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1. MKSSS’s
Cummins College of Engineering for Women, Pune
Department of Mechanical Engineering
Final Year of Engineering
Unit I
Solar Energy

2. Unit 1: Solar Energy
• Solar potential, Solar radiation geometry, Solar radiation data, radiation measurement
• Types of Solar Collectors, Collection efficiency, Testing of Solar collectors
• Applications of Solar Energy, Solar Desalination system, Solar dryer, Solar Energy storage
• Solar PV Principle, Photo-cell materials, Applications

3. The SUN
• The sun is the most prominent feature in our solar system.
• The sun’s great energy is the result of an elaborate chemical process in the
sun’s core – a thermonuclear fusion.
• This energy is radiated from sun in all directions and a very small fraction of
it reaches to the earth.
• The sun’s outer visible layer is called the photosphere and has temperature
of about 6000°C.

4. • Solar energy is created deep within the core of the sun.
• In the core the temperature and pressure is so intense that nuclear reactions
take place.
• This reaction causes four protons or hydrogen nuclei to fuse together to form
one alpha particle or helium nucleus.
• The alpha particle is about 0.7% less in mass than the four protons.
• The difference in mass is expelled in the form of energy and is carried to the
surface of the sun, through a process convection, where it is released as light
and heat.

6. Earth’s orbit around the sun

7. Solar Radiation
• The sun is a hot sphere of gas heated by nuclear fusion reactions at its
Centre.
• Every second the sun emits a total energy flux about 4*10^23 Kw out of
which only a very small fraction reaches to earth.
• Solar radiation is the electromagnetic radiation emitted by the sun.
• This radiation can be converted into useful forms of energy, such as heat
and electricity by the different types of technologies

8. Solar Radiation
• Radiation: The transfer of energy via electromagnetic waves that travel at
the speed of light.
• The velocity of light in a vacuum is approximately 3 x 10^8 m/s.
• The time it takes light from the sun to reach the Earth is 8 minutes and 20
seconds.
• Heat transfer by electromagnetic radiation can travel through empty space.

9. Solar Radiation
• Types of radiation is defined by its wavelength.
• The Electromagnetic radiation emitted by the sun shows a wide range
of wavelengths.
• It can be divided into major regions
• Ionizing radiation(x-rays & gamma rays)
• Non-Ionizing radiation(UVR, visible and infrared radiations)

10. Solar Radiation
• Solar radiation has wavelengths distribution from short wavelength
radiation(X-rays and gamma rays) to long wavelengths .
• The visible range of electromagnetic radiation is most useful part for
humans.
• Short wavelength radiation has a higher energy level than long wavelength
radiation.

11. Types of solar radiation
• Diffuse solar radiation: As sunlight passes through the atmosphere,
some part of it is absorbed, scattered and reflected by air molecule,
water vapors, clouds, dust and pollutants. This is called diffuse solar
radiation. It does not have unique path.
• Direct Beam solar radiation: The solar radiation that reaches the
surface of earth without being diffuses is called Direct Beam solar
radiation
• Global/Total Solar radiation: The sum of the diffuse and direct solar
radiation is called total or global solar radiation.

13. Global and diffuse radiation

14. Solar Radiation Map of India

15. Global Solar Radiation Map

23. Solar Radiation Geometry

25. • The Slope is the angle made by the plane surface with the horizontal.

26. Zenith angle
• θ is the angle between an incident beam of flux and the normal to a
tilted surface.
• θz is the angle between an incident beam of flux and the normal to a
pane surface.

28. • The latitude ɸ of a location is the angle made by the radial line joining
the location to the center of the earth with the projection of the line
on the equatorial plane.
• Varies between -900
to + 900
(by convention the latitude is measured
as positive for the northern hemisphere.)

29. The declination (δ) is the angle made by the line joining the
centers of the sun and the earth with the projection of this line on
the equatorial plane.

31. The surface azimuth is the angle made in the horizontal plane between the horizontal line due south and the
projection of the normal line to the surface on the horizontal plane.(-180 0
to +1800
)

32. Cosθ = sin ɸ (sin δ cos β + cos δ cos γ cos ω sin β)
+cos ɸ(cos δ cos ω cos β-sin δ cos γ sin β)
+ cos δ sin γsin ω sin β

34. For Vertical Surface (β=90)
Cosθ = sin ɸ cos δ cos γ cos ω
- cos ɸ sin δ cos γ
+ cos δ sin γ sin ω

35. For Horizontal surface (β=0)
Cosθ = sin ɸ sin δ
+cos ɸ cos δ cos ω

36. For inclined surface facing due south (γ = 0
)
Cosθ = sin δ sin (ɸ - β)
+ cos δ cos ω cos (ɸ - β)

37. 3. Calculate the angle made by beam radiation with the normal to a flat
plate collector on May 1 at 09:00 AM (Solar Time). The collector is
located in new Delhi(280
35’ N, 770
12’E). It is tilted at an angle 360
with
the horizontal and is pointing due south.

38. 4. Calculate the angle made by beam radiation with the normal to a flat
plate collector on April 12 at 11:00 AM. The collector is located in
Mumbai (180
54’ N, 720
49’E). It is tilted at an angle 250
with the
horizontal and is pointing due south.

39. Sunrise, Sunset and Day Length
• Sunrise and Sunset angle
Cos ωs = - tan ɸ tan δ
• Day Length
Td = ωs
Td = Cos-1
(- tan ɸ tan δ )

40. • Calculate the number of daylight hours at Delhi(280
35’ N, 770
12’E) on
December 21 and June21.

41. • Calculate the hour angle at sunrise and sunset on June 21 and
December 21 for a surface inclined at an angle of 10° and facing due
south (γ = 0°). The surface is located in Mumbai (19°07’ N, 72°51’ E).
Also calculate the day length.

42. Local Apparent Time (Solar Time)
• Dong, in the
Anjaw district
of Arunachal
Pradesh
• 28.1702° N,
97.0417° E
• Guhar Moti in
Gujarat
• 23.6352°N
68.5424°E
The Indian standard time (IST), is based on longitude 82.5°, which passes through Mirzapur, near Allahabad in
Uttar Pradesh

44. • Determine the local apparent time corresponding to 14.30 hrs (IST) on
July 1, at Mumbai (Latitude 19°07’ N, longitude 72°51’ E). Equation of
Time = -4’.

45. • Calculate today’s sunrise and sunset time (IST) at Pune (18.52°N,
73.85°E). Equation of time is 3’46”.

46. Solar Collectors
• Solar energy can be utilized directly by two technologies:
namely
(i) Solar Thermal
(ii) Solar Photovoltaic

47. Solar Collectors
• Solar power has low density per unit area (1 kW/sq. m. to 0.1 kW/sq. m.).
• Hence it is to be collected by covering large ground area by solar thermal
collectors.
• Solar thermal collector essentially forms the first unit in a solar thermal
system
• It absorbs solar energy as heat and then transfers it to heat transport fluid
efficiently.
• The heat transport fluid delivers this heat to thermal storage tank / boiler /
heat exchanger, etc., to be utilized in the subsequent stages of the system.

48. Classification

50. Solar Collectors
• Flat plate collector
• Evacuated tube collector
• Concentrating Parabolic collector

51. Flat plate collector
• A flat plate collector is placed
at a location in a position such
that its length aligns with line
of longitude
• And it is suitably tilted
towards south to have
maximum collection.

52. Construction
• Transparent cover (one or two sheets) of glass or
plastic
• Blackened absorber plate usually of copper,
aluminium or steel
• Tubes, channels or passages, in thermal contact
with the absorber plate.
• Weather tight, insulated container to enclose the
above components

54. Collector Efficiency
• Collector efficiency is defined as the ratio of the energy actually absorbed and
transferred to heat transporting fluid by the collector (useful energy) to the
energy incident on the collector.
• The instantaneous collection efficiency of a flat plate solar collector is given by,
where,
IT = instantaneous radiation energy rate incident on collector face (W/m2)
Ac = the collector gross area (area of the topmost cover including the frame)

55. Solar Collector Testing and IS Code
• Static Pressure Leakage Test
• Outdoor No Flow Exposure Test
• External Thermal Shock Test
• Internal Thermal Shock Test
• Rain Penetration Test
• Impact Resistance Test
• Thermal Efficiency Test
• Determination of Time Constant
• Incident Angle Modifier Test
IS 12933

56. Evacuated Tube Collector
• The performance of a flat plate collector can be
improved by suppressing or reducing the heat
lost from the collector by convection and
conduction.
• This is done by having vacuum around the
absorber.
• The collector consists of a number of long tubular
modules stacked together.

59. Cylindrical Parabolic Concentrator
• It consists of a cylindrical parabolic trough reflector and a metal tube receiver at
its focal line

60. • The receiver tube is blackened at the outside surface to increase absorption.
• It is rotated about one axis to track the sun.
• The heat transfer fluid flows through the receiver tube, carrying the thermal energy
to the next stage of the system.
• This type of collector may be oriented in any one of the directions: East-West, North-
South.

61. Applications of Solar Energy
• Solar Water Heater
• Solar Desalination system
• Solar Dryer
• Solar Cooker

62. SOLAR WATER HEATER
• A tilted flat plate solar collector with water
as heat transfer fluid is used.
• A thermally insulated hot water storage
tank is mounted above the collector.
• The heated water of the collector rises up
to the hot water tank and replaces an equal
quantity of cold water, which enters the
collector.

63. • The cycle repeats, resulting in all the
water of the hot water tank getting
heated up.
• When hot water is taken out from hot
water outlet, the same is replaced by
cold water from cold-water make up
tank fixed above the hot water tank.

64. • In average Indian climatic conditions solar water heater can be used for about
300 days in a year.
• A typical 100 liters per day (LPD) rooftop, solar water heater costs approximately
Rs.17000 and delivers water at 60–80 °C.
• It has a life span of 15–20 years and payback period of 2-6 years.

65. SOLAR DRYER
• Drying process removes the moisture and helps in the preservation of the product.
• Solar crop drying is perhaps the most ancient and widespread direct use of solar
energy.
• The customary way is to spread the material to be dried in a thin layer on the
ground.

66. SOLAR DRYER
• The disadvantages associated with this method are:
(i) the process is slow,
(ii) the product is vulnerable to attack by insects and
(iii) dust gets mixed with the product.
The use of solar dryer helps to eliminate these disadvantages.

67. SOLAR DRYER
• A simple cabinet type solar dryer is shown in Figure.
• It is an enclosure with transparent cover.
• The material to be dried is placed on perforated trays.
• Solar radiation enters the enclosure and absorbed by the product as well as surrounding
internal surfaces of the enclosure, increasing its temperature.

68. SOLAR DRYER
• The inside air heats up to
temperature ranging from 50 to
80°C, and rises above.
• Natural circulation of air is ensured
by providing suitable openings at
the bottom and top.
• The circulating air removes the
moisture from the product.

69. SOLAR DISTILLATION (DESALINATION OF WATER)
• Potable or fresh water (water with less than 500-ppm salt content) is one of the
fundamental necessities of life for a human.
• Industries and agriculture also require fresh water without which they cannot thrive.
• Human has been dependent on rivers, lakes and underground water reservoir to fulfill
his need of fresh water.
• Because of rapid industrialization and population explosion the demand of fresh
water has been increasing enormously.

70. Solar Desalination system
• A simple basin type solar still consists of a
shallow blackened basin filled with saline or
brackish water to be distilled.
• The depth of water is kept about 5–10 cm.
• It is covered with sloppy transparent roof.

71. • Solar radiation, after passing through the roof is absorbed by the
blackened surface of the basin and thus increasing the temperature of
water.
• The evaporated water increases the moisture content, which gets
condensed on the cooler underside of the glass.
• The condensed water slips down the slope and is collected through
the condensate channel attached to the glass.

72. • The still is erected in open area with its long axis facing East-West direction.
• The still can be fed with saline water either continuously or intermittently.
• The supply is generally kept at twice the rate at which the fresh water is produced
but may vary depending on the initial salinity of input water.
• The output of a typical solar still in Indian climate varies from 5.3 l/m2 day (in
summer) to 0.9 l/m2 day (in winter).

73. SOLAR COOKERS
• Thermal energy requirements for cooking purpose forms a major share of total
energy consumed, especially in rural areas.
• Variety of fuels like coal, kerosene, cooking gas, firewood, dung cakes and agricultural
wastes are being used to meet the requirement.
• Fossil fuel is a fast depleting resource and need to be conserved, firewood for cooking
causes deforestation and cow dung, agricultural waste, etc., may be better used as a
good fertilizer.
• Harnessing solar energy for cooking purpose is an attractive and relevant option.

74. SOLAR COOKERS
• A variety of solar cookers have been developed, which can be clubbed in four
types of basic designs:
(i) Box type solar cooker
(ii) Dish type solar cooker
(iii)Community solar cooker
(iv)Advance solar cooker.

75. Box Type Solar Cooker
• The external dimensions of a typical family size (4 dishes)
box type cooker are 60 × 60 × 20 cm.
• An insulated box of blackened aluminum contains the
utensils with food material.
• The box receives direct radiation and also reflected
radiation from a reflector mirror fixed on inner side of
the box cover hinged to one side of the box.
• A glass cover consisting of two layers of clear window
glass sheets serves as the box door.

76. • The glass cover traps heat due to greenhouse effect.
• Maximum air temperature obtained inside the box is around
140–160 °C.
• This is enough for cooking the boiling type food slowly in
about 2–3 hours.
• It is capable of cooking 2 kg of food and can save 3–4 LPG
cylinder fuel in a year.
• Electrical backup is also provided in some designs for use
during non-sunshine hours.

77. Paraboloidal Dish Type (Direct Type) Solar Cooker
• A specially designed paraboloidal reflector
surface concentrates the beam radiation at its
focus, where a cylindrical brass vessel containing
food material is placed.
• The vessel directly receives the concentrated
solar radiation.
• The reflector is periodically adjusted to track the
sun.

78. • A fairly high temperature of about 450 °C can
be obtained and a variety of food requiring
boiling, baking and frying can be cooked for
10–15 persons.
• It can save on fuel up to 10 LPG cylinders
annually on full use.
• Cooking time is approximately 20–30
minutes.

79. Energy Storage
• Energy storage in solar energy systems refers to capturing excess energy
generated by solar panels during peak sunlight hours.
• Use when sunlight is not available, such as during the night or cloudy days.
• This ensures a steady supply of energy regardless of weather or time.

80. Types of Energy Storage
• Electrical Storage
• Thermal Energy Storage
• Mechanical Storage

81. Electrical Storage
• Technology: Lithium-ion, lead-acid, or flow batteries.
• Working: Converts and stores electrical energy as chemical energy.
During discharge, the chemical energy is converted back to electricity.
• Applications: Residential solar systems, grid stabilization.

82. Mechanical Storage
• Pumped Hydroelectric Storage: Uses surplus solar energy to pump
water to a higher elevation. The stored potential energy is converted
to electricity when the water flows back down.
• Compressed Air Energy Storage: Compresses air using solar power,
which is later released to drive turbines.

83. Thermal Energy Storage
• Technology: Molten salts, phase change materials (PCMs), or water
tanks.
• Working: Stores heat energy generated by solar thermal collectors.
Heat can be used directly (for heating) or converted to electricity
using turbines.
• Applications: Concentrated Solar Power (CSP) plants.

84. Solar Pond
• Sunlight penetrates the pond, heating the
bottom.
• The salinity gradient in the medium salt
gradient prevents convection currents,
reducing heat loss.
• The retained heat in the bottom can reach
temperatures of 80–90°C and is used for
various applications.

85. Solar Photovoltaic System
• Solar photovoltaic (PV) systems convert solar energy directly into
electrical energy.
• Basic conversion device used is known as a solar photovoltaic cell or a
solar cell.

86. • Solar cell is the most expensive component in a solar PV system
(about 60 per cent of the total system cost).
• It can approximately produce an electrical energy of about 1 kW per
sq. m per day in ordinary sunshine.
• As a PV system has no moving parts it gives almost maintenance free
service for long periods and can be used unattended at inaccessible
locations.

87. Solar cell, module and Array
• From one solar cell only fraction of
electricity is obtained.
• Which is then provided in a considerable
amount by connecting these solar cells
in series and parallel combination called
solar photovoltaic modules.
• These modules are again fabricated in
series and parallel combination to form
photovoltaic array

88. Solar cell working
• The solar cell is made of semiconductor materials
(like silicon). When sunlight hits the cell, photons
(light particles) are absorbed by the
semiconductor material.
• The energy from the photons excites electrons in
the semiconductor, causing them to jump from
their valence band to the conduction band,
creating electron-hole pairs.

89. Solar cell working
• A p-n junction is formed by combining p-
type (positive) and n-type (negative)
semiconductors.
• When the solar cell is connected to an
external circuit, the movement of
electrons from the n-side to the p-side
generates a current (electricity). This flow
of charge is the electric current.

90. Solar PV system

91. • Solar Module -- the essential component of any solar PV system that converts sunlight directly into
DC electricity.
• Solar Charge Controller -- regulates voltage and current from solar arrays, charges the battery,
prevents battery from overcharging and also performs controlled over discharges.
• Battery -- stores current electricity produced from solar arrays for use when sunlight is not available.
• Inverter -- a critical component of any solar PV system that converts DC power into AC power.
• Lightning protection -- prevents electrical equipment from damage caused by lightning or induction
of high voltage surge. It is required for the large size and critical solar PV systems, which include
grounding.

92. Application
• Major uses of photovoltaic have been in household application, space
satellites, remote radio communication booster stations and marine
warning lights.
• These are also increasingly being used for street lighting, water
pumping and medical refrigeration in remote areas especially in
developing countries.
• Solar powered vehicles and battery charging are some of the recent
interesting application of solar PV power.

93. Major advantages of solar PV systems
• It converts solar energy directly into electrical energy without going
through thermal-mechanical link.
• Solar PV systems are reliable, modular, durable and generally
maintenance free.
• These systems are quiet, compatible with almost all environments,
respond instantaneously to solar radiation and have an expected life span
of 20 years or more.
• It can be located at the place of use and hence no or minimum
distribution network is required, as it is universally available.

94. Disadvantages
• At present the costs of solar cells are high, making them economically
uncompetitive with other conventional power sources.
• The efficiency of solar cells is low. As solar radiation density is also low,
large area of solar cell modules are required to generate sufficient useful
power.
• As solar energy is intermittent, some kind of electrical energy storage is
required, to ensure the availability of power in absence of sun.

95. PV Array Fields
PV Array Fields
• In order to generate large amounts of electricity which can be fed into
the electric grid, large number of arrays can be wired together to form
an Array Field.
• Some utility companies are turning to large PV systems to help meet
peak power demand and reduce the need for building new power
plants.

96. PV Array Fields