Solar Water Heating Systems

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 hat to the riser pipes underneath the absorber panel. 
The water passing through the risers get heated up and is delivered 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. 

Broadly, the solar water heating systems are of two categories. They are : closed 
loop system and open loop system. In the first one, heat exchangers are installed to 
protect the system from hard water obtained from borewells or from freezing 
temperatures in the cold regions. In the other type, either thermosyphon or forced 
circulation system, the water in the system is open to the atmosphere at one point or 
other. The thermosyphon systems are simple and relatively inexpensive. They are 
suitable for domestic and small institutional systems, provided the water is treated and 
potable in quality. The forced circulation systems employ electrical pumps to circulate 
the water through collectors and storage tanks. 

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 easy for operation in warm countries like ours. 

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

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. There are 60 BIS approved manufacturers of Solar Flat Plate Collectors. 

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. There are 44 MNRE approved ETC 

based solar water heating suppliers.

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.  

¾ Around 60 deg. – 80 deg. C temperature can be attained depending on solar 

radiation, weather conditions and solar collector system efficiency 

¾ Hot water for homes, hostels, hotels, hospitals, restaurants, dairies, industries etc. 

¾ 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 

¾ 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 

¾ Stainless Steel is used for small tanks.