The use of solar water heaters to heat water for domestic purposes is increasing, especially in countries like India, China, US, some African countries and other places where sunlight is available abundantly. In fact in the US the first solar water heater dates back to 1890s. By the year 1920 tens of thousands of solar water heaters were sold in US. However, when the cheaper fossil fuels were available the use of solar water heaters started decreasing. In the present days they have again made a comeback in US.
Heating water using electricity is very expensive as you will need electric heaters of at least 1KW, which consume lots of electricity. Heat from sun is available freely so solar water heaters are much cheaper in the long-run though their initial cost is somewhat bit higher.
Types of the Solar Water Heaters
There are two type of solar water heaters:
1) Active solar water heating systems: In these systems there are pumps that enable the flow of water through the solar water heating system.
2) Passive solar water heating systems: In these systems most of the circulation of water occurs naturally and no pumps are used.
Types of Solar Panels
There are three types of solar collectors used commonly used in the solar water heaters, these are:
1) Flat-plate collectors: As the name suggests these solar collectors are flat in shape. There is a big box with different layers of plate surfaces. At the top there is one or more layer of glass or plastic cover on which the sunlight falls. The light is then absorbed by the absorber plate, which is usually the metal plate like aluminum and it kept below the top cover. Around the absorber plate there are piping of water which absorb the heat from the absorber plate. The whole box of the flat plate collector is insulated and weather shielded. Flat-plate collectors are most commonly used in solar water heaters.
2) Integral collector-storage systems: These solar collectors are installed in the areas where the temperature is very low and heating from solar energy is not sufficient. In these systems cold water is first heated in the solar collector and it is passed to the insulated tank. The water is then passed to the conventional water heater that ensures the heating of water to required temperature levels.
3) Evacuated-tube solar collectors: These solar collectors comprise of the parallel rows of the glass tubes which are exposed directly to the sunlight. The tubes comprise of the outer glass tube and the metal tube that acts as the absorber of the heat. These solar collectors are used for the commercial applications where maximum amount of heat is to be absorbed and the losses due to radiations have to be reduced.
>>>Also Read: Applications of Solar Energy: Part-2: Solar Cooker