Hot Water Solar System..

Solar hot water systems use the sun’s energy to heat water in liquid-based solar collectors; they are almost always used along with conventional water heaters. Solar collectors for these systems are typically 3–6 m2 in area and the systems are sold as a standard package like appliances. A typical solar hot water system can provide about 50% of the water heating energy needs in a home.

How It Works.

Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don’t.

Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank.

Three types of solar collectors are used for residential applications:

  • Flat-plate collectorsGlazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors – typically used for solar pool heating – have a dark absorber plate, made of metal or polymer, without a cover or enclosure.
  • Batch collectorsAlso known as integral collector-storage (ICS) system, these feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.
  • Evacuated-tube solar collectorsThese feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin’s coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for commercial applications.


There are two types of active solar water heating systems:

  • Direct circulation systemsPumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes.
  • Indirect circulation systemsPumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.


Passive solar water heating systems are typically less expensive than active ones, but they’re usually not as efficient. However, passive systems can be more reliable and may last longer. There are two basic types of passive systems:

  • Batch collector-storage systemsThese work best in areas where temperatures rarely fall below freezing. They also work well in households with significant daytime and evening hot-water needs.
  • Thermosiphon systemsWater flows through the system when warm water rises as cooler water sinks. The collector must be installed below the storage tank so that warm water will rise into the tank. These systems are reliable, but contractors must pay careful attention to the roof design because of the heavy storage tank. They are usually more expensive than integral collector-storage passive systems.


Solar water heating systems almost always require a backup system for cloudy days and times of increased demand. Conventional storage water heaters usually provide backup and may already be part of the solar system package. A backup system may also be part of the solar collector, such as rooftop tanks with thermosiphon systems. Since an batch (integral-collector storage) system already stores hot water in addition to collecting solar heat, it may be packaged with a demand water heater for backup.

For more information about solar water heating system components, see the following:

  • Heat exchangers for solar water heating systems
  • Heat-transfer fluids for solar water heating systems

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