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Large scale industrial solar water heater at customer site
Solar water heater for domestic use

SWH is the conversion of sunlight into heat for water heating using a Solar thermal collector. it is the most competitive alternative than conventional water heating methods such as electric geysers and fuel-fed boilers.



A solar water heater consists of PV cells 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 total system with solar collector, storage tank and pipelines is called solar hot water system.


SWHs are widely used for residential and some industrial applications. it is economical, pollution free and easy for operation in warm countries like ours.

Solar water heaters run on a free fuel (i.e. sunshine), thus saving energy costs that help recover its initial cost in just 2-4 years. These are inexpensive, safe, and reliable and are easy to maintain. More importantly, they are eco-friendly and provide trouble free service for years together.The beauty of a solar hot water is its simple design and durability.


There are two types of collectors used in a solar hot water service:

  • Flat plate collectors (FPC)

  • Evacuated tubes (ETC)

Flat plate solar collectors

Flat plate collector’s work on copper pipes running through a glass covered collector, often connected to a water storage tank on the roof. The sun heats the copper pipes and the resulting hot water is thermo-siphoned out of storage tank.

Evacuated tube solar collectors

Evacuated tubes (as the name suggests) consist two glass tubes fused at the top and bottom. The space between the two tubes is evacuated to form a vacuum. A copper pipe (called a heat pipe) running through the center of the tube meets a common manifold that is then connected to a slow flow circulation pump that pumps water to a storage tank below, thus heating the water during the day. The hot water can be used at night or the next day due to the insulation of the tank.

The evacuation tube systems are superior as they can extract the heat out of the air on a humid day and don’t need direct sunlight. Due to the vacuum inside the glass tube, the total efficiency in all areas is higher and there’s better performance when the sun is not at an optimum angle – such as when it’s early in the morning or in the late afternoon.


A 100-liter per day water heater can save yearly electricity units in various parts of India as per the table mentioned below:

                                                        Northern Region    Eastern Region    Southern Region    Western Region

Expected no. of days of

use of hot water per year

Expected yearly electricity

saving on full use of solar

hot water (units of electricity)

The units used for water heating depend on the amount of water that is heated, so the number of unit increases proportionately as the size increases.

Annual cost of using hot water = No. of units consumed * (Cost/unit+ Service tax.)


 3-4 years


 it last for 20-25 years.


Solar water heaters available in market start from size of 100 ltr per day. The other sizes that are available are 200, 250, 300 and 500 lts per day. The maximum area required for the collectors to be installed on terrace/open area is:

Capacity (liters per day)         Area in sq. m. for ETC system          Area in sq. m. for FPC system

100                                      1.5                                                 2

200                                      3                                                    4

250                                      3.75                                               5

300                                      4.5                                                 6

350                                      7.5                                                 10

The liter per day mentioned above is liters of hot water at (60-70oC).

A 100 liters size is suitable for a family of 4.

200 Days

200 Days

300 Days

250 Days





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