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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 is 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 light.

How much sunshine will I need?

Solar panels are directed at solar south in 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 panels generate 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 heating?

Because-- Solar water heaters save electricity 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 to understand for a layperson/ How do they work?

The working of solar water heaters is very 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 heating 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 of collectors?

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 collector?

Bureau of Indian standards has laid down 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 of hot water storage tank?

The hot water storage tank in domestic solar 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 aluminum. 

Electrical heating elements controlled by 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 heater?

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 high winds.

 How big a system should one purchase?

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.



Typical  Requirement of Hot Water at 60OC.

Household bathing using buckets

10-20 liters per person per bath.

Household bathing using shower with a mixing tap

20-30 liters for 10-15 minute bath

Shaving, while a tap runs

7-10 liters

Household bathing in bathtub (one filling)

50-75 liters

Wash basin with a mixing tap (hand wash, brushing of teeth, etc.)

3-5 liters per person per day.

Kitchen washing

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 for hot 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 required values.  

How much would a solar water heater cost?

The total cost of a solar water heating system 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 for installation of a solar water heating system?

 The basic requirement for functioning of 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 somewhere 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?

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 supply is irregular ?

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 days?

The heating of water by the solar system will 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 days.

 How much electricity and money can be saved?

The table below gives approximate likely 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

200 days

200 days

250 days

250 days

Expected yearly  electricity saving with  use of full  capacity,  kwh





Monetary savings at different prices of electricity, Rs/year

Rs. 4/kwh





Rs. 5/kwh





Rs. 6/kwh





 * The use pattern and savings for 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 solar water heater?

Typical solar water heaters made using materials as per BIS specifications could last for 15 -20 years depending upon the general upkeep, etc.

 Is any electricity required for 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 system during 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 from the 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 with the building exteriors?

Though aesthetics are a matter of individual 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 the aesthetics.

 Who are the suppliers of domestic solar water heating systems?

We Off Course

 What are the operational requirements?

Domestic solar systems do not require any 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 heated water 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 temperature.

 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 collector partially.

 Dust deposition on the collector would reduce its efficiency. Try to get it cleaned at least once in a week.

 What are the maintenance requirements?

Domestic solar water heating system do not 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 Water Heaters

Problem faced

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

Cloudy weather

Consumption too high

Frequent on-off of hot water tap

Collector dirty

Vapour lock in the collector  which can be removed by

allowing it to cool and draining the system