Types of Solar Heaters

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Types of Solar Water Heaters

Indirect, active solar water heating system: Schematic diagram showing the components of an active, indirect solar water heating system. Antifreeze or another heat transfer fluid is pumped through the plate collector, where it is heated by the sun. When it is warm, the fluid is passed through a coil in the water storage tank to heat the water.Most solar water heating systems for buildings include a:

  • Solar collector — the mechanism in which fluid (water or diluted antifreeze, for example) is heated by the sun

  • Storage tank — holds the hot fluid after it has been heated by the collector.

Solar water heaters are generally classified as "direct" or "indirect" based on the types of fluids they circulate, and as "active" or "passive" based on how they circulate those fluids:

  • Direct versus indirect systems. Systems that heat pressurized water in the collector are referred to as "open-loop" or "direct" systems. Those that place a heat exchanger (for freeze protection) between the collector and the pressurized, potable water are referred to as "closed loop" or "indirect" systems. Indirect systems are used in cold climates.

  • Active versus passive systems.Thermosiphon systems rely on convection to circulate water between the collector and the storage tank (above the collector).
    "Passive" solar water heating systems use natural convection or municipal waterline pressure to circulate the fluid through the collector to the storage tank. They have no pumps or controllers, and are less expensive, more reliable, and easier to maintain than active systems. Passive systems are used only in mild climates where the potable water pipes running to the system will not freeze. Batch heaters Definition (also known as "bread box" or integral collector storage systems) and thermosiphon systems Definition are the most common types of passive systems for buildings.

    Flat-plate collectors are commonly used in active system for buildings."Active" systems use a pump to circulate the fluid through the system (many systems are now sold with a small solar electric collector to power the pump). Active systems are usually more expensive than passive systems, but they are also more efficient. They must be used in cold climates where hard freezing occurs. Flat-plate collector Definition systems are the most common type of active system for buildings (although systems that use evacuated-tube collectors Definition are also available).

The amount of hot water your system produces and the efficiency with which that water is produced depends, in part, on the amount of solar energy at your site, the type and size of your system, and proper installation. In almost all climates, you will need a conventional backup system to supply water when there is not enough solar-heated water to meet the demand. In fact, many building codes require you to have a conventional water heater as the backup.