How Does Solar Hot Water Work? How Does Solar Hot Water Work?

An alternative to an electric or natural gas-powered hot water heater, a solar hot water heater is powered by heat captured from the sun and transferred to the water in your home. Although the end result is the same, the manner in which the cold water flowing into your home is heated is drastically different from a conventional water heater. There are several different variations of solar water heaters. They each use the sun’s energy to heat the water, but they do so in slightly different ways.

Passive vs. Active Systems

There are 2 basic systems of solar water heaters. The first is called active, the other is passive. They essentially perform the same task, except that an active system uses powered pumps and controls, whereas a passive system does not. Pumps on an active system move the cold water into the solar collector and back into the storage tank. Passive systems use no pumps to move the water. Rather, water enters the solar collector, is heated and then moves up to the storage tank. This is possible because hot water rises in cold water. Beyond this basic distinction between system types, there are several other variables with solar hot water heaters.

Active Circulation Systems

Two different means of water circulation in active systems are possible for installation. The first is known as direct circulation. The other is indirect circulation. Direct circulation systems use pumps to bring the cold water directly through the solar collector where it is heated, then returned to the storage tank. They are customary in warmer climates.

An indirect system, on the other hand, pumps a heat transfer liquid to be heated by the solar collector. This liquid, which can be air, hydrocarbon oil or refrigerant, is then pumped back into the storage where it heats the water for use. Indirect systems work well in climates where freezing temperatures are common.

Passive Systems

There are 2 main types of passive systems: Integral Collector Storage systems and thermosyphon systems.

  • ICS or “batch” systems move water into the solar collector which uses the sun to heat up a batch of water. It is then moved into the insulated storage tank for use.
  • A thermosyphon system relies on the fact that hot water rises. This system places the solar collector below the storage tank so the water, once heated, will rise into it. Thus, both the solar collector and the storage tank are installed on the roof.

The type of roof on a home will determine whether or not it is safe to install a thermosyphon system.

Solar Collectors

Additionally, there are several different types of solar collectors which work to gather the solar energy and heat either water or a transfer liquid. Tubes, tanks or solar absorbent plates are used to harness the sun’s energy and heat water. All solar collectors are contained within a sealed box and covered either with glazed glass or some type of plastic polymer.  

The basic idea of a solar hot water heater is that a solar collector is installed to capture solar radiation. Cold water or a heat transfer liquid is pumped or enters into the solar collector where it is preheated. From there, it moves to a storage tank that is well insulated to prevent heat loss. At this point, it is ready for use in the home.

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