The document discusses different types of solar collectors. It describes flat plate collectors, evacuated tube collectors, and focusing collectors, including line focus and point focus collectors. It also discusses cylindrical parabolic collectors, central receiver collectors, and compound parabolic collectors. The document outlines the advantages of solar collectors such as reduced energy costs over time and the ability to heat water for personal use or generate electricity. It also notes some disadvantages like increased maintenance needs and optical losses.

1. Lecture Notes on Solar Collectors
for
Open Educational Resource
on
Fundamentals of SPV Thermal Engineering (EC362)
by
Dr. Piyush Charan
Assistant Professor
Department of Electronics and Communication Engg.
Integral University, Lucknow

2. Contents
• Solar collectors
• Types of Solar Collectors and their structures
– Flat Plate Collectors
– Evacuated Tube Collectors
– Focusing Collectors
• Line Focus Collector
• Point Focus Collector
– Types of Focusing Collectors
• Cylindrical parabolic collector
• Central receiver collector
• Compound parabolic collector
• Efficiency aspect of Solar Collectors
• Advantages of Solar collectors
• Disadvantages of Solar collectors
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 2

3. Solar Collectors
• A solar collector is a device that collects
and/or concentrates solar radiation from the
Sun. These devices are primarily used for
active solar heating and allow for the heating
of water for personal use.
• These collectors are generally mounted on the
roof and must be very sturdy as they are
exposed to a variety of different weather
conditions.
• The use of these solar collectors provides an
alternative for traditional domestic water
heating using a water heater, potentially
reducing energy costs over time.
• As well as in domestic settings, a large number
of these collectors can be combined in an array
and used to generate electricity in solar
thermal power plants.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 3
Figure 1. Solar Collector

4. Types of Solar Collectors
• There are many different types of solar collectors, but all of them are
constructed with the same basic premise in mind. In general, there is some
material that is used to collect and focus energy from the Sun and use it to
heat water.
• The simplest of these devices uses a black material surrounding pipes that
water flows through. The black material absorbs the solar radiation very
well, and as the material heats up the water it surrounds.
• This is a very simple design, but collectors can get very complex.
• Absorber plates can be used if a high temperature increase is not
necessary, but generally devices that use reflective materials to focus
sunlight result in a greater temperature increase.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 4

5. 1. Solar Flat Plate Collectors
• These collectors are simply metal boxes that have
some sort of transparent glazing as a cover on top
of a dark-colored absorber plate.
• The sides and bottom of the collector are usually
covered with insulation to minimize heat losses to
other parts of the collector.
• Solar radiation passes through the transparent
glazing material and hits the absorber plate. This
plate heats up, transferring the heat to either water
or air that is held between the glazing and absorber
plate.
• Sometimes these absorber plates are painted with
special coatings designed to absorb and retain heat
better than traditional black paint. These plates are
usually made out of metal that is a good conductor
- usually copper or aluminum.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 5
Figure 2. Flat Plate Solar Collector

6. 2. Evacuated-Tube Collector
 This type of solar collector uses a series of evacuated tubes to heat water for use.
 These tubes utilize a vacuum, or evacuated space, to capture the suns energy while
minimizing the loss of heat to the surroundings.
 They have an inner metal tube which acts as the absorber plate, which is connected to
a heat pipe to carry the heat collected from the Sun to the water. This heat pipe is
essentially a pipe where the fluid contents are under a very particular pressure.
 At this pressure, the "hot" end of the pipe has boiling liquid in it while the "cold" end
has condensing vapor.
 This allows for thermal energy to move more efficiently from one end of the pipe to
the other.
 Once the heat from the Sun moves from the hot end of the heat pipe to the condensing
end, the thermal energy is transported into the water being heated for use.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 6

7. 01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 7
Figure 3.
A diagram of an evacuated tube solar collector.

8. Focusing Collectors
• Focusing collector is a device to collect solar energy with high
intensity of solar radiation on the energy absorbing surface.
• A focusing collector is a special form of flat collector modified by
introducing a reflecting ( or refracting) surface (concentrator)
between the solar radiations and the absorber.
• Focusing collectors can have radiation increases from low value of
1.5 to 2, high values of the order of 10,000.
• Reach temperature up to 450-500 ⁰C.
• Receivers can be convex, flat, cylindrical or concave and can be
covered with glazing or uncovered.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 8

9. Solar Concentrators and
Receiver Geometries
• There is wide variety of means for increasing the flux of radiation on receivers.
• They can be classified on basis of:
– lenses or reflectors
– By the types of mounting and orienting systems
– By the concentration of the radiation they are able to accomplish
– By materials used of construction, or by orientation
– Concentrator is a component used to increase the intensity of energy flux on a receiver.
• Concentration ratio (CR): It is the ratio of the area of the concentrator aperture to
the energy absorbing area of the receiver.
𝐶𝑅 =
𝐴𝑎
𝐴𝑟
• It is determines the effectiveness of a concentrator.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 9

10. Types of Solar Trackers
• There are two methods by which the sun motion can be readily
tracked.
1. The first is the altazimuth method which requires the tracking device
to turn in both altitude and azimuth. Paraboloidal solar collectors
generally use this system.
2. The second one is the one-axis tracking in which the collector tracks
the sun in only one direction either from east to west or from north to
south.
• Parabolic trough collectors (PTC) generally use this system. These
systems require continuous and adjustment to compensate for the
changes in the sun orientation.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 10

11. 3. Line Focus Collectors
• These collectors, sometimes known as parabolic troughs, use highly reflective
materials to collect and concentrate the heat energy from solar radiation.
• These collectors are composed of parabolically shaped reflective sections
connected into a long trough.
• A pipe that carries water is placed in the center of this trough so that sunlight
collected by the reflective material is focused onto the pipe, heating the
contents.
• These are very high powered collectors and are thus generally used to generate
steam for Solar thermal power plants and are not used in residential
applications.
• These troughs can be extremely effective in generating heat from the Sun,
particularly those that can pivot, tracking the Sun in the sky to ensure
maximum sunlight collection.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 11

12. 01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 12
Figure 4.
A diagram of a typical Line Focus Collector

13. 4. Point Focus Collectors
• These collectors are large parabolic dishes composed of some reflective
material that focus the Sun's energy onto a single point. The heat from
these collectors is generally used for driving Stirling engines.
• Although very effective at collecting sunlight, they must actively track the
Sun across the sky to be of any value. These dishes can work alone or be
combined into an array to gather even more energy from the Sun.
• Point focus collectors and similar apparatuses can also be utilized to
concentrate solar energy for use with Concentrated photovoltaics.
• In this case, instead of producing heat, the Sun's energy is converted
directly into electricity with high efficiency photovoltaic cells designed
specifically to harness concentrated solar energy.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 13

14. 01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 14
Figure 5.
A Point Focus Collectors

15. Types of Concentrating or Focusing
Collectors
• There are different types of concentrating or
focusing collector depending upon the
concentrator and receiver geometries.
• There are as Follows:
a. Cylindrical parabolic collector
b. Central receiver collector
c. Compound parabolic collector
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 15

16. a. Cylindrical Parabolic Collector
• It is a system consisting of a parabolic reflector and having receiver
at its focal point.
• The concentration ratios are very high and therefore can be used
where high temperatures are required.
• In a cylindrical system, the concentration ratio is lower than
paraboloid counterparts.
• In both the cases the receiver is placed at the focus, i.e. along the
focal line in cylindrical parabolic system and at the focus point in
paraboloidal system.
• The parabolic geometry is given by the relation 𝑌2
= 4𝑎𝑋
where; a = semi major axis.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 16

17. 01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 17
Figure 6.
A typical cylindrical parabolic collector

18. b. Central Receiver Collector
• The concept of central receiver collector is simple.
– 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.
– To implement the concept, one needs a field of mirrors provided with
the means of directing reflected sunlight to a central location, or a
location at one edge of the field of mirrors.
– In the typical central receiver, the reflector is composed of many
smaller mirrors each with its own heliostat to follow the sun.
– The heliostat are generally located in the horizontal plane, but when the
situation is favorable, can simply follow the existing terrain.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 18

19. • The basic difference between a
single mirror concentrator and the
heliostat system is that the heliostat
system has a dilute mirror.
• This diluteness is generally termed
as the fill factor.
• A central receiver with a fill factor
of 40% means that 40% of the land
area is covered by mirrors.
• Schematic arrangement of central
receiver- heliostat array.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 19
Figure 7.
A typical heliostat collector

20. c. Compound Parabolic Collector (CPC)
• It is possible to concentrate solar radiation by a factor of 10 without
diurnal tracking using this type of collector.
• A compound parabolic concentrating collector is show in Fig. ( in
next slide)
• It consists of two parabolic reflectors which funnel the radiation
from aperture to absorber.
• The right and left half belong to different parabolas (hence the name
compound parabolic concentrator).
• The axis of the right branch, for instance, makes an angle Ѳc , with
the collector mid plane, and its focus is at A. At the end points C and
D, the slope is parallel to the collector mid-plane.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 20

21. • The compound parabolic collector
developed by Winston represents what may
be called as ideal concentrator in the sense
that for a given field of view it achieves the
maximum possible concentration ratio
given by:
𝐶𝑅 =
𝑊
𝑏
=
1
sin 𝜃𝑐
• Where,
 W = entrance aperature
 b = exit aperture, covered by the absorber
 Ѳc = field of view (half angle)
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 21
Figure 8.
Geometry for compound parabolic concentrator (CPC)

22. Efficiency aspects of Solar Heating
through collectors
• Colder water supply temperatures increase system efficiency, since the
fluid being heated loses less heat to the surrounding air until it reaches
higher temperatures.
• Colder air temperatures reduce system efficiency by increasing the loss of
heat from the collectors to the air.
• Potential for system freezing is a serious problem, and many solutions
result in reducing system efficiency.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 22

23. Advantages of Concentrating Type
Collectors
• Surface required less material or provide high collection of
radiation.
• For a concentrator system the cost per unit area of solar collecting
surface is therefore potentially less than that of the flat-plate
collector.
• Heat loss rate is less than flat-plate collection low maintenance.
• Can be used for power generation.
• We can get high concentration or radiation.
• Litter or no antifreeze is required to protect the absorber in
concentrator systems.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 23

24. Disadvantages of Concentrating Type
Collectors
• Only beam radiation collected because diffuse component cannot be
reflected and is thus lost.
• Additional requirement of maintenance particularly to retain the
quality of reflecting surface against dirt, weather, oxidation etc.
• Non- uniform flux on the absorber whereas flux in flat-plate
collector is uniform.
• Additional optical losses such as reflectance loss and the intercept
loss, so they introduce additional factors in energy balances.
• These disadvantage have restricted the utility of focusing collectors
and no long time practical applications of focusing collectors other
than for furnaces are being made.
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 24

25. Thanks!!
Contact:
piyush@iul.ac.in
piyushcharan@ieee.org
01 Dec 2021 Dr. Piyush, Charan Dept. of ECE, Integral University, Lucknow 25