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Heating Your Home with an Active Solar Energy System

Active solar heating systems consist of collectors that collect and absorb solar radiation and electric fans or pumps to transfer and distribute the solar heat in a fluid (liquid or air) from the collectors. They may have a storage system to provide heat when the sun is not shining. An active system may be more flexible than a passive system in terms of siting and installation.
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Choosing the appropriate solar energy system depends on factors such as the site, design, and heating needs of your house. Local covenants may restrict your options; for example homeowner associations may not allow you to install solar collectors on certain parts of your house. If you are unsure about what type of solar energy system to install, contact a solar energy specialist or engineer. No matter what system you choose, you should learn about it before making a purchase.

How Much Heat Should Active Systems Provide?
The local climate, the type and efficiency of the collector(s), and the collector area determine how much heat a solar heating system can provide. It is usually most economical to design an active system to provide 40% to 80% of the home's heating needs. Systems providing less than 40% of the heat needed for a home are rarely cost-effective except when using solar air heater collectors that heat one or two rooms and require no heat storage. A well designed and insulated home that incorporates passive solar heating techniques will require a smaller and less costly heating system of any type, and may need very little supplemental heat other than solar. There are computer programs/software available to assist in properly siting and designing solar heating systems.

Supplementary Heating
Besides the fact that designing an active system to supply enough heat 100% of the time is generally not practical or cost effective, most building codes and mortgage lenders require a back-up heating system. Supplementary or back-up systems supply heat when the solar system can not meet heating requirements. They range from a wood stove to a conventional central heating system.

Positioning Collectors to Perform Optimally
In general, the optimum collector orientation is true south. True south is the highest apparent point in the sky that the sun reaches during the day. (True south should not be confused with magnetic south as indicated on a compass.) Collector orientation may deviate up to 20 from true south without significantly reducing the performance of the system. Collectors should be tilted at an angle equal to your latitude plus 15 for optimum performance. A collector receives the most solar radiation between 9:00 a.m. and 3:00 p.m. Trees, buildings, hills, or other obstructions that shade collectors reduce their ability to collect solar radiation. Even partial shading will reduce heat output.

You can position collectors in different locations. Collectors usually receive the most sunlight when placed on the roof. In some cases, however, the roof may be too shady or you (or your neighbors) may not like the look of collectors on the roof. If this is the case, you may mount the collectors on a supporting structure on the ground, or on the south wall of the house, where there is enough sunlight for the collectors to perform satisfactorily.

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Types of Active Heating Systems
There are two basic types of active solar heating systems based on the type of fluid heated in the collectors: liquid or air. "Liquid systems" heat water or an antifreeze solution in a "hydronic" collector, whereas "air systems" heat air in an "air collector." Both of these systems collect and absorb solar radiation, then transfer the solar heat directly to the interior space or to a storage system, from which the heat is distributed. If the system cannot provide adequate space heating, an auxiliary or back-up system provides the additional heat. Liquid systems are more often used when storage is included.

Air Systems
An air system uses air as the working fluid for absorbing and transferring solar energy. Solar air collectors can directly heat individual rooms or be integrated into a central heating system. Depending on your needs and location, you may find the advantages of an air system outweigh its disadvantages. Air collectors produce heat earlier and later in the day than liquid systems. Therefore, air systems may produce more usable energy over a heating season than a liquid system of the same size. Also, unlike liquid systems, air systems do not freeze, and minor leaks in the collector or distribution ducts will not cause problems. (Do not, however, ignore leaks; they will reduce the overall performance of the system.)

Room Air Heaters - Not everybody wants to invest in a large system that supplies most of the heat for the home. Air collectors can be installed on a roof or an exterior (south facing) wall for heating one or more rooms. These systems are easier and less expensive to install than a central heating system. They do not have a dedicated storage system or extensive ductwork. The floors, walls, and furniture will absorb some of the solar heat, which will help keep the room warm for a few hours after sunset. Masonry walls and tile floors will provide more thermal mass, and thus provide heat for longer periods. A well-insulated house will make a solar room air heater more effective. Factory-built collectors for on-site installation are available. If you are a do-it-yourselfer, you may choose to build and install your own air collector.

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