2. Solar energy
Solar energy is radiant light and heat from the
Sun that is harnessed using a range of ever-
evolving technologies such as solar heating,
photovoltaics, solar thermal energy .
It is the largest source of energy received on
Earth, but its intensity on the earth’s surface is
quite low.
Solar energy is rapidly becoming the ultimate energy
source because of its non-pollluting charcter and its
inexhaustible supply .
3. THE SUN
Sun is the ultimate source of most of our
renewable energy supplies.
The sun is an enormous nuclear fusion reactor
which converts hydrogen into helium at the rate of
4 million tonnes per second.
It radiates energy by virtue of high surface temp,
app. 6000°C.
4. SOLAR ENERGY COLLECTOR
Solar energy collector is a device which absorbs
the incoming solar radiation, converts it into heat,
and transfers this heat to a fluid (usually air,
water, or oil) flowing through the collector.
The solar energy thus collected is carried from
the circulating fluid either directly to the hot water
or space conditioning equipment, or to a thermal
energy storage tank from which can be drawn for
use at night and/or cloudy days.
5. Solar collectors are classified as low, medium or high
temperature collectors. Low –temperature collectors
are used for smaller non-intensive requirements.
Medium-temperature collectors are used for heating
water or air for industrial and commercial use. High
temperature collectors concentrate sunlight using
mirrors or lenses and are used for fulfilling heating
requirements up to 400ᴼC/20 bar pressure in
industries.
Temperature range of solar thermal technologies:-
Temp. range
Low temperature heat <150˚C
Medium temperature heat 150-400ᴼC
High temperature heat >400ᴼC
6. Types of Solar Collectors
Non-Concentrating
collectors
Concentrating
Collectors
In these type, the
collector area is the
same as the absorber
area.
The whole solar panel
absorbs light.
Non concentrating
solar collectors are
generally used for low
and medium
temperature
Concentrating
collectors have a
larger interceptor than
absorber.
Concentrating
collectors are used for
high temperature
requirements.
8. Non Concentrating Technology
Non concentrating solar thermal collectors are
generally used for low and medium energy
requirements.
Solar water heating is the perfect example of a non –
concentrating
Common collectors used for solar water heaters are -
Flat Plate Collectors and Evacuated Tube Collectors.
type of solar thermal application.
9. Flate Plate Collector
Flat Plate Collectors -consist of a thin metal box with
insulated sides and back, a glass or plastic cover (the
glazing) and a dark colour absorber. The glazing
allows most of the solar energy into the box whilst
preventing the escape of much of the heat gained.
The absorber plate is in the box painted with a
selective dark colour coating, designed to maximize
the amount of solar energy absorbed as heat.
Running through the absorber plate are many fine
tubes, through which water is pumped.
As the water travels through these tubes, it absorbs
the heat. This heated water is then gathered in a
larger collector pipe to be transported into the hot
water system.
10. Components of flat plate
collector:-
1. A metallic flat absorber plate
2. Tubes or Channels
3. A transparent toughened glass sheet
4. Fibre glass insulation
11. Evacuated Tube Collector
Evacuated tube collectors are more modern and more
efficient in design.
In evacuated tube systems, this heat loss is reduced
by almost totally eliminating conduction and
convection heat losses.
These can heat water to much higher temperatures
and require less area. However, they are also
correspondingly more expensive.
Instead of an absorber plate, water is pumped though
absorber tubes (metal tubes with a selective solar
radiation absorbing coating), gaining heat before
going into the collector pipe.
12. Concentrating Collector
Concentrating collector is a device to collect solar
energy with high intensity of solar radiation on the
energy-absorbing surface. A concentrating collector
is a special form of flat plate collector modified by
introducing a reflecting (or refracting) surface
(concentrator) between the solar radiation and the
absorber.
Here the receiving area of solar radiation is several
times greater than the absorber area and the
efficiency is high. Mirrors and lenses are used to
concentrate sun rays on the absorber. The
temperature of working fluid can be raised only up to
500 0C. For better performance, the collector is
mounted on a tracking equipment to always face the
14. Types of Concentrating
Collectors
There are different types of concentrating or focusing
collector
These are as follows:
A. Point Focus Technology
1. Fresnel Reflector based dish (ARUN dish)
2. Dual axis tracked paraboloid dish
B. Line Focus Technology
1. Parabolic troughs collectors (PTC)
2. Linear Fresnel Reflector (LFR)
C. Non Focusing Technology
1. Compound Parabolic collectors (CPC)
15. Fresnal Reflector Based Dish
Fresnel Reflector Based Dish (ARUN Dish) is made
from panels of flat mirrors mounted on a frame such
that the incident sunlight is reflected on to a cavity
receiver which is specially designed to reduce heat
losses.
Usually Fresnel Dishes are large and could have an
aperture area of 100 m2 or 160 m.
The reflector and the receiver mounted on top are
moved to track the Sun such that the reflectors faces
the Sun at all times throughout the year.
Fresnel Dishes have high efficiencies throughout the
year.
17. Paraboloid Dish Collector
Paraboloid Dish consists of mirrors mounted on a
truss structure such that the incident sunlight is
reflected on to a cavity receiver which is specially
designed to reduce convective and radiation heat
losses.
The entire array of mirrors and receiver move to track
the sun.
The reflector and receiver mounted on top are moved
to track the sun such that the reflector faces the sun
at all times throughout the year.
These systems have light structures.
Paraboloid Dishes have high efficiencies throughout
the year.
19. Parabolic Trough Concentrator (PTC)
Parabolic Trough Concentrators (PTC) are troughs
made from shaped metal and coated with a reflecting
material such as highly polished metal (usually
aluminium) or metallised plastic which can withstand
sunlight as well as rain and the elements.
These surfaces reflect the incident sunlight on to a
metallic collector pipe (the receiver) that runs axially
along the trough.
PTCs can be connected in series on a common axis.
21. Linear Fresnel Reflecting
Concentrator
Linear Fresnel Reflecting Concentrator (LFRC) is
made from multiple strips of straight reflecting
material which are mounted on specially designed
frames.
The mirrors are arranged in a fresnelized manner
which reflects the incident sunlight on to a focal line of
metallic collector pipe (the receiver) that runs axially
above the array of reflectors.
The reflector strips are moved such that they always
reflect the incident sunlight on to the receiver tube.
23. Heliostat field collectors
Heliostat field collectors (HFCs) also known as “Power
Tower” or “Central Receiver Plant”.
In order to avoid the cost and heat losses in transporting
a working fluid to a central location, use of sunlight itself
as the transfer medium is proposed.
In the typical central receiver, the reflector is composed
of many smaller mirrors each with its own heliostat to
follow the sun.
They are nearly flat mirrors that collect and concentrate
the solar energy on a tower-mounted receiver located
100 to 1000 meters distant.
To maintain the sun’s image on the solar receiver,
heliostats tracks the sun throughout the day.
25. Advantages of HFCs
1. They solar energy is collected optically and
transferred to a single receiver point, thus minimizing
thermal-energy transport requirements;
2. They typically achieve concentration ratios of 100–
1500 and so are highly efficient both in collecting
energy and in converting it to electricity;
3. They can conveniently store thermal energy;
4. They are quite large (generally more than 10 MW)
and thus benefit from economies of scale.
