Unit 1 Solar Energy

7/30/2019 Unit 1 Solar Energy

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ME458 - RENEWABLE ENERGY

Unit -1Solar Energy Solar Radiation Heat

Transfer Equations


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Energy can be neither created nor destroyed, but only

transformed.

Solar Energy

Example: You have electricity available at your house. If you

plug a lamp into an receptacle, the energy is converted fromelectricity to light and heat. We convert energy from a variety

of forms into forms we can more easily use.

So.What Is Solar Energy?

SOLAR ENERGY is energy from the sun that is converted into

thermal or electrical energy.


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Introduction To Solar Energy


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Cont..

Enormous amount of heat and light is

produced by nuclear fusion reactions

Energy in the form of radiation is used for

heating and producing electrical energy


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Cont..

Energy that is converted

from sun light.

Photovoltaic cell: collects

sunlight and converts it into

electricity. Can be useddirectly or stored in a

battery. Used in chips,

panels, roofing tiles


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Cont..

The heat and light received from the sun support the environment on

the earth through the following natural effects,

Temperature balance on earth

Photosynthesis by biological plants, production of oxygen and organic

materials

Wind due to unequal heating of water, land surfaces

Water cycle: evaporationcloudsrainswater evaporationrains

Heating of ocean water: ocean thermal energy (OTEC)

Waves in ocean: ocean wave energy

Tides in ocean: ocean tidal energy


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Significance of Solar Energy

Solar energy is the most readily available source of energy.

It is free.

It is also the most important of the non-conventional sources

of energy because it is non-polluting.


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Fact About Solar Energy

Solar energy is received on earth in cyclic, intermittent and

dilute form with very low power density from 0 to 1 kW/m2

Direction of solar energy changes during the day and with

season

It is affected by atmospheric clarity, degree of latitude, etc.

Solar spectrum has waves ranging from infra-red frequencies

to ultraviolet frequencies


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Applications of Solar Energy

Passive heating applications

Solar thermal energy application of medium temperature and high

temperature for,

Producing process heat, steam

Producing electrical energy through solar, thermal, electrical

energy conversion in central receiver power plants

Solar to electrical energy direct conversion by photovoltaic cells for

low and medium power rating

Large solar central receiver thermal power plants in MW range


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Zenith angle (z) is the angle of incidence for a

horizontal surface. It indicates the position of sun in

the sky. It is the angle b/w vertical line and the sun

ray.

Solar altitude angle (a) is the angle b/w the sun rays

and the projection of the sun rays on the horizontal

plane.


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http://en.wikipedia.org/wiki/File:Azimuth-Altitude_schematic.svg


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Merits and Limitations of Solar Energy

Merits LimitationsRenewable energy available free of cost Low energy density 0.1 to 1 kW/m2

Available naturally in most parts of the

world in every consumers premises

Large area covered by solar collector

Clean, pollution free Direction of rays changes continuously

Solar PV systems are economical and

feasible for remote and stand alone power

plant

Direction of rays changes continuously .

Varies during the day, season and with

weather conditions.

Solar thermal power plants are feasible in

deserts, dry sunny areas where other

sources of energy is not available

Energy not available at night and during

clouds

Earth receives vast solar energy. Cost

effective technologies are being evolved.

These will help in solving energy crises in

the world

High cost of conversion. Required hybrid

plant with storage facility for supplying

energy during non/sun period

Active And Passive Methods


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Cont


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Cont..


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Solar thermal energy applications of medium and high temperature


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S b t I S l E Pl t


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Subsystems In Solar Energy Plant

Solar collector or concentrator

Energy transport medium

Energy storage

Energy conversion plant

Power conditioning, control and protection system

Alternative / standby power supply

S l ll t t t


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Solar collector or concentrator

It receives solar rays and collect energy, following collectors

Flat plate type

Parabolic through with line focusing

Paraboloid dish with central focusing

Fresnel lens with central focusing

Heliostates with central receiver focusing


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Heat transport fluid

(in tubes)

Insulation

Absorber

Transparent

Cover

Solar radiation

(Direct and Diffuse)Cushion

Supports &

Seats for

glass


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ll


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Concentrating Collector: Focusing Type

Focusing collector is a device to collect solar energy with high

intensity of solar radiation on the energy-absorbing surface.

Concentrating or Focusing collectors may be considered intwo general categories:

Line focusing

Point focusing

Line Focusing Collector

Th li i ll i

Point Focusing Collector

Th i i ll l


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- The line is a collector pipe

through which the heat

transport fluid flows.

The point is a small volume

through which the heat

transport fluid flows.

Fig. Parabolic Trough Fig. Parabolic Dish


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Fresnel Reflectors


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A linear Fresnel reflector power plant uses a series of long,

narrow, shallow-curvature (or flat) mirrors to focus light onto

one or more linear receivers positioned above the mirrors. On

top of the receiver a small parabolic mirror can be attached

for further focusing the light.

Power Tower


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Power Towers (also known as 'central tower' power plants or'heliostat' power plants) use an array of flat, moveable mirrors

(called heliostats) to focus the sun's rays upon a collector

tower (the receiver).

The advantage of this design above the parabolic troughdesign is the higher temperature. Thermal energy at higher

temperatures can be converted to electricity more efficiently

and can be more cheaply stored for later use.

The disadvantage is that each mirror must have its own dual-axis control, while in the parabolic trough design one axis can

be shared for a large array of mirrors.

Power Tower


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E T t M di


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Energy Transport Medium

Such as water/steam, liquid metal, gas which

transports thermal energy from collector to heat

exchanger / thermal storage

In solar PV system energy transport is by electrical

energy


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Energy Storage

As solar energy not available continuously, we need

substantial energy storage for supplying power to the load

during nights and cloudy periods, etc.

3 types of storage commonly used

Thermal energy storage

Energy storage in electrical form by means of batteries

energy storage by pumped storage hydro electric plants

l


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Energy Conversion Plant

Thermal energy collected from solar collector is used for

producing process-steam, hot water etc

Solar energy used to heat swimming pool

Power Conditioning, Control And Protection System


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Load requirement of heat, process steam etc vary with time.

Energy supply has certain specification and quality requirement

such as,

Temperature and pressure of steam

Voltage, current, frequency power of electrical energy, etc

The power conditioning unit perform several functions such as

control, regulation, conditioning, protection, automation, etc

Alternative/Standby Power Supply


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Alternative/Standby Power Supply

Solar energy alone cant satisfy the load requirements during

night hours, cloudy hours, etc (low power density 0 to 0.2

kW/m2

Alternative may be

Power from electrical network

Power from standby diesel generator


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Unit 1 Solar Energy

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