Solar Water Heating Systems

Power cut is a consistent problem at the peak hours in summers as well as winters in most of the North Indian cities. In such cases, switching the heating load over to non-conventional sources of energy from the conventional type of resources can eradicate this problem and inconvenience that arise especially during early hours of peak winter season when the hot water is needed the most. The gap between the demand and supply of electricity can be bridged to a great extent by using solar energy based appliances such as Solar Water Heater.

China stands at the top position in the world in the Installations of Solar Water Heating Systems with approx. 80.3% of total installations in the world.

Solar Energy Appliances not only bridge the gap between demand and supply of the electricity but also save a lot of money due to their negligible running cost and also they help in maintaining the ecological balance by reducing pollution.

Solar Water Heaters are designed to heat water by using the solar energy which is available on earth free of cost. Water can be easily heated to a temp. of 60-70˚C.

A typical solar water heater

Main components of solar water heater system are:

A) Solar Collector (to collect solar energy)

B) Insulated tank (to store hot water)

C) Supporting stand

D) Connecting pipes and instrumentation etc. 

Solar Water Heaters can be of following two types:

1- FPC :Flat Plate Collector based

2- ETC :Evacuated Tube Collector based

In 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  tempered glass sheet. Inside there are blackened metallic absorber 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. Most flat plate collectors have two horizontal pipes at the top and bottom, called headers, and many smaller vertical pipes connecting them, called risers. The risers are welded to thin absorber fins. Heat-transfer fluid (either water or water-antifreeze mixture) is pumped from the hot water storage tank (direct system) or heat exchanger (indirect system) into the collectors' bottom header, and it travels up the risers, collects heat from the absorber fins, and then exits the collector out of the top header.

In ETC based Solar Water Heaters Evacuated Tube Collector is made of double layer concentric borosilicate glass tubes evacuated for providing insulation. Since heat loss due to convection cannot cross a  vacuum, it forms an efficient isolation to keep heat inside the collector pipes.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.

Flat plate collectors are generally more efficient than ETC in full sunshine conditions. However, the energy output of flat plate collectors is reduced slightly more than evacuated tube collectors in cloudy or extremely cold conditions.

FPC based systems with metallic collectors are costlier than the ETC based systems with glass tubes for the same system capacity (Ltr/Day).