Solar Water Heater-How does it works?

Solar water heater is used to heat water by using sunlight. It mainly consists of:

1.A thermal panel (solar collector) which is installed on the roof.

2.A tank used to store hot water.

3.Circulating pump to carry the solar energy from the collector to the tank, and a thermal regulator.

Solar water heaters come in a wide variety of designs.

Working of a Solar Water Heater

The solar water heater absorbs light by means of a collector placed on the roof and converts it into heat. It passes this heat to a water tank by means of a circulating pump. This exchange is triggered by the thermal regulator, but only when the collector is hotter than the water in the tank. This prevents the circulating pumps using electricity needlessly. Conversely, it also prevents overheating.

The efficiency of the collectors is at its highest at midday, in summer, when the sky is cloudless, and when the collectors face south.

When there is insufficient sunlight, the water is preheated and a back-up system takes over to bring the water to the required temperature. This system can therefore be used to produce hot water at a constant temperature throughout the year without emitting any CO2.

Solar water heaters are typically described according to the type of collector and the circulation system.

Collector types

Batch collectors, also called Integrated Collector-Storage (ICS) systems, heat water in tanks .Water can remain in the collector for long periods of time making it very hot if household demand is low. A tempering valve is there for protection from scalding at the tap. It mixes in cold water to decrease the water's temperature before it's delivered to the tap. Batch collectors are incompatible with closed-loop circulation systems. They are generally not used in cold climates.

Flat-plate collectors consist of copper tubes fitted to flat absorber plates. The most common configuration is a series of parallel tubes connected at each end by two pipes, the inlet and outlet manifolds. The flat plate assembly is contained within an insulated box and covered with tempered glass.

Evacuated tube collectors are the most efficient collectors available. A glass or metal tube containing the water or heat transfer fluid is surrounded by a larger glass tube. The space between them is a vacuum, so very little heat is lost from the fluid.

Circulation Systems

Direct systems circulate water through solar collectors where it is heated by the sun. The heated water is then stored in a tank, sent to a tankless water heater, or used directly.

Closed-loop,or indirect, systems use a non-freezing liquid to transfer heat from the sun to water in a storage tank. The sun's thermal energy heats the fluid in the solar collectors. Then, this fluid passes through a heat exchanger in the storage tank, transferring the heat to the water. The non-freezing fluid then cycles back to the collectors.

Active,or forced-circulation, systems use electric pumps, valves and controllers to move water from the collectors to the storage tank. These are common in the U.S.

Passive systems require no pumps. Natural convection moves water from the collectors to the storage tank as it heats up.

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