Solar water heater advantages compared to conventional fuels

We are blessed with Solar Energy in abundance at no cost. The solar radiation incident on the surface of the earth can be conveniently utilized for the benefit of human society. One of the most popular devices that harness the solar energy is “Redsun” solar hot water system (SWHS).


A solar water heater consists of a collector to collect solar energy and an insulated storage tank to store hot water. The solar energy incident on the absorber panel coated with selective coating transfers the heat to the riser pipes underneath the abosorber panel. The water passing through the risers get heated up and is delivered to the storage tank. The re-circulation of the same water through absorber panel in the collector raises the temperature to 80 C (Maximum) in a good sunny day. The total system with solar collector, storage tank and pipelines is called solar hot water system.

This type of systems are called Thermosyphon systems which are simple and relatively inexpensive. They are suitable for domestic and small institutional systems, provided the water is treated and potable in quality.

The Solar Water Heating systems are economical, pollution free and easy for operation in warm countries like India.

Based on the collector system, solar water heater can be of two types.

Flat Plate Collectors (FPC) based Solar Water Heaters:

The solar radiation is abosrbed by Flat Plate Collectors which consist of an insulated outer metallic box covered on the top with toughened glass sheet. Inside there are blackened metallic absorber (selectively coated) copper sheets with built in channels or risers tubes to carry water. The absorber absorbs the solar radiation and transfers the heat to the flowing water.

Evacuated Tube Collectors (ETC) based Solar Water Heaters:

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 and transfers the heat to the water which flows through the inner tube.

Solar Water Heating is now a mature technology. Wide spread utilization of solar water heaters can reduce a significant portion of the conventional energy being used for heating water in homes, factories and other commercial and institutional establishments. Internationally the market for solar water heaters has expanded significantly during the last decade.

Salient Features of “Redsun” Solar Water Heating System:

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 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 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 anti-corrosion coating inside are used for large tanks.
  • Solar Water Heaters of 100-300 litres per day capacity are suited for domestic application.
  • Larger systems can be used in restaurants, guest houses, hotels, hospitals, industries etc.

Fuel Savings:

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 saving of 1 MW.

Environmental Benefits:

A SWH of 100 litres capacity can prevent emission of 1.5 tonnes of carbon-dioxie per year.

Payback period:

2-3 years when electricity is replaced.

4-5 years when furnace oil is replaced.

5-6 years when coal 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 pay back period depends on the site of installation, utilization period and fuel replaced.

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