Basic solar water heaters are of two types depending upon the collector technology used: Flat Plate Collector (FPC) type and Evacuated Tube Collector (ETC) type.

1. Flat Plate Collector based solar water heater

The Flat Plate Collector consists of an insulated metallic box covered on the top with toughened glass. The metallic box contains an absorber sheet (normally made of copper) that is coated with a selective coating to increase the absorption of solar energy. Vertical tubes made of copper, known as riser tubes are attached to the absorber and carry the water to be heated. The riser tubes are connected to two horizontal tubes called headers, one placed at the bottom and the other at the top. The bottom header is used for flow of water into the collector whereas the top header is used to take out the heated water. There are 60 BIS approved manufacturers of Solar Flat Plate Collectors.

2. Evacuated Tube Collector based solar water heater

The Evacuated Tube Collector consists of two co-axial glass tubes fused at both ends with air between the tubes evacuated to create vacuum that works as insulation. The outer surface of the inner tube forms the collector area and it is selectively coated to increase the absorption of solar energy. There are 44 MNRE approved ETC based solar water heating supplier.

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 temperatures 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 (SWHs) of 100-300 litres capacity are suited for domestic application.
• Larger systems can be used in restaurants, guest houses, hotels, hospitals, industries etc.

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.