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.
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| 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).
