2. Contents
1.1 Learning Outcomes
1.2 Solar thermal Energy Definition
1.3 Why use solar thermal energy?
1.4 Solar radiation/Solar Constant definition
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3. 1.1 Learning Outcomes
The students will able to understand use of solar thermal energy.
The students will be able to identify the different solar radiations and
its method of measurements.
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4. 1.2 Solar Thermal Energy
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Solar thermal energy is a form of energy and a technology for harnessing solar
energy to generate thermal energy or electrical energy for use in industry, and in the
residential and commercial sectors.
5. 1.3 Why use solar thermal energy?
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âť– Solar thermal energy is mostly used because of big efficiency compared
with other renewables.
âť– It is becoming cheaper than other alternatives.
âť– Solar thermal energy usage is environmentally friendly.
6. 1.3.1 To use solar thermal energy are three different ways:
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â–Ş The first method collects
the energy of the sun to
heat water or air for direct
use in solar home heating.
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• The second method is used
by large power utilities to
indirectly create electricity
through concentrated solar
heat energy.
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• The third method, known as
passive solar, leverages energy
efficiency and the design of a
building to regulate the
amount of solar energy it
receives in order to regulate
it’s temperature.
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The Solar Radiation is subdivided into two parts:-
â–Ş Extraterrestrial Radiation(S)
â–Ş Terrestrial Radiation(L)
the above division is based on location of measurement.
The typical values of solar constant are
S= 1.366 KW/m^2
L= 1 KW/m^2 per hour of day light
1.4 Solar Radiation
10. 1.4.1 Extraterrestrial Radiation
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• The solar radiation at the top of the earth's atmosphere is called
extraterrestrial radiation and the current accepted value for this “solar
constant” is 1366 W/m2.
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1.4.2 TERRESTRIAL SOLAR RADIATION
▪ It is the electromagnetic radiation which originates from earth’s atmosphere to earth’s
surface.
▪ When the terrestrial solar radiation reaches the earth’s surface, it is broken into two
components i.e., diffuse radiation and beam radiation.
â–Ş Beam Radiation is the solar radiation which moves through the atmosphere in a straight
line without being scattered, reflected or absorbed by particles in the air.
â–Ş Diffuse Radiation is the solar radiation which is being scattered, reflected or absorbed
by the particles while passing through the atmosphere but ultimately reaches the earth’s
surface.
19. Contents
•Solar collector
•Types of Solar Collectors
•Flat Plate Collectors
•Evacuated Tube Collectors
•Line Focus Collectors
•Point Focus Collectors
•Concentrating Collector
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20. • Learning Outcomes
The students will learn the basic concept of Solar Collectors.
The students will be able to describe the working of various types of
Solar Collectors.
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21. • Solar Collector
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âš« A solar collector is a device that collects and/or concentrates solar
radiation from the Sun.
âš« These devices are primarily used for active solar heating and allow for the
heating of water for personal use.
âš« The use of these solar collectors provides an alternative for
traditional domestic water heating using a water heater, potentially
reducing energy costs over time.
22. Types of Solar Collectors
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23. • Evacuated Tube Collector
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âš« This type of solar collector uses a series of evacuated tubes to heat water for use.
âš« These tubes utilize a vacuum, or evacuated space, to capture the suns energy while
minimizing the loss of heat to the surroundings.
âš« 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.
âš« 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 vapour.
24. Line Focus Collectors
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•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.
25. Point Focus Collectors
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• These collectors are large parabolic dishes composed of some reflective material that
focus the Sun's energy onto a single point.
• 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.
• Point focus collectors and similar apparatuses can also be utilized
to concentrate solar energy for use with Concentrated photovoltaics.
26. • Concentrating Collector
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âš« A collectors are oriented to track the sun so that the beam radiation will be
directed onto the absorbing surface Collector: Receiver and the concentrator.
âš« Receiver: Radiation is absorbed and converted to some other energy form
(e.g. heat).
âš« Concentrator: Collector that directs radiation onto the receiver. The aperture
of the concentrator is the opening through which the solar radiation enters the
concentrator
27. • Concentrating Collector
Fresnel Lens: An optical device for concentrating light that is made of concentric rings that
are faced at different angles so that light falling on any ring is focused to the same point.
Parabolic trough collector: A high-temperature (above 360K) solar thermal concentrator
with the capacity for tracking the sun using one axis of rotation.
It uses a trough covered with a highly reflective surface to focus sunlight onto a linear
absorber containing a working fluid that can be used for medium temperature space or
process heat or to operate a steam turbine for power or electricity generation.
Central Receiver: Also known as a power tower, a solar power facility that uses a field of
two-axis tracking mirrors known as heliostat (A device that tracks the movement of the sun).
Each heliostat is individually positioned by a computer control system to reflect the sun's
rays to a tower-mounted thermal receiver.
The effect of many heliostats reflecting to a common point creates the combined energy of
thousands of suns, which produces high-temperature thermal energy.
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28. • Parabolic Concentrator
If the incident beam of parallel rays is even slightly off normal to the mirror aperture, beam
dispersion occurs, resulting in spreading of the image at the focal point.
For a parabolic mirror to focus sharply, therefore, it must accurately track the motion of the
sun to keep the axis (or plane) of symmetry parallel to the incident rays of the sun.
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29. • Parabolic and Cylindrical Trough Concentrator
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Parabolic trough must track about its linear axis so that when the sun’s rays are projected
onto the plane of curvature, they are normal to the trough aperture.
30. • Parabolic and Cylindrical Trough Concentrator
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The aperture of a cylindrical trough need not track at all to maintain focus.
To avoid a dispersed focus, cylindrical troughs would have to be designed with low rim
angles in order to provide an approximate line focus.
The advantage of a cylindrical mirror geometry is that it need not track the sun in any
direction as long as some means is provided
to intercept the moving focus.
36. Learning Outcomes
The students will able to describe solar geometry and its fundamental
parameters.
The students will be able to calculate solar insolation at specific place
and time.
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37. Introduction
Solar Geometry: Solar geometry provides the parameters to estimate the solar radiation
(Insolation) receive at specific time and place.
The fundamental parameter are following:
•Declination angle (δ)
•Hour Angle (ω)
•Latitude’s angle (φ)
•Inclination Angle/ Solar altitude (α)
•Zenith angle (θz)
•Azimuth angle (γs)
To describe above parameters we have to know the special coordinates where these are
defined.
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38. Earth centric coordinate
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• It is a similar to spherical coordinate system with
certain different axis.
• Here a sphere is considered as a earth and z axis
considered as Polar axis (p)
• Origin is consider as centre of earth which is a
reference point.
• x axis is consider as Meridian axis (m) which define as
line joining centre of earth to intersection of meridian
(0Ëš) and equator.
• y axis is consider as east of meridian (e).
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Locale centric coordinate
• It is similar to rectangular coordinate with
certain change in axis.
• It define with respect to a point on earth’s
surface.
• The figure shows both coordinate where
horizon plane is tangential to meridian which
defines the locale centric coordinate.
• Axis orthogonal to horizon plane is called
zenith axis (Z).
• Axis perpendicular to zenith axis (Z) in the
direction of south called south axis (S) similarly
in direction of east is east axis(E).
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Fundamental Parameters
• Insolation line is imaginary line joining
centre of earth to centre of sun.
• Declination angle (δ) or solar declination is
angle of Insolation line from equatorial plane.
• To measure the solar declination we use
following relation
δ = 23.45*sin [ 0.9863 *( N + 284 ) ]
where the argument of the sine here is in
degrees and N denotes the number of days
since January 1.
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Fundamental Parameters
•Hour angle (ω) the angular distance between
meridian axis and projection of insolation line in
equatorial plane.
• To measure the hour angle we use following
relation
ω= 15*(t-12) in degree
Where
t denotes Local Solar time which is given by
equation
t= IST±4*(standard time longitude-location’s
longitude)+ time correction
If IST is before/at 12 noon then + sign applicable
else negative.
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Fundamental Parameters
•Angle of Latitude (φ) the vertical
angle between line joining center of
earth to specific point of interest and
its projection in equatorial plane.
• φ measures the angle with respect
to equator.
• Value of φ will be ±90 at poles.
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Fundamental Parameters
•Inclination angle (α) the vertical angle
between sun’s ray and its projection in
horizon plane.
• α measures by following formula
α= 90-θz
sin(α)=sin φ *sin δ +cosφ *cosδ *cos ω
• Where θz denoted zenith angle.
• Value of α will be 0 degree at sun rise and
sunset.
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Fundamental Parameters
•Zenith angle (θz) the vertical angle between
sun’s ray and normal to horizon plane.
• θz measures by following formula
cos(θz)=sin φ *sin δ +cosφ *cosδ *cos ω
• Where θz =zenith angle, ω= hour angle, φ=
latitude angle, δ= declination angle.
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Fundamental Parameters
•Azimuth angle (γs) the angle on horizon
plane between line due north and projection
of sun’s ray in horizon plane.
• γs measures by following formula in degree
Where θz =zenith angle, ω= hour angle, φ=
latitude angle, δ= declination angle.
53. Contents
I. Learning Outcomes
II. Introduction
III. Types of Solar Collectors
IV. Flat Plate Collectors
V. Concentrating Collectors
VI. Radiation incident on Solar Collectors
VII. Performance evaluation of Solar Collector
VIII. Material Selection
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54. 1. Learning Outcomes
The students will be able to explain solar collector.
The students will able to list different kind of solar collectors.
The students will be able to calculate the performance evaluation of flat plate
collector.
The students will be able to analyze the different parameters required for material
selection for flat plate collector.
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55. 2. Introduction
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A solar collector is a receiving device which
absorbs the incident solar radiation and heat
through a fluid like water or air.
Solar radiation converted in to useful heat can be
used as such or converted into electrical power.
Collectors can be classified into low temperature,
medium temperature and high temperature
collectors.
Mainly two types of collectors are there
Flat plate collectors
Concentrating collectors
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3. Classification of solar collectors
1 - Flat-plate collectors – The absorbing surface is approximately as large as the overall
collector area that intercepts the sun rays .
2 - Concentrating collectors – Large areas of mirrors or lenses focus the sun light onto a
smaller absorber .
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Flat-plate collectors, developed by Hottel and Whillier in the 1950s, are the most
common type of solar collector which are widely used for domestic household
hot-water heating and space heating, where the demand temperature is low.
Flat plate collector is basically a black surface that is placed at a convenient path of a
sun.
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Cross sectional view of solar flat
plate collector
They consist of..
1. A dark flat-plate absorber.
2. A transparent cover that reduces heat losses,
called “GLAZING”.
3. A heat-transport fluid (air, antifreeze or water)
to remove heat from the absorber.
4.A heat insulating backing
5. Flow passage
6. Enclosure.
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Components of solar flat plate collector
Absorber plate:
It is usually made of copper , steel or plastic . The surface is covered with a flat
black material of high absorption . If copper or steel is used it is possible to apply a
selective coating that maximizes the absorption of solar energy and minimizes the
radiation emitted by plate.
Flow passages:
The flow passages conduct the working fluid through the collector. If the working
fluid is a liquid , the flow passage is usually a tube that is attached to or is a part of
absorber plate. If the working fluid is air , the flow passage should be below the
absorber plate to minimize heat losses.
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Components of solar flat plate collector
Cover plate:
To reduce convective and radiating heat losses from the absorber , one or two
transparent covers are generally placed above the absorber plate . They usually be
made from glass or plastic.
Insulation:
These are some materials such as fiberglass and they are placed at the back and
sides of the collector to reduce heat losses.
Enclosure:
A box that the collector is enclosed in holds the components together, protect them
from weather ,facilitates installation of the collector on a roof or appropriate frame.
70. Learning Outcomes
The students will able to describe direct and indirect hot water system
and the applications of flat plate collector .
The students will be able to design flat plate collector.
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Applications
• It has many applications in a medium temperature range ≅100 °C from domestic to preheating
to industrial sectors.
• Used for household Water/Air heating.
• Used for active and passive space heating and cooling.
• The hot water available from flat-plate collectors can be also used to conserve fossil fuel.
• In meeting electric requirements of rural and remotes areas such as development of solar
cookers, small solar driven refrigeration units, solar water irrigation pumps, solar dryers,
• Used to produce electricity for street lightning.
84. Contents
I. Learning Outcomes
II. Introduction
III. Collector Configurations
IV. Types of Solar Collectors
V. Performance Evaluation of Concentrating Collector
VI. Comparison of performance of different collectors
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85. Learning Outcomes
The students will be able to explain concentrating solar collector.
The students will able to list different kind of concentrating solar collectors.
The students will be able to calculate the performance evaluation of concentrating
solar collector.
The students will be able to Compare the performance of different collectors
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86. Introduction of concentrating solar collector
• Converging solar radiation from large area to small area
• Beam radiation utilized
• Optical methods( reflection, refraction)
• Solar tracking required
• Diffused radiation cannot be concentrated
• High temp attained.
• Flexible construction
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87. Concentrating Collectors components
•Collectors are oriented to track the sun so that the beam radiation will
be directed onto the absorbing surface
•Collector: Receiver and the concentrator
•Receiver: Radiation is absorbed and converted to some other energy
form (e.g. heat).
•Concentrator: Collector that directs radiation onto the receiver. The
aperture of the concentrator is the opening through which the solar
radiation enters the concentrator
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88. Collector Configurations
•a) Tubular absorbers with diffusive back reflector; b) Tubular absorbers with
specular cusp reflector; c) Plane receiver with plane reflector; d) parabolic
concentrator; e) Fresnel reflector f) Array of heliostats with central receiver
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Concentrating
Type
Focus
Type
Point
Focus
Non-Foc
us
(a) Cylindrical parabolic
concentrator
(b) Fixed mirror solar
concentrator
(c) Linear Fresnel lens
collector
(a) Parabolic dish
collector
(b) Hemispherical bowl
mirror concentrator
(c) Circular Fresnel lens
collector
(d) Central Tower
receiver
(a) Modified flat plate
collector
(b) Compound parabolic
concentrating type
91. Concentration Types
•Planar and non-concentrating type which provides concentration ratios
of up to four and are of the flat plate type.
•Line focusing type produces a high density of radiation on a line at the
focus. Cylindrical parabolic concentrators are of this type and they could
produce concentration ratios of up to ten.
•Point focusing type generally produce much higher density of radiation
in the vicinity of a point. Paraboloids are examples of point focus
concentrators.
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92. Concentrating Collectors
•Fresnel Lens: An optical device for concentrating light that is made of
concentric rings that are faced at different angles so that light falling on
any ring is focused to the same point.
•Parabolic trough collector: A high-temperature (above 360K) solar
thermal concentrator with the capacity for tracking the sun using one axis
of rotation. It uses a trough covered with a highly reflective surface to
focus sunlight onto a linear absorber containing a working fluid that can
be used for medium temperature space or process heat or to operate a
steam turbine for power or electricity generation.
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93. Concentrating Collectors
•Central Receiver: Also known as a power tower, a solar power facility
that uses a field of two-axis tracking mirrors known as heliostat (A device
that tracks the movement of the sun). Each heliostat is individually
positioned by a computer control system to reflect the sun's rays to a
tower-mounted thermal receiver. The effect of many heliostats reflecting
to a common point creates the combined energy of thousands of suns,
which produces high-temperature thermal energy.
•In the receiver, molten nitrate salts absorb the heat energy. The hot salt is
then used to boil water to steam, which is sent to a conventional steam
turbine-generator to produce electricity.
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