In expressing this concern as
part of our
daily activity and in acting upon this premise, we endeavour to be recognised
as exemplary in this field. We look forward to take this iniatative
forward. We do believe that everyone has the necessary
expertise that we could harness in our endeavours .We are looking at
partners who could with their strengths further the cause of Renewable Energy
What is Solar Energy ?
Using solar power to produce electricity
not the same as using solar to produce heat. Solar thermal principles
are applied to produce hot fluids or air. Photovoltaic principles are
used to produce electricity. A solar panel (PV panel) is made of the natural
element, silicon, which becomes charged electrically when subjected to sun
How much sunshine will I need?
Solar panels are directed at solar
the northern hemisphere and solar north in the southern hemisphere (these are
slightly different than magnetic compass north-south directions) at an angle
dictated by the geographic location and latitude of where they are to be
installed. Typically, the angle of the solar array is set within a range of
between site-latitude-plus 15 degrees and site-latitude-minus 15 degrees,
depending on whether a slight winter or summer bias is desirable in the system.
Many solar arrays are placed at
an angle equal
to the site latitude with no bias for seasonal periods. How many solar panels
you will need based on the amount of sunshine available daily in your area
It is presumed that at "peak sun", 1000 W/mē of power reaches
the surface of the earth. One hour of full sun provides 1000 Wh per mē = 1
kWh/mē -representing the solar energy received in one hour on a cloudless
summer day on a one-square meter surface directed towards the sun.
An eco-friendly electric generator. Solar
free power from the sun by converting sunlight to electricity with no moving
parts, zero emissions, and no maintenance. The solar panel, the first component
of a electric solar energy system, is a collection of individual silicon cells
that generate electricity from sunlight.
Why should one go for solar water
Because-- Solar water heaters
and thus money; electricity is becoming more and more expensive; they could
even turnout to be more reliable than electric power supply (at least in many
parts of our country); they are clean and green and thus reflect one's
commitment for preservation of environment; they are safer than electric
geysers as they are located on the roof; and, if well designed, may even look
good on the house top.
Do they really work?
Of course they do. After all,
more than 20,000
domestic systems are being installed every year all over the country.
Is their working difficult
for a layperson/ How do they work?
The working of solar water heaters
simple to understand. Two common phenomena observed in everyday life are the
key to functioning of solar water heaters. These are, first, a black surface
heats up when left in the sun, by absorption of solar radiation; and second,
the inside of a car becomes very hot, if it is left in the sun with windows
closed. A car becomes hot in sun because solar radiation can pass through the
glass windows but cannot come out. It is trapped inside and thus heats up the
car. The heat trapping principle is the famous Green House Effect. The good
absorption property of black surfaces is used to improve solar energy
absorption in a solar heater. These two phenomena are utilized in flat plate
collectors of commonly available solar water heaters. A typical domestic solar
water heater consists of a hot water storage tank and one or more flat plate
collectors. The collectors are glazed on the sun facing side to allow solar
radiation to come in. A black absorbing surface (absorber) inside the flat
plate collectors absorbs solar radiation and transfers the energy to water
flowing through it. Heated water is collected in the tank which is insulated to
prevent heat loss. Circulation of water from the tank through the collectors
and back to the tank continues automatically due to density difference between
hot and cold water (thermosyphon effect).
What is a flat plate collector?
It is the heart of a solar water
system. It consists of an absorber plate which is coated on its sun facing
surface with an absorbent coating, also called selective coating. The absorber
consists of a grid of metallic tubes and sheets. Water flows through the tubes.
Sheet absorbs the solar radiation falling on it and transfers it to water. The
absorber plate is placed in a top open box to protect it from weather. The
space between back and sides of the absorber and the box is filled with
insulation to reduce heat losses. The front of the box is covered with a high
transmittance glass plate. Flat plate collectors are specified on the basis of
their area and are of commonly 1x2 m size
Are there any other types
Flat plate collectors are the
most common type
used in the domestic solar water heating systems, specially in India,
in view of their cost economics. Evacuated tube collectors have also been
proposed for domestic solar water heating systems, but are not commonly
available. Concentrating collectors are
likely to be more useful for higher
temperature applications such as power generation and industrial use.
What should one look for in a
good flat plate
Bureau of Indian standards has
specifications of flat plate collectors for use in solar water heating systems
and thus the IS mark is an assurance on use of proper materials. The important
characteristics are, the materials of construction of the absorber plate, the
type of absorbent coating on it, the quality of the glass plate used, the
material of the box, the insulation thickness, etc.
What are the desirable characteristics
water storage tank?
The hot water storage tank in
water heating systems is typically a double walled tank. The space between the
inner and the outer tanks is filled with insulation to prevent heat losses. The
inner tank is generally made of copper or stainless steel to ensure long life.
The outer tank could be made of stainless steel sheet, painted steel sheet or
Electrical heating elements controlled
thermostats can be provided as an option in the tank itself to take care of
those days when sun is not there or demand of water has gone up. The capacity
of the tank should be in proportion to the collector area used in the system. A
commonly used thumb rule is to provide 50 liters of storage for every sq. m of
collector area. Too large or too small tanks are both detrimental to efficiency.
How does one identify a
good solar water
First and foremost requirement
of a good solar
heater is that it should have sufficient collector area for the capacity
claimed. Collector area used in the system determines the capacity of water
heating. Fox example, in typical north Indian weather conditions, on a sunny
winter day, a sq. m. of collector area can be expected to heat around 50 liters
of water by a temperature of 30-40 C. Typical flat plate collectors made
in the country have an area of around 2 sq. m and are thus capable of heating
around 100 liters of water in a day. This proportion serves as a
benchmark. Further, the collectors should use good materials and the absorbers
should carry a good quality coating (BIS approved collectors are being provided
by large number of established manufacturers). The system should be mounted on
a rigid structure and should be firmly fixed with the roof to prevent damage in
How big a system should
The fundamental rule is that it
is better to
buy a system smaller than your requirement and use back up when you fall short
of hot water, rather than buy a system much bigger than your requirement
(because you can afford it). This will lead to inefficiencies and may even
cause operational problems. The best is to make an actual estimate of daily
demand of hot water by measurements on the main use points. Do remember that
the solar system is capable of heating only an approximately fixed quantity of
water and is designed for typical sunny days. Thus in this characteristic it is
unlike an electric geyser which can supply widely varying quantities of hot
water in a day. Also remember that the temperature of water in the solar system
is determined by the combination of collector area and the tank capacity.
Typically it would be 50 – 60 C, which is much hotter than the bathing water
temperature (around 40 C). Estimation of your demand can also be made with
the help of the table given below. As a typical example on sizing of solar
systems, it may be mentioned that a 100 liters system is considered generally
optimum for family of 4 adult members.
ESTIMATES OF REQUIREMENTS OF HOT WATER - SOME
USEFUL THUMB RULES
Typical Requirement of Hot Water at 60OC.
Household bathing using buckets
10-20 liters per person per bath.
Household bathing using shower with a
20-30 liters for 10-15 minute bath
Shaving, while a tap runs
Household bathing in bathtub
Wash basin with a mixing tap (hand
wash, brushing of teeth, etc.)
3-5 liters per person per day.
2-3 liters per person per day.
40-50 liters per wash cycle
Clothes washing machine
40-50 liters per cycle
Note: All the estimates are given
water at 60OC. This hot water has to be mixed with cold water to bring down its
temperature to endurance limits. Mixing will also increase quantity to actually
How much would a solar water heater
The total cost of a solar water
is dependent upon many things. These include, the capacity, the kind of back-up
used, the materials used for the inner and outer tanks, the length of
distribution piping required to take hot water to the bathrooms, and not
insignificantly, the brand value. Typically, for an Indian make system with
single BIS approved flat plate collector of 2 sq. m area, the current market
costs are reported to be in the range of Rs. 15,000-20,000, excluding the
distribution piping. However this range is indicative, and could vary from
manufacturer to manufacturer.
What are the site requirements
installation of a solar water heating system?
The basic requirement for
a solar system is availability of unobstructed sunlight for the whole day.
Typically, domestic solar water heating systems are installed on the roof of
the house. The collectors of the system have to face the sun and hence should
be oriented due south for maximum interception of sunlight. Thus there should
be no obstruction to sunlight in the south, west and east directions in that
order of preference (an arc of about 120, 60 both sides of the
southern direction should ideally be shadow free). As a thumb rule, the
requirement of shadow free area is around 3 sq. m for each 1 x 2 m collector
used. As far as possible, the area should be flat, away from rain water drains
and as far as possible, close to the bathrooms where hot water is to be
supplied. Cold water should be available at the height of around 2.5 m from the
base of the system.
Can the system be installed
other than on the roof?
The system can also be installed
on a bracket
on a south facing wall, close to the bathrooms. However, the installation is
difficult and leads to extra cost. The fixing of the system to the bracket
should be proper. Access to the system for repairs should also be ensured. Cost
of hot water distribution piping could be reduced in such installations as the
system will be close to the use point.
How can the system be installed
In multistoried buildings even
if the space
for installation can be made available on the roof, and the systems are
installed there, the piping from the system to the use point will become long
leading to extra cost as well as to extra heat losses. A better option in such
cases could be installation of the systems on the wall mounted brackets, close
to the bathrooms. However, this has not been practiced frequently inIndia
What would happen if water
A regular cold water supply, at
a height of
around 2.5 m is necessary for functioning of the solar system. In case cold
water is not available continuously, a separate cold water tank may have to be
installed , at least equal in capacity to the capacity of the solar system. In
case cold water supply is interrupted during the day, the heating of water by
the solar system may not be affected significantly, although hot water cannot
be drawn for use till the water supply is restored.
What would happen on cloudy
The heating of water by the solar
obviously be affected. If it is so cloudy that energy received from the sun is
almost zero, the output of solar collectors also will be nil. On partially
cloudy days some output can be expected. But, the system can be designed with a
suitable electrical back up heater to take care of hot water demand on cloudy
How much electricity and
money can be
The table below gives approximate
electricity and money savings for typical 100 Liters per day solar water
heating systems located in different parts of the country. Likely savings of
electricity and money by use of a 100 liters domestic solar water heater
(using 2.0 sq.m collector area)
Expected no. of days of use per year
Expected yearly electricity saving
with use of full capacity, kwh
Monetary savings at different prices of
* The use pattern and savings
southern region pertains to the typical climate ofBangalore, while those for
western region relate typically to Pune climate.
What is the expected life of a
Typical solar water heaters made
materials as per BIS specifications could last for 15 -20 years depending upon
the general upkeep, etc.
Is any electricity required
operation of the solar water heater?
Domestic solar water heaters work
on the principle
of thermosyphonic action in which water circulates through the system by virtue
of density difference between hot and cold streams. No electricity is required
for circulation of water or for any other operation in such systems. However,
in case a back up heater is provided to take care of hot water requirement
during cloudy days, electricity will be required.
How long will the water
heated by solar
energy remain hot in the tank? Will one get hot water in early morning when sun
is not there?
Hot water produced by the solar
the day is stored in an insulated storage tank. The insulation of the tank is
such that water should remain hot without significant drop in temperature for
around 24 hrs. Thus water heated during the previous day should be available
for use in the next morning.
Are there any financial incentives
government on these systems?
The Central Government through
its Ministry of
Non-Conventional Energy Sources provides soft loans for installation of
domestic solar water heating systems. These loans are being provided through 7
Nationalized banks and the interest rate on the loans is 5%. The details of the
scheme can be obtained from this website under "soft loan programme or
solar water heating systems ".
Will the solar system match
Though aesthetics are a matter
preference, most domestic solar water heating systems can be either designed to
blend with the building exteriors or can be designed so that they are hidden
from view. If systems are well installed and maintained, they might even add to
Who are the suppliers of
water heating systems?
What are the operational
Domestic solar systems do not
special operational skills. However, if following are observed, the
efficiency of the systems will be maintained at a high level:
Try to consume most of the
at one time - either in the morning or in the evening. Frequent on and off of
the hot water tap would lead to reduced electricity savings. If an electrical
back up is provided in the tank, set the thermostat at the lowest acceptable
� In the north Indian climate, hot water may
not be used for
bathing in summers. If the system is to be put totally out of use, it should be
drained of water and the collector should be covered. Alternatively, if the hot
water requirement remains in summers also, though at a reduced level, cover the
� Dust deposition on the collector would reduce
efficiency. Try to get it cleaned at least once in a week.
What are the maintenance
Domestic solar water heating system
need significant maintenance requirements. Occasional leakages in the plumbing
could be easily repaired by common plumbers. In case quality of water is hard,
scale deposition in the collectors may result over the years. This may require
descaling with acids for which it is best to contact the suppliers. Broken
glass may also have to be replaced by the suppliers. If outside exposed
surfaces are painted, the paint may have to be redone every 2-3 years to
prevent corrosion of the surfaces.
Trouble Shooting Guide for Domestic Solar
Probable cause and remedies
No water in the tap
No cold water supply
Wall at the outlet of the system
Airlock in Pipes
Water not heated at all, although cold
water flow is normal
Consumption of hot water may be too high;
Check use points and use pattern
Collector may be shaded
No flow of water through th Collector
as it might be choked due to scaling; Get it
checked from the manufacture
Water not hot enough or
sufficient quantity of hot water is not available
Consumption too high
Frequent on-off of hot water tap
Vapour lock in the collector which can
be removed by
allowing it to cool and draining the