In a solar rooftop system, the solar panels are installed in the roof of any residential, commercial,
institutional and industrial buildings. This can be of two types (i) Solar Rooftop System with
storage facility using battery, and (ii) Grid Connected Solar Rooftop System.
2. What is a Solar Rooftop System with Storage facility?
Such rooftop system has battery as storage facility. The solar electricity is stored in the battery and
can be utilized during night also when the sun is not available.
3. What is a Grid Connected Solar Rooftop System?
In grid connected rooftop or small SPV system, the DC power generated from SPV panel is
converted to AC power using power conditioning unit and is fed to the grid either of 33 kV/11 kV
three phase lines or of 440/220 Volt three/single phase line depending on the capacity of the
system installed at institution/commercial establishment or residential complex and the
regulatory framework specified for respective States.
These systems generate power during the day time which is utilized fully by powering captive
loads and feed excess power to the grid as long as grid is available. In case, where solar power is
not sufficient due to cloud cover etc., the captive loads are served by drawing power from the
4. Where such plants can be installed?
Such rooftop systems can be installed at the roofs of residential and commercial complex,
housing societies, community centers, government organizations, private institutions etc.
5. What is the size of grid connected rooftop solarsystem?
The rooftop solar systems from 1 kWp upto 500 kWp or in combination can be set up on the
6. How much roof area is required to set up the grid connected rooftop solar system?
About 10sq.m area is required to set up 1 kWp grid connected rooftop solar system.
7. What are the advantages of Grid-Connected Rooftop Solar System?
Electricity generation at the consumption center and hence Savingsin transmission and distribution losses
Low gestation time
No requirement of additional land
Improvement of tail-end grid voltages and reduction in system congestion with higher selfconsumption of solar electricity
Local employment generation
8. Net metering
The grid connected rooftop system can work on net metering basis wherein the beneficiary pays to the
utility on net meter reading basis only. Alternatively two meters can also be installed to major the
export and import of power separately. The mechanism based on gross metering at mutually agreed tariff
can also be adopted.
TIn feed-in-tariff the Government offers a tariff for purchase of the solar power generated from
10.Among net metering and feed-in-tariff what is preferred?
Net metering mechanism is more popular among States.
11. In case of grid failure, is there any chance for shocksto the person who is repairing?
In case the grid fails, the solar power has to be fully utilized or stopped immediately feeding to the grid so
as to safe-guard any grid person/technician from getting shock (electrocuted) while working on the grid for
maintenance etc. This feature is termed as ‘Islanding Protection’.
Solar Water Heater
Q. What is Solar Water Heater?
A Solar Water Heater is a device which provides hot water for bathing, washing,
cleaning, etc. using solar energy. It is generally installed at the terrace or where
sunlight is available and heats water during day time which is stored in an insulated
storage tank for use when required including mornings.
Q. How does it work?
A Solar Water Heater comprises of a or an array of solar collectors to collect solar
energy and an insulated tank to store hot water. Both are connected to each
other. During the day time, water in solar collectors gets heated which is either
pumped or flown automatically on thermosyphon principle to the storage tank. Hot
water then stored in the tank can be used for various applications.
Q. What are different types of Solar Water Heaters?
Two types of Solar Water Heaters are available; one based on flat plate collectors and
the other based on evacuated tube collectors. Flat plate collector (FPC) based
systems are of metallic type and have longer life as compared to Evacuated tube
collector (ETC) based system because ETCs are made of glass which are of fragile
Both these systems are available with and without heat exchanger. They can also
work with and without pump. Systems without pump are known as thermosyphon
systems and those with pump are known as forced circulation systems.
Q. Which type of solar water heater is suitable for different places/category of users?
ETC based systems are cheaper than FPC based system. They perform better in
colder regions and avoid freezing problem during sub-zero temperature. FPC based
systems also perform good with anti-freeze solution at sub zero temperature but their
cost increases. In other regions, both perform equally good.
Systems working on thermosyphon principle are simple and relatively inexpensive.
They are suitable for domestic and small institutional applications, provided water
quality is good and it doesn’t have large chlorine contents. Forced circulation
systems are generally preferred in industries or large establishments.
At places where water is hard and have larger chlorine content, if FPC based system
is being installed, it must be with heat exchanger as it will avoid scale deposition in
copper tubes of solar collectors which can block the flow of water as well reduce its
thermal performance. ETC based systems will not block the flow of water but its
performance may go down due to deposition of salt contents on inner surface of glass
tubes, which could be cleaned easily once in a year or so.
Q. Why should I go for a Solar Water Heater? What do I save from it?
A 100 litre per day capacity system suitable for 3-4 people can save upto 1500 units
of electricity in a year, depending on hot water used. It can also save around 140
litres of diesel in an establishment using oil fired boiler besides reducing green house
gas emissions in the atmosphere. Higher capacity systems will save higher amount of
electricity/fuel oil besides reducing higher amount of GHG emissions.
Electricity is expensive and is not available due to power cuts in many areas when
required for heating water. Solar Water Heater, since it stores hot water in an
insulated tank, provides water all the time when required. Fuel oil is also expensive
and creates pollution. Storing the fuel oil for long term use in commercial
establishments is another problem.
Q. What happens on cloudy/rainy day? Do I still get hot water?
On cloudy days also, if it is for a day or two, you still get warm water as water gets
heated due to diffused radiation available in the atmosphere. The system, however,
is either connected to an electric geyser in the house or an electrical back-up
is provided in the storage tank of the system which is switched on when water
is not sufficiently hot. So, you get hot water all the time even on rainy days.
Q. How do I decide about the size/capacity of the system to be installed?
For a house with one bathroom and 3 to 4 members, 100 liter per day capacity
system should be sufficient. For more numbers of bathrooms, the capacity will
increase accordingly due to pipe losses & more number of family members.
Generally the capacity is decided based on hot water required in mornings for
bathing. If the usage is in evening & at other times also, the capacity is decided
8. Are there any 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 de-scaling 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.