Solar water heating (SWH) systems are prevalent in countries like Japan, Australia, Israel and China where sunshine is abundantly and suitable infrastructure is available.

For domestic purpose, solar water heaters are typically used to meet the need for heated bathing water. Solar panes are installed on the individual roof top of the house and the incumbents can enjoy running hot water at a cost effective price.

Primary installation of solar panes is more expensive than the conventional water heaters, but due to its long service life the cost comes down to be lesser than its counterpart. Solar water heating systems also store energy that can be used for the cloudy days.

This renewable source of energy has won attention of the promoters of green energy.

Working of solar water heater is simple to comprehend. Solar panes are installed in a manner that they are exposed to direct sunlight. These are known as heat collectors. During the day time these solar panes collect energy from scattered sunrays. These panes are connected to coils in a tank. One inlet supplies room temperature water into the water tank. When the coils are sufficiently hot they warm the water and the heated water is supplied for use.

The most crucial part of the solar water heating system is the heat collector. Basically there are three types of heat collectors namely flat plate collector (PFC), evacuated based collector (ETC), and concentrating collectors.

Amongst these three, flat plate collector is most widely used. It comprises of an insulated tank containing a dark absorber plate beneath transparent or translucent covers.

Evacuated based collectors are made up of rows of transparent glass tubes. Each glass tube has a subset of inner and outer glass tube which acts as heat absorber. Each of these tubes is covered with a chemical coating that absorbs solar energy well and at the same time prevents heat loss.

Finally the concentrating collectors are peculiarly used for residential applications. It uses mirrored surfaces to collect the sun's scattered energy on an absorber tube called ‘receiver’. This tube carries heated water to the outlets.

Solar water heating systems are extensively used by hotels that are located in places blessed with clear sky and glittering sunshine. Excess solar energy is stored within the SWH system which can be used at the night time or when the sky is not clear.

Apart from being cost competitive, solar water heater has environmental and economic advantages to them. Some governments give credits to industries that use green energy.