Solar Water Heater

Solar Water Heating System is the most commonly used solar system equipment that work on the basis of solar energy. It saves the cost of fuel with utilization of solar energy and keeps the environment green, free from pollution.

A Solar Water Heater System consists of Four parts:-

  • Solar Collector
  • Solar Storage Tank
  • Water Transfer Pipes
  • Panel Stands.



A Thermosyphon Solar Water Heating System takes advantage of the fact that hot water rises and cool water sinks. As water is heated it expands and so, as gravity pulls down the relatively heavier cool water molecules, the warmer molecules rise up.

The diagram below shows how this works in a real world thermosysphon solar water heating system. Such a system offers the advantage that no pump or controller is required to run everything and so it is very simple and less liable to failure.

During the day water in the solar collector (flat panel or evacuated tube) is heated by the sun. As the water heats up, it rises pushing up into the insulated tank. Cooler water at the bottom of the tank is then pushed down to re-enter the bottom of the solar collector where it is heated further. This cycle continues throughout the day with the water stored in the tank getting hotter and hotter.



  • Solar Hot Water System turns cold water into hot water with the help of sun’s rays.
  • Around 60 deg. – 80 deg. C temperature can be attained depending on solar radiation, weather conditions and solar collector system efficiency.
  • Hot water generated can be used for homes, hostels, hotels, hospitals, restaurants, dairies, industries etc.
  • Can be installed on roof-tops, building terrace and open ground where there is no shading, south orientation of collectors (solar panels) and over-head tank above SWH system.
  • SWH system generates hot water on clear sunny days (maximum), partially clouded (moderate) but not in rainy or heavy overcast day.
  • Only soft and potable water can be used.
  • Stainless Steel is used for small tanks whereas Mild Steel tanks with anticorrosion coating inside are used for large tanks.
  • Solar water heaters (SWHs) of 100-300 litres capacity are suited for domestic application.
  • Larger systems can be used in restaurants, guest houses, hotels, hospitals, industries etc.



  • Operates from free Sunlight.
  • Avoids Cold water wastage.
  • Hot water is readily available on the turn of the tap.
  • They are efficient. Approximately 80% radiation is turned into heat energy.
  • Can be operated lifelong.
  • Easy to operate and maintain.
  • No electricity required.



Fuel Savings: A 100 litres capacity SWH can replace an electric geyser for residential use and saves 1500 units of electricity annually.

Avoided utility cost on generation: - The use of 1000 SWHs of 100 litres capacity each can contribute to a peak load shaving of 1 MW.

Environmental benefits:- A SWH of 100 litres capacity can prevent emission of 1.5 tonnes of carbon dioxide per year.

Life :- 15-20 years.

Approximate cost :- Rs.15000- 20,000 for a 100 litres capacity system and Rs.110-150 per installed litre for higher capacity systems.

Payback period : 1.5-2 years when electricity is replaced.

Though the initial investment for a solar water heater is high compared to available conventional alternatives, the return on investment has become increasingly attractive with the increase in prices of conventional energy. The payback period depends on the site of installation, utilization pattern and fuel replaced.



  • Based on the collector system, solar water heaters can be of two types:-
  • Flat Plate Collectors (FPC)
  • Evacuated Tube Collectors (ETC)


Flat Plate Collectors (FPC)

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 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.