Solar Hot Water System (SHWS)

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 popular devices that harness the solar energy is solar hot water system (SHWS).

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 selected coating transfers the heat to the riser pipes underneath the absorber 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.

The choice of system depends on heat requirement, weather conditions, heat transfer fluid quality, space availability, annual solar radiation, etc. The SHW systems are economical, pollution free and appropriate for operation in warm countries like India.

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

1. Flat Plate Collectors (FPC) based Solar Water Heaters

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.

2. 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 of solar radiation 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 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.
  • Soft and Hard 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.
Environmental benefits
  • A Solar Water Heater of 200 litres capacity can prevent emission of 1.5 tonnes of carbondioxideper year.
  • Life: 15-20 years.
Payback period
  • 3-4 years when electricity is replaced.
  • 4-5 years when furnace oil is replaced.
  • 5-6 years when coal is replaced.
Electricity Savings

A Minimum 100 Lpd system (5sq.m of collector area) installed in a home can save 4-6 units of electricity/day depending on the place of installation & hot water use. On an average it could be taken as 5 units/day. So it saves Monthly 150 units,annually1800 units and 9,000 units in total five year or during warranty period.

As a Standard, State Electricity Board will charge For LT Load the average rate per unit would be Rs. 10/-so an average electricity bill can be save uptoRs. 18,000/-Annual and for total five year it would be Rs. 90,000/-