Solar Water Heater

We are blessed with Solar Energy in abundance at no cost. The solar radiation incident on the surface of the earth can be conveniently utilized for the benefit of human society. One of the popular devices that harness the solar energy is SOLAR WATER HEATING SYSTEM.

A solar water heater consists of a collector to collect solar energy and an insulated storage tank to store hot water. The solar energy incident on the absorber panel coated with selected coating transfers the heat to the riser pipes underneath the absorber panel. The water passing through the risers get heated up and are delivered the storage tank. The re-circulation of the same water through absorber panel in the collector raises the temperature to 80 C (Maximum) in a good sunny day. The total system with solar collector, storage tank and pipelines is called solar hot water system. Broadly, the solar water heating systems are of two categories. They are: Pressurized and Non-Pressurized.

Pressurized Solar Water Heaters


In the Pressurized system, heat exchangers are installed to protect the system from hard water and Pressure Pumps. The forced circulation systems employ Pressure pumps to circulate the water through collectors and storage tanks. The choice of system depends on heat requirement, weather conditions, heat transfer fluid quality, space availability, annual solar radiation, etc. The SHW systems are economical, pollution free and easy for operation in warm countries like ours. Pressurized systems are generally preferred in industries or large establishments.

Non-Pressurized Solar Water Heaters


In the Non-Pressurized system, the water in the system is open to the atmosphere at one point or other. These systems are simple and relatively inexpensive. They are suitable for domestic and small institutional systems.

Flat Plate Collectors


In the Flat Plate Collector (FPC) based Solar Water Heaters the solar radiation is absorbed by Flat Plate Collectors which consist of an insulated outer metallic box covered on the top with glass sheet. Inside there are blackened metallic absorber (selectively coated) sheets with built in channels or riser tubes to carry water. The absorber absorbs the solar radiation and transfers the heat to the flowing water.

Evacuated Tube Collectors


In the Evacuated Tube Collector (ETC) based Solar Water Heaters, Evacuated Tube Collector is made of double layer borosilicate glass tubes evacuated for providing insulation. The outer wall of the inner tube is coated with selective absorbing material. This helps absorption of solar radiation and transfers the heat to the water which flows through the inner tube. ETC based systems are cheaper than FPC based system. They perform better in colder regions and avoid freezing problem during sub-zero temperature. FPC based systems also perform well with anti-freeze solution at subzero temperature but their cost increases. In other regions, both perform equally well. Systems working on thermosyphon principle are simple and relatively inexpensive. They are suitable for domestic and small institutional applications, provided water quality is good and it doesn’t have large chlorine contents.