University of Duhok
College of Engineering
ECE Department
Mechanic II
REPORT
Solar Water Heaters
Student Name: Naleen Mahmood
Solar Water Heater:
These use solar energy to heat the water. They are composed of three
parts: a collector, circuit piping, and heat storage tanks. In most modern
water heater, water and antifreeze solution moves between the tank and
the collector in a closed cycle by circuit piping. The collector absorbs the
sun's heat energy and transfers it to the working fluid. Heated fluid moves
toward the storage tank where it passes through a heat exchanger and
transfers its heat to the water in storage tank; after cooling down it goes
back to the collector again so without mixing with consumable water, it
always moves in closed cycle. Solar water heaters fit into two categories,
open and closed circuit systems. In both categories, they can work in
thermosyphon (natural flow – a passive heat exchange) or a pump (forced
heat exchange).The important part of the solar water heaters is the
collector, in which the plate is heated by solar radiation and transferred its
heat to the working fluid. This plate is always a dark color and has a special
coating that maximizes energy absorption and minimizes heat dispersion.
To achieve high temperatures, the plate and tube are set inside an
insulated box covered with glass to optimize the greenhouse effect.
Figure 1: Solar water heater diagram
How a Solar Collector Works:
The sun sends a huge amount of energy to earth every day. As a rough
estimate, approximately one kilowatt of energy is arriving per square meter
of the earth’s surface that is receiving direct sunlight. A solar collector tries
to collect as much of this energy as possible and convert it into a usable
form, usually either heat energy or electrical energy. A solar collector is
basically a flat box and is composed of three main parts, a transparent
cover, tubes which carry a coolant and an insulated back plate. The solar
collector works on the greenhouse effect principle; solar radiation incident
upon the transparent surface of the solar collector is transmitted through
though this surface. The inside of the solar collector is usually evacuated,
the energy contained within the solar collect is basically trapped and thus
heats the coolant contained within the tubes. The tubes are usually made
from copper, and the back plate is painted black to help absorb solar
radiation. The solar collector is usually insulated to avoid heat losses. Solar
thermal heat can provide hot water for an entire family during the summer.
The collector size needed per person is about 1,5 m2. An average family of
four people therefore needs a collector about 6 m2.
Figure 2: Example
Selection of suitable Solar Water Heating Systems:
1. Flat plate collector (FPC) based systems are of metallic type and have
longer life as compared to Evacuated tube collector (ETC) based system
as ETCs are made of glass which are of fragile in nature.
2. ETC based systems are 10 to 20% 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.
3. At places where water is hard and have larger chlorine content, FPC
based system with heat exchanger must be installed 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 do not
face such problem.
4. 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 accordingly.
5. A 100 lpd capacity may cost Rs. 20,000 to Rs.25,000 depending on type
& location. The cost, however, does not increase linearly with increase in
capacity, rather it comes down proportionately as we go for higher capacity
system. The system cost does not include the cost of cold water tank, & its
stand which is required if overhead tank is not installed in a house/ building.
Cost of hot water insulated pipe line also, may be extra if number of
bathrooms are more than one. Additional cost towards all these
components may increase by 5 to 10%.
6. Avoid putting of electricity back up in storage tank of solar system. If you
have electric geyser of say less then 10 lpd capacity or an instant geyser it
would be better if you connect the outlet line of solar system with inlet of
geyser & set thermostat at 40oC. Your geyser will start only when you get
water below 40oC from solar system and will switch off when temperature
goes above say 42oC or so. This will save lot of electricity and heat water
according to your requirement. However, if you have storage geyser of
higher capacity, better to have a separate tap for solar system and use
your electric geyser when you don’t get hot water from solar water heater.
Hot Water Storage Tank:
The tanks are generally made of stainless steel to avoid corrosion and are
insulated to reduce heat losses. They are also fitted with electrical heater
as a backup during monsoon days. The tanks may also be made of G.I.
Cold Water Tank & Pipelines:
Cold water comes from the over head tank. Hot water from the system is
transferred to various utility points through insulated pipelines. A heat
exchanger may be provided when the water is hard.
Economics (Tentative):
• A 100 lpd domestic solar water heating system (SWHS) can cater to a
family of 4-5 persons and costs about Rs.20,000 to Rs.25,000
• It saves about 1500 units of electricity per annum equivalent to about
Rs.5000/- per year.
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Reference: http://kredlinfo.in/solaroffgrid/solar%20water%20heater.pdf
