A solar water heating (SWH) system uses energy from the sun to heat water for bathing, washing, and other uses, saving electricity or gas. It consists of solar collectors, usually flat plate or evacuated tube, that absorb sunlight to heat water, which is then stored in an insulated tank. Water circulates through the system via a thermosyphon (gravity-driven) or pumped (active) system, with the heated water stored in a tank for use during the night or cloudy days. A backup heater is often included to ensure a continuous hot water supply.

 

How a Solar Water Heater Works

1. Solar Collection:

Sunlight is absorbed by a dark surface (the absorber) within the solar collectors. 

2. Heat Transfer:

This absorbed solar energy heats water flowing through tubes in the collector. 

3. Circulation:

Thermosyphon Systems: Heated water, being less dense, rises into the insulated storage tank, while colder, heavier water from the bottom of the tank flows down to the collector. 

Active Systems: A pump is used to circulate water from the tank to the collectors and back, allowing for more flexible placement of the collector and tank. 

4. Storage:

The hot water is stored in an insulated tank to prevent heat loss, ensuring hot water is available even when the sun isn't shining. 

5. Backup:

Most systems include a backup heater (electric or gas) to provide hot water during periods of low sunlight or high demand. 

Key Components 

Solar Collector: Absorbs sunlight and transfers heat to the water. Common types include:

Flat Plate Collectors: Consist of a black absorber plate with tubes for water, covered by a glass sheet and insulation.

Evacuated Tube Collectors: Use vacuum-insulated glass tubes with a selective coating to absorb more solar radiation and achieve higher temperatures.

Storage Tank: An insulated tank that holds the hot water for later use.

Piping: Connects the collectors to the storage tank for water circulation.

Benefits

Reduced Costs: Significantly lowers electricity and gas bills for hot water. 

Environmental: Utilizes a free, renewable energy source, reducing reliance on conventional energy. 

Mature Technology: Solar water heating is a well-established and reliable technology for residential, commercial, and industrial use.