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UNIT-1 Material.pdf
1. ALTERNATIVE SOURCES OF ENERGY
Professional Elective- III (20ME4701C)
COURSE OUTCOMES:
Upon successful completion of the course, the student will be able to
1. Demonstrate Different alternate sources of Energy and energy conversion
methods.
2. Illustrate Solar energy Principles, various solar collectors, energy storage
methods and applications.
3. Summarize various wind energy, biomass energy, Geothermal Energy and
Ocean Energy concepts and applications.
4. Select suitable fuel cell and energy conversion methods.
3. Role and potential of new and renewable
source
Energy
➢Energy is the ability to do work.
➢ The word ‘work’ means transferring energy from one place to another. energy
is neither destroyed nor created. It can only be changed.
➢A systematic study of various forms of energy and its transformations,
involving human observations is called “energy Science”.
➢The applied part of energy science useful for human society is called “energy
Technology”.
➢1785- James Watt found steam engine
4. CLASSIFICATION OF ENERGY RESOURCES
1. Based on Usability of Energy:
✓ Primary Resources: fossil fuels, uranium, hydro energy etc.,
✓ Intermediate Resources
✓ Secondary resources: electrical energy, chemical energy, etc.,
2. Based on Traditional Use:
✓ Conventional: fossil fuels, nuclear, hydro
✓ Non-Conventional: Solar, Wind, etc.,
5. CLASSIFICATION OF ENERGY RESOURCES
3. Based on Long term Availability:
a. Non-Renewable: fossil fuels
b. Renewable: solar, wind, ocean
4. Based on Commercial Application:
a. Commercial energy resources: electricity, petrol, etc.,
b. Non Commercial energy resources: wood, crop residue etc.,
6. 5. Based on Origin:
a. Fossil fuel energy
b. Nuclear
c. Hydro
d. Solar
e. Wind
f. Biomass
g. Geothermal
h. Ocean
CLASSIFICATION OF ENERGY
RESOURCES
7. Renewable Energy
➢ Renewable energy is energy which is generated from
natural sources i.e. sun, wind, rain, tides and can be
generated again and again as and when required.
➢ They are available in plenty and by far most the cleanest
sources of energy available on this planet.
➢ For ex: Energy that we receive from the sun can be used
to generate electricity.
➢ Similarly, energy from wind, geothermal, biomass from
plants, tides can be used to generate energy
8. ➢Non-Renewable energy is energy which is taken from
the sources that are available on the earth in limited
quantity and will vanish fifty-sixty years from now.
➢Non-renewable sources are not environmental
friendly and can have serious affect on our health.
➢They are called non-renewable because they can
not be re-generated within a short span of time.
➢Non-renewable sources exist in the form of fossil fuels,
natural gas, oil and coal.
Non-Renewable Energy
9. Advantages of using non-conventional
sources of energy
✓ They are inexhaustible – they will always be available – they
are renewable
✓ They are clean and Environment friendly
✓ There are several types – so one or more of them is present
in each country
✓ Most natural sources can be used on a small scale and
serve local needs therefore cutting costs of transmitting the
energy
✓ Low gestation period
10. X High initial cost of investment.
X Solar energy can be used during the day time
X Geothermal energy has side effects too.
▪ It can bring toxic chemicals beneath the earth surface onto the
top and can create environmental changes.
X Hydro energy- expensive and also affects natural flow and wildlife.
X Wind energy- choose suitable site to operate them. Also, they can
affect bird population as they are quite high.
X Low Yield Ratio
X Uncertainty of availability
X Costly to transport energy
Dis-Advantages of using non-conventional sources of
energy
11. Solar Energy Option
ADVANTAGES:
✓ Clean
✓ Inexhaustible
✓ Abundantly and universally available
✓ More predictable than wind energy
LIMITATIONS:
X Dilute form of energy
X Availability is intermittent and
uncertain
• Even over the vast distance, an enormous amount of
energy reaches Earth from the sun.
• One Astronomical Unit = 1.495X1011m
12. SOLAR ENERGY- THE SUN
• Basic source of energy
• Available in the form of electro magnetic radiation
• Largest sphere of very hot gases
• Heat is generated by fusion reactions
• Diameter of Sun =1.39x106 km
• Sun subtends an angle of 32’ at earth’s surface
• The beam /direct radiation is parallel to earth’s surface
• Brightness of sun is assumed to be uniform through out the sphere for
engg. calculations
13. THE EARTH
❖Diameter of Earth =1.27x104
km
❖ Earth rotation about its own
axis takes 24 hours
❖Revolution around sun takes
365.25 days
❖Its axis is inclined at an angle of 23.50.
❖The earth reflects 30% of sunlight falls on it known as
ALBEDO
15. ➢ The Sun generates an enormous amount of energy- app 1.1x1020
KWH/second
➢ The earth’s outer atmosphere intercepts about 1.5x1018
KWH/Year
➢ Due to REFLECTION, SCATTERING AND ABSORPTION by gases and
other particles in earth’s atmosphere only 47%
(7x1017KWH/Year)of energy reaches the surface of earth
SOLAR ENERGY ON EARTH
16. ➢ Solar radiation is received as
✓ Direct Radiation
✓ Diffuse Radiation
➢ Global radiation = Direct Radiation + Diffuse
Radiation + Reflected Radiation
➢ At any moment the Amount of incident
energy /unit area/ day depends on
✓ Solar radiation Geometry
✓ Local Climate
✓ Inclination of collecting surface
17. Solar constant (Isc)
➢ A measure of flux density
➢ Def: The amount of solar radiation received per unit time (or Rate of
solar radiation) per unit area that would incident on a plane perpendicular
to the rays, on earth’s outer atmosphere, at a mean distance of earth from
sun.
Isc =1367W/m2
➢ Solar constant includes all types of solar radiation.
➢ Hence avg. incoming solar radiation is calculated by taking the angle of
incidence into account
18. ❖The variation in this to solar constant is because of
i) Variation in solar radiation emitted by sun(±1.5%)
ii) Variation in distance arising b/w earth and sun because of Earth’s elliptical
Path (±3%)
EXTRA TERRESTRIAL AND TERRESTRIAL RADIATIONS
Iext = Isc[1.0+0.033cos(360n/365)]W/m2
❖Solar radiation incident on the
outer atmosphere of the earth
is known as Extra terrestrial
Radiation (Iext)
19. ❖ Measured w.r.t solar noon, when the sun is exactly at the
observer’s meridian.
❖ Sun traverses each degree longitude in 4 min.
❖ Solar Time = Std. Time ± 4(Lst-Lloc)+E
Where,
❖ Lst – standard longitude of the country
❖ Lloc- local longitude
❖ Equation of time, E =9.87Sin2B-7.53CosB-1.5Sin B min.
❖ Where B= (360/364)(n-81)
❖ n= Day of the Year starting from
1st January
SOLAR TIME (Local Apparent Time)
20. solar Radiation Geometry
Latitude or Angle of latitude(φ): The
latitude angle is the angle between a line
drawn from a point on the earth’s surface to
the center of the earth and the earth’s
equatorial plane.
Declination angle (δ):
If a line is drawn between the center of the
earth and the sun, the angle between this
line and the earth's equatorial plane is called
the declination angle (δ).
Observer’s meridian at P
δ = 23.45 x sin[(360/365)(284+n)] degrees
21. Hour angle (ω): is the angular distance between the meridian of the
observer and the meridian whose plane contains the sun.
(or) The hour angle at any moment is the angle through which the earth
must turn to bring the meridian of the observer directly in line with the sun
rays.
ω=[Ts-12:00] x 15,
where ω=Hour Angle(Degrees) , Ts = Solar time
ω +ve in afternoon and –
ve in fore noon since at
solar noon the hour angle
is zero
22. Solar azimuth angle (γs): measured
clockwise on the horizontal plane, angle
between due south and the projection of
the sun’s central ray.
Solar altitude angle (α): is defined as
the angle between the central ray from
the sun, and its projection on horizontal
plane containing the observer.
Solar zenith angle (θz): Angle between
the sun ray and the normal to the
horizontal plane.
23. Slope or Tilt Angle(β): It is the angle
between the inclined plane surface of
collector and the horizontal.
+ve when sloping is towards south
Surface azimuth angle(γ): It is the angle
in the horizontal plane , between the line
due south and the horizontal projection of
the normal to the inclined plane surface.
+ve when measured from south towards
west.
24. Angle of incidence (θi):
It is the angle between the sun’s ray incident on the earth plane surface and
the normal to that surface.
Expression for θi can be given as,
cos θi= (cos φ cos β + sin φ sin β cos γ) cosω cosδ + cosδ sinω sin
βsin γ + sinδ (sin φ cos β - cos φ sin β cos γ)
25. Special Cases:
i) For surface facing due south, γ =0
cos θi= cos (φ- β) cosω cosδ + sinδ sin (φ- β)
ii) For a horizontal surface, β = 0, θi = θZ
cos θz= cos φ cosω cosδ + sinδ sin φ
iii) For a vertical surface facing due south
cos θi= - sinδ cos φ+cosω cosδ sin φ
26. Solar day Length:
At sunrise the rays are parallel to the horizontal surface. Then Angle of
incidence, θi = θZ =900
, the corresponding hour angle, ωs from above
eq. becomes
cos θi=0 = cos φ cosωs cosδ + sinδ sin φ
ωs =cos-1 (-tanφ tanδ)
The angle between sunrise and sunset,
2ωs =2cos-1 (-tanφ tanδ)
Since, 150 of hour angle is equivalent to one hr. duration, the duration
of the daylight hours(td) is given by,
td= (2/15) cos-1 (-tanφ tanδ)
27. Measurement of solar Radiation
❖Solar meter: A Solar meter is an instrument used for measuring
the solar radiation. It uses the photovoltaic effect to measure the
amount of solar radiation reaching a given surface.
❖Pyranometers :The Pyranometers are instruments used to
measure the global radiation on a surface (direct and diffuse
radiation).
❖Pyrheliometer: A Pyrheliometer is an instrument for direct
measurement of solar irradiance
❖Sunshine Recorder: A sunshine recorder is a device that records
the amount of sunshine at a given location.
28. # Uses the photovoltaic effect to measure the amount of solar radiation
reaching a given surface.
# It produces an electrical signal as a function of incident light, especially
responds to visible light and its response depends on the temperature of the
cell.
# Solar meter with a silicon cell is able to capture light waves with a spectrum
range of approximately 330nm to 1100nm.
# In order to obtain a measure not influenced by the temperature, the values
measured by a solar meter using the photovoltaic effect must be corrected
according to the temperature of the photovoltaic cell.
# This measurement can be done thanks to a thermocouple, and the fix factor
should have a level of precision is not easy to achieve.
Solar meter
29.
30. ♣ The operating principle is generally based on the measurement of the difference
in temperature between a clear surface and a dark one.
♣ A dark surface can absorb most of the solar radiation, while a clear surface
tends to reflect, and so it absorbs less heat.
♣ The potential difference that is generated in the thermopile due to the
temperature gradient between the two surfaces, allows to measure the value of
global solar radiation incident.
♣ It responds to radiation of all wavelengths, hence measures total power in the
incident spectrum accurately.
♣ It has a thermopile whose sensitive surface consists of circular, blackened, hot
jn. Exposed to sun, the cold jn. being completely shaded.
♣The temp. difference between hot and cold jns. is the fn. of radiation falling on
the sensitive surface.
PYRANOMETER
31. ♣ The sensing element is covered with two hemispherical glass domes to shield
from wind & dust and reduce convection currents.
♣ A radiation shield is provided coplanar with the outer dome to prevent direct solar
radiation from heating the base of the instrument.
♣ The instrument has a voltage output of approximately 9µV/W/m2 and has an
output impedance of 650Ω .
♣ When provided with shadow band to prevent beam radiation from reaching the
sensing element, measures the diffused radiation only.
♣ Inexpensive instruments based on cadmium-sulphide photocells and silicon
photodiodes can also be used but they cannot be accurately
♣ Pyranometers are frequently used in meteorology, climatology, solar
energy studies and building physics
35. ❖ A pyrheliometer is often used in the same setup with a pyranometer.
❖ Typical pyrheliometer measurement applications include scientific meteorological
and climate observations, material testing research, and assessment of the efficiency
of solar collectors and photovoltaic devices.
36. ❖ It is used with a solar tracking system to keep the instrument aimed at the sun
and to get continuous readings.
❖ It uses long collimator tube to collect beam radiation whose field of view is
limited to a solid angle of 5.50 by appropriate diaphragms inside the tube.
❖The inside of the tube is blackened to absorb any radiation incident at angles
outside the collection solid angle.
❖ At the base of the tube a wire wound thermopile is placed which converts heat to
an electrical signal that can be recorded.
❖ The signal voltage is converted via a formula to measure watts per square
metre.
❖ The tube is sealed with dry air to eliminate absorption of beam radiation with in
the tube by water vapour.
❖ The instrument has a voltage output of approximately 8µV/W/m2 and has an
output impedance of 200Ω .
38. ❖ The results provide information about the weather and climate of a
geographical area. This information is useful in meteorology, science,
agriculture, tourism and other fields.
❖This recorder consists essentially of a glass sphere mounted concentrically
in a section of a spherical metal bowl, the diameter of which is such that the
sun`s rays are focused sharply on a card held in the grooves, in the bowl.
❖Three overlapping pairs of grooves are provided in the bowl to taken up
cards suitable for the different seasons of the year.
39. ➢ This instrument measures the duration in hours of bright sunshine during
the course of a day.
➢ The card is prepared from a special paper bearing a time scale.
➢ As the sun moves, the focused bright sunshine burns a path along this
paper.
➢ The length of the trace thus obtained on the paper is a measure of the
duration of the bright sunshine.
40. SOLAR ENERGY APPLICATIONS
➢ Solar Heating/Cooling technique,
➢ Solar Distillation
➢ Solar drying,
➢ Central Power Tower,
➢ Photovoltaic energy conversion.
41. WATER HEATING
➢ Main components: Flat plate collector, storage tank placed at higher level than
collector.
➢ Working:
Water heated by solar energy in the collector automatically flows to the top of
the tank and cold water replaces the bottom of the tank.
FEATURES
➢Auxiliary heating system is provided
for use on cloudy and rainy days.
➢ Used most commonly in olden
days.
➢ Small capacity natural circulation
➢ Low efficiency.
➢ Direct use of solar energy
42. ✓Small capacity domestic water heater in which the fn. of collector and storage tank are
combined in one unit.
✓It consists of a closed shallow rectangular box of 5 to 10 cm deep made of sheet metal
placed in a housing, that supports glass cover, insulated at the bottom and sides.
✓ Water is filled in the morning and with drawn in the evening for use.
✓ Less costly than natural circulation system
✓ Lesser efficiency
43. ➢ For large amount of water requirement large array of flat plate collectors are used.
➢ Forced circulation is maintained with water pump.
➢ Water from the storage tank is pumped through the collector array, where it is heated up
and flows back to the storage tank.
➢ When hot water is withdrawn for use cold makeup water takes its place because of ball
float control.
➢ The pump for maintaining forced circulation is operated by an on off controller which
senses the difference between the exit temp. of water from collectors and that of storage
tank.
➢ The pump is switched off when the temp. difference crosses certain value
44. SPACE HEATING
➢Water is heated in the solar collectors (A) and stored in the tank (B)
➢Energy is transferred to the air circulating in the house by means of the water to air
heat exchanger(E)
➢Two pumps (C) provide forced circulation between the tank and the heat exchanger.
➢Air can also be heated directly in the collectors. The heat is stored in a tank packed
with rocks, pebbles etc,.
➢Space heating is of importance in colder countries where a significant amount of
energy is required for this purpose.
45. Passive Method of Space Heating
→Space heating with passive method gives a fair degree of comfort.
→Thermal energy flows through the living space by natural means with out the help of
any pump or blower.
→The south facing wall of the house is double glazed, behind it a thick black concrete
wall absorbs solar radiation and acts as storage.
→Vents that can be opened or closed are provided at top and bottom of the storage wall.
→During daytime both A and B are opened, the air between inner glazing and the wall
gets heated up and flows into the living space, simultaneously cold air is pulled out by
forming a natural circulation of air.
→Energy transfer also takes place because of radiation between the inner surface of the
wall and the room
→During nights, both A and B are closed and space heating is purely by radiation.
46. ❖It can also be used for summer ventilation by proving vents at C and D, keeping A closed
and B, C, D open.
❖ The north side wall is glazed in summer instead of south.
❖The variation in temp is about 100C and cannot handle extreme climatic conditions
47. DISTILLATION
❖ To supply drinking water to some small communities, where the natural supply of
fresh water is inadequate.
Principle:
A conventional basin type solar still, which consists of a shallow air tight basin lined
with a black, impervious material, contains saline water.
A sloping transparent cover is provided at the top
Solar radiation is transmitted through the cover and is absorbed in the black lining
It is thus heated up the water by 100 to 200C and causes to evaporate
The resulting vapour rises, condenses as pure water on the under side of cover and
flows into condensate collection channel on the sides
Out put: 3 lit/m2 with an efficiency of 30 to 35%
48. DRYING
✓A cabinet type solar dryer, suitable for small scale use, consists of an enclosure with
a transparent cover.
✓The matl. to be dried is placed in perforated trays.
✓Solar radiation entering the enclosure is absorbed in the product itself and the
surrounding internal surfaces of the enclosure.
✓As a result moisture is removed from the product and air inside is heated .
✓Suitable openings at the bottom and top ensure a natural circulation of air.
✓Temp. ranges from 500c to 800c are usually attained
✓The drying time ranges from 2 to 4 days
✓The products that can be dried with this method are
Dates, apricots, chilies, grapes etc.,
Features:
✓This method is used for Agricultural drying.
✓Drying can be done in faster and in controlled fashion
✓A better quality product is obtained
49. ❖ For large scale drying Active device with forced
circulation of air is used.
❖ This systems are used mostly in drying of Timber
❖ For large scale drying an indirect type Active
device with forced circulation of air is used where
solar radiation with direct type is not sufficient or
the temp. of products need to be controlled.
❖The air is heated separately in the array of solar air
heaters and then ducted to the chamber where the
product to be dried is stored.
❖ This systems are used mostly in drying of food
grains, tea, spices etc.,
50. POWER GENERATION WITH CENTRAL POWER TOWER
❖Molten salt (Hitec) is use as heat transfer fluid.
❖Cold salt at 2900c is pumped to the receiver at the top.
❖It is heated up to a temp. of 5560c.
❖It flows back to another tank and allowed to enter a steam generator where super heated steam is
produced.
❖This steam runs a turbine with Rankin cycle where mechanical work is produced and thus
converted to electricity.
51.
52.
53. SPACE COOLING AND REFRIGERATION
Principle:
# Works on Absorption refrigeration cycle which require most of its energy input as heat,
# Cooling is required mostly in summer
# so there is seasonal matching between energy needs of space cooling system and
available solar radiation.
54. Working:
➢ Water heated in a flat plate collector array is passed through the heat exchanger ,where
the heat is transferred to a solution mixture of absorbent and refrigerant.
➢Refrigerant vapour is boiled off at a high pressure and goes into the condenser, where it is
condensed into a high pr. Liquid
➢The high pr. Liquid is throttled to low pr. and temp. in an expansion valve, and passes
through the evaporator coil.
➢Here, the refrigerant vapour absorbs heat and cooling is obtained in the space surrounding
the coil.
➢The refrigerant vapour is now absorbed into the solution mixture withdrawn from the
generator, which is weak in refrigerant concentration.
➢This yields a rich solution which is pumped back to the generator, there by completing the
cycle.
➢ Common refrigerant absorbent mixtures:
Ammonia –water, Water- Lithium Bromide
➢ COP Value : between 0.5 to 0.8
➢ High cost to erect array of collectors
55. SOLAR COLLECTORS
NEED:
➢ Solar power has low density of 0.1KW/m2 to 1 KW/m2
➢ Hence it is collected by covering large ground area by solar thermal
collectors.
➢ Solar collector is the first unit in solar thermal system
PRINCIPLE:
❖ Absorbs solar energy as heat and then transfers it to the heat transport
fluid efficiently.
❖ Heat transport fluid delivers this heat to a thermal storage tank/boiler/
heat exchanger to be utilized in the subsequent stages of the system
56. Solar
collectors
Non
concentrating
Liq. Flat plate
collector
Flat plate air
heating
collector
Concentrating
Focus Type
Line
Focus
a) Cylindrical parabolic
b) Fixed mirror scale
c) Linear Fresnel Lens
Point
Focus
a) Parabolic Dish
b) Hemi spherical bowl
mirror
c) Circular Fresnel lens
d)Central tower receiver
non focus
type
Modified
Flat plate
collector
Compound-
Parabolic
concentrating
collector(CPC)
Classification of Collectors
57. COMPARISON
Concentrating collectors Non Concentrating collectors
Solar radiation is converged from large
area to smaller area using optical means
Require large areas for collection of
solar radiation
Only beam radiation which has unique
direction and travels in st.line can be
converged. Diffused radiation cannot be
captured
Captures all types of radiation
Complex in construction, requires sun
tracking
Simple in construction and does not
require sun tracking
High maintenance Low maintenance
Heat loss is less. High temperatures can
be obtained.
High temp. cannot be obtained due to
large heat loss, because of absence of
optical concentration
58. PERFORMANCE INDICES
♣Collector Efficiency: Ratio of energy actually absorbed and transferred to the
heat transport fluid by the collector ( Useful energy) to the energy incident on the
collector
♣Concentration Ratio: The ratio of the area of aperture of the system to the area
of the receiver.
♣Temperature Range: The range of temp. to which the heat transport fluid is
heated up by the collector
❖Flat Plate collectors:
Concentration Ratio =1, Temp Range is less than 1000 C
❖Concentration collectors:
❑ Line focus : CR up to 100 and Temp. Range 1500 C to 3000 C
❑ Point Focus: CR up to 1000 and Temp. Range 5000 C to10000 C
59. Liquid Flat Plate collector
Positioning:
• placed at a location in a position
such that its length aligned with
the line of longitude and is
suitably tilted towards south to
have max collection.
Basic Elements
➢ Transparent cover of glass or plastic
➢ Blackened absorber plate usually of copper, Al or
steel
➢ Tubes, channels or passages in thermal contact
with the absorber plate
➢ Weather tight insulated container to enclose the
above components
60. Liquid Flat plate collector
❖A liquid, most commonly water or mixture of water and ethylene glycol is used as the
heat transport medium from the collector to the next stage of the system
❖As solar radiation strikes on a specially treated absorber plate, it is absorbed and
rises the plate temperature.
❖The heat is transferred to the liquid circulating in the tube, beneath the absorber
plate and in intimate contact with it.
61. Absorber Plate and Tubes:
❖Flat plate collector utilizes both beam and diffuse components of solar radiation.
❖The absorber plate is usually made of thickness 0.2 to 1mm and the tubes are of dia. ranging from
1 to 1.5 cm.
❖Tubes are welded , brazed or pressure bonded with the absorber plate with a pitch range of 5
to12cm.
❖Header pipes of app. 2 to 2.5cm thickness lead water in and out of the collector and distribute to
tubes.
❖The most commonly used metal is copper, sometimes Al sheets fixed to copper or galvanized steel
sheets and tubes.
62. Transparent cover:
❖Plain or toughened glass of 4 or 5cm thickness.
❖Use one or two covers with spacing ranging from 1.5 to 3cm
Insulation:
❖Bottom and sides are insulated by mineral wool, rock wool or glass wool with a
covering of Al foil and has a thickness ranging from 2.5 to 8cm.
❖Collector box is made of Al, Steel sheet, or fibre glass.
Advantages:
✓ Light in weight
✓ Easy to manufacture
✓ Less cost
✓ Require less energy input for their manufacture.
LIMITATIONS:
¤ Generally originated from fossil fuels.
¤As the volume of production increases, The above considerations of energy input and
raw material origin will become increasingly important
64. a) Pipe and fin type:
❖ The liquid flows only in the pipe.
❖ Low wetted area and liq. Capacity
❖ For domestic and Industrial applications
where high temp. are req.
b) Water sandwich or rectangular type:
➢Both wetted area and water capacity is high.
➢ Applied for low temp applications
c) Semi-water –sandwich or Roll- bond type:
It is intermediate between the above two types.
Absorber Plate Designs
(a)
(b)
65. FLAT PLATE AIR HEATING COLLECTORS
♣Similar to flat plate collector with change in the configuration of the absorber and tube
♣The value of Heat transfer coeff. Between the absorber and the air is low.
♣For this reason the surfaces are roughened and longitudinal fins are provided in the air
flow passage
Applications:
❖Drying for agricultural and industrial purposes.
❖Space heating
66. Advantages:
✓ It is compact, Simple and requires less maintenance
✓ No need to transfer energy form working fluid to other fluid
✓ No Corrosion
✓ No freezing of working fluid in pipes
✓ Pressure inside the collector does not become high
Limitations:
X Due to low density large amount of fluid is to be handled.
X Heat Transfer between absorber plate and air is poor
X Less storage of thermal energy due to low density
67. Evacuated Tube Collector
➢ To improve the performance of flat plate collector by reducing the losses by conduction
and convection provide vacuum around the absorber.
➢ To with stand the stresses introduced by the pressure differences, as a result of vacuum,
glass tube is used.
➢ The collector consists of a no. of long tubular modules stacked together.
68. ❖In simplest design , each module consists of metal absorber plate with two fluid tubes
housed in an evacuated , cylindrical glass tube.
❖The absorber plate has “selective surface coating”.
❖Two tubes are joined at the other end in side the glass cover and form a U path for the
fluid
❖Glass to metal seal is provided between the absorber tubes and the end cover of vacuum
tube
❖Precautions are required for thermal contact between absorber and the outer tube through
seal
69. •Metal to glass seal is avoided by using three concentric tubes with the space between the
outer two tubes
•The outer surface of the middle tube acts as absorbing surface
•Liquid flows through in the innermost tube and flows out through the annuals
70.
71. ➢Concentrating solar collectors use mirrors and lenses to concentrate and focus sunlight onto
a thermal receiver, similar to a boiler tube.
➢ The receiver absorbs and converts sunlight into heat.
➢The heat is then transported to a steam generator or engine where it is converted into
electricity.
➢These technologies can be used to generate electricity for a variety of applications, ranging
from remote power systems as small as a few kilowatts (kW) up to grid connected
applications of 200-350 megawatts (MW) or more.
Concentrating solar collectors
73. ➢Through like arrangement of two facing parabolic mirrors
➢Solar radiation of any type can be reflected towards the bottom absorbing
surface.
➢Concentration ratio of 3-10 can be achieved, that is equal to maximum
possible value for a given acceptance angle.
➢Suitable for a temp range of100-1500C.
➢If evacuated 2000C can also be achieved
➢With selective coating and evacuation 3000Cis also possible.
➢Only seasonal tracking is required
74. FOCUS TYPE
LINE FOCUS:
❖PARABOLIC THROUGH
❖FIXED MIRROR SCALE
❖LINEAR FRESNEL LENS
POINT FOCUS:
✓ PARABOLIC DISH
✓ HEMI SPHERICAL BOWL MIRROR
✓ CIRCULAR FRESNEL LENS
✓ CENTRAL TOWER RECEIVER
75. CYLINDRICAL PARABOLIC COLLECTOR
OR
PARABOLIC THROUGH
➢These solar collectors use mirrored parabolic troughs to focus the sun's energy to a
fluid-carrying receiver tube located at the focal point of a parabolically curved trough
reflector .
➢Many troughs placed in parallel rows are called a "collector field."
76. ❖Basic Components:
✓Absorber tube
✓Concentric transparent cover
✓Parabolic concentrator
❖Aperture area: 1 to 6 m2
❖ CR Value Range: 10 to 80
❖ Rim Angles: 700-1200
❖ Annular Gap :1 or 2 cm
For High performance
✓ The absorber plate has “selective surface coating”.
✓ Space Between tube and glass surface is evacuated
❖ Reflecting surface: Curved back silvered glass
❖ Organic Heat Transfer Fluids ( Thermic Fluids)
77.
78.
79. Linear Fresnel Lens Concentrator:
❖Fine linear grooves on refracting matl.
with one side plane surface.
❖Designed similar to the behavior of
optical spherical lens.
❖Beam incidenting normally converges
on focal line where a receiver tube is
provided.
❖Conc. Ratio- 10-30
❖Temp. range- 150-3000C
80.
81. Parabolodal Dish collector
✓ Beam Radiation is focused at a point in
the paraboloid.
✓ This require two axis tracking.
✓ Conc. Ratio- 10 to few thousands
✓ Temp up to 30000C
✓ 6-7 m in dia.
82. Circular Fresnel Lens Concentrator
✓ Used when high flux is desired along with
gallium arsenide solar cell receiver
✓ Divided into no of circular zones, such that
tilt of each zone is so adjusted such tat it
acts as spherical lens.
✓ Conc. Ratio: about 2000
84. Methods of Storage:
➢ Sensible Heat Storage: No Phase Change Occurs
𝐸 = 𝑚
𝑇1
𝑇2
𝑐𝑝dt
➢ Latent Heat Storage: Undergo Phase Change
E=mλ
Where λ is latent heat of Fusion
➢ Chemical Storage: With reversible Chemical Reaction between two elements
85. Consideration for selection of Thermal energy storage:
✓ Operating Temperature Range
✓ Capacity of storage required
✓ Minimum Heat loss
✓ Cost of Storage
✓ Selection of suitable material for container
✓ Means adopted for transferring heat
✓ Power requirements
86. Sensible Heat Storage:
➢ Heat energy stored and extracted by heating or cooling a liquid or solid that
doesn’t under go phase change
➢ Materials used:
Water, Heat transfer oils, Inorganic Molten salts, Rocks & pebbles, Refractories
➢ In case of solids material is in porous form and heat is stored and retrieved by
passing gas or liquid
➢ Choice depends on operating temperatures
Ex: water - <1000C ,Refractory Materials - around 10000C
➢ Features:
✓ Simple in Design
✓ Low Cost
✓ Bigger in size
✓ Cannot store or deliver energy at const. temp.
87. Liquids used for storage
Water:
➢ Most commonly used medium
➢ Storage tanks located either inside or outside of buildings or underground for
solar heating application.
➢ Size vary from few hundreds to thousands cubic meters containing app. 75-
100lits. of storage/ sq. of collector area.
➢ Storage tanks are made of steel, concrete fibre class insulated with glass
wool, mineral wool etc., with a thickness of 10-20cm.
➢ For underground storage earth acts as insulator after reaching steady state
88. ➢ If water is pressurized a temperature little above 1000c can be attained
➢ To reduce cost naturally occurring aquifers can be used
89. ✓ The need for tank is eliminated
✓ Cold ground water is displaced to
another well as hot water is pumped
✓ Low investment
90. Heat Transfer Oils
➢ Used for temp ranging from 100-
3000c
➢ US brands- Caloria HT43 and
Therminol T66
➢ Indian Brand Servotherm
➢ Limitations:
X Tend to degrade with time
X Safety problems with flash point
X High Cost
Molten Inorganic salt
➢ Used for temp above 3000c
➢ Ex: Hitec- Eutectic mixture of 40%
NanO2,7% NaNO3, and 53% KNO3 by wt.
➢ Hitec has Low melting point 1650c can be
used up to 4250c
➢ Liquid metals can also be used for high
temp.
➢ Ex: Liq. Sodium
91. Solids used for storage:
Rocks & Pebbles:
➢ Packed in insulated vassals
➢ Used for temp up to 1000c conjunction with air heaters
➢ Rock size varies from 1 to 5 cm and 300 to 500kg of rocks & pebbles are
required for 1 sq. m area of collector plate.
➢ Used for space heating applications
➢ Undisturbed earth can also used for long term storage
➢ In such case heat transfer takes place through a network of heat exchanger
pipes buried in earth
92. Refractory materials:
➢ Magnesia (MgO), Alumina, Silicon Oxide are suitable for SHS and used in the
form of bricks
➢ They are available with Electric heater elements embedded in the bricks.
➢ Storage is done by switching on electrical heater at night and is supplied during
day for space heating by allowing air to pass through them.
➢ The cop & K Value are very high.
➢ Compactness in storing at high temperatures
➢ Expensive
➢ Combinations of liquid and solid can also be used for SHS
93. Latent Heat Storage
➢ Phase changing materials are used for this type of storage
➢ Heat is stored in the material when it melts and extracted when freezes
➢ The Phase Changing Materials(PCMs) are Organic materials, Hydrated salts, Inorganic
materials.
➢ Ex: Paraffin Wax is the organic material having 400C-600C melting point.
➢ Suitable for Space heating and cooling applications.
➢ Other Organic materials are Fatty acids, Easters and alcohols having melting points in the
range of 70C-1870C
➢ Hydrated salts have operating temp. range from 100C-1000C.
➢ Ex: Calcium chloride hexa hydrate, (CaCl. 6H2O)
Sodium sulphate deca hydrate, (Na2SO4. 10H2O)
Magnesium Nitrate hexa hydrate, (Mg(NO3)2. 6H2O)
➢ Sodium sulphate deca hydrate, (Na2SO4. 10H2O) [Glauber’s Salt] is the first salt used for
solar applications.
➢ Hydrated and dehydrated at 320C
➢ Salts Thermal Performance decreases with repeated usage due to phase segregation
94. ➢ Ice is a good PCM in Inorganic materials
➢ if the heat is to be stored at 00C
➢ Eutectic mixtures are considered for higher temperatures
➢ Ex: Sodium Nitrate and Sodium Hydroxide
➢ But the heat exchange system is difficult.
➢ Compact in size compared to SHS
PROPERTIES OF PCMS
✓ Melting point should be with in operating range of application
✓ High value of latent heat of fusion.
✓ Small vol. change during phase change
✓ High thermal conductivity in both cases
✓ Low vapour pr. At operating temperatures
✓ Non Corrosive.
95. ➢It is difficult to extract heat as the material freezes on the transferring system.
➢To overcome this difficulty two types of arrangements are used
ARRANGEMENT-1
ARRANGEMENT-2
96. THERMO CHEMICAL STORAGE
➢ Two or More chemicals are used for reaction to store thermal energy through
endothermic reaction.
➢ Heat is extracted with reversible reaction i.e Exothermic reaction.
97. Considerations for selection of Materials for Thermo-chemical storage:
➢Forward reaction should occur in Temp range of collectors.
➢Reverse Reaction should occur at Temp range where heat is extracted.
➢Two reactions Temperatures should be close to each other.
➢To reduce storage size, The energy absorbed per unit vol. must be as high as
possible.
➢Material are preferred in liquid form.
➢Both reactions should be fast and completely reversible.
➢Cost should be economical and easy to handle.
98. SOLAR POND
➢ Normal ponds receive sunlight a part of which is reflected at the surface, a part is
absorbed and the remaining is transmitted to the bottom
➢ Due to this the lower part gets heated up and the density decreases as a result of which
it rises up and convection currents are set up.
➢ As a result, the heated water reaches top layer and looses its heat by convection and
evaporation.
➢ One way to tap solar energy is through the use of solar ponds.
➢ Solar ponds are large-scale energy collectors with integral heat storage for supplying
thermal energy.
➢ It can be use for various applications, such as process heating, water desalination,
refrigeration, drying and power generation .
99. GENERAL CONSTRUCTION FEATURE
➢ They are 1-3 m deep.
➢ Constructed on level ground by combination of excavation and embankments.
➢ Membrane liners are used to make the basin leek proof.
➢ Membranes are covered with clay to protect them and improve their durability.
➢ Since solar ponds are horizontal collectors sites should be at low to moderate northern
latitude and southern latitude i.e. -40 to +40 degree latitude.
➢ Evaluation of geological salt character as underline earth should be free from stresses,
strains and fissures.
➢ Thermal conductivity of soil increases with moisture, so water table of site must be low.
100. A solar pond is an artificially constructed water pond in which significant temperature
rises are caused in the lower regions by preventing the occurrence of convection
currents.
Zones of Solar Ponds
A salt-gradient non-convecting solar pond consists of three zones:
1) UCZ ( Upper Convecting Zone) : top layer
2) NCZ ( Non Convecting Zone) : middle layer
3) LCZ (Lower Convecting Zone) : bottom layer
101. Upper Convective Zone
✓ This is a zone, typically .3 m thick, of almost low salinity which is almost close
to ambient temperature.
✓ UCZ is the result of evaporation, wind induced mixing, and surface flushing.
✓ Usually this layer is kept as thin as possible by use of wave suppressing mesh
or by placing wind breaks near the ponds.
Non Convective Zone
✓ In this zone both salinity and temperature increases with depth.
✓ The vertical salt gradient in the NCZ inhibits convection and thus gives the
insulation effect.
102. Lower Convecting Zone
✓This is a zone of almost constant, relatively high salinity (typically 20% by
weight) at high temperature.
✓Heat is stored in the LCZ, which should be sized to supply energy
continuously throughout the year.
SALINITY GRADIENT
103. ➢ The design of solar ponds reduces either convection or evaporation in order to store the
heat collected by the pond. They can operate in almost any climate.
➢ A solar pond can store solar heat much more efficiently than a body of water of the
same size because the salinity gradient prevents convection currents.
➢ Solar radiation entering the pond penetrates through to the lower layer, which contains
concentrated salt solution.
➢ The temperature in this layer rises since the heat it absorbs from the sunlight is unable
to move upwards to the surface by convection.
➢ Solar heat is thus stored in the lower layer of the pond.
➢ This allows the use for collection and storage of solar energy which may ,under ideal
conditions, be delivered at temperature 40-500C above normal.
WORKING OF SOLAR POND
104. Different Methods of Maintaining Layered
Structure
1) Maintaining Density Gradient by salt water
2) Use of horizontal and vertical membranes.
3) Polymer gel layers.
Maintenance of salt-gradient
❖ The concentration gradient that exists in pond lead to diffusion from higher to lower
concentration i.e. from bottom to top.
❖ Therefore, to maintain stability salt must be added to lower layer and remove from
upper layer.
❖ Now as the sunlight falls on the pond, the part which is transmitted to the bottom
heats the lower layer and as a result inverse temperature gradients are set up.
105. ADVANTAGES:
✓ Low investment costs per installed collection area.
✓ Thermal storage is incorporated into the collector and is of very low cost.
✓ Diffuse radiation (cloudy days) is fully used.
✓ Very large surfaces can be built thus large scale energy generation is possible.
✓ Expensive cleaning of large collector surfaces in dusty areas is avoided
HINDERANCES:
X Cleanliness of pond as contaminants can reduce transmittance.
X Increase in thickness of UCZ ( Upper convective zone) due to surface waves and
evaporation.
X Algae growth.
X Horizontal temperature gradient caused by salt solution removal and addition.
