred from an air collector’s absorber than from a liquid collector’s absorber, it requires a larger surface area of air system collectors to deliver an equivalent quantity of heat from a liquid system.

Liquid based solar home heating systems use the same solar hot water panels and other components as are used to produce solar hot water for domestic consumption.  Therefore, with liquid systems, it is often very efficient and cost-effective to concurrently install integrated domestic solar hot water and solar home heating systems. 

Flat-plate solar panels are the most used heat collector for solar hot water in homes and solar home heating.   Their construction is typically an insulated metal box with a transparent covering of glass or plastic and a black metal or plastic absorber plate. They typically heat liquid or air at temperatures less than 180°F.  In active liquid systems the liquid is heated as it is pumped through tubes in or adjacent to the absorber plate.  In active air systems the air is heated as a fan blows the air past the absorber plate. 

Below are illustrations of both liquid and air heat collectors. 

Air flat-plate solar panel for heating

Both of these panel types are commercially available for purchase.  They are also relatively easy to build, especially when using a high-quality DIY project kit.  If interested in investigating the DIY approach, take a look at the GreenDIYenergy at the top right.  I have researched numerous alternative energy DIY products and this one is as good as or better than any others I have seen.