Off the Grid Sustainable Housing Options
Active Verses Passive Solar Design:
There are many differences between an active and passive solar design for the home and basically a passive solar system does not involve any type of mechanical device or use of conventional energy sources to collect solar energy whereas an active solar design uses blowers, pumps and other types of equipment to store and convert solar energy.
Passive Solar Design
A passive solar system does not involve mechanical devices and classic examples of basic passive solar structures are greenhouses, sunrooms and solariums. The sun's rays will pass through the glass windows and the interior will absorb and retain the heat. This concept can cut heating costs by half compared to heating the same home by traditional means. The success of the passive solar system depends on orientation and the thermal mass of the structure's exterior walls, which means their ability to store and redistribute heat.
Passive Solar Collectors
A passive solar system typically relies on south-facing windows as collectors to capture solar energy, although some systems may also use supplemental PV panels. The goal is to redistribute the energy collected and move the heat from warm to cool areas and surfaces. The simplest method of transferring the heat from passive solar collectors is through convection so that a sunroom with windows on a southern wall will have heat directed into the room. It then rises to areas where the air is cooler, including other rooms beyond and above.
Active Solar Design
Active solar systems use external sources of energy to power blowers, pumps and other types of equipment to collect, store and convert solar energy. Once energy from the sun is absorbed, it is stored for to furnish electricity for heating and cooling systems in the home.
Active Solar Collectors
Solar collectors are more complex than passive collectors in both design and mechanism. They consist of flat-plate PV panels that are usually mounted and remain stationary, although some are designed to rotate with the sun throughout the course of the day. In some designs, multiple panels are connected together to form modules and active solar collectors contain either air or a liquid as a conductor and makes an active solar heating system the most cost-effective in terms of reducing reliance on traditional energy sources.
Active Verses Passive Solar Design Examples:
An active solar water or space-heating system is one that uses pumps or fans to circulate the fluid from the solar collectors to a storage tank subsystem. There are two basic types of active solar heating systems based on the type of fluid – either liquid or air – that is heated in the solar energy collectors. Liquid-based systems heat water or an antifreeze solution in a "hydronic" collector, whereas air-based 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, and are well suited for radiant heating systems, boilers with hot water radiators, and even absorption heat pumps and coolers. Both air and liquid systems can supplement forced air systems.
Figure 1: (Left) Active solar collector where energy is store in batteries to run electrical generator for lighting and electrical needs for the home. This type of system can be combined with a wind turbine to maximize power output.
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Figure 2: (Right) Liquid Based System for heating and hot water
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Figure 3: (Lower Bottom) PV Solar Collector Active system for typical home
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