Solar energy

Solar Energy
By,
Prof. Mayur B. Gohil
SSASIT, Surat

GTU Question Paper Statistical Analysis
May
2011
Dec
2011
May
2012
Dec
2012
May
2013
Dec
2013
May
2014
Dec
2014
May
2015
May
2016
Dec
2016
Marks 28 42 28 28 49 35 28 21 42 35 21
Repeated
Que. Marks
- 7 14 21 21 7 28 21 28 35 21

What is solar Energy?
• In general, the energy produced and radiated by the sun, more specifically
the term refers to sun’s energy that reaches the earth.
• Solar energy, received in the form of radiation, can be converted directly
or indirectly into other forms of energy, such as heat and electricity.
• Since the sun is expected to radiate at an essentially constant rate for a
few billion year, it may be regarded as an in-exhaustible source of useful
energy.

• Sun has Spherical shape
• Radius : 1.39 *109
meters
• Temperature of inner most core: 80*106 K to 40* 106 K
• Outer surface: 5762 °K
• Density of sun varies from center to surface
• Density at inner most point: 105
kg/𝑚3
• Density at outer most surface: 10−6 kg/𝑚3

• Core:
• 0 to 0.23 R.
• Temperature : 8-40 million K.
• Density is 100 times of water.
• Radiation Zone (0.23 R to 0.7 R):
• Energy transmitted from core to this region by radiation.
• Temperate: 1.3*105 K.
• Density: 7 * 104
kg/𝑚3
.
• Radiation from core is absorbed by one atom which retains it for some time and then radiates it
to the next atom. This process is very slow. It takes 1,70,000 years for the radiation to finally
come out of radiation zone

• Convection Zone (0.7 R to 1 R):
• Temperature: 7000 °K.
• Density : 10−5
kg/𝑚3
• Heat transfer by convection due to low temperature.
• Photosphere:
• It is visible sphere of the sun.
• It is also called as apparent surface of the sun.
• Temperature : 5800 °K.
• Radiation

• Reversing layer:
• Temperature again starts rising.
• Extends up to several hundreds of kilometers.
• Since temperature starts rising across region, its called as reversing layer.
• Chromosphere:
• 2000 km in thickness.
• Reddish in appearance hence the name chromosphere.
• Radiation.

• Transition layer:
• Thickness is about 200 km.
• This may be consider as a part of chromosphere only.
• Temperature of the outer most layer of chromosphere is about 20000 K.
• From this temperature suddenly rises to about 2 million K in the corona.
• The reason for this sudden rise in temp across this region is not clearly understood.
• Corona:
• Outer layer
• Particles in corona are very thin and stretches far out into the space.
• Temperature of corona is about 2*10^6 K

Solar Constant
• It is defined as “Amount of solar energy per unit time received on unit
surface area at the top of the atmosphere perpendicular to radiation
direction at the mean distance between the earth and the sun.”
• It is denoted by 𝐼𝑠𝑐 and the value is 1353 W/𝑚2.
• World Radiation Centre (WRC) has adapted a value of 𝐼𝑠𝑐 = 1367 W/𝑚2
.
• Based on solar constant, total solar energy incident on the earth could be
calculated.
• Unit- Watts per sq. meter.

Variation of solar constant
• The solar constant varies with place to place i.e. altitude and latitude.
• It is also varies with seasons as distance of earth surface changes in
year.
• This is not affected by earth’s atm, gases, clouds etc.
• An approximate equation is given as,
𝐼 𝑜𝑛 = 𝐼𝑠𝑐 (1+0.033 cos
360∗𝑛
365
)
Where, 𝐼 𝑜𝑛 = Solar radiation on the top of the atmosphere,
n = days of the year counted from January first.

Sun’s Radiation
1. Beam radiation/Direct radiation:
• Sun rays travel in straight parallel lines.
• These are radiations received at earth’s surface without change in direction.
• We normally called as sun shine.
2. Diffuse/Scattered radiations:
• Those radiations received at earth’s surface from all parts of the sky’s hemisphere after being
scatted in the atm.
• Thanks to these optical processes such as scattering, reflections and refractions, we do not get
sudden darkness.

3. Global radiation:
• it is sum of beam radiation and diffuse radiation.
• It is also called as total radiations.
• Total solar energy falling on unit area on any part of the earth is called as
global radiation.
• Air Mass (m):
• It is ratio of path of the sun rays through the atmosphere to the length of the
path when the sun is directly over head

Composition of Suns Radiation
• Suns radiation could be considered in three different aspect:
• Terrestrial radiation: It is the radiation, received on the earth’s surface after the
solar radiations have traversed through the layer of atmosphere.
• Extra terrestrial radiation: extra terrestrial radiation on the other hand is the
radiation incident on a surface kept out side atmosphere.
• Albedo: The earth reflects about 30 % of all the incoming solar radiation back to
extraterrestrial region through atmosphere.

Spectrum of solar radiation
• Suns radiation consists of a range of wavelengths. This is called the spectrum
of solar radiation.
• The intensity of each wavelength would be different.

Angle of latitude of a particular location(Φ):
• It is vertical angle between the line joining that point of location to
the center of the earth and its projection on an equatorial plane.
• O° for a point on the equator.
• When point is north of equator, the angle is +90° represented by Φ °N
• When point is south of equator, the angle is -90° represented by Φ °S

Declination angle (δ)
• It is the angle made between the line joining the sun and earth and its
projection on the equatorial plane.

• Due to inclination of earth’s axis, the line joining sun and earth will not lie on
the equatorial plane.
• It varies through out the earth from +23.45° to -23.45° as shown in figure.
• Declination has two zero values which are called Equinoxes (meaning equal
days)

• The relationship between δ with the day of the year could be
mathematically expressed by,
δ= 23.45 sin [360
365
(284+n)]

Hour angle (ω)
• It is the angle representing the position of the sun with respect to
clock hour and with reference to sun’s position at 12 noon.
• In others words it represents the angle through which the earth must
rotate so that the meridian at a point comes into alignment with sun’s
rays.
• It is constant and equal to 15°/hr.

Altitude angle (α)/ solar altitude angle
• Angle α between the line joining the sun rays and the center of the
horizontal Plane and its projection on the horizontal plane is called Altitude
Angle.
• it could be seen that at sunrise and at sunset angle is zero.

Zenith angle (ϴz)
• From previous fig. if vertical line is drawn to this horizontal plane, at
this center, the line joining sun and the center of the plane will make
an angle ϴz with this vertical . This angle is called zenith angle.
• Obliviously zenith angle is nothing but the compliment of altitude
angle,

Sunrise/Sunset hour angle (ωs)
• The angle corresponding to sunrise or sunset on a horizontal surface
is called sunrise or sunset hour angles.
• The sunrise and sunset hour angle at any place depends on its
latitude and declination at that place and it is given by equation,
cos ωs = - tan Φ* tan δ

Day length (td)
• Day length is the time elapsed between sunrise to sunset.
• Knowing the values of sunrise and sunset hour angle, we can
calculate the day length as follows:
• If ωs is the hour angle corresponding to sunrise and sunset, the
altitude angle changes from +90 to -90°
• For 90 ° rotation cos ωs = 1
• For -90 ° rotation cos ωs = 1

Local solar time (LST)
• This is also called Local Apparent Time (LAT) can be calculated using
various values of ϴz.
• This will vary from the actual clock time by approximately 4 minutes.
• This variation changes with the month of the year.
• LST = IST + or – 4 (standard time longitude – the longitude of the
location) + Equation of the time correction
Negative sign is used for location in eastern hemisphere

Solar azimuth angle (γs)
• It is horizontal angle measured on plane from north to the projection of
suns rays on this plane as shown in figure.

Tilt angle (β) (Slope of surface)
• The vertical angle between one edge of a surface and its projection
on the horizontal plane is called tilt angle.

• Slope is taken as positive if the surface is sloping towards south.
• Slope is taken as negative if the surface is sloping towards north.

Surface azimuth angle (γ)
• It is defined as the horizontal angle between the projection of the
normal to the horizontal surface and the north-south line as shown in
previous figure.
• As shown in previous figure PM= normal to the sloping surface
PM’ = projection of PM on horizontal plane

Angle of incidence (ϴ)
• It is defined as an angle between the sun ray and a line perpendicular
to the surface as shown in figure.
• Radiation intensity normal to the surface 𝐼 𝑛 = 𝐼 𝑏𝑛cos ϴ

Measurement of solar Radiations
• Three types of instruments are generally used , which can measure,
three different aspect of solar radiation. These are:
• The global or diffuse radiation:
The instrument used in this type of measurement are called
Pyranometers.
• The Beam radiation or direct radiation:
This could be measured using Pyrheliometers.
• Sun shine recorders:
used to measure the hours of sunshine over a day.

Types of Pyrheliometers
1. Angstrom Pyrheliometers
2. Abbot silver disc Pyrheliometers
3. Eppley Pyrheliometers

Solar Energy Collectors
• It is device for collecting or absorbing the solar radiations on a surface
called absorber and transfer of a part of radiant energy to fluid like
water or air in contact with it.
• The surface of collector is designed for high absorption and low
emissions.

Types of Solar Collectors
1. Flat plate collectors:
• Used for low temperature applications in the range from ambient
temperature up to 100° C.
• Application: solar water heating, space heating and cooling, drying, low
temperature power generation etc.

2. Concentrating type solar collectors:
• it is also known as focusing collectors.
• Used for medium to high temperature applications.
• There are two types:
1. cylindrical parabolic collectors: suitable for range of 100°C to 300° C. it is
used for vapor engine and turbine, process heating in industry, refrigeration,
cooking etc.
2. Parabolloid mirror arrays: Used for production of temperature above 300° C.
Suitable for thermo-electric power generation.

• Used for low temperature up to 100° C.
• The liquid generally used is water.
• In surrounding where temperature are below 0°C, water mixed with
ethylene glycol to avoid freezing of water.
• The orientation of flat plate collector is kept at the place it is installed
to get maximum output.

Advantages
• It absorbs direct, diffused and reflected components of solar
rediations.
• It is fixed in orientation thus there is no need for tracking.
• It has low cost and it is almost maintenance free.

Construction and materials for flat plate collectors
Absorber plate and tubes:
• Material should have high tensile strength, high thermal conductivity and it
should be corrosion resistant.
• It is made of metal thickness 0.2 mm to 1 mm. The absorber plate and tubes
generally made of copper, aluminium and steel.
• Absorption plate is coated with black paint having high absorptivity.
• Size of tube varies from 1cm to 1.5 cm having the pitch between 5 cm to 12
cm.

Different types of absorber plates and tubes

Pipe and fin type collectors
1. tubes in plate

2. Tube bonded in upper surface of plate

3. Tube bounded in lower surface of plate

4. Tubes fitted in grooved plate

Different types or roll band collectors

Sandwich type collector
• In these type of collectors water flows having high capacity of wetted
area and high capacity of water.
• Such type of collectors are used for very low temper requirement of
heating the water in swimming pools.

Thermal Insulation
• Insulating materials are used to reduce the heat losses.
• Materials have low thermal conductivity, stability at high temperature
up to 200°C, non-corrosive with ease of application.
• Thermal insulation used in 25 mm to 80 mm thickness.

Casing or Container
• It is in the form of box which encloses all the above components.
• Box is made of aluminum, steel or fiber glass in rectangular shape.
• Area of collector is generally 2𝑚2

Testing of solar collectors
• Standard testing procedures have been evolved which enables us to
evaluate the performance of various flat plate collectors with uniform
criteria similar conditions.
• It helps us to compare the performance of various solar collectors
more accurately and evaluate the yield from any given solar collector.

Main purpose of testing
1. To provide information about the performance of solar collection
system.
2. Comparison of performance of collectors for commercial purposes.
3. To give information about the parameters for the purpose of study
and development of flat plate collectors.

Testing Methods
1. Outdoor testing: In this method, the collector is placed in the sun
and tested under actual outdoor conditions.
• This method gives more realistic results but adverse weather
conditions can hamper the test.
2. Indoor testing: In this method, testing is done inside the laboratory
under artificially simulated conditions.
• Advantage of this method is that results are not dependent on the
weather conditions and testing can be carried out at any time.

Testing Procedures
1. Instantaneous procedure
2. Calorimetric procedure

Instantaneous Procedure
• This can be used to determine the instantaneous collector efficiency.
• In this method, collector is exposed to sun until steady state is
reached.
• Collector efficiency would be, Ƞc =
𝑞 𝑢
𝐼 𝑇 𝐴 𝑐
=
𝑚 𝐶 𝑝(𝑇2 − 𝑇1)
𝐼 𝑇
• Where, 𝑞 𝑢=Useful heat output (W),
𝐴 𝑐 = Collector area (𝑚2
),
𝐼 𝑇 = Total solar energy incident om the collector (W/𝑚2),
𝑇1= Inlet steady state temp. of fluid (K)
𝑇2 = Outlet steady state temp. of fluid (K)

Calorimetric Procedure
• In this method, outlet fluid is fed back to the inlet so as to form closed
system. Thus temperature of the fluid in this method continuously
increase.
• Collector efficiency would be, Ƞc =
𝑞 𝑢
𝐼 𝑇 𝐴 𝑐
=
𝑚∗𝐶 𝑝∗ ∆𝑇
∆𝑡
𝐼 𝑇
Where, ∆𝑇 = change in temperature measured (K),
∆t = Time interval during which temperature change was noted (s)

Limitations of Flat Plat Collectors
• These are heavy in weight.
• Suitable for low temperature applications up to 100 ° C like water and
space heating..
• Not suitable for large scale power generations.
• Low collector efficiency.

Concentrating Type Collectors
• It is also know as focussing collectors.
• Used when temperatures higher than 100° are required.
• The concentrator is an optical system in the form of reflecting mirrors
or reflecting lenses.

Types of solar concentrating collectors
1. Focussing type or concentrating type collectors:
• In this collectors, optical system focuses the solar radiations on the
absorber. These are further classified as :
1. Line focussing concentrators.
2. Point focussing concentrators.
2. Non-focusing type collectors: In this collectors, solar radiations are
allowed to fall on the absorber using reflecting in the mirror.

Focusing type concentrators
• Types,
1. Parabolic trough reflector.
2. Mirror strip reflector.
3. Fresnel lens collector.
4. Paraboloid dish collector.

• This type is line focussing type collector.
• Parabolic trough reflectors are usually made of highly polished or
silvered glass.
• In order that the solar radiations are always focused on a line with
respect to change in sun’s elevation by the parabolic reflector, either
the trough or the collector pipe is rotated continuously about the axis
of absorber.

• It is line focussing type collector.
• It has plane or slightly curved mirror strips mounted on a flat base.
• The individual mirrors are placed at such angles that the reflected
solar radiations fall on the same focal line where the absorber pipe is
placed.
• The collector pipe is rotated so that the reflected rays on the absorber
remain focused with respect to changes in sun’s elevation.

• This is also line focussing type collector.
• The angles of each groove is so designed that the optical behaviour of
the fresnel lens is similar to spherical lens.
• A fresnel lens collector is generally made of acrylic sheets having
overall dimensions of 4.7 mm in length and 0.05 in width.

Paraboloid dish collector (Point focussing)

Non-focussing type concentrators
• In these type of collectors the solar radiations are allowed to fall on
the absorber after using reflection in the mirror.
1. Flat plate collector with plane reflector.
2. Compounded parabolic concentrator (CPC).

Flat plate collector with plane reflector

• The concentrating ratio up to 4 can be achieved by such system.
• concentrating ratio is ratio of area of concentrating aperture to the
energy absorbing area of the receiver.
• In order that the attached mirror are effective , the angles of mirrors
should be adjusted continuously as the sun’s elevation changes.
• The temperature up to 140 °C can be attained with use of mirror
reflectors.

Compounded parabolic concentrator (CPC)

• It is also know as Winston collector.
• Both diffuse and direct radiations are collects.
• The concentrating ratio achieved in this collector ranges from 3-7.
• Temperature attained in range of 100 °C to 150 ° C.

Central tower receiver using heliostat mirrors

• A concentrating ratio up to 3000 can be achieved with this type of
system.
• It can generate high pressure and high temperature of steam suitable
for power generation in steam power plant.
• Design is quite complicated and costly.

Advantages of concentrating collectors
• Cost per unit area is less since it require less reflecting surface.
• Require less absorber area.
• Has high collector efficiency since heat losses are less.
• Suitable for large power generation

Disadvantages
• System needs tracking of sun which increase the cost of installation.
• Diffuse solar radiations cannot be collected in focusing type of
collectors.
• Require higher maintenance to retain the quality of reflecting surfaces.

Vertex, focus and sun in a line

Advantages of concentrating collector
• Due to higher concentrating ratio, the temperature attained is higher.
• Cost per unit area of solar collecting surface is less.
• Absorber is very small, hence heat loss to the surrounding per unit of
solar energy collecting area is less

Storage of solar energy
• There is always a mismatch between availability of solar energy and
energy demand on the system.
• It is clear from figure, that available energy is either surplus of
deficient to meet demand if solar energy is utilized directly by the
system.
• In order to balance generation with consumption and maintain grid
stability, it is necessary to store excess energy at appropriate times
and supply this energy.

Advantages of energy storage
1. It helps make renewable energy resources(wind, solar) more viable.
2. The size and cost of equipment of power plant can be reduced by 20-40
percent.
3. Reduces use of power plant which produces more emissions.
4. Increases load factor of generation up to 25 percent.
5. Delays the need for additional power plant.
6. Energy storage reduces size of stand by or peak load unit.

Energy storage methods
• Thermal
• Mechanical
• Electrical
• Chemical
• Electrochemical
• biological

Estimated worldwide installed main energy
storage capacity

Thermal energy storage
• Sensible heat storage: Heating a liquid or a solid, without changing
phase, energy stored due to change in internal energy of a material.
• Latent heat storage: Heating a material, this undergoes a phase
change (using melting).
• Bond energy storage: Using heat to produce a certain physiochemical
reaction and then storing the products.

Sensible heat storage
• In this method, energy is stored or extracted by heating or cooling a
liquid or a solid, which does not change its phase during process.
• Sensible heat storage system utilizes the heat capacity and change in
temperature of material during process of charging and discharging.
• Sensible energy stored can be expressed by,
E = m 𝑇1
𝑇2
𝐶𝑝 ∗ 𝑑𝑇

• Where, m = mass of medium,
Cp = specific heat of medium,
T1 = initial temperature of medium,
T2 = final temperature of medium.
• The amount of heat stored depends on the mass of medium, specific
heat of the medium and temperature change in medium.
• A variety of medium have been used in such systems like solids like
rocks, bricks, metals, sand, etc.

• Water is most commonly used medium in a sensible liquid heat
storage system for storing thermal energy at low temperature
because of its low cost, highest specific heat, high density, high
thermal conductivity, easy to handle, etc.
• Most small and medium solar water heating and space heating
systems use hot water insulated storage tanks.
• An approximate thumb rule followed for fixing the size is to use about
75 to 100 liters of storage per square meter of collector area.

Long term thermal energy water storage in
underground layers

• Rocks, metals, concrete, bricks, sand, etc. are used in packed bed to
store thermal energy.
• Size of rocks used varies from 1 to 5 cm.
• An approximate rule of thumb for sizing is to use 300 to 500 kg of
rock per square meter of collector area for space heating applications.
• Rock or pebble-bed storage can also be used for much higher
temperature up to 1000° C.

Advantages
• It is simple in design and relatively inexpensive.
• High temperature is possible.
• No freezing and corrosion problem.
• Rocks acts as its own heat exchanger, there is no need of heat
exchanger.

Disadvantages
• Larger amounts of solids are needed than using liquid (water) storage
system.
• The cost of storage media per unit energy storing is higher.
• Simultaneous charging and discharging are not possible.
• High pressure drop.

Latent heat storage or phase change energy storage

• Materials that have large amount heat stored in the form of latent
heat which is absorbed or released when materials change state from
solid to liquid or vice versa is called phase change materials (PCM).
• There are several materials that undergo a change of phase are used
for latent heat storage system as steam/water/ice, cryogenic liquid air
or nitrogen, paraffin, alcohols, etc.
• PCM is able to absorb or release large quantities of energy at a
constant temperature.

Solar water heater
• A solar water heater is a solar system that uses the thermal energy of
the sun to heat water.
• The basic idea behind the solar water heater is a piece of black piping,
fitted with water, and laid in the sun for the water to heat up.
• To heat up more water you increase the number of pipes to make a
“collector” and add a tank to store the heated water in.

Basic operations of solar water heater
• Collector: solar radiation is captured by solar collector.
• Transfer: circulating fluid transfer this energy to a storage tank,
circulation can be natural or forced, using a circulator.
• Storage: hot water is stored until it is needed at a later time in a
room, or on the roof.

Advantages
• Operating cost of solar water heater is zero.
• A solar water heater do not produce any noise and vibrations.
• It cannot give you a shock or set fire to your house like electrical or
flame-based water heating systems.
• Solar water heater do not make any smoke, so they don’t make your
home smell or get dirty.

Application
• Service hot water:
• Domestic hot water systems.
• Providing hot water for commercial and institutional applications, including
multi-unit houses and apartment building, in schools, health center's, etc.
• Small commercial and applications such as car washes, laundries and fish
farms, etc.

• Swimming pools: the water temperature in swimming pools can also
be regulated using solar water heating system.
• Solar water heating systems can also be used for large industrial loads
and for providing energy to district heating networks.

Solar heating and cooling of buildings
• Worldwide the energy consumption for cooling and air conditioning is
rising rapidly.
• Usually electrically driven compressor chillers consume most energy
in peak-load periods during summer.
• To reduce this power consume solar energy is a solution.

Passive space heating / cooling systems
• In this system, all the three functions of collection, storage and
distribution of solar energy is done by natural means for transport of
energy by convection, conduction and radiation, i.e. system operate
without pumps, blowers or other mechanical devices.
• In this cooling and heating system, a special building design is
necessary.
• In passive solar heating, solar radiations are collected by an element
of structure itself and solar energy directly admitted into the building
through large south facing window.

Active space heating/cooling system
• In this system, pumps, blowers or other mechanical devices are used to
circulate the working fluid for transportation of heat and therefore a
special building design is not necessary.
• The air or any other fluid is circulated past solar heated surface and
through the building by convection.
• The air or any fluid is circulated past solar heated surface and through the
building by convection.

Passive space heating/cooling systems Active space heating/cooling system
This system operates without pumps, blowers or other
mechanical devices.
This system operates with pumps, blowers or other mechanical
devices.
A special building design is necessary. A special building design is not necessary.
In this system, the solar radiation are collected by an element
of the structure itself. Various elements of the buildings like
walls, roof, windows are so selected and so architecturally
integrated that they participate in the collection, storage,
transportation and distribution of thermal energy.
In this heating system, solar radiation are collected using some
kind of separate collectors. Solar energy may be stored in
sensible heat storage materials, or in latent heat storage
materials and energy is redistributed in building space using
pumps, blowers, fans, etc.
It is less expensive than active system to construct and operate. It is more expensive than passive system to construct and
operate.

Passive solar space heating systems
1. Direct gain
2. Thermal storage wall (indirect gain)
3. Thermal storage roof (indirect gain)
4. Attached sun space
5. Convective loop

Sun space passive solar heating system

Convective loop passive solar heating system

Active hot water solar space heating system

Active hot air solar space heating system

Shading of window using overhang
•Window, walls and
roof are shaded.
•Louvers are
designed to admit
direct solar radiation
in winter and exclude
it in summer.

Solar passive cooling through dehumidification
•Incoming air first gets
dried by solid adsorbent
material.
•Evaporatively cooled by
passing over water baths.
•Circulation is maintained
by naturalchimney effect.

Solar passive cooling through evaporation
•A water film over the
roof absorbs heat from
roof, it evaporates and
it does not allow the
roof top get hot

Solar pumping
• A solar water pump is a socially and environmentally attractive
technology to supply water.
• Solar energy can be used for pumping of water in two ways as:
1. Direct conversion method: solar energy is directly converted in to
electricity using photovoltaic (solar) cell.
2. Thermodynamics conversion method: solar energy is first converted
in to mechanical energy and then mechanical energy used for
pumping water.

Photovoltaic water pumping system

Solar thermal water pumping system

Solar cooker
• A solar cooker, or solar oven is a device which uses the energy of
sunlight to heat food/drink to cook it.
• Using solar energy for cooking purposes is an attractive and relevant
option.
• Flat plate box cooker with and without reflector,
• Box type solar oven- multi reflector type
• Parabolic disc concentrator type solar cooker
• Scheffler cooker
• Panel cooker
• Hybrid cooker

Advantages
• Solar cooker use no fuel.
• Solar box cooker attain temperature up to 165˚ C.
• Solar cooker do not produce any smoke as a product of combution.

Disadvantages
• Solar cooker less usable in cloudy weather.
• Many solar cooker take longer time to cook food than fuel based
oven.
• Cooks may need to learn special cooking techniques to fry common
foods.
• Some solar cooker designs are affected by strong winds, which can
slow the cooking process, cool food and disturb the reflector.

Box type solar cooker (150˚ C)

Box type solar oven (250˚C in winter & 350˚C in summer)

Parabolic disc concentrator solar cooker

Solar still
• A solar still is a simple device which converts saline water into fresh
water using the heat of the sun.

Direct mode with forced convection type drier

Indirect mode with forced convection type drier

Photovoltaic operated refrigeration system

Solar driven mechanical power cycle

Temperature and concentration profile for a
typical solar pond

Solar power plants
1. Solar photovoltaic technology
2. Solar thermal power plants:
1. Classification based on temperature
• low temperature cycles (100°C)
• Medium temperature (150-300°C)
• High temperature (300° C)
2. Classification based on collector
• Solar pond
• Solar distributed collector
• Central receiver system
• Solar chimney

Low temperature power generation cycle
using liquid flat plate collectors

Low temperature power generation cycle
using solar pond

Medium temperature solar power plant

Solar distributed collector thermal power plant

Solar central receiver thermal power plant

• Solar furnace is a structure that uses the concentrator solar radiations
to produce very high temperatures in range of 1000˚ C to 3500˚ C.
• Solar furnace can be used in space to provide energy for
manufacturing purpose.
• The solar furnace can be utilized to produce high temperature for
metallurgical and chemical operation.
• High initial cost.

Solar photovoltaic system
• A solar cell or photovoltaic cell is a electrical device that converts
solar energy directly into DC electric power.
• This makes the PV system far more convenient and compact
compared to thermal method of solar energy conversion.
• Its works on photovoltaic effect, the generation of potential
difference at the junction of two different materials in response to
visible or other radiation.

Principle of working of solar cell

Classification of solar cell
• Single crystal silicon solar cell
• Multicrystalline silicon solar cell
• Bulk material solar cell
• Thin film solar cell, etc

Advantages of solar cell
• It converts solar energy directly into electric energy.
• Solar cells are reliable, durable and generally maintenance free.
• These are compactable with all environments and response is instantaneous.
• Simple stand alone system for use at remote location can be built.
• Sunlight is free, and no noise or pollution is created from operating
photovoltaic system.

Disadvantages
• Conversion efficiency of solar cell is very low and is of the order of
only 30%.
• Large area is needed to generate sufficient power.
• Solar cell materials are very costly.
• At present, the high cost of PV modules and euipment is primary
factor for the technology.

Applications
• Remote lighting system
• Water treatment
• Portable power supplies
• Toys, watches and calculators
• Water pumping

Solar energy

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