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5. NON-CONVENTIONAL ENERGY RESOURCES

5.1 NON-CONVENTIONAL ENERGY SOURCES weather condition.
RELEVANT TO INDIA:  India has reasonably good potential for geothermal; the
There is separate Ministry in the Government of India to potential geothermal provinces can produce 10,600 MW of
exclusively focus on this important area of power generation. power.
National Electricity Policy lays down that the state Electricity  At present there are no operational geothermal plants in
Regulators Commissions should prescribe a proportion of India. There is also no installed geothermal electricity
power which should be produced and supplied to the grid generating capacity as of now and only direct uses (e.g.
through the non-conventional sources. Drying) have been detailed.
 India’s Gujarat state is drafting a policy to promote
5.2 Need to develop Non-conventional Sources of Energy: geothermal energy.
1. Conventional sources are energy are reducing with phrase of  Potential Sites:
time. e.g. oil is likely to last up to 2025 and coal another 200 (a) Puga Valley (J&K), (b)Tatapani (Chhattisgarh),
years. (c)Godavari Basin Manikaran (Himachal Pradesh)
2. Conventional sources are one of the main cause of air (d) Bakreshwar (West Bengal), (e) Tuwa (Gujarat),
pollution which is causing global warming and climate (f) Unai (Maharashtra), (g) Jalgaon (Maharashtra).
change.
3. It causing reduction in agricultural production per capita. 5.3.1 MAGNETO HYDRODYNAMIC GENERATOR:
4. Reduced fresh water supply. MHD is a device which converts heat energy of an ionized
fluid at high temperature directly through the applied magnetic
5.3 Present Status of Non-conventional Energy Sources: field, without a conventional electric generator. In such
(i) Solar Energy: systems power generation is based on the Faraday’s law of
 A potential for 30MW/km2 in India. electromagnetic induction.
 Solar Photovoltaic (SPV) contributes 2.5% of power In such condition when plasma passes through a strong
generation from renewable energy. It aggregate capacity of magnetic field then force begin to act on its ions, this force act
47 MW have deployed for various applications. on plate P1 for +ions and towards P2 for –ions. Due to
 Maximum efficiency possible below 30%. But Carbon Nano migration of these charges a potential difference creates
Tube (CNT) based PV cell hold promise of higher efficiency between the plates. If a load is connected between these plates
upto 35%. then electricity begin to flow. This process takes place in
 Generation cost is still 4 times higher than a thermal power MHD channel.
plant.
 Gujarat has been a leader in solar power generation and 5.3.2 WORKING PRINCIPLE:
contributes 2/3rd of the 900 MW of photo-voltaic in the When a charged particle moving in a magnetic field, having
country. charge q and velocity v, then the force acting on it:
F  q (v  B )
(ii) Wind energy scenario:
 India ranks fifth amongst the wind-energy-producing If E is the electric field acts, then the total force:
countries of the world after USA, China, Germany and F  q( E  v  B) (1)
Spain and produces 12009 MW as on 30 June 2011.
 Gross wind energy potential: 65,000 MW and technical The velocity to be used in above equation (1) is the vector sum
potential: 45,000 MW. of gas velocity v and the particle drift velocity u. Thus force is
 States with high potential: Tamil Nadu, Gujarat, Andhra given by: F  q ( E  v  B  u  B) (2)
Pradesh, Karnataka, Kerala, Maharashtra.
 Capital cost of wind power projects ranges from Rs. 5-6 can be written as: F  q( E '  u  B)
corer/MW and the cost of generation is estimated to be Rs. where E '  ( E  v  B) (3)
2.5-3/kwh.

(iii) Bio-fuels:
 These fuels are in preliminary stages of development, and Z Magnetic
Y P1 flux B
will take several years to develop.
 But no surplus oil seeds available for bio-fuels. In this case,
Velocity v
Jatropha seems to available alternative.
 India has 60 million acres waste-land, and 30 million of that d Ionized Gas 1 2
is suitable for Jatropha plantation. X P2
O Load R
(iv) Geothermal Energy:
 Geothermal energy supplies more than 10,715 MW to 24
countries worldwide which is expected to generate 67,246 FIG.5.1 DIRECTIONS OF MAGNETIC FLUX, GAS
GWh of electricity in 2010. VELOCITY AND FORCE IN MHD SYSTEM
 It is reliable source of energy which is available From figure, the motion of gas is in x-direction, magnetic field
continuously throughout the year and independent of

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B is in y-direction and the force on the particle is in z- field produces DC current through generator in this section.
direction. The duct is water cooled to remove the heat.
If the distance between the plates be d, then the electric
V
intensity b/w the plates is: E z   (4)

FLUE GAS
d

K
1

A
C
T
S
The total electric field is: E '   E z  Bv  ( Bvd  V ) (5)
d
The electromagnetic fields Ez and B acting on the moving

REMOVAL
OF N2 & S
gas produce the same force on the ions as the electromagnetic
field E z and B produce on gas with zero average velocity. The

AC SUPPLY
term Bvd gives the internal e.m.f. (or open circuit voltage) of
the MHD generator.

RECOVERY
If R0 and RL be the internal resistance of generator and load
resistance respectively, then the current I through the circuit

SPEED
V0
be: I (6)
R0  R L
2
 V0 
So the power output: P  V0 I  I R0  
2  .R0

HEATER
AIR PRE

 R0  R L 

INVERTER
The power delivered to the load is maximum when load
resistance = RL = R0
V02 ( Bvd ) 2 B 2 v 2 dA

MHD GEN
Pmax    (7)

ET
N ET
4 R0 4 R0 4

N
σ = conductivity of gas (Ω-1/m);

MAG
MAG
A = electrode surface area (m2)
B 2 v 2

COMBUSTOR
So maximum power output per unit volume =
4 SEEDING
V0 Bvd ABv
The maximum current: I max    (8)
R0  R L 2 R0 2
COAL
5.3.3 MHD CYCLES & WORKING FLUIDS:
(i) OPEN CYCLE MHD SYSTEMS:
In an open cycle system the working fluid is used on the
once through basis. The working fluid after generating FIG.5.2 OPEN CYCLE MHD SYSTEM
electrical energy is discharged to the atmosphere through a
stack. Generally coal is used as fuel as it produces more (f) Inverter: The generated DC is converted into AC by using
conductive plasma; this is because of more carbon atom as the inverter before supply to grid.
compared to hydrogen atom. The working temperature of such (g) Gas Chamber: The exhaust hot gasses passes through the
MHD generators lies approximately in the range above air cleaner to control the pollution & remove harmful gases.
23000C. (h) Speed Recovery System: Seed material is expensive &
The different parts of open cycle generator are: need recovery system along with open MHD power cycle for
(a) Compressor: Compressor is used to raise the pressure of further use. The removed seeds are supplied back in the
the air supplied in combustion chamber for efficient burning of combustor.
fuel. Thepre-cooled air is compressed in compressor before
being supplied in the pre-cooler. (ii) CLOSED CYCLE MHD SYSTEM:
(b) Pre-heater: The compressed air pre-heated in the pre-  In this system the very high thermal efficiency is achieved
heater at 11000C from the exhaust gases of the generator to with low cycle cost in closed plant & provides more useful
increase the combustion efficiency of working fluid. power at low temperature at 16000C. The ducts of these
(c) Combustor: The fluid is burnt in this section of generator units are small because of high pressure.
in the presence of hot air coming from pre-heater & gas is  Helium or argon is used as working fluid, heated in heat
seeded with cesium to ionize the gas. exchanger & get ionized, alkali metals is mixed with inert
(d) Nozzle: The high temperature gases after combustor pass gas to provide the necessary conductivity is closed cycle
through convergent-divergent nozzle to increase its velocity of plant, where recovery is possible.
order of 1000 m/s.  The working fluid in closed cycle is seeded with Cesium and
(e) Generator Dust: It is made of heat resisting & insulating circulated in a closed loop. Gas is burned in the combustor is
material. The high magnetic flux is applied in this section of supplied in the heat exchanger, where the heat is transferred
the duct at perpendicular to flow direction of gases. As the to the working fluid.
moving gas cuts the line of magnetic flux the induced electric  The ionized gas passes through the magnetic field to

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produce DC power. with velocity of 150 m/s.
 The electrical conductivity of metallic vapour is poor. That
brings the overall conversion efficiency lower than that of

ALTERNATOR
COMPRESSOR
gas as a working substance.

(iii) HYBRID MHD GENERATOR:

 The hybrid MHD generator is developed to improve the
thermal efficiency of plant. The efficiency up to 60% is
achieved in the hybrid system.
 The working gas enters in the MHD at 30000C and will
leave at 20000C through the steam turbine coupled with
S.T
S.T

generator.
 A steam power plant is connected along with MHD
generator to use the remaining energy of exhaust gases of
MHD generator and converted it into electrical energy.
 The MHD plant may be open or a closed type. This steam
STEAM

power plant works on Rankine cycle.

5.3.4 ADVANTAGES OF MHD SYSTEM:

HX2

ARGON

1. These systems having higher efficiency (60-65%) because of

INVERTER

WATER
higher operating temperature.
2. Requires less area and maintenance as compare to
conventional power plants of same capacity.
MHD GEN

ET
N ET

3. Less pollution to the environment because of less fuel

COMPRESSURE

INTERCOOLER
N

consumption as compared to other conventional power

MAG
MAG

plants.
WITH

4. They are compact in size, have low specific weight and high
power density, having instant operation and suitable as peak
load.
ARGON

5. Provides direct conversion of heat directly into electrical

Cs

energy.
COMBUSTION

5.3.5 DISADVANTAGES:
PRODUCT

1. Power generation in MHD is directly proportional to square

COMBU-

of magnetic flux, it needs very large power to create it which

HEATER
AIR PRE

STOR
HX1

increases to cost of the system.

2. High temperature gases causes corrosion and chemical
erosion.
3. It is difficult to built equipments to withstand very high
ARGON temperature, used in MHD.
4. High initial cost due to large sized magnets and equipments.
5. High thermal and frictional losses.
GASIFIER

5.4 SOLAR POWER PLANT:

STACK

A solar power plant converts solar energy into electrical

energy. They can be divided into following categories:
1. Low temperature solar power plant using flat plate
collectors
STEAM
AIR

2. Medium temperature solar power plant using concentrated

COAL

solar collectors
3. High temperature solar power plant using tower system.

HX1-Heat exchanger-1, HX2- Heat exchanger-2, 1. LOW TEMPERATURE SOLAR POWER SYSTEM:
Cs- Cesium injection, ST-Steam turbine,  The low temperature solar power plants use the working
fluid temperatures in the range of 600C to 1000C which can
be obtained using flat plate collectors.
FIG.5.3 CLOSED CYCLE MHD SYSTEM
 Since the water can be only heated 800C in FPC, the systems
 The combustion products are discharged to the atmosphere needs to use a working fluid having low boiling temperature
after removal of heat in heat exchanger like butane gas.
 It shows the schematic of liquid metal MHD generator. The  The cold water is circulated into the collector with the help
superheated metallic vapour is expanded through the of a circulating pump.
supersonic nozzle and enters in the generator in liquid form  The heated water is circulated in a heat exchanger called

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butane boiler, where it generates the butane gas at high
pressure. This butane gas supplied to a butane turbine to  The general range of working temperature is between 2500C
produce mechanical power due to expansion of butane gas. to 4000C.
 The vapour coming out of the turbine is condensed in a  The working fluid, usually water, is heated as it circulates
condenser and sent back for recirculation with the help of through the receivers.
feed pump.  This heat is transferred to storage tank and fed to water
 The mechanical power output of turbine is converted into where the steam is generated in the steam generator.
electric power by generator.  This steam is utilized to run a turbine coupled to a electric
generator, which converts it into electrical energy by electro-
Turbine mechanical energy conversion.
 The exhaust of steam turbine is condensed in the condenser
with the help of cold water circulated in the condenser.
Heat
 A 30 MW plant have been installed in Rajasthan under the
Exchanger
or department of non-conventional energy sources.
ect
C oll
e
lat Storage

Compressor
a tP 3. HIGH TEMPERATURE SOLAR THERMAL POWER
Fl Tank
PLANTS:
 Such plants use heliostats and have high thermal efficiency,
can build in the capacity of 50 MW to 200 MW.
Water  The solar dish collectors receive solar radiations which are
Pump collected at a common focusing point. Small volumes of the
Pump Working
Fluid fluid are heated at this point high temperature.
 In central tower receiver an array of plane mirrors called
FIG.5.4 LOW TEMPRATURE SOLAR POWER PLANT
heliostats which are individually controlled and tracked to
reflect the solar radiations on a receiver kept on a tower of
2. MEDIUM TEMPERATURE SOLAR POWER PLANT: tower of about 500 m height.
 These systems employ an array of parabolic through
concentrating collectors spread over a large area. Incident Receiver Power
Radiation Subsystem Generation
System Generator
Boiler
Generator

Turbine

Condenser
Turbine

Cooling
Pump

Tower

Collector
Exchanger

Subsystem
Heat

Boiler
Feed Water

FIG.5.6 HIGH TEMPRATURE SOLAR POWER PLANT

Storage
Tank

 The feed water in the absorber-receiver called boiler is

converted into high steam of about 6000C- 7000C.
 This steam is supplied in a conventional steam power plant
coupled to an electric generator to generator electrical
power.
Array of Solar
Concentrating
Solar Radiation

Collectors

5.5 WIND ENERGY:

5.5.1 Wind Energy and Its Sources: Wind energy is an
indirect form of solar energy. They are caused by the uneven
heating of earth’s surface and its rotation. The winds can be
classified in two categories:
(i) Local Winds: Local wind is caused due to unequal heating
FIG.5.5 MEDIUM TEMPRATURE SOLAR POWER and cooling of ground surface and water bodies at day and
PLANT night. During day time land is hotter than sea due to which air

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near the surface becomes hot faster than the sea which creates from tall buildings, towers etc.
a pressure difference between surface and sea shore and due to  Fatal collisions of birds caused by rotating turbine blades.
this difference in pressure cool air at high pressure zone (from 5.5.3 SITE SELECTION: Following factors are to be
sea) will move towards the land and these breeze are known as considered for selection of good site for wind power
sea breeze. Its vice versa action is taken place at night and generation:
now air starts to move from surface to sea and such breeze are  High annual wind speed (should have an average wind speed
known as land breeze. in the range of 6 m/s to 30 m/s throughout the year).
(ii) Planetary Wind: These are caused due to unequal heating  Historic data of wind mean speed must be collected for
of the earth’s surface near the equator and the northern or average velocities during the year to select the site for
southern poles. Because of this, warm air from tropical regions availability of wind velocities needed for installation of
flows upward and moves towards the poles and cool air from wind farms.
poles moves towards the tropical region.  Tower design must be adequate to withstand maximum wind
speeds observed in the last few years in the installation area.
5.5.2 CLASSIFICATIONS OF WIND TURBINES:  No tall obstructions for a radius of 3 Km.
Wind turbines may be classified into two categories:  Open plain or open shore
(1) Horizontal axis, (2) Vertical axis.  Top of a smooth, well rounded hill with gentle slopes
 Mountain gap which produces wind funneling.
Rotor Blade
5.6.1 GEOTHERMAL ENERGY: Geothermal energy is a
form of renewable energy, having the source of natural heat
Rotor inside the earth. It is renewable since the earth’s interior will
Diameter continue to energy having high energy density. It is
GearboxGenerator inexhaustible like solar or wind energy. The geothermal
energy in the form of heat energy can be utilized economically
and efficiently for power generation and other applications
Rotor Diameter

with the existing available technologies. Though the amount of

thermal energy within the earth is very large, useful
geothermal energy is limited to certain site only in the world
Rotor Blade

because of the feasibility to access and extract heat. The sites

from where the thermal energy can be extracted are called
geothermal fields. The commercial utilization of this energy
started first in Italy in Larderello in 1904, Lardell (1913),
Tower Iceland (1930) and other part of the world by 2000. In India
about 50 shallow wells are drilled for steam production in J&K
belt. The thermal springs are found in different parts of India
i.e. Himachal Pradesh, Maharashtra, Cambay of Gujarat, Uttar
Gear Pradesh and some parts of Bihar and near Jawai in Assam.
box Generator
5.6.2 ORIGIN OF GEOTHERMAL ENERGY:
 The earth’s interior having mass of hot liquids, gases and
(a) HORIZONTAL AXIS (b) VERTICAL AXIS steam is cooling slowly and the temperature of the earth’s
core is estimated to be about 40000C.
FIG.5.7 WIND TURBINE
 The average geothermal heat dissipated from the land is
5.5.3 FEATURES OF WIND ENERGY: about 0.06 W/m2 as compare to solar heat energy of 1
ADVANTAGES kW/m2.
 It is renewable & free of cost.  Below the solid crust is the molten mass called magma
 Pollution free and not release toxic gases. which is still in the process of cooling.
 Have low maintenance cost.  The earth’s vibrations caused the magma to come near the
 Doesn’t require any transportation. earth surface thus causes active volcanoes, hot springs and
 Doesn’t require consumption of water. geysers water exists.
 The hot magma near the surface solidifies into igneous rock.
DISADVANTAGES The heat of magma is conducted upwards into this rock and
 High capital cost. ground water that finds its way down to this rock through
 Having low efficiency. fissures in it will be by the heat of the rock or by mixing
 Depends on location, season and wind speed. with hot gases and steam emanating from the magma.
 Causes sound pollution.  The heated water will then rise upward by convection into
 Storage of wind is not possible. porous and permeable reservoir above the igneous rock. It is
covered by the layer of solid impermeable rock. It traps the
ENVIRONMENTAL IMPACT hot water in the reservoir called hydrothermal field.
 Wind Turbines can safely within the range of 5m/s to 24m/s  A well made by drilling hole in the upper crust in the region
wind speed. of geothermal field can be used to trap steam for use in a
 Proper land is required for installation of wind turbines, free conventional power plant. The steam originating from

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magma is called meteoritic steam, largest source of  This cold water is either sent to chemical recovery or it is re-
geothermal steam. injected into hot field with the help of condensate pump.
 The main drawbacks of these plants are the presence of
5.6.3 CLASSIFICATIONS OF GEOTHERMAL ENERGY corrosive gases and abrasive materials which cause the
RESOURCES/SYSTEMS: Geothermal resources vary in environmental problems.
temperature from 30-3500C and consist of dry, a mixture of
steam and water or hot water only. The water is the transfer (b)Wet Steam / Liquid Dominated Systems: The
medium in order to extract geothermal heat from the earth. temperature range of such fields is in the range of 1000 - 3150C
Table given below lists the basic technologies normally and these fields deposits hot water without much amount of
utilized according to resources temperature. steam. These can be further classified and explained in
following categories:
The geothermal energy systems may be classified as:
1. Hydrothermal; (i) High Temperature Wet Steam System:
2. Hot dry rock (HDR);
3. Geo-pressured system. Generator
(1) Hydrothermal (Convective) Resources: These resources
are located at shallow to moderate depths of 100 m to 5 km Separator Turbine
and in such, water is heated by contact with the hot rock
and high pressurized steam is generated up to about 3500C. Exhaust Steam
These resources further divided into following categories,
depending upon whether steam or hot water is the dominating

Condenser
product. Cold water
(a). Dry steam fields (Vapour dominated); Hot water
(b). Wet steam fields (Liquid dominated);

(a) Dry Steam / Vapour Dominated Systems: Hot Brine

 Such system delivers steam with little or no water of high
pressure and temperature up to 2500C.

Generator Geothermal Zone

Separator

Turbine Production well Injection well

Dry Steam

Exhaust Steam FIG.5.9 HIGH TEMPRATURE STEAM

POWER PLANT
Condenser

Cold water  The high temperature wet steam system having resource
temperature above 1800C, suitable for power generation.
Hot water  In such systems the hot water with steam at high pressure
and high temperature is extracted by deep wells drilled into
Condensate to the ground.
chemical  This hot water from underground from a depth of about 1
Pump recovery km (point. A) at high pressure (about 35 – 40 bar) reaches
the well head (point. B) at lower pressure, this process
Geothermal Zone produces two phase mixture having the steam of low
quantity.
 This mixture is feed to flash chamber / brine separator which
Production well Injection well separates dry steam from brine (which is collected from
bottom).
FIG.5.8 DRY STEAM POWER PLANT
 This dry steam is supplied to steam turbine which is coupled
to a generator, produces electrical energy.
 The hot brine is re-injected into the ground along with steam
 This steam is used to generate electrical energy by condensate from the condenser.
electromechanical energy conversion.
 The steam extracted from such fields may contain some (ii) Low Temperature-Binary Fluid System:
amount of water and solid particles; those are removed in a  These hydrothermal resources are available in the
centrifugal separator. temperature range of 90 – 1700C which is not suitable for
 This pure dry steam is then directly supplied to a steam production of two phase mixture of steam.
turbine, which is coupled to a generator.  In such situation to utilize this geothermal heat, a fluid of
 The condenser is used to condense the exhaust steam from low boiling point (e.g. isobutane) is used under pressure in a
the turbine for recirculation purpose of cold water. primary heat exchanger.

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 The fluid vapour so generated is passed through a turbine  To prevent mixing of water in the reservoir the depth of
where it expands and this mechanical power of turbine is production well is kept slightly less than reinjection well.
converted into electrical energy by a generator.
 The exhaust of the turbine is passed through a heat (3) Geo-pressured Systems:
exchanger and condenser where it is cooled and then  These reservoirs were developed by sand deposits carried
condensed. down by rivers and entrapped brine and natural gas at depth
 The thermal fluid after transferring heat is re-injected of 4-6 km and are located at different levels and at different
through a well into the ground. places.
 These systems comprise of heavily compressed sediments
Generator that contain heat, methane and pressurized hot water.
 When well is drilled in this zone the reserve energy comes
out in the form of high pressurized water having temperature
(Isobutane)

Turbine
about 1600C, heat and natural gas (methane) which are
Vapour

Condenser
useful for power generation.
Regenerator  These sources have been found in offshore wells in Texas
Cold water and US Gulf Coast areas
Hot water
5.6.4 FEATURES OF GEOTHERMAL ENERGY:
ADVANTAGES:
Heat Exchanger Pump 1. It may be used in both energy supply, with power generation
and direct heat use.
2. It is an inexhaustible source of energy.
3. It is almost free of pollution.
4. Independent of weather condition.
Geothermal Zone 5. More reliable source of power generation than other
renewable energy sources.
Production well Injection well
DISADVANTAGES:
1. Causes corrosion, erosion, and chemical deposition due to
FIG.5.10 LOW TEMPRATURE BINARY FLUID the presence of sufficient amount of CO2, CH4, N2, NH3
SYSTEM and H2S.
age 3 2. Noise pollution because of well drilling, centrifugal
(2) Hot Dry Rock (HDR) or Petro-Geothermal Systems: separators.
 Hot dry rock receives heat energy from molten rock 3. Proper re-filling of water is necessary.
(magma). 4. It causes settlement of land.
5. Life of plant is low compared to conventional power plants.
Heat Exchanger
5.6.5 POTENTIAL OF GEO-THERMAL RESOURCES
IN INDIA: In India about 150 known geothermal sites which
can produce working fluids up to 1700C. Main locations of
such fields are:
(i) Geothermal Fields of Puga-Chhumathang valley in
Pump

Power J&K: A pilot project for space heating involved construction

Plant of a shed at an altitude of 4000m and 4400m in Ladakh
Production well

district, Jammu & Kashmir and using steam at 1250C.

(ii) Manikaran (Himachal Pradesh): This project “cold
Injection well

storage plant” has been recently commissioned by the

Geothermal Zone collaboration of Geological Survey of India, IIT Delhi, and
Hot Granite
H.P. Government.
(iii) Geothermal Fields of Beas and Parbati Valleys,
Geothermal Resorvior Himachal Pradesh: Beas and Parbati valleys are well known
for their hot springs in Kulu district, Himachal Pradesh. The
spring’s temperature varies from 220C to 590C in Beas and
FIG.5.11 HOT DRY ROCK or PETRO- 210C to 960C in Parbati valley at an altitude between 1300 m
GEOTHERMAL SYSTEM to 3000 m.
 These reservoirs are artificially created by fracturing deep (iv) Sohana near Delhi,
compact rocks up to depth of 8 -15 km by hydraulically / (v) Tuwa in Gujrat
chemically or by nuclear explosion for injecting high
pressure water. 5.7.1 TIDAL ENERGY: Tidal energy is a form of
 The water is pumped into the fractured well (injection well) hydropower that converts the energy of tides into useful forms
and withdrawn from another well (production well) to of power, mainly electricity. Among sources of renewable
extract heat to generate steam for power production. energy, tidal power has traditionally suffered from relatively

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high cost and limited availability of sites with sufficiently high and it is also possible to generate almost continuously.
tidal ranges or flow velocities, thus constricting its total When the water level in upper basin is maximum during
availability. high tide the inlet sluice is closed and the level of water in
lower basin keeps on rising due to discharge of water by the
5.7.2Tidal Power Plants: Tidal power plant can be classified turbine.
on the basis of basin used for power generation. There are two When the level of water in lower basin equals during the ebb
types of basin systems: tide, the outlet sluice is opened and it is closed when the
water level reaches to its minimum level. This cycle is
(1) Single Basin System: repeated, which is responsible for rotation of turbine.
This is the simplest system to generate tidal power. This Two-basin schemes are very expensive to construct due to
scheme has only one basin which is separated from the sea the cost of the extra length of barrage.
by a dam.
5.7.3 FEATURES OF TIDAL ENERGY POWER PLANT:
ADVANTAGES:
1. Freely available and inexhaustible.
2. Pollution free.
3. Monsoon independent.
4. No extra submerging of land is involved.

DISADVANTAGES:
1. High initial cost.
2. Difficult to install due to less location.
3. Sea water is corrosive.
4. Uneven operation.
5. Because of variable tidal range, the efficiency of plant is
affected.
The sluiceway is opened during high tide to fill the basin, 6. Sedimentation of basins is a problem.
and used to empty the basin during the low tides.
The water during high tides is first trapped in basin and then ENVIRONMENTAL EFFECTS:
allowed to escape during the period of low tides. 1. Changes the hydrology and salinity.
The water while escaping to run a hydraulic turbine coupled 2. Marine life is affected.
to a generator. 3. Changes environmental climate.
In such systems the power house is situated at the mouth of
basin. The hydraulic turbine in the power house only 5.8.1 OCEAN THERMAL ENERGY CONVERSION
operates during the discharge of water from the basin during (OTEC): Ocean thermal energy conversion (OTEC) uses
ebb tide. the temperature difference between cooler deep and warmer
We also have double cycle system in which the power shallow or surface ocean waters to run a heat engine and
generation is affected during the ebb as well as flood tides. produce useful work, usually in the form of electricity. OTEC
The direction of flow through the turbine during the ebb and is a base load electricity generation system, i.e. 24hrs/day all
flood tides alternates and generation of power is year long. However, the temperature differential is small and
accomplished, both during the filling and emptying of basin. this impacts the economic feasibility of ocean thermal energy
for electricity generation.
(2) Double Basin System:
This system has two basins at different levels and a dam is 5.8.2 AVAILABILITY: The oceans cover more than 70% of
provided in between these basins as shown in figure 8. Earth’s surface and capture about 80% of the sun’s radiation
One basin is filled at high tide and the other is emptied at incident on the earth, making them the world’s largest solar
low tide. Turbines are placed between the basins. collectors and energy storage system. It stores an annual
energy flux of 0.8510 kWh. Utilizing just a small portion of
this energy, can cover the global energy need. The energy
source of OTEC is free, available abundantly and is
continually being replenished as long as the sun shines and the
natural ocean currents exist. The solar radiation absorbed in
the surface layer of the ocean water in the equatorial zone heat
the water upto 27-300C depending on the season. The surface
temperature varies both with latitude and season.

5.8.3 TYPES OF OTEC SYSTEMS: OTEC systems are

classified as:

(1) OPEN OR CLAUDE CYCLE OTEC SYSTEM:

Two-basin schemes offer advantages over normal schemes Open-cycle OTEC uses warm surface water directly to make
in that generation time can be adjusted with high flexibility electricity.

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The warm seawater is “flashed evaporated” into a low-
pressure container, which causes it to boil. 5.8.4 ADVANTAGES & DISADVANTAGES OF OTEC
In some schemes, the expanding steam drives a low-pressure SYSTEMS:
turbine attached to an electrical generator. ADVANTAGES
The steam, which has left its salt and other contaminants in 1. Power developed is almost constant and independent of
the low-pressure container, is pure fresh water. weather.
It is condensed into a liquid by exposure to cold 2. There is small variation in power output from season to
temperatures from deep-ocean water. season.
This method produces desalinized fresh water, suitable for 3. Small changes are required to use as conventional power
drinking water, irrigation or aquaculture. plant.
A heat exchanger is not required and direct-contact with 4. Useful to produce desalinated water and nutrients.
between the exhaust steam and cold water spray makes a
heat exchanger. DISADVANTAGES
In such scheme, the generated steam is at very low pressure, 1. High capital cost.
this requires a large volume of steam. 2. Low efficiency.
3. Expensive working fluids in case of closed cycle.
Generator 4. High generation cost of power per kWh.

Warm
Evaporator Turbine
Water

To Ocean
Condenser
Water from
Deep Ocean

To Ocean
FIG.5.14 OPEN CYCLE OTEC SYSTEM

(2) CLOSED OR ANDERSON CYCLE OTEC SYSTEM:

Closed-cycle systems use fluid with a low boiling point,
such as ammonia, Freon-12, butane to power a turbine to
generate electricity.
Warm surface seawater is pumped through a heat exchanger
which acts as boiler to vaporize the fluid at high pressure.
The expanding vapor turns the turbo-generator. Cold water,
pumped through a second heat exchanger, condenses the
vapor into a liquid, which is then recycled through the
system.
The overall efficiency of such plant is very low in the range
of 2 – 3% only.

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