solar applications.ppt

7/27/2019 solar applications.ppt

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THERMAL APPLICATIONS

Water Heating

Space Heating

Power generation

Space cooling and Refrigeration

Distillation

Drying

Cooking


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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


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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


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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When hot water is withdrawn for use cold makeup water takes its place because of ball float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


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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.


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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.

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


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POWER GENERATION

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.


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Solar Chimney

Tall central chimney is surrounded at its base by a circular green hose consisting of a transparent

cover supported a few meters above the ground by a metal frame

Sunlight passing through the transparent cover causes the air trapped in the green house to heat

up by 100 to 200 .

A convection system is set up in which this air is drawn up through the central chimney, turning

a turbine located at the base of the chimney and then into electrical energy by conventional

electrical generators

The conversion efficiency is low.

Cost is less compared to central power tower system.


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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.


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Common refrigerant absorbent mixtures:Ammonia water

Water- Lithium Bromide

COP Value : between 0.5 to 0.8

High cost to erect array of collectors

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, whereit 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.


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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%


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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


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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.,


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COOKING

BOX TYPE COOKER:

A slow cooking device suitable for domestic purposes

Consists of rectangular enclosure insulated at sides and bottom and having one or two glass covers at the top.

Solar radiation enters the top and heats up the enclosure in which the food to be cooked is placed in shallowvessels.

Temp. around 100o C can be obtained in sunny days.

Suitable for cooking only rice, pulses etc,.

Time taken for cooking is from half an hr. to two and half hrs ( app)

Additional mirrors attached my reduce the cooking time by increasing the temp. around 150C more.

Operator need not

to spend much

time in sun with

experience Important domestic

Application.

Many models are

available


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DISH SOLAR COOKER

Radiation is concentrated by

Paraboloid reflecting surface

The cooking vessel is placed at the

focus of the reflecting Paraboloid mirror

and is thus directly heated.

Temp. well above 2000c are obtained

in it

It can be used to prepare food items

that require roasting, frying or boiling

Features:

It requires manual tracking for every 15

or 20 min.

Cooking is done outdoors, hence, the

operator has to spend more time in sun


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solar applications.ppt