Indira Gandhi

National Open University

OEY-001
School of Engineering and Technology ENERGY RESOURCES
AND CONVERSION
PROCESSES

Block

2
RENEWABLE ENERGY RESOURCES
UNIT 1
Renewable Energy Scenario : Solar Energy 5

UNIT 2
Biomass Energy 19

UNIT 3
Biogas Energy 35

UNIT 4
Wind Energy 51

UNIT 5
Other Forms of Renewable Energy 61

References 72
GUIDANCE

Prof. V. N. Rajasekharan Pillai, Vice Chancellor, IGNOU

COURSE CURRICULAM DESIGN COMMITTEE

Prof. Ajit Kumar Dr. Ashwani Kumar Dr. S.P. Singh

Director Scientist ‘F’ / Director Head, School of Energy and
SOET, IGNOU Solar Thermal (ST) Environmental Studies
Maidan Garhi Ministry of New and Devi Ahilya Vishwavidyalaya
New Delhi-110 068 Renewable Energy Khandwa Road Campus
Block. No. 14, CGO Complex Indore-452 001
Lodi Road, New Delhi-110003 Madhya Pradesh
Dr. Ram Chandra Dr. Jugal Kishor Prof. Santosh Kumar
Regional Director Scientist ‘F’/ Director Professor and Head (Retd.)
IGNOU, Regional Centre Ministry of New and NIT
Delhi-I Renewable Energy Patna
Block. No. 14, CGO Complex Bihar
Lodi Road, New Delhi-110 003
Prof. S. Maji Prof. R.R. Gaur Dr. A.S. Guha
SOET, IGNOU Dept. of Mechanical Engineering Joint Director, RSD, IGNOU
Maidan Garhi IIT, Hauz Khas Maidan Garhi
New Delhi-110 068 New Delhi-110 016 New Delhi-110 068

Dr. S. C. Sinha Mr. Sitaram Singh Mr. J. K. Sinha

Project Officer Principal Director
Bihar Renewable Energy Govt. Polytechnic Bihar Renewable Energy
Development Agency Patliputra Colony Development Agency
Sone Bhawan, 3rd Floor Patna Sone Bhawan, 3rd Floor
Birchand Patel Marg Bihar Birchand Patel Marg
Patna, Bihar Patna, Bihar

BLOCK PREPARATION TEAM

Dr. Ram Chandra Prof. S. Maji Prof. S. P. Singh
Regional Director SOET, IGNOU School of Energy & Environment Std.
New Delhi Indore, Madhya Preadesh
IGNOU, Regional Centre, Delhi-1
Units 1 and 5 have been written by Dr. Ram Chandra and Units 2 and 3 have been written by
Prof. S. P. Singh while Unit 4 has been written by Prof. A. Mubeen and Prof. S. Maji

BLOCK EDITED BY

Dr. Rajender Gujral Dr. Ram Chandra

Regional Director Regional Director
IGNOU Regional Centre, Delhi – III IGNOU Regional Center, Delhi - I

PRINT PRODUCTION

Mr. A. S. Chhatwal Mr. S. C. Pant

Asstt. Registrar (P), Sr, Scale CRC Management

September 2010
ISBN :
© Indira Gandhi National Open University, 2010
All rights reserved. No part of this work may be reproduced in any form, by mimeograph of any other means, without
permission in writing from the Indira Gandhi National Open University.
Further information on the Indira Gandhi National Open University courses may be obtained from the University’s office at
Maidan Garhi, New Delhi – 110 068.
Printed and published on behalf of Indira Gandhi National Open University, by Director, SOET, IGNOU.
Printed at : M/s Public Printing (Delhi) Service, C-80, Okhla, Phase –I, New Delhi-110 020
 RENEWABLE ENERGY RESOURCES
Energy has always been a driving force in the development of human culture, living style,
and the overall development since ages but it reached new heights during the later half of
the 20th century and at its peak during first decades of the 21st century. If we go back to
the history of energy utilization, it can be broadly categorized into the wood era, coal era,
and the present oil era based on the utilization of energy sources.
Although energy was present in many forms since inception of life on earth or even
before it, its end-use applications have been discovered and modified from time-to-time
by the mankind. For example, when the wheel was invented, it was given energy by
human beings and later on by draught animals. Using the then available known form of
energy has always influenced the invention for the use of mankind. For example, the
diesel engine was designed to function by using peanut oil as fuel; a bicycle was invented
for using human energy; aeroplane was invented that uses aviation fuel; and so on. There
has always been a quest to exploit various forms of energy and in this context many
inventions have been made. For example, the energy available in nature around us, that
is, sun, wind, flowing water, woody material from tree, crop waste, and so on is being
utilized for various end use applications since ages but their mode and methods of
utilization have changed/improved as the technologies developed from time to time.
The present use of renewable energy available from sun, wind, flowing water, woody
material, and waste involves the developed technologies, systems, and devices
commercially available in the market. There is a need for changing the attitude in
adopting renewable energy devices in our daily life, which will also ensure our
contribution towards mitigating green house gas emissions and global warming as well.
The Ministry of New and Renewable Energy (MNRE), Govt. of India has taken several
new initiatives by introducing number of schemes such as demonstration programme on
tail-end grid connected solar power plants, rooftop SPV systems and national rating
system, and energy-efficient green buildings.
A number of renewable energy technologies have become commercially available. These
include biogas plants, improved wood stoves, solar water heaters, solar air heaters, solar
cookers, solar lanterns, street lights, pumps, wind electric generators, water-pumping
wind mills, biomass gasifiers, and small hydro-electric generators.
Energy technologies for the future such as hydrogen, fuel cells, and bio-fuels are being
actively developed. India is implementing one of the world’s largest programmes in
renewable energy. The country ranks second in the world in biogas utilization and fifth in
wind power and photovoltaic production. Renewable sources already contribute to about
5% of the total power generating capacity in the country.
Akshay Urja has also been providing information on the availability of renewable energy
systems and devices that are useful in our daily life and are commercially available in the
market (Akshay Urja, Volume 2, issue 4, February 2009).
In this course, we will discuss about renewable energy resources.
CERTIFICATE IN ENERGY TECHNOLOGY AND
MANAGEMENT (CETM)

COURSE STRUCTURE SUMMARY

Course Code Course Title Credits
OEY 001 Energy Resources and Conversion Processes 4
OEY 002 Renewable Energy Technologies and Their Uses 6
OEY 003 Energy Management: Audit and Conservation 6
OEYP 004 Energy Projects 4

OEY 001 Energy Resources and Conversion Processes

Block /Unit Block / Unit Title

Block 1 Conventional Energy Sources
Unit 1 Introduction to Energy and its Various Forms
Unit 2 Conventional Energy Sources
Unit 3 World Scenario of Conventional Energy Sources
Unit 4 Calorific Values of Fuels
Block 2 Renewable Energy Sources
Unit 1 Renewable Energy Scenario: Solar Energy
Unit 2 Biomass Energy
Unit 3 Biogas Energy
Unit 4 Wind Energy
Unit 5 Other Forms of Renewable Energy
Block 3 Energy Conversion Processes
Unit 1 Principles of Energy Conversion
Unit 2 Fuels and their Characteristics
Unit 3 Combustion of Fuels
Unit 4 Energy Efficiency and Energy Conversion
Unit 5 Environmental Impact of Energy Conversion
 Renewable Energy
UNIT 1 RENEWABLE ENERGY SCENARIO : Scenario : Solar Energy

SOLAR ENERGY

Structure
1.1 Introduction
Objectives
1.2 Expectations from the Renewable Energy during 11th Plan
1.3 Estimated Potential and Installed Capacity of Major Renewable
Energy Technologies in India
1.4 Advantages and Disadvantages of Renewable Energy
1.5 Solar Energy Potential
1.6 Solar Energy Uses
1.7 Direct use of Solar Energy
1.8 Solar Collectors
1.8.1 Low Temperature Solar Collectors
1.8.2 Medium Temperature Solar Collectors
1.8.3 High Temperature Solar Collectors
1.9 Model Solar Cities
1.10 Advantages and Disadvantages of Solar Energy
1.11 Let Us Sum Up
1.12 Key Words
1.13 Answers to SAQs

1.1 INTRODUCTION

Sources of energy are generally classified as renewable energy sources and

non-renewable energy sources.
Renewable Energy Sources : The renewable energy or non-conventional energy
source refer to sources which are almost unlimited or which can be replenished
over a short span of time. Such sources are – sun, wind, water, agricultural
residue, natural geysers, firewood, animal dung, etc. The total renewable energy
sources in India have the potential to supply about 100,000 MW of power. Some
of the major renewable energy sources are given in Figure 1.1.
Non-Renewable Energy Sources : The non-renewable energy sources are the
fossil fuels such as coal, crude oil, natural gas and nuclear energy sources like
uranium etc. (see Figure 1.2). The developed countries have about 20% of the
world’s population and use about 60% of the world’s non-renewable energy
resources.
5
Renewable Energy
Resources

Figure 1.1 : Renewable Energy Sources (Source : eia.doe.gov)

Figure 1.2 : Non-renewable Energy Sources (Source : eia.doe.gov)

Let us briefly describe different forms of renewable energy.
Solar Energy : The energy generated from the sun is known as solar energy.
India receives solar energy equivalent to over 5000 trillion KWh/year which is far
more than total energy consumption in the country.
Hydel Energy : The energy generated from water is known as hydel energy.
Biomass Energy : The energy available from firewood and agro-residue is
known as biomass energy. The traditional chulha, which is used in Indian
villages, is an inefficient way of using biomass energy. Ninety per cent of the
energy in the fuel is lost into the atmosphere; only ten per cent of the energy goes
to actually heat the pot for cooking purposes.
6
Gasifiers convert wood, charcoal and other biomass to a combustible gas which Renewable Energy
Scenario : Solar Energy
may be used to produce electricity. About 1000 MW of power can be generated
from urban and municipal solid waste and up to 700 MW from Industrial waste in
India. You may refer to Unit 2 for more details.
Biogas Energy : The energy available from animal dung and city biodegradable
waste etc is called biogas energy. Depending on how much dung can be collected,
biogas can meet the cooking energy needs of nearly 40 percent of the rural
households of the country.
There are about 232 million cattles in the country. Even if one-third of the dung
produced annually from these is available for biogas production and for recycling
as farm manure, 12 million biogas plants of family size can be installed. Each
biogas plant could save about 1260 Kg of fuel wood per year. You may refer to
Unit 3 for more details
Wind Energy : The energy available from wind is known as wind energy. The
Indian wind energy programme is one of the largest in the world, having an
installed wind capacity of over 800 MW. India is ranked fifth in the world with a
total wind power capacity of 1080 MW, out of which 1025 MW have been
established in commercial projects. You may refer to Unit 4 for more details.
Geothermal Energy : The energy available from hot dry rocks, hot water
springs, natural geysers, etc is known as geothermal energy.
All the renewable sources of energy are fairly non-polluting and considered clean.
Objective
After studying this unit, you should be able to
· know renewable energies in general and solar energy in particular
and its potential
· understand various thermal applications of solar energy
· understand direct use of solar energy

1.2 EXPECTATIONS FROM THE RENEWABLE

ENERGY DURING 11TH PLAN

As per the Rural Electrification Policy-REP (2006), the lifeline energy, i.e.
minimum energy required by a house hold is 1 kWh/household/day. Renewable
energy technologies can play a major role to achieve this target. During 11th plan
the power generation from renewable sources, mainly small hydro, wind and bio
is expected to be at least 12.5 per cent power generation installed capacity in the
country.
The aim for the 11th Plan is a capacity addition of 15,000 MW from renewable.
By the end of the 11th Plan, renewable power capacity could be 25,000 MW in a
total capacity of 200000 MW accounting for 12.5 per cent and contributing
around 5 per cent to the electricity mix.
Renewable power capacity by the end of the 13th plan period is likely to reach
54,000 MW, comprising 40,000 MW wind power, 6,500 MW small hydro power
and 7,500 MW bio-power, which would correspond to a share of 5% in the then
electricity-mix.

7
Renewable Energy
Resources 1.3 ESTIMATED POTENTIAL AND INSTALLED
CAPACITY OF MAJOR RENEWABLE ENERGY
TECHNOLOGIES IN INDIA
The estimated potential and current use of renewable energy is given in Table 1.1.
1 (MNRE, Govt. of India).
Table 1.1 : Estimated Potential and Current Progress
of Renewable Energy Use
Achievement as
S. No. Source/system Estimated potential on 31 January
2009
I Power from Renewables
A Grid-interactive renewable power (MW) (MW)
1. Wind power 45 195 9755.85
2. Bio power (agro residues and plantations) 16 881 683.30
3 Bagasse cogeneration 5 000 1033.73
4 Small hydro power (up to 25 MW) 15 000 2344.67
5 Energy recovery from waste (MW) 2 700 58.91
6 Solar photovoltaic power - 2.12
B Captive/combined heat and power/distributed renewable power (MW)
7 Biomass/cogeneration (non-bagasse) - 150.92
8 Biomass gasifier - 160.31
9 Energy recovery from waste - 31.07
Sub total (B) - 342.30
Total (A+B) - 14220.22

II Remote village electrification 5410

villages/hamlets
III Decentralized energy systems
10 Family –type biogas plants 120 lakh 40.90 lakh
11 Solar photovoltaic systems 50 MW/km2 120 MWp
i) Solar street lighting system - 70 474 nos
ii) Home lighting system - 434692 nos
iii) Solar lantern - 697419 nos
iv) Solar power plants - 8.01 MWp
v) Solar photovoltaic 7148 nos
12 Solar thermal systems
i) Solar water heating systems 140 million m2 2.60 million m2
collector area
ii) solar cookers 6.37 lakh
13 Wind pumps 1347 nos
14 Aero generator/hybrid systems 0.89 MWeq
IV Awareness programmes
16 Energy parks - 504 nos
17 Aditya Solar Shops - 284 nos
21 Renewable energy clubs - 521 nos
22 District Advisory Committees 560 nos

MW– megawatt; KW– kilowatt; MWp – megawatt peak; m2 – square metre;

Km2 – kilometer square
Source : MNRE, Govt. of India, Akshay Urja, Vol-2, issue 4th, Feb. 2009.

8
The perspective plan for grid-interactive renewable power is summarized in Renewable Energy
Scenario : Solar Energy
Table 1.2.
Table 1.2 : Perspective plan for grid-interactive renewable power for 2022,
i.e. end of 13th Plan period (capacity in MW)

Upto 12th and

Resource 10th Plan 11th Plan Total
9th Plan 13th Plans

Wind power 1667 5333 10500 22,500 40000

Small hydro power 1438 522 1400 3140 6500
Bio power 368 669 2100 4363 7500
Solar Power 2 1 - - 3

Total 3475 6525 14000 30003 54003

SAQ 1
(a) State the norm of minimum lifeline supply of energy
(b) State the expectations from the renewable energy during 11th Plan
………………………………………………………………………………………………
………………………………………………………………………………………………

1.4 ADVANTAGES AND DISADVANTAGES OF

RENEWABLE ENERGY
The renewable energy or alternative energy sources are solar, wind, biomass,
hydro, geothermal, ocean thermal, tidal etc. All these renewable energies are
having several advantages as well as disadvantages. A bird eye view is given in
Table 1.3. A quick view of the advantages of renewable energy is given in
Figure 1.3.
Table 1.3 : Advantages and Disadvantages of Renewable Energy
Renewable Energy Advantages Disadvantages
Solar Always available as long as sun is Low efficiency
shining High initial costs
No pollution Lack of storage
Wind Power in windy areas Highly variable source
No pollution Low efficiency (about 30%)
Efficient energy storage needed
Hydro High Efficiency May alter hydrological cycle
No pollution Change watershed characteristics
Little waste heat
Low cost to the user
Geothermal High efficiency Highly local resource
Low initial costs Non-renewable
Biomass Biomass are natural Pollution from biomass burners
Re-use is attractive Transport is difficult because of
Gives cogeneration facilities moisture
Practical for individual farmer
Tidal Steady source Low duty cycle
Capable of exploiting tides for Huge modification in coastal
maximum efficiency environment
High costs
Ocean Thermal Enormous energy Highly technical
Steady flow Damage to coastal environment
Large scale use is possible
9
Renewable Energy
Resources

Renewable
energy is
perennial

Well suited Renewable

for energy is
decentralized modular in
applications nature

Advantages
of
Renewable
Energy

Renewable Renewable
energy is energy is
available environment-
locally friendly

Renewable
energy does
not need
elaborate
transport

Figure 1.3 : Advantages of Renewable Energy

We will now discuss solar energy. The other forms of renewable energies will be
discussed in the subsequent units.

1.5 SOLAR ENERGY POTENTIAL

You must have learnt in your school text books that Sun is a fusion reactor and is
the ultimate source of energy. You may be aware that Sun is located at a distance
of 150 million kilometer from the Earth and is about hundred times bigger than
the earth in size. Most of the earth’s energy comes from the sun. Our sun and the
other stars are nuclear reactors that fuse hydrogen atoms together to form helium
atoms. A large amount of energy is released in the process. The reaction is similar
to what goes on in the explosion of a hydrogen bomb.
In fact all forms of energy that human beings have consumed so far and are still
consuming are in one way or another due to sun.

Point to Remember
Solar energy comes to us in the form of electromagnetic radiation. Sun is the ultimate source
of energy. Some interesting facts about Sun are the following:
· A sun ray emitted from the Sun, travelling at the speed of 3 x 108 km/s, takes about 9
minutes to reach the Earth.
· The earth receives about 1.3 x 1017 W/h. of energy.
· The temperature of the Sun at the centre is 15 million 0K and at the surface it is about
6000oK.
10
About 50% of the energy received outside Earth’s atmosphere actually reach the Renewable Energy
Scenario : Solar Energy
Earth and is about 698 joules/sq. m.sec at sea-level.

Point to Remember
We receive every minute enough energy on the earth to meet our demand if harnessed
properly.

Solar energy is the most readily available source of energy. It does not belong to
anybody and is, therefore, free. It is also the most important of the
non-conventional sources of energy because it is non-polluting and, therefore,
helps in reducing the greenhouse effect.
Solar energy has been used since ancient times, but in a most primitive manner.
Before 1970, some research and development was carried out in a few countries
to exploit solar energy more efficiently, but most of this work remained mainly
academic. After the dramatic rise in oil prices in the 1970s, several countries
began to formulate extensive research and development programmes to exploit
solar energy.
When we hang out our clothes to dry in the sun, we use the energy of the sun. In
the same way, solar panels absorb the energy of the sun to provide heat for
cooking and for heating water. Such systems are available in the market and are
being used in homes and factories.
In the next few years it is expected that millions of households in the world will
be using solar energy. India is one of the few countries with long days and plenty
of sunshine. Solar energy could be easily harnessed. Solar thermal energy is
being used in India for heating water for both industrial and domestic purposes.

1.6 SOLAR ENERGY USES

India receives solar energy equivalent to over 5000 trillion kWh/year, which is far
more than the total energy consumption of the country. In principle solar energy
can also be used to meet all our energy needs, both thermal as well as electricity.
The solar energy can be broadly classified in two categories on the basis of its use
as shown in Figure 1.4 :
(1) Solar Active Applications i.e. direct use of solar energy to produce
electricity
(2) Solar Passive Applications i.e. indirect use of solar energy usually
called solar thermal applications.
Thermal energy can be used for Cooking/Heating, Drying/Timber seasoning,
Distillation, Electricity/Power generation, Cooling, Refrigeration, Cold storage,
etc.
Some of the gadgets and other devices for exploiting thermal energy are :
Solar cooker, flat plate solar cookers, concentrating collectors, solar hot water
systems (domestic and industrial), solar pond, solar hot air systems, solar dryers,
solar timber kilns, solar stills, solar pond, concentrating collectors, air
conditioning, solar collectors coupled to absorption and refrigeration systems, etc.
Although solar photovoltaic systems are used to convert solar energy directly into
electricity, the heat generated during the process can be used for solar thermal
applications.
11
Renewable Energy
Resources

Solar Energy Uses

Direct Use Indirect Use

(Active) (Passive)

Solar PV Solar Thermal

Solar Thermal

Figure 1.4 : Solar Energy Uses

The solar energy is directly converted in the desired application form. It is usually
divided into following two forms :
(1) Solar thermal for heating applications
(2) Solar Photovoltaic for electricity generation
The use of solar energy for thermal applications is called Solar Thermal
Applications. Here solar energy is collected and then converted to heat energy for
applications such as water and air heating, cooking and drying, steam generation,
distillation by making use of an appropriate solar energy device.
Basically a solar thermal device consists of the following :
(a) a solar energy collector called absorber
(b) a heat transferring medium
(c) a heat storage or heat tank
You will now learn the basic concepts of these components.

1.7 DIRECT USE OF SOLAR ENERGY

The solar energy is directly converted in the desired application form by using
Solar Cell technology. You will earn more about this in OEY 002, block 2. Solar
photovoltaic technology is now gaining importance because we are running out
fossil fuel in the times to come.
Through Solar Photovoltaic (SPV) cells, solar radiation gets converted into DC
electricity directly. This electricity can either be used as it is or can be stored in
the battery. This stored electrical energy then can be used at night. SPV can be
used for a number of applications such as: domestic lighting
· street lighting
· village electrification
· water pumping
· railway signals.
If all the means to make efficient use of solar energy are implemented, it would
reduce our dependence on non-renewable sources of energy and make our
environment cleaner.

12
 Renewable Energy
1.8 SOLAR COLLECTORS Scenario : Solar Energy

When solar energy comes into contact with matter, one of three things will
happen to it :
· It may be reflected off of the matter, or
· It may be transmitted through the matter, or
· It may be absorbed by the matter and turned into heat.
These three phenomena have much to do with the design and use of solar
collectors. There are three main types of thermal solar collectors :
· low temperature solar collectors
· medium temperature solar collectors
· high temperature solar collectors
You will learn in detail about these collectors in Course OEY 002, Block 1.
A brief description is given below.
1.8.1 Low Temperature Solar Collectors
The low temperature solar collector operates at relatively low temperature. Solar
swimming pool collector is a good example. The heat transfer or loss takes place
by the following three processes :
Conduction : When the molecules of one material come in contact with the
molecules of another, heat is transferred from the warmer one to the colder one by
kinetic energy of the molecules.
Convection : A warm surface heats the fluid (water or air) that comes in contact
with it, and the fluid flows away by gravity.
Radiation : All matter gives off long wave infrared radiation in proportion to its
temperature. If the object gives off more radiation than it receives from the
environment, it will lose heat. Because the low temperature solar collector does
not control any of these heat loss factors, performance falls off very rapidly as
collector temperature rises above the ambient temperature.
1.8.2 Medium Temperature Solar Collectors
Many of our heating requirements occur at temperatures well above the ambient
air temperature. At these higher temperatures, simple collectors rapidly reach the
point where they are losing as much heat as they are receiving, and the efficiency
drops to almost zero. What we need to do is construct a heat trap; something that
will let the sun’s energy in, but not let it out again. With respect to the three heat
loss parameters identified above, here are some of the things that we can do to
reduce heat losses :
Conduction We can put the absorber plate inside an insulated box. In that way,
heat energy will be less able to escape by conduction process.
Convection We can put a cover over the absorber plate. In that way, when the
absorber plate heats the air above it by conduction, the heated air is
not able to float away and escape. Of course, we will be looking
for a cover that lets the sun’s energy in.
Radiation We want our cover material to transmit short wave solar energy
coming in, but block long wave infrared radiation going out. There
are only a few materials that will meet these requirements. Some
plastic will work, but they are not stable enough at higher
temperatures. The most commonly used material is glass.
13
Renewable Energy
Resources 1.8.3 High Temperature Solar Collectors
There are several ways by which we can conserve more of the energy that comes
into the collector. We can add thicker insulation, or we can add additional cover
sheets, or we can evacuate the air from the solar collector. All of these measures
will result in a collector that can operate at a higher temperature. Such measures
that conserve more energy may prevent even more solar energy from striking the
absorber plate. We have to make a balance amongst all the relevant parameters so
as to maximize the collector efficiency.

Simplicity has many advantages in solar design. Low- medium solar collectors are
efficient and reliable. They do not have the material degradation problems that high
temperatures cause, and they are safer.

SAQ 2
Identify which one is true: Renewable energy is
(a) perennial
(b) available locally
(c) does not need elaborate arrangements for transport
(d) modular in nature
(e) environment-friendly
(f) well suited for decentralized applications
(g) well suited for use in remote areas.
(h) All above

………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

1.9 MODEL SOLAR CITIES

The MNRE (Ministry of New and Renewable Energy), Govt. of India proposes to
develop 60 solar cities during the Eleventh Plan Period. At least one city in each
state, to a maximum of five cities in a state, will be supported by the ministry.
This scheme has been developed to meet the peak electricity demand of cities,
reduce dependence on fossil fuels and expensive oil and gas for energy, and
promote increased use of renewable energy.
MNRE, Govt. of India has already launched a programme of developing Nagpur
as a model solar city in 2009. Nagpur will be the first solar city in the country and
will become a model solar city by 2012. Up to 10% of energy consumption of this
city has been targeted to be met through renewable energy and energy efficiency
measures. Major solar energy systems will also be installed including streetlights,
garden lights, traffic lights, hoardings, and solar water heaters. Energy-efficient
green buildings will also be promoted on a large scale in the city.
14
 Renewable Energy
Scenario : Solar Energy
1.10 ADVANTAGES AND DISADVANTAGES OF
SOLAR ENERGY

Solar energy is available in the most natural and attractive form. It has
wide-spread distribution, it is time-specific and definite, it has virtually
inexhaustible supply, it has antibacterial and disinfecting qualities, and with
proper exposure to human body, it can provide Vitamin-D, helpful for building of
bones. It is environment-friendly and has now emerged as an effective alternative
source of power. Solar power is supposed to be better than nuclear power. We
will now discuss advantages and disadvantages of solar energy.
Advantages of solar energy :
· Solar energy is free.
· Solar energy does not produce waste and pollution.
· In sunny areas having no grid power, solar power can be used.
· Low power areas are very handy like solar powered batteries, lights,
etc.

Solar power is reliable. Sun will continue to shine so there is a sense to use solar energy.

Disadvantages of solar energy

· Solar energy is not available in the night.
· Solar power stations are relatively expensive.

1.11 LET US SUM UP

India lies in the sunny regions of the world. India receives solar energy equivalent
to over 5000 trillion KWh/year. This is far more than the total energy
consumption in the country. Daily average of incident solar energy ranges from
4 to 7 KWh/m2 depending upon the location. The highest annual radiation energy
is received in western Rajasthan while the north-eastern region of the country
receives the lowest annual radiation. It has been estimated that we have
250-300 days of clear sunny weather. Annual radiation being 1600 to
2200 KWh/m2, even if 1 per cent of the nation’s land is used, we could have
nearly 1000 giga watts (GW) of power.
Solar energy, experienced by us as heat and light, can be used through two
routes : the thermal route uses the heat for water heating, cooking, drying, water
purification, power generation, and other applications; the photovoltaic route
converts the light in solar energy into electricity, which can then be used for a
number of purposes such as lighting, pumping, communications, and power
supply in un-electrified areas.
Energy from the sun has many features, which make it an attractive and
sustainable option : global distribution, pollution free nature, and the virtually
inexhaustible supply.

15
Renewable Energy
Resources 1.12 KEY WORDS
Biomass
A renewable source of energy derived from organic matter like wood,
agriculture waste; also include algae, sewage and other organic substances
that may be used to make energy through chemical processes
Bio-fuels
Fuels made from biomass; include ethanol, biodiesel and methanol
Biogas
A combustible gas derived from decomposing biological waste; normally
consists of 50 to 60 percent methane
Geothermal Energy
The energy available from hot dry rocks, hot water springs, natural geysers,
etc is known as geothermal energy.
Hydel Energy
The energy generated from water is known as hydel energy.
Non-renewable Energy
The nonrenewable sources are the fossil fuels such as coal, crude oil and
natural gas
Renewable Energy
Energy resources that constantly renew themselves or that are regarded as
practically inexhaustible; include solar, wind, geothermal, hydro and wood
Renewable Resources
Renewable energy resources are virtually inexhaustible in duration; include
biomass, hydro, geothermal, solar, wind, ocean thermal, wave, and tidal.
Solar Energy
The energy available from the sun is called solar energy. Solar energy can
also be used to meet our energy needs, both thermal as well as electricity
requirements.
Wind Energy
The energy available from wind is known as wind energy.

1.13 ANSWERS TO SAQs

SAQ 1
(a) The lifeline energy norm of is 1kWh/household/day, as given in the
Rural Electrification Policy -REP (2006).
(b) Power generation from renewable sources, mainly small hydro, wind
and bio is expected to be at least 10 per cent power generation
installed capacity in the country. Out of the overall target of
70,000 MW power generation installed capacity addition during the
11th Plan period, 14,500 MW (about 20%) capacity additions is
proposed from renewable.
SAQ 2
(h)
16
 Renewable Energy
REFERENCES Scenario : Solar Energy
Web Link for more information on Energy
· http://www.energy.ca.gov/
· http://www.eia.doe.gov/
· www.fe.doe.gov/education
· www.ase.org/greenschools
· www.conserinfo.org

17
 Biomass Energy
UNIT 2 BIOMASS ENERGY
Structure
2.1 Introduction
Objective
2.2 Resources of Biomass
2.2.1 Classification of Biomass Resources
2.3 Availability of Biomass
2.4 Composition of Biomass
2.5 Energy Content of Biomass
2.6 Characterisation of Biomass
2.6.1 Effect of Calorific Value
2.6.2 Effect of Moisture Content
2.6.3 Effect of Ash Content
2.6.4 Effect of Volatile Matter
2.6.5 Effect of Fixed Carbon
2.6.6 Effect of Ash Melting Point
2.6.7 Effect of Bulk Density
2.7 Environment Effects of Biomass
2.8 Let Us Sum Up
2.9 Key Words
2.10 Answers to SAQs

2.1 INTRODUCTION
You know that wood was once our main fuel. We burned it to produce heat and
cook our food. We still use wood as the energy source. Sugar cane is grown in
many areas; when crushed the resulting pulp (called “bagasse”) can be burned, to
make steam to drive turbines. Other solid wastes, can be burned to provide heat,
or used to make steam for a power station. The bioconversion uses plant and
animal wastes to produce "biofuels" such as methanol, natural gas, and oil.
The ever growing population coupled with large number of developmental
activities has led to resource scarcity in many parts of the country. A judicious
choice of energy utilisation is required to achieve growth in a sustainable manner.
It is estimated that about 70% of population still live in rural areas resulting in to
tremendous demand on resources such as fuel wood, agricultural residues, etc. to
meet the daily fuel requirements. The dependence on biomass resources to meet
the daily requirement of fuel, animal fodder, etc. in rural areas is more than 85%
while in urban area the demand is about 35%.
19
Conventional Energy
Sources
All the living plants on earth belong to the category of biomass. All the plants in
the presence of sunlight produce continuously biomass through photosynthesis.
Amongst different sources of renewable energy, biomass residues hold special
promise due to their inherent capability to store energy and subsequent
conversion to convenient solid, liquid and gaseous fuels. Further, it is the only
renewable source of carbon and a host of other chemicals. Recovery of chemical
and industrial grade carbon for chemicals and explosives and value added
amorphous silica from rice husk, a suitable reinforcing filler in plastic and rubber
molding, are a few typical examples. With worldwide shortage of wood,
especially in developing countries, and need for reforestation to maintain global
ecological balance, increasing demand is being made for proper utilization of
agro and forestry residues to play the role hitherto carried out by wood.
Development of technologies, to utilize this major resource and their
management need to be emphasized to meet the demands of domestic as well as
industrial sector. However, agro-residues do suffer from two major constraints
i.e. their high moisture content and relatively low bulk density. These constraints
inhibit their economical transportation over long distances; thereby necessitate
their utilization near the sources of production. Unlike fossil fuels, which are
concentrated sources of energy and chemicals, the agro-residues utilization
management strategy have to be different. These are most appropriate for
decentralized applications in rural environments. The processing of agricultural
produce and utilization of agro-residues therefore, can contribute their maximum
share for rural development. In addition to their use as fuel, agro-residues also
compete with other traditional uses, namely for food, fodder, fiber applications,
and fertilizers. Therefore, the utilization strategies should be such as not to
basically disturb the social fabric of the society and deprive their accessibility to
the poor rural population to meet their needs for thatched roofing and traditional
trades of making ropes mats, etc.

Objectives
After reading this unit, you will be able to understand
· Different types of biomass,
· Availability of biomass,
· Properties of biomass, and
· Technique for conversion of biomass into energy.

2.2 RESOURCES OF BIOMASS

If you see the quantitative energy consumption and its pattern in rural and urban
areas, you will find a sharp contrast between rural and urban energy systems as
shown in Figure 2.1.
It can be seen that the urban systems largely depend on commercial energy
sources, while the rural system is primarily dependent on non-commercial energy
sources like fuel wood, cow dung etc. Biomass fuels meet about 85-90% of
domestic energy demand and about 75% of the rural energy demand. Firewood is
the primary energy source for cooking used by rural households (Ram Chandra, J.
Sharma and M.S. Sodha 1994). The fuels like LPG have just started penetration
into the domestic sector for cooking in rural India.

20
The biomass is renewable. We can always plant and grow more agro wastes like Biomass Energy

sugar cane and more trees, which are renewable.

Energy Requirements Dependence on

of Urban System commercial energy
sources like coal, oil,
gas and electricity etc.

Energy Requirements Dependence on non-

of Rural System commercial energy
sources like fuel
wood, cow dung,
agriculture waste etc

Figure 2.1 : Energy Requirements of Urban and Rural Systems

Since the availability of commercial energy sources in rural areas is still not there
in the desired quantity because of several factors, the biomass use in rural areas is
continuously increasing. An increased dependence on fuel wood in rural areas has
been indicated with the share of fuel wood in cooking increasing from about
50-56% in 1990 to about 60-62% in 1995. Thus, the rural population continues to
depend on bio-resources to meet the daily requirement of fuel, food and fodder.
2.2.1 Classification of Biomass Resources
In its simplest form, the biomass is the organic matter in trees, agricultural crops
and other living plant material. It is made up of carbohydrates-organic compounds
that are formed in growing plant life. Biomass is solar energy stored in organic
matter. As trees and plants grow, the process of photosynthesis uses energy from
the sun to convert carbon dioxide into carbohydrates (sugars, starches and
cellulose). Carbohydrates are the organic compounds that make up biomass.
When plants die, the process of decay releases the energy stored in carbohydrates
and discharges carbon dioxide back into the atmosphere. Biomass is a renewable
energy source because the growth of new plants and trees replenishes the supply.
The use of biomass for energy causes no net increase in carbon dioxide emissions
to the atmosphere. As trees and plants grow, they remove carbon from the
atmosphere through photosynthesis. If the amount of new biomass growth
balances the biomass used for energy, bioenergy is carbon dioxide "neutral." That
is, the use of biomass for energy does not increase carbon dioxide emissions and
does not contribute to the risk of global climate change.
The biomass is generally termed for the following :
· land and water based vegetation
· organic wastes
· photosynthetic organisms.

Point to Remember

Biomass is also defined as the weight of all the living organisms in a given population, area,
volume or other units being measured.

21
Conventional Energy
Sources
The primary step in the buildup of biomass is photosynthesis. In photosynthesis,
sunlight is absorbed by chlorophyll in the chloroplasts of green plant cells and is
utilized by the plant to produce carbohydrates from water and carbon dioxide.
Biomass can be categorised broadly as woody, non-woody and animal wastes.
Biomass is also characterized as natural resources and derived resources. We will
briefly discuss them.
Woody Biomass : All the biomass from forests, agro industrial plantations, bush
trees, urban trees and farm trees are termed as woody biomass. Woody biomass is
generally a high valued product because it has diverse uses such as timber, raw
material for pulp and paper, pencil and matchstick industries, and cooking fuel.
Non-woody Biomass : Non-woody biomass is referred to as crop residues like
straw, leaves and plant stems (agro wastes), processing residues like saw dust,
bagasse, nutshells and husks, and domestic wastes (food, rubbish, sewage). Many
of these are harvested at the village level and are essentially used either as fodder
or cooking fuel.
Animal Wastes : Animal wastes constitute the wastes from the animal
husbandry. Animal dung is a potentially large biomass resource and dried dung
has almost the same energy content as wood. About 150 Million tonne (dry) of
cow dung are used for fuel each year across the globe, 40% of which is in India.
The efficiency is only about 10% when dung is burnt to produce heat. The
important example is cook stoves used in the rural areas. The efficiency of
conversion of animal residues could be raised to about 60% by digesting
anaerobically (to produce biogas) as shown in Figure 2.2.

Efficiency about 10% when

burned to produce heat
Use of
Dry Dung and
conversion
Efficiency 60% when
Efficiency
converted to Biogas

Figure 2.2 : Conversion Efficiencies of Dung

More commonly, biomass resources are also classified as follows :

Natural Biomass Resources : Biomass resources include wood and wood
wastes, agriculture crops and their waste by products.
Agricultural Waste : Begasse, soya husk, cotton straw, rice husk, arhar stalk,
wheat straw, and peanuts, peanut stalk, etc.
Derived Biomass Resources : Municipal solid waste, animal wastes, waste from
food processing and aquatic plants, etc.
Forest Products : Wood, logging residues, trees, shrubs and wood residues,
sawdust, bark etc. from forest cleanings.
Energy Crops : Energy crops are short rotation woody crops, herbaceous woody
crops, grasses, starch crops (corn, wheat, and barley), sugar crops (cane and beet),
oilseed crops (soya bean, sunflower, safflower). These are the biomass materials,
which can be used during the pyrolysis process and to produce the bio-oil.
22
The amount of crop residues available for energy purposes will depend on the Biomass Energy

cultivation practices, recovery and storage technologies. The recovery and

delivery costs of these residues to bioenergy will vary considerably, depending on
the crop, lignin and cellulose content, climate, topography, cost of labour as well
as the opportunity costs associated with using the biomass for energy instead of
other purposes.
The biofuels will help us to reduce our reliance on fossil-fuel oil. But it will take a
huge amount of land to grow enough crops to make the amount of biofuels we'd
need. Not only this, we have to keep in mind that more use of biofuels will lead to
similar CO2 emissions from biofuel-powered vehicles as from petrol-powered
ones.

SAQ 1

(a) Define biomass.

(b) What are the resources of biomass?
(c) How is the biomass used?
(d) What are the benefits of using biomass for energy generation?
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

2.3 AVAILABILITY OF BIOMASS

Biomass being so versatile and scattered in nature, sufficient database and
documentation, are not always available. It includes a wide range of plant and
animal materials, which can be broadly classified into wood, oil-bearing trees,
residues, aquatic and marine biomass, and waste. Availability of biomass is
estimated from time to time by different researchers.
As per an estimate, globally photosynthesis produces about 220 billion dry
tonnes of biomass per year. In our country, biomass available from
agricultural crop residues in the year 2008-09 is about 244 million tonnes. If
only 50 % of the available biomass is considered for power generation, it has
potential to produce about 100 million unit/year.
The biomass availability estimated are given in Table 2.1
Table 2.1 : Availability of Biomass

Year Production Surplus

2004-05 619.0 157.9

2010-11 701.2 178.8

2024-25 938.0 239.2

Source : http://lab.cgpl.iisc.ernet.in/CropReport/Default.aspx

23
Conventional Energy
Sources 2.4 COMPOSITION OF BIOMASS
Biomass wastes generally contain cellulose, hemi-cellulose and lignin. A
detailed discussion of cellulose, hemi-cellulose, lignin chemistry is beyond the
scope of this unit. However, cellulose, hemi-cellulose and lignin percentages
are given in Table 2.2.
Table 2.2 : Compositions of Biomass
S.No. Species Cellulose (%) Hemi- Lignin Ash (%)
cellulose (%) (%)
1 Soft wood 40-45 24-37 25-30 0.4
2 Hard wood 40-45 22-40 19.5 0.3
3 Rice straw 30.2 24.5 11.9 16.1
4 Bagasse 33.6 29 18.5 2.3

2.5 ENERGY CONTENT OF BIOMASS

The energy content of biomass that can be obtained after transformation is an
important characteristic of biomass. The energy content is measured as the
heating value. For woody biomass resources, the moisture content of the wood is
the main determinant of the available energy. For non-woody biomass, the ash
content and the moisture content affect its energy value.
The moisture content is variable and depends on the extent to which the wood is
dried. That is why the energy content of fuel varies from 10.9-21.3 GJ per ton,
with an average of about 16.9 GJ for oven-dried wood (moisture content of
0 percent). One tonne of air-dried wood (average 20% moisture content) has an
energy value of about 13.5 GJ.
One of the interesting aspects of wood is that it can be used for fuel purposes
without any treatment or modification except that of being cut into small pieces.
This is because of its high volatility, high char reactivity, and low sulphur and ash
content.
Lignin is more abundant and has a higher degree of polymerisation in softwoods
than in hard woods. Woods having higher lignin content and plenty of extractives
will have a higher heating value. Cellulose and hemi-cellulose contain only
around 17.5 MJ/kg while lignin has about 26.5 MJ/kg and extractives can
approach 35 MJ/kg.
Wood has another interesting property that it can be modified into various forms
that are convenient to use as shown in Figure 2.2.

Charcoal obtained from destructive

distillation of wood

Woody
Biomass Liquid Fuels like methanol and ethanol

Producer gas (carbon monoxide and

nitrogen)

Figure 2.2 : Conversion of Woody Biomass

24
It can be seen that woody biomass can be converted to charcoal, liquid fuels like Biomass Energy

methanol and ethanol and producer gas (carbon monoxide and nitrogen).
Charcoal is mainly made of carbon and is obtained by the destructive distillation
of wood. It has a relatively high-energy value of 28.9 GJ/ton. Producer gas is
obtained by the burning of carbon in a supply of air insufficient to convert it to
charcoal.
The ultimate analysis of different plant residues in % of dry matter is given in
Table 2.3. It is seen that the ash content varies considerably among the residues.
The carbon content is typical of organic substrates, being between 40% and 50%.
Hydrogen content at 5-6% and oxygen content mainly below 40% are nearly
uniform. Nitrogen content is a measure of the protein content of the residue. The
nitrogen content is in most cases far below 1%, indicating that the residues have
low protein content.
Table 2.3 : Analysis of plant residues (Percentage of dry matter)
(Hall and Overend, 1987)
Residue Ash C H O N S
Wheat straw 6.53 48.53 5.53 39.08 0.28 0.05
Barley straw 4.30 45.67 6.15 38.26 0.43 0.11
Maize straw 5.77 47.09 5.54 39.79 0.81 0.12
Rice straw 17.40 41.44 5.04 39.94 0.67 0.13
Bagasse 3.90 46.95 6.10 42.65 0.30 0.10
Coconut shell Fibre 1.80 51.05 5.70 41.00 0.35 0.10
Potato stalks 12.92 42.26 5.17 37.25 1.10 0.21
Beet leaves ---- 40.72 5.46 39.59 2.28 0.21
Wheat chaff 7.57 47.31 5.12 39.35 1.36 0.14
Barley chaff 5.43 46.77 5.94 39.98 1.45 0.15

Biomass has nearly twice as much of hydrogen and nearly an order of magnitude
more oxygen per carbon atom than coal. The calorific value and heat utilisation
efficiency of various fuels are given in Table 2.4.
Table 2.4 : Calorific value and heat utilisation efficiency of various fuels
(Veena, 1988)
Fuels Heating values Heat Utilisation Efficiency
(kcal/kg) (%)
Firewood 4,708 18.9
Vegetative Wastes 3,500 12.0
Dung cake 2,092 11.2
Soft coke 5,772 26.6
Charcoal 6,930 25.7
Kerosene 9,122 50.8

SAQ 2

What is the difference between biomass and biogas?

………………………………………………………………………………………………
………………………………………………………………………………………………

25
Conventional Energy
Sources 2.6 CHARACTERISATION OF BIOMASS
Since biomass differs greatly in their chemical, physical and morphological
properties, they make different demands on the method of their utilization and
consequently require different types of technologies.
Most important properties, which may affect the gasification/pyrolysis, are
calorific value, moisture content, ash content, volatile matter, fixed carbon, ash
melting point and bulk density. The moisture content, ash content, volatile matter
and fixed carbon content of a particular fuel can be determined by proximate
analysis of the fuel.
The method of gradation takes into account the comparative effect of different
properties of the fuel in the gasification process. A brief description is given
below.

2.6.1 Effect of Calorific Value

As the calorific value increases, the amount of gas produced at the normal
temperature and pressure increases. This simply means that with the increase in
calorific value, the material consumption also decreases.

2.6.2 Effect of Moisture Content

With increasing moisture content, the calorific value of wood decreases and
correspondingly the amount of gas produced at normal temperature and pressure
(NTP) and fraction of useful components decrease. For practical consideration,
the wet biomass has also bad flow and handling characteristics and gives
inconsistent operation, especially for biomass having 25% moisture on wet basis.
High moisture contents reduce the thermal efficiency since heat is used to drive
off the water and consequently this energy is not available for the reduction
reactions. Therefore, high moisture contents result in low gas heating values.
Moisture content is defined on the wet basis as well as dry basis. The moisture
content on the dry basis is defined as follows :
Wet weight - Dry Weight
MC dry = ´100% . . . (2.6.1)
Dry weight

Alternatively, the moisture content on a wet basis is defined as:

Wet weight - Dry Weight
MC wet = ´100% . . . (2.6.2)
Wet weight

2.6.3 Effect of Ash Content

With increasing ash content, the removal of the ash from the gasifier becomes
more power consuming and fraction of useful components also decrease. If the
ash content is very high, the biomass can be taken as unsuitable for gasification
because due to removal of large amount of ash, material flow problems in the
gasifier can arise.

2.6.4 Effect of Volatile Matter

The volatile matter helps in the complex reactions of gasification but if the
volatile matter content is high, tar formation is also high. Tar is one of the
products of thermal decomposition of solid fuels. The tar yield is therefore related
to the volatile matter in a fuel.
26
 Biomass Energy
2.6.5 Effect of Fixed Carbon
With increasing fixed carbon, the amount of gas produced and the calorific value
of the producer gas so obtained increase. The conversion of carbon to CO which
is one of the main components of producer gas is the result of many complex
reactions taking place during gasification.
2.6.6 Effect of Ash Melting Point
The ash melting point is essential to determine to maximum temperature that can
be achieved at any zone in the gasifier. When the temperature of any zone the
gasifier exceeds the ash melting temperature, there are chances of clinker
formation. The clinkers once formed can cause breakdown of the ash removal
mechanism of the gasifier.
2.6.7 Effect of Bulk Density
Bulk density is one of the important factors for designing of a gasifier to obtain
proper material flow. Biomass with very low bulk density have problem of proper
fall through different zones of gasifier. The bulk density varies significantly with
moisture content and particle size of the fuel. The average bulk density of few
biomasses is given in Table 2.5.
Table 2.5 : Average Bulk Density of Biomass

Fuel Bulk Density (Kg/m³)

Wood 300 - 550

Charcoal 200 - 300

Peat 300 - 400

SAQ 3
What would be the effect on production of producer gas and other outputs in the following
conditions?
(a) If volatile matter is high in feed material
(b) If fixed carbon is high
(c) If Ash melting point is low
(d) If moisture content is high
………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

………………………………………………………………………………………………

Example 2.1
15 Kg biomass was kept in oven for drying. After drying its weight was found as
12.5 Kg. The dried biomass (after grinding) was kept in muffle furnace for
volatile matter removal, after volatile matter removal biomass weight was
observed as 7.5 Kg. Finally it was again kept in muffle furnace for conversion in
Ash. Ash was found as 1.2 Kg. Now calculate % age of moisture content (wet
basis and dry basis), % age of volatile matter, % age of Ash and % age of fixed
carbon.
27
Conventional Energy
Sources
Solution
The sequence of process given in the example is depicted below :

Biomass
Ash 1.2
Biomass Dried after
Kg
15 Kg volatile
Biomass
removal
12.5 Kg
7.5 Kg

Drying
Volatile Ash
Process Conversion
Removal
Process
Initial weight of biomass = 15 kg
Weight of biomass drying = 12.5 kg
Moisture removed from the biomass = 15 – 12.5 = 2.5 kg
The moisture content on wet basis is given by the following relation :
( Wet weight of biomass - dry weight of biomass )
MC wet = ´100
Wet weight of biomass

MC wet = (15 - 12.5 ) ´ 100 /15 = 2.5 ´ 100 /15 = 16.67%

The moisture content on dry basis is given by the following relation :

( Wet weight of biomass - dry weight of biomass )
MCdry = ´100
Dry weight of biomass

MC dry = (15 - 12.5 ) ´ 100 /12.5 = 20%

Dried weight of biomass = 12.5 Kg

Weight of biomass after volatile matter removal= 7.5 kg
Volatile matter removal from biomass = 12.5 – 7.5 = 5.0 kg
Volatile matter removed from biomass
VM dry = ´ 100
Dry weight of biomass

VM dry = 5 /12.5 ´ 100 = 40%

Ash in the biomass = 1.2 g

Ash in the biomass
Ash = ´ 100
Dry weight of biomass

Ash = 1.2 /12.5 ´100 = 9.6%

Fixed carbon = 100 – VMdry – Ash

= 100 – 40 – 9.6 = 50.4%
Example 2.2
The fixed carbon and ash content of wood was found to be 13.1% and 0.2% on
wet basis, respectively. Estimate the volatile matter of the wood on dry basis
considering moisture content of the wood as 5 %.
28
Solution Biomass Energy

Volatile matter + fixed carbon + ash + moisture = 100 (wet basis)

Volatile matter (wet basis) = 100 – 13.1 – 0.2 – 5 = 81.7 %
Volatile matter (dry basis) = volatile matter (wet basis)/(1 – moisture)
= 81.7/(1 – 0.05) = 0.86 = 86%
Example 2.3
Ultimate analysis (dry basis) of rice husk is given as follows :
Carbon : 38.5%, hydrogen : 5.7%, nitrogen : 0.5%, sulfur : 0.0%, oxygen : 39.8%
and ash : 15.5%.
Derive its fuel formula and fuel weight.
Solution
Let us take 100 g of dry rice husk.
You know the atomic weight of carbon, hydrogen, nitrogen, and oxygen. This 12,
1, 14, and 16, respectively.
Now divide the weight of carbon, hydrogen, nitrogen, and oxygen by the
respective atomic weight to get the number of moles :
Number of moles of Carbon = 38.5/12 = 3.208
Number of moles of Hydrogen = 5.7/1 = 5.7
Number of moles of Nitrogen = 0.5/14 = 0.035
Number of moles of Oxygen = 39.8/16 = 2.487
Now divide the number of moles of each element by the number of moles of
carbon to give the formula as CHlNmOn.
where l = 5.7/3.208 = 1.77
n = 0.035/3.208 = 0.01
o = 2.407/3.208 = 0.77
The fuel formula is CH 1.77 N 0.01 O0.77
Combining the molecular weight of each element as per the fuel formula gives the
molecular weight as 26.23.
Example 2.4
Calculate the specific gas production rate as a function of moisture content of
biomass. The calorific value of producer gas is 20.1 MJ/Kg.
Solution
Let the fractional moisture content of biomass used for gasification is ‘m’ on wet
basis.
Therefore amount of dry biomass = (1 − m)
Now energy required to evaporate this moisture
= m ´ latent heat of steam (neglecting sensible heat)
= m ´ 2.54 MJ (Latent heat of steam is 2.54 MJ)
Calorific value of biomass = (1 − m) ´ 20.1 − m ´ 2.54.

29
Conventional Energy
Sources
Amount of energy in the producer gas produced per Kg of biomass
= [(1−m) x 20.1 − m ´ 2.54] ´ ήth/Calorific value of producer
gas at NTP
where, th is the overall thermal efficiency = 80% for 10% moisture content,
and Calorific value of producer gas at NTP = 5.23 x 273/298 = 4.79
Calorific value of producer at standard temperature and presure (STP)
= 5.23MJ/m3
Amount of gas = [(1−0.1) ´ 20.1 – 0.1 ´ 2.54] ´ 0.8/4.79 = 2.98 m3/Kg of
biomass.

2.7 ENVIRONMENTAL EFFECTS OF BIOMASS

The use of biomass energy provides a number of environmental benefits. Some of
them are :
· It can help mitigate climate change
· It can reduce acid rain
· It can prevent soil erosion and water pollution
· It can minimize pressure on landfills
· It can provide wildlife habitat
· It can help maintain forest health through better management.
The use of biomass will greatly reduce the greenhouse gas emissions. Biomass
releases carbon dioxide as it burns, but the plants also need CO2 to grow. This
creates a closed-carbon cycle. All the CO2 released during the combustion of
biomass materials is recaptured by the growth of these same materials. Thus, with
biomass combustion there is no net increase in carbon dioxide released into the
atmosphere. In addition, substantial quantities of carbon can be captured in the
soil through biomass root structures, creating a net carbon sink.
Biomass has other environmental benefits. The waste land may be utilized to
grow biomass crops that will restore soil carbon, reduce erosion and chemical
runoff, and enhance wildlife habitat.

2.8 LET US SUM UP

For conversion of biomass to energy numbers of technologies are available.
However one has to choose correct technology depending upon the characteristics
of biomass and its end use. Biomass based technology are cheaper and
economical. Moreover, the raw materials for these technologies are available at
locally. It also helps in deforestation and improves the eco-system.
Biomass means burning wood, dung, sugar cane or similar things. We can plant
more trees, grow more sugar cane and hence biomass is renewable. Biofuels can
be used for vehicles instead of petrol or diesel.

30
 Biomass Energy
2.9 KEY WORDS

Woody Biomass
All the biomass from forests, agro industrial plantations, bush trees, urban
trees and farm trees are termed as woody biomass.
Non-woody Biomass
Non-woody biomass is referred to as crop residues like straw, leaves and
plant stems (agro wastes), processing residues like saw dust, bagasse,
nutshells and husks, and domestic wastes (food, rubbish, sewage).
Animal Wastes
Animal wastes constitute the wastes from the animal husbandry. Animal
dung is a potentially large biomass resource.
Natural Biomass Resources
Natural Biomass resources include wood and wood wastes, agriculture
crops and their waste by products.
Agricultural Waste
Beaasse, soya husk, cotton straw, rice husk, arhar stalk, wheat straw, and
peanuts, peanut stalk, etc.
Derived Biomass Resources
Municipal solid waste, animal wastes, waste from food processing and
aquatic plants, etc.
Forest Products
Wood, logging residues, trees, shrubs and wood residues, sawdust, bark,
etc. from forest cleanings.
Energy Crops
Energy crops are short rotation woody crops, herbaceous woody crops,
grasses, starch crops (corn, wheat, and barley), sugar crops (cane and beet),
and oilseed crops (soya bean, sunflower, safflower).

2.10 ANSWERS TO SAQs

SAQ 1
(a) Biomass is defined as land and water based vegetation, organic wastes
and photosynthetic organisms. Thus, biomass is the organic matter
produced by plants. The solar energy trapped by these plants can be
converted to electricity or fuel.
(b) The different resources of biomass are Woody Biomass, Non-woody
Biomass and Animal Wastes
(c) The society has been using biomass for heating and cooking for
thousands of years. With today’s technology, plant materials can be
used to generate electricity, heat, or liquid fuels for motor vehicles
that have substantially lower environmental impacts than traditional
fossil fuels.

31
Conventional Energy
Sources
(d) Biomass is capable of addressing the energy needs or our country.
Increased use of biomass for energy would lead to reduced
greenhouse gas emissions, reduced dependence on fossil fuels and an
improved rural economy.
SAQ 2
Biogas is produced by fermenting biomass (organic materials) through a
process called anaerobic digestion. The resulting byproducts are heat than
can be used for space heating and gases than can power electrical generators
or may be used for cooking.
Biomass uses organic materials such as plants and animal waste, including
forest industry residues, agricultural residues, organic solid waste and
energy crops like corn, to produce heat. These products can be burned as is
or in pellets, which are becoming increasingly popular.
SAQ 3
The effect on production of producer gas and other outputs with the
different conditions would be as follows :
(a) If volatile matter is high in feed material: The high value of
volatile matter content will lead to high formation of tar.
(b) If fixed carbon is high: The amount of gas produced and the
calorific value of the producer gas will also be high.
(c) If Ash melting point is low: If the temperature of any zone the
gasifier exceeds the ash melting temperature, there are chances
of clinker formation.
(d) If moisture content is high: If the moisture content is high, the
calorific value of wood will decrease and correspondingly the
amount of gas produced will also decrease.

32
 Biomass Energy
REFERENCES
1. S. Kohli, P. Raman and V.V.N. Kishore, Evaluation of Fuels for
Gasification, New Delhi.
2. www.eren.doe.gov/biopower.
3. http://www.fao.org/documents/show_cdr.asp?url_file=/docrep/t0512e/T051
2e00.htm
4. Veziroglu, T.N. (1991): Energy and Environmental Progress I – Volume
B : Solar energy Applications, bio-conversation and synfuel. Edited by
T. N. Veziroglu, New York: Nova Science Publishers, c1991.
5. Ghaly AE, Ramkumar DR, Sadaka SS and Rochon JD (2000) Effect of
reseeding and pH control on the performance of a two-stage mesophilic
anaerobic digester operating on acid cheese whey Canadian Agricultural
Engineering 42(4) : 173-183.
6. Veziroglu, T.N. (1991): Energy and Environmental Progress I – Volume
B : Solar energy Applications, bio-conversation and synfuel. Edited by
T. N. Veziroglu, New York: Nova Science Publishers, c1991
7. Boyle, G. (ed) (1996) Renewable energy – power for a sustainable future.
The Open University and Oxford University Press, Oxford.
8. Ghaly AE (1996) A comparative study of anaerobic digestion of acid cheese
whey and dairy manure in a two-stage reactor Biosource Technology
58 : 61-72.

33
 Biogas Energy
UNIT 3 BIOGAS ENERGY
Structure
3.1 Introduction
Objective
3.2 Energy, Environment and Health
3.3 Main Sources of Biomass for Biogas Production
3.4 Biogas
3.5 Plant Size and Requirement of Number of Cattles
3.6 Characteristics of Feed Materials
3.6.1 Process
3.6.2 Stoichiometric Calculations of the Biogas Yield and Composition
3.7 Process Parameters Affecting the Biogas Production
3.7.1 Organic Loading Rate (OLR)
3.7.2 pH-Value
3.7.3 Alkalinity
3.7.4 Temperature
3.7.5 Carbon to Nitrogen Ration
3.7.6 Nutrients and Trace Elements
3.7.7 Hydraulic Retention Time (HRT)
3.7.8 Toxicity
3.7.9 Degree of Mixing
3.8 Efficiency of Gas Production and Uses
3.9 Major Benefits
3.10 Let Us Sum Up
3.11 Key Words
3.12 Answers to SAQs

3.1 INTRODUCTION
More than two billion people cannot access affordable energy services based on
efficient use of conventional energy sources (coal, gas, oil) and electricity.
Without access to energy, their opportunities for economic development and
improved living standards are heavily constrained. Due to the wide disparities in
urban areas and rural areas in accessing the affordable commercial energy and
energy services create a huge gap in human development, and threaten social
stability. The decentralized small-scale energy technologies can play a vital role
to reduce this gap and also become an important element of successful poverty
alleviation. Another serious issue is of the environmental impacts on human
health. The human heath is threatened by high levels of pollution resulting from
particular types of energy use at the household, community, and regional levels.
35
Renewable Energy
Resources
Major changes are required in energy system development worldwide due to the
emissions of greenhouse gases, mostly from the production and use of
conventional energy. These emissions are altering the atmosphere resulting in
adverse effects on the regional or global climatic patterns. Finding ways to
expand energy supplies while simultaneously addressing the environmental
impacts associated with conventional energy use represents a critical challenge to
humanity. The resources and technology options available to meet these
challenges are identified as energy efficiency, renewable energy sources, and
advanced energy technologies.
Objectives
After reading this unit, you will be able to understand
· Biomass used for biogas production,
· Characteristics of Biogas,
· Biogas production and factors affecting the production, and
· Advantages of biogas.

3.2 ENERGY, ENVIRONMENT AND HEALTH

The relationship between energy and social issues is related to address the energy
needs of the majority of rural people, specially the poor. A large majority of rural
masses has very low ability to pay for energy in our country and require major
structural changes. The productivity and income generating potential of a family
is highly dependent on the availability of convenient and affordable energy. The
contribution of supply of affordable energy can help families and communities
break out of the cycle of poverty. The economic levels of villages can be
increased by more energy inputs in agricultural sector (such as increase in
irrigated land area) and by reducing the inputs of chemical fertilizers, which can
be replaced by bio-fertilizers (such as biogas manure).
The human health and quality of life always have close relationship with energy
consumption and its clean production. The energy potential for enhancing human
well -being is unquestionable. Therefore, the realization of absolute link between
meeting the needs of rural areas economic growth and energy security, dispersed
resources like dung etc. can make the energy system more reliable and
sustainable.
On the other hand, in developing countries, most of the inhabitants in rural areas
are dependant on dung and organic residue as fuel for cooking and heating. Such
is the case, for example, in the treeless regions of India (Ganges plains, central
highlands), Nepal and other countries of Asia. The burning of dung and plant
residue is a considerable waste of plant nutrients.
Other than land, labor, capital and water; energy and manure has also become the
most crucial factor for economic and social growth of villages. The efforts has to
be made in this direction to create self-reliant villages in energy and manure
production by bio-methanation technology using local resources like cattle dung.
This effort would provide a firm basis for the economic and social development
and long-term sustainability.
Biomass is the World’s 4th Energy Source and its usage is widespread in both
industrial and developing countries. The majority is used to provide heat
worldwide 15 PWh as thermal energy and about 150 TWh electricity (15% and
1% of world total energy consumption).
36
 Biogas Energy

3.3 MAIN SOURCES OF BIOMASS FOR BIOGAS

PRODUCTION

The major resources which can be used for biogas production are :
· Animal Manure
· Poultry Waste
· Pig Waste
· Night soil
· Municipal Organic Waste
· Agricultural Residues
· Forests Residues (Leafs etc)
· Aquatic Plants (like water hysinth)
· Organic waste water from Industries (Food processing, milk
processing etc.)
· Hotels and Restaurants
· Sanitary Land fills

3.4 BIOGAS

The byproducts of anaerobic digestion of organic materials are commonly

referred to as ‘biogas’ because of the biological nature of gas production. Biogas
technology refers to the production of a combustible gas (called biogas) and a
value added fertilizer (called slurry or sludge) by the anaerobic fermentation of
organic material under certain controlled conditions. Biogas is produced by
microbial activities and can be used only at the place where it is produced. The
main constituents of biogas are :
· about 55-65% Methane (CH4)
· 30-45% Carbon dioxide (CO2)
· traces of hydrogen sulfide (H2S)
· fractions of water vapors
Waste like cow dung, poultry slurry, pig manure and other crop residue have the
following biogas composition :
· Methane 50-60%
· Carbon Dioxide 38-45%
· Trace component 2% (Hydrogen, Hydrogen Sulphide, Non Methane
Volatile organic, etc.).
The comparative value of energy and their efficiencies of different fuels are given
in Table 3.1.
37
Renewable Energy
Resources
Table 3.1 : The Calorific Value and Efficiency

Commonly Used Fuels Calorific Values Thermal Efficiency

Bio-gas 4000-5000 KCal/m3 55%-60%

Dung cake 1900-21003 KCal/Kg 5%-11%

Firewood 2100-4300 KCal/Kg 15-20%

Diesel (HSD) 10550 KCal/Kg 60-70%

Kerosene 10850 KCal/Kg 50-55%

SAQ 1
(a) What is Biogas?
(b) What is its composition?
(c) Can biogas be used in place of fossil fuels? How?
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

3.5 PLANT SIZE AND REQUIREMENT OF

NUMBER OF CATTLES

The large numbers of biogas plants are working on cattle dung in India. The
simple estimation of dung may be done on the basis of number of cattle’s. The
plant size and number of animals required is given in Table 3.2.
Table 3.2 : Biogas Plant Size and Cattle Head Needed
Minimum Number
Plant Size in m3
of Cattle Required
2 3
3 4
4 6
6 10
8 15
25 45

SAQ 2
What is anaerobic digestion?
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

38
 Biogas Energy
3.6 CHARACTERISTICS OF FEED MATERIALS
The most important parameters for characterizing the slurries made up from
different feed materials are total solids content (TS) and volatile solids content
(VS). There is an upper limit for (TS) content above which the material is no
longer slurry, and mixing and pumping becomes problematic.
3.6.1 Process
The different pathways of bio-methanation process are suggested by several
investigators. Macro level energy conversion of organic waste in bio-methanation
is shown in Figure 3.1. In this process of conversion of energy from organic mass
is mainly utilized in cell synthesis and formation of methane and carbon dioxide
besides some part of it remains in the effluent.
A simple flow chart may describe the three step process of bio-methanation as
shown in Figure 3.1. These are briefly described below :
· Hydrolysis : saprophytic bacteria converts complex organic
compounds into less complex organic compounds, which are
water-soluble.
· Acid formation : acid forming bacteria degrades organic compounds
to volatile fatty acids and ammonia.
· Methane formation : methane forming bacteria utilizes these acids to
form methane (CH4) (Veziroglu, 1991).

Cell
Synthesis

Energy in
Organic
Effluent
Matter
substrate

Methane and
Carbon Dioxide
Production

Figure 3.1 : Energy Conversion in Process

Each stage is being carried out by different types of bacteria with different
environmental requirements.
Hydrolysis
Hydrolysis is the first step in anaerobic degradation and also the rate limiting step.
The hydrolysis of organic polymers such as polysaccharides, fats and proteins
converts these polymers into smaller units, such as sugars, long-chain fatty acids
and amino acids. This group of bacteria called as facultative anaerobes/microbes.
Acid forming Microbes or Acitogenesis :
The sugars, long-chain fatty acids and amino acids resulting from hydrolysis are
used as substrates by a wide variety of bacterial generation of different
fermentative organisms or by anaerobic oxidizers. The complex organic matters
39
Renewable Energy
Resources
in liquid phase digestion convert the small water-soluble molecules by
fermentation into acetate, carbon dioxide and hydrogen. The acid forming
bacteria also converts the intermediate products to acetic acid, carbon dioxide and
hydrogen.
The three stages of Biogas production
End products of
Step 3: Biogas
Biogas Production Production
Step 1: Liquefaction Step 2:
from
Acid Production
Manure
Methane forming
Acid forming bacteria
Liquefying bacteria bacteria Simple organic
acids
Liquefied (including Biogas
soluble organic odors) (Methane,
compounds CO2,
impurities)
Complex organic
matter (raw
manure,
milk house
waste, fine Insoluble compounds
bedding (water,
material) inorganic material,
insoluble Low
organic matter) Odor effluent

Figure 3.2 : Three Stage Process of Bio-methanation

Methane forming Microbes or Methanogenesis
Acetate, carbon dioxide and molecular hydrogen can be directly utilized as a
substrate by the group of anaerobic microorganisms called Methane genesis or
methane forming bacteria. Methane can be synthesized via two different
pathways, of which one involves acetate and the other molecular hydrogen. The
estimations indicated that about 70% of the methane is produced from acetate and
30% comes from hydrogen. The Volatile Fatty acids (VFA) accumulation is to be
avoided in the digester to produce the high gas content.

SAQ 3
(a) What materials can "feed" your digesters?
(b) Besides biogas, what comes out of the digesters?
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

………………………………………………………………………………………………
………………………………………………………………………………………………

40
 Biogas Energy
3.6.2 Stoichiometric Calculation of the Biogas Yield and
Composition
Bio-methanation process is carried out by symbiotic action of methane- and acid-
producing bacteria. The interrelated behaviors of all classes of bacteria create the
environment for each other to survive and grow simultaneously. The estimation of
biogas production form the organic waste materials may be done on the basis of
Stoichiometric equation of the conversion process.
The simple equation is considered by Ghaly and Ramkumar (1999) for
calculations of the theoretical yield of methane and carbon dioxide, i.e. biogas,
produced by anaerobic digestion using the Buswell’s formula :
Cn Ha Ob + (4n – a- 2b) H2O → (4n + a – 2b)/8 CH4 + (4n – a + 2b)/8 CO2
Veziroglu, (1991) has given the formula for the biogas production from organic
substances which are not containing sulfur materials and can be written as :
CaHbOcNd + (4a - b - 2c + 3d)/4 H2O → (4ª + b - 2c - 3d)/8 CH4
+ (4a-b+2c+3d)/8 CO2 + d NH3
The formula for the conversion of organic substance in an aqueous environment
into CH4 and CO2 and into ammonia and hydrogen sulphide, (if N and S are
contained in the substrates) is Boyle (1996)
CnHaObNcSd + (4n – a – 2b + 3c + 2d)/8 H2O →
(4n – a + 2b + 3c + 2d)/8 CO2 + (4n + a - 2b - 3c - 2d)/8 CH4
+ cNH3 + d H2S
It is interesting to note that any organic matter will generate biogas, but the higher
the energy of the materials, the more biogas they will create. For example, deep
fryer oil can generate about 60 times as much biogas as cow dung for any given
quantity.

3.7 PROCESS PARAMETERS AFFECTING THE

BIOGAS PRODUCTION

All kinds of organic waste such as kitchen waste and garden waste, cattle dung
and sewage, etc. can be used in a biogas plant. The efficiency of the biogas
production is affected by the following factors :
1. Amount of organic material
2. Digestibility of the material
3. A combination of microbial and engineering factors such as
(a) Organic loading rates
(b) Solids Concentration
(c) Retention Times
(d) Temperature
(e) Carbon to Nitrogen Ratio
(f) Toxicity, etc.

41
Renewable Energy
Resources 3.6.1 Organic Loading Rate (OLR)
The organic loading rate (OLR) of a process is a measure of how much organic
material is fed to each cubic meter of reactor volume during one day (i.e. Kg of
VS /m3 or COD/m3 day).The biogas is formed from the anaerobic degradation of
volatile solids (VS). The volatile solids fed per Kg in reactor will normally
produces maximum biogas in the range of 0.25-0.70 m3 depending on the
operating conditions of reactor.
Accordingly, the loading rate should be in the range of 1-1.5 Kg volatile solids/m3
digester/day which is highly dependent on the reactor design. The biogas
production is also affected by overfeeding or underfeeding of the feed materials.
In continues feed digesters, the large fluctuations of flow and concentration of
substrate will also give low biogas production. Volatile Solids (VS) is measured
as the weight of solids that is combustible “volatilized” at a temperature of
550°C. It is reported as a percent of the total weight of the manure sample.
Methane production is often based on the volatile solids portion of the manure.
Approximately 50-70% of the VS can be converted to biogas depending on the
design of the digesters.

3.7.2 pH-value
The pH value is defined as follows :
The pH affects severely the biogas and methane production rate which decreases
with high and low pH values. The pH value should be between 7 and 7.4 and the
dilution for water and fresh dung ratio 1:1 by weight. The maximum percentage
of methane can be produced in the optimum range of pH vales 6.8-7.2. The
methane forming bacteria cannot survive below 5.5 pH, while acid forming
bacteria can survive up to 4.5 pH. Therefore, the water is normally used for
buffering solution and to be used in sufficient quantities for anaerobic
digestion/fermentation process.
The control of decrease in pH of an anaerobic reactor may be done by stopping
the feeding and increase the buffering capacity, e.g. through adding some
chemicals as calcium carbonate, sodium bicarbonate or sodium hydroxide.

3.7.3 Alkalinity
Alkalinity of a liquid is mainly a measure of its acid neutralizing capacity.
Carbonate, bicarbonate and hydroxide ions are normally used for as neutralizing
agents.
3.7.4 Temperature
The biogas production is highly dependent on operating temperature of anaerobic
digester. Three ranges of temperatures and their respective retention times are
given in Table 3.3 for the operation of digesters.
Table 3.3 : Temperature and Retention Time
Temperature Range Retention Time
Ø Psychrophilic 0 to 20°, 100-120 days
Ø Mesophilic 20 to 42°C and 30- 60 days
Ø Thermophilic 42 to75°C 3- 20 days

42
Methanogenesis is also possible under psycrophilic conditions (temperatures Biogas Energy

below 200C) but occurs at lower rates. The quantity and quality of biogas
production is different in different temperature ranges. Optimum gas production
is also found at 330C and 520C in Mesophilic and Thermophilic ranges
respectively. The trend in biogas production with temperature in different ranges
is shown in Figure 3.3.
The fluctuations in temperature in any range leads to inhibition of methane
formation.

3.7.5 Carbon to Nitrogen Ratio

Microorganisms need both nitrogen and carbon for assimilation into their cell
structures. The C/N ratio varies from a feedstock to another as shown in
Table 3.3. It is mentioned as an important parameter, affecting the biogas
production.
Psychrophilic Mesophilic Thermophilic

10 20 30 40 45 50 60
O
Temperature in the digester ( C)
Figure 3.3: Temperature Effect on Gas Production

3.7.6 Nutrients and Trace Elements

Microorganisms require the macro and micro nutrients as trace elements such as
phosphorous, nitrogen, sulfur, calcium, potassium, iron, nickel, cobalt, zinc and
copper. These are essential required for optimum activity of the microorganisms
involved in anaerobic digestion. The most important nutrients are nitrogen and
phosphorous and it has been suggested that the C : N : P ratio should be kept at a
minimum of 100 : 28 : 6.
3.7.7 Hydraulic Retention Time (HRT)
Hydraulic retention time varies with operating temperature of the anaerobic
digester. It may be defined as the average time a volume element of the liquid
medium resides inside the reactor. A better production of biogas found at an
increase in HRT, if all other parameters kept constant.
Anaerobic digestion can be performed with a relative short HRT, i.e. “high rate”
systems, or with long HRT, i.e. “low rate” systems. Low rate systems are
normally used to digest slurries and solid wastes, while high rate systems are
usually used for treatment of wastewater.

43
Renewable Energy
Resources Table 3.4 : C/N Ratios of different Types of Feedstock

Feedstock C/N ratio Range

Poultry litter waste 5-10

Grass clippings 12-25
Horse stable manure 25-27
Fruit waste 28-35

Leaves 30-80
Straw, wheat 100-138
Night soil 6-10
Sewage sludge 6-8

Animal manure (without litter) 11-25

Farmyard manure (average with litter) 14-20

Green vegetable wastes, weeds 11-20

Cereal straw 45-130

Potato peels 22-25
Cow dung 25-30
Poultry manure 8-15
Pig manure 18-20
Garbage 16-22

3.7.8 Toxicity
Methanogens are most sensitive to any kind of toxicity in comparison to other
microorganisms in anaerobic degradation. The Table 3.5 lists the limit
concentrations (mg/l) for various inhibitors.
Table 3.5 : Limiting Concentrations for various inhibitors
of bio-methanation
Substance [mg/l]

Copper 10-250
Calcium 8000
Sodium 8000
Magnesium 3000
Nickel 100-1000
Zink 350-1000
Sulphur 200

(Reference : Biogas_gtz_de.pdf, Eschborn, Germany)

3.7.9 Degree of Mixing

Mixing is a control process to keep uniform the pH and other environmental
conditions of slurry in the digester. It distributes the buffering agents throughout
the reactor volume and prevents localized build up of high concentrations of
intermediate metabolic products, which may inhibit methanogenic activities.
44
 Biogas Energy
3.8 EFFICIENCY OF GAS PRODUCTION AND USES
The efficiency of Biogas production is measured in terms of yield as a fraction of
the theoretical yields of gas. The biogas production per Kg of raw material may
be a good indicator for performance of digester. The efficiency of plant can also
be measured on the basis of gas production per unit reduction in total solids,
volatile solids, Chemical Oxygen Demand (COD) or Biological Oxygen Demand
(BOD). The Total solids and volatile solids are normally used to measure the
efficiency as biomass is solid material.
The efficiency of the biogas production depends on the retention time (percentage
of daily input of biomass related to total volume). Normally, the efficiency can be
expected around 60%. The biogas production also depends on the Biological
Oxygen Demand (BOD) in the wastewater. The BOD reduction will generate
0.8 m3 of biogas each Kg of BOD removal. Adding water with low BOD from the
end of the anaerobic process will dilute the high inlet BOD and improve the
biogas process.
Uses for Biogas (methane)
The biogas may be used for variety of applications. Some of the application areas
are :
(1) producing steam (i.e. heat)
(2) generating electricity (with power generators)
(3) producing “CNG”(with purifiers and compressors).

3.9 MAJOR BENEFITS

The cooking in rural areas is still largely depending on the use of traditional cook
stoves (Chullha’s). They are burning dung cake, fire-wood and agricultural waste
in addition to kerosene up to some extent. The installation of bio-gas plants would
directly replace the use of above three and in saving them, following gains would
be made :
(a) Reduction in pollution due to burning of dung and other biomass
materials. Dung can be conserved, if biogas plants are used. Again,
the dung after digestion in gas plant preserves more of Nitrogen,
Phosphorus and Potash. The slurry coming out after digestion from
different capacity plants are given in Table 3.6.
(b) The rural people would not be dependent on wood which is used for
cooking. The deforestation and ecological imbalances can be reduced.
(c) In rural areas instead of kerosene the biogas can be used for lighting.
This would reduce the dependence on fossil oil directly and in saving
foreign exchange.
(d) The most important benefit would be in keeping the clean inhabitation
and environment. The human beings can be saved form bacterial
infections and other insects.
(e) The combustion of biogas produces carbon dioxide (CO2), a
greenhouse gas. The carbon in biogas comes from plant matter that
fixed this carbon from atmospheric CO2. Thus, biogas production is
carbon-neutral and does not add to greenhouse gas emissions.
Further, any consumption of fossil fuels replaced by biogas will lower
CO2 emissions.
45
Renewable Energy
Resources
Table 3.6 : Slurry manure from Biogas Plants
Size (m3) Slurry Manure (Tonnes/yr)

10 49275
15 73912
20 98550
25 123187
35 172462
45 221737
60 295650
85 418837

SAQ 4
(a) What are the environmental impacts of producing/using biogas?
(b) Does biogas contribute to climate change?
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

3.10 LET US SUM UP

Biogas is produced from almost any feedstock containing organic compounds,

both wastes and biomass (energy crops), animal manure, sludge settled from
wastewater, and at landfills containing organic wastes. Carbohydrates, proteins
and lipids are all readily converted to biogas. Many wastewaters contain organic
compounds that may be converted to biogas including municipal wastewater,
food processing wastewater and many industrial wastewaters. Solid and
semi-solid materials that include plant or animal matter can be converted to
biogas. Providing the reliable affordable and environmentally clean
biomethanation technology can raise the economic and social level of the
villagers. In short the per capita income of the villager can be enhanced by
conserving their own resources in the village in addition to providing the energy
from the available local resources.

3.11 KEY WORDS

Alkalinity : Alkalinity of a liquid is mainly a measure of its acid neutralizing

capacity.
Biochemical Oxygen Demand (BOD) : Amount of oxygen needed by bacteria
and other microorganisms to decompose organic matter in water.
Bio-energy : Renewable energy produced from organic matter
Bio-fuels : Fuels made from biomass; include ethanol, biodiesel and methanol

46
Biogas : A combustible gas derived from decomposing biological waste; Biogas Energy

normally consists of 50 to 60 percent methane.

Biomass : A renewable source of energy derived from organic matter like wood,
agriculture waste; also include algae, sewage and other organic substances that
may be used to make energy through chemical processes
Bio-fuels : Fuels made from biomass; include ethanol, biodiesel and methanol
Fluidised Bed Combustion : A process of burning powdered coal with air or
gases; reduces sulfur dioxide emissions from coal combustion
Methane Genesis : Acetate, carbon dioxide and molecular hydrogen can be
directly utilized as a substrate by the group of anaerobic microorganisms called
Methane genesis.
Organic Loading Rate (OLR) : Organic loading rate (OLR) of a process is a
measure of how much organic material is fed to each cubic meter of reactor
volume during one day (i.e. Kg of VS /m3 or COD/m3 day).
pH Value : pH is defined as follows:
Hydraulic Retention Time (HRT) : HRT varies with operating temperature of
the anaerobic digester. It is defined as the average time a volume element of the
liquid medium resides inside the reactor.

3.12 ANSWER TO SAQs

SAQ 1
(a) Biogas results from bacteria in the process of bio-degradation of
organic material under anaerobic (without oxygen) conditions. The
natural generation of biogas is an important part of the
biogeochemical carbon cycle. Methanogens (methane producing
bacteria) degrade organic material and return the decomposition
products to the environment. In this process biogas is generated,
which is a source of renewable energy.
(b) Biogas is a mixture of many kinds of gases which comprises of :
Methane (CH4) : 55-75%
Carbon dioxide (CO2) : 25-45%
Hydrogen Sulfide (H2S) : 0.1-1.0%
Hydrogen (H2) : 0-2 %
(c) Methane is the principal gas in biogas. Methane is also the main
component in natural gas, a fossil fuel. Biogas can be used to replace
natural gas in many applications including: cooking, heating, steam
production, electrical generation, vehicular fuel, and as a pipeline gas.
SAQ 2
Anaerobic digestion is the process by which organic materials, in an
enclosed vessel, are broken down by micro-organisms in the absence of
oxygen. Anaerobic digestion produces biogas, consisting primarily of
methane and carbon dioxide. Anaerobic digestion systems are also often
referred to as biogas systems.
47
Renewable Energy
Resources SAQ 3
(a) Biogas production is capable of reducing the pollution in wastewater
by converting oxygen demanding organic matter that could cause low
oxygen levels in surface waters. Nutrients, like nitrogen and
phosphorous are conserved in biogas effluents and can be used to
displace fertilizers in crop production.
(b) While combustion of biogas, like natural gas, produces carbon
dioxide (CO2), a greenhouse gas, the carbon in biogas comes from
plant matter that fixed this carbon from atmospheric CO2. Thus,
biogas production is carbon-neutral and does not add to greenhouse
gas emissions. Further, any consumption of fossil fuels replaced by
biogas will lower CO2 emissions.
SAQ 4
(a) Biogas digesters operate with the manure from cattle or pigs. In
addition, the digesters make use of kitchen waste, brewery waste,
industrial food processing waste, energy crops like corn, fish and
poultry remnants, ethanol production waste, etc.
(b) The liquid that results from the anaerobic digestion process has solids
which are separated out, composted, and sold to local gardeners,
landscapers and farmers. The liquids are returned to the farmer as
nutrient rich natural fertilizer, which replaces imported nutrients and
thereby cuts costs.

48
 Biogas Energy
REFERENCES
1. Archer, D B (1983) “The microbial basis of process control in
methanogenic fermentation of soluble waste”, Enzyme microbial
Technology, PP : 162-169.
2. Buswell A M (1952)”Mechanism of methane fermentation”, Industrial and
Engineering Chemestry, Vol.44 PP : 550.
3. Biomass based Decentralised Power Generation (2005) Edited by B S
Pathak and N S L Srivastva, Technical Publication No. SPRERI/2005/03.
4. Biomass Systems – Principles and applications (1996) by K M Mital,
Published by New Age International (P) Ltd.
5. Composting – Sanitary disposal and reclamation of organic waste (1956),
by Harold B Gotaas, Published by WHO Geneva
6. C A Edwards and J R Lofty, Biology of Earthworms, Published by
Chapman and Hall Ltd.
7. Hamoda M F; Qdais H A Abu and Newham j (1998) “Evaluation of
municipal solid waste composting kinetics” Resource Conservation and
Recycling Vol. 33 pp : 209-223.
8. Gysson A Engene, “Mechanical Volume Reduction” Hand book of Solid
Waste Management.
9. Gujert, W; Zehnder, A J B (1983),” Conversion Processes in anaerobic
digestion” Water Science and Technology, pp:127-167.
10. Jalan, R K and Srivastava V K “Utilization of Biomass from Muncipal
Solid Waste for Energy Recovery, Recycling and Disposal” Biomass
Energy System, TERI.
11. Jain, M C; Chhonkar, P K; and Kumar Sushil “Analytical method in Biogas
Technology”.
12. Renewable Energy Engineering and Tecchnology – A knowledgr
compendium (2008), edited by V V N Kishore and Published by TERI
Press, TERI, New Delhi.
13. http://www.efe.or.th/download/Chapter7.pdf.

49
 Wind Energy
UNIT 4 WIND ENERGY

Structure
4.1 Introduction
Objectives
4.2 The History of Wind
4.3 How Wind Machines Work
4.4 Types of Wind Machines
4.4.1 Horizontal-axis
4.4.2 Vertical-axis
4.5 Wind Power Plants
4.6 Wind Production
4.7 Wind and the Environment
4.8 Wind Energy for Water Pumping and Off-grid Power Generation
4.8.1 Water-pumping Windmill
4.8.2 Aerogenerator
4.8.3 Wind–solar Hybrid Systems
4.8.4 System Availability and Repair/Servicing Facility
4.8.5 Potential and Achievement
4.8.6 Success Stories
4.9 Let Us Sum Up
4.10 Key Words
4.11 Answers to SAQs

4.1 INTRODUCTION
Wind is the natural movement of air across the land or sea. Wind is caused by
uneven heating and cooling of the earth's surface and by the earth's rotation. Land
and water areas absorb and release different amount of heat received from the
sun. As warm air rises, cooler air rushes in to take its place, causing local winds.
The rotation of the earth changes the direction of the flow of air.
Wind is simple air in motion. It is caused by the uneven heating of the earth’s
surface by the sun. Since the earth’s surface is made of very different types of
land and water, it absorbs the sun’s heat at different rates (Figure 4.1).
During the day, the air above the land heats up more quickly than the air over
water. The warm air over the land expands and rises, and the heavier, cooler air
rushes in to take its place, creating winds. At night, the winds are reversed
because the air cools more rapidly over land than over water.
In the same way, the large atmospheric winds that circle the earth are created
because the land near the earth's equator is heated more by the sun than the land
near the North and South Poles.
Today, wind energy is mainly used to generate electricity. Wind is called a
renewable energy source because the wind will blow as long as the sun shines.
51
Renewable Energy
Resources

Figure 4.1 : Wind Movement

Objectives
After studying this unit, you should be able to
· know the history of wind,
· describe the uses of wind energy,
· explain how wind machines work,
· get familiarity with wind power plants, and
· know the wind and the environment.

4.2 THE HISTORY OF WIND

Since ancient times, people have harnessed the winds energy. Over 5,000 years
ago, the ancient Egyptians used wind to sail ships on the Nile River. Later, people
built windmills to grind wheat and other grains. The earliest known windmills
were in Persia (Iran). These early windmills looked like large paddle wheels.
Centuries later, the people of Holland improved the basic design of the windmill.
They gave it propeller-type blades, still made with sails. Holland is famous for its
windmills.
American colonists used windmills to grind wheat and corn, to pump water, and
to cut wood at sawmills. As late as the 1920s, Americans used small windmills to
generate electricity in rural areas without electric service. When power lines
began to transport electricity to rural areas in the 1930s, local windmills were
used less and less, though they can still be seen on some Western ranches.
The oil shortages of the 1970s changed the energy picture for the country and the
world. It created an interest in alternative energy sources, paving the way for the
re-entry of the windmill to generate electricity. In the early 1980s wind energy
really took off in California, partly because of state policies that encouraged
renewable energy sources. Support for wind development has since spread to
other states, but California still produces more than twice as much wind energy as
any other state.

4.3 HOW WIND MACHINES WORK

Basic technology
Wind electric generator converts kinetic energy available in wind to electrical
energy by using rotor, gearbox and generator.
52
The Basic Process Wind Energy

The wind turns the blades of a windmill-like machine. The rotating blades turn
the shaft to which they are attached. The turning shaft typically can either power a
pump or turn a generator, which produces electricity.
Most wind machines have blades attached to a horizontal shaft. This shaft
transmits power through a series of gears, which provide power to a water pump
or electric generator. These are called horizontal axis wind turbines.
There are also vertical axis machines, such as the Darrieus wind machine, which
has two, three, or four long curved blades on a vertical shaft and resembles a giant
eggbeater in shape.
The amount of energy produced by a wind machine depends upon the wind speed
and the size of the blades in the machine. In general, when the wind speed
doubles, the power produced increases eight times. Larger blades capture more
wind. As the diameter of the circle formed by the blades doubles, the power
increases four times.
Like old fashioned windmills, today’s wind machines use blades to collect the
wind’s kinetic energy. Windmills work because they slow down the speed of the
wind. The wind flows over the airfoil shaped blades causing lift, like the effect on
airplane wings, causing them to turn. The blades are connected to a drive shaft
that turns an electric generator to produce electricity. With the new wind
machines, there is still the problem of what to do when the wind isn’t blowing. At
those times, other types of power plants must be used to make electricity.

4.4 TYPES OF WIND MACHINES

Wind energy is the kinetic energy associated with the movement of atmospheric
air. It has been used for hundreds of years for sailing, grinding grain, and for
irrigation. Wind energy systems convert this kinetic energy to more useful forms
of power. Wind energy systems for irrigation and milling have been in use since
ancient times and since the beginning of the 20th century it is being used to
generate electric power. Windmills for water pumping have been installed in
many countries particularly in the rural areas.
Wind turbines transform the energy in the wind into mechanical power, which
can then be used directly for grinding, etc. or further converting to electric power
to generate electricity. Wind turbines can be used singly or in clusters called
‘wind farms’. Small wind turbines called aero-generators can be used to charge
large batteries.
Five nations – Germany, USA, Denmark, Spain and India – account for 80% of
the world’s installed wind energy capacity. Wind energy continues to be the
fastest growing renewable energy source with worldwide wind power installed
capacity reaching 14,000 MW.

Points to Remember
Wind power is the conversion of wind energy into useful form, such as electricity,
using wind turbines.
India ranks 5th in the world with a total wind power capacity if 1080MW out of which
1025MW have been established in commercial projects.
This energy is used for : Sailing ships, Pumping water/Irrigation, Grinding Grains,
Power generation.
Some of the gadgets and other devices : Sails, Windmills, Wind turbines.
53
Renewable Energy
Resources
Realizing the growing importance of wind energy, manufacturers have steadily
been increasing the unit size of the wind electric generators since the late 1980s.
Another important development has been the offshore (i.e. in the sea) wind farms
in some regions of Europe, which have several advantages over the on-shore
ones. The third major development has been the use of new techniques to assess
the wind resource for techno-commercial viability.
In India the states of Tamilnadu and Gujarat lead in the field of wind energy. At
the end of March 2000 India had 1080-MWs capacity wind farms, of which
Tamilnadu contributed 770 MW capacity. Gujarat has 167 MW followed by
Andhra Pradesh, which has 88 MW installed wind farms.There are about a dozen
wind pumps of various designs providing water for agriculture, afforestation, and
domestic purposes, all scattered over the country.
The design of the Auroville multi-blade windmill has evolved from the practical
experience gained in operating these mills over a period of 20 years or so. It has a
high tripod tower and its double-action pump increases water output by about
60% compared to the conventional single-action pumps.
In windmills, wind energy is directly used to crush grain or to pump water. At the
end of 2007, worldwide capacity of wind-powered generators was 94.1 GW.
Although wind currently produces just over 1% of world-wide electricity use, it
accounts for approximately 19% of electricity production in Denmark, 9% in
Spain and Portugal, and 6% in Germany and the Republic of Ireland. Globally,
wind power generation increased more than fivefold between 2000 and 2007.
Wind power is produced in large scale wind farms connected to electrical grids,
as well as in individual turbines for providing electricity to isolated locations.
There are two different types of wind machines namely :
· Horizontal-axis wind Machines
· Vertical-axis wind Machines
Now you will be introduced to both types of wind machine.
4.4.1 Horizontal-axis
Most wind machines being used today are the horizontal-axis type. Horizontal-
axis wind machines have blades like airplane propellers. A typical horizontal
wind machine stands as tall as a 20-story building and has three blades that span
200 feet across. The largest wind machines in the world have blades longer than a
football field! Wind machines stand tall and wide to capture more wind
(Figure 4.2).

Figure 4.2 : Wind Machine

54
 Wind Energy
4.4.2 Vertical-axis
Vertical-axis wind machines have blades that go from top to bottom and the most
common type (Darrieus wind turbine) looks like a giant two-bladed egg beaters.
The type of vertical wind machine typically stands 100 feet tall and 50 feet wide.
Vertical-axis wind machines make up only a very small percent of the wind
machines used today.
The Wind Amplified Rotor Platform (WARP) is a different kind of wind system
that is designed to be more efficient and use less land than wind machines in use
today. The WARP does not use large blades; instead, it looks like a stack of
wheel rims. Each module has a pair of small, high capacity turbines mounted to
both of its concave wind amplifier module channel surfaces. The concave
surfaces channel wind toward the turbines, amplifying wind speeds by 50 percent
or more. Eneco, the company that designed WARP, plans to market the
technology to power offshore oil platforms and wireless telecommunications
systems.

4.5 WIND POWER PLANTS

Wind power plants, or wind farms as they are sometimes called, are clusters of
wind machines used to produce electricity. A wind farm usually has dozens of
wind machines scattered over a large area. The world's largest wind farm, the
Horse Hollow Wind Energy Center in Texas, has 421 wind turbines that generate
enough electricity to power 220,000 homes per year.
Unlike power plants, many wind plants are not owned by public utility
companies. Instead they are owned and operated by business people who sell the
electricity produced on the wind farm to electric utilities. These private
companies are known as Independent Power Producers.
Operating a wind power plant is not as simple as just building a windmill in a
windy place. Wind plant owners must carefully plan where to locate their
machines. One important thing to consider is how fast and how much the wind
blows.
As a rule, wind speed increases with altitude and over open areas with no
windbreaks. Good sites for wind plants are the tops of smooth, rounded hills,
open plains or shorelines, and mountain gaps that produce wind funneling.
Wind speed varies throughout the country. It also varies from season to season. In
Tehachapi, California, the wind blows more from April through October than it
does in the winter. This is because of the extreme heating of the Mojave Desert
during the summer months. The hot air over the desert rises, and the cooler,
denser air above the Pacific Ocean rushes through the Tehachapi mountain pass to
take its place. In a state like Montana, on the other hand, the wind blows more
during the winter. Fortunately, these seasonal variations are a good match for the
electricity demands of the regions. In California, people use more electricity
during the summer for air conditioners. In Montana, people use more electricity
during the winter months for heating.

4.6 WIND PRODUCTION

In 2006, wind machines in the United States generated a total of 26.6 billion KWh
per year of electricity, enough to serve more than 2.4 million households. This is
enough electricity to power a city larger than Los Angeles, but it is only a small
55
Renewable Energy
Resources
fraction of the nation's total electricity production, about 0.4 percent. The amount
of electricity generated from wind has been growing fast in recent years. In 2006,
electricity generated from wind was 2 1/2 times more than wind generation
in 2002.
New technologies have decreased the cost of producing electricity from wind, and
growth in wind power has been encouraged by tax breaks for renewable energy
and green pricing programs. Many utilities around the country offer green pricing
options that allow customers the choice to pay more for electricity that comes
from renewable sources.
Wind machines generate electricity in 28 different states in 2006. The states with
the most wind production are Texas, California, Iowa, Minnesota, and Oklahoma.
Most of the wind power plants in the world are located in Europe and in the
United States where government programs have helped support wind power
development. The United States ranks second in the world in wind power
capacity, behind Germany and ahead of Spain and India. Denmark ranks number
six in the world in wind power capacity but generates 20 percent of its electricity
from wind.

4.7 WIND AND THE ENVIRONMENT

In the 1970s, oil shortages pushed the development of alternative energy sources.
In the 1990s, the push came from a renewed concern for the environment in
response to scientific studies indicating potential changes to the global climate if
the use of fossil fuels continues to increase. Wind energy is an economical power
resource in many areas of the country. Wind is a clean fuel; wind farms produce
no air or water pollution because no fuel is burned. Growing concern about
emissions from fossil fuel generation, increased government support, and higher
costs for fossil fuels (especially natural gas and coal) have helped wind power
capacity in the United States grow substantially over the last 10 years.
The most serious environmental drawbacks to wind machines may be their
negative effect on wild bird populations and the visual impact on the landscape.
To some, the glistening blades of windmills on the horizon are an eyesore; to
others, they’re a beautiful alternative to conventional power plants.

SAQ 1
(a) What is wind energy?
(b) How is the energy in the wind captured?
(c) How big are wind turbines?
(d) What is wind turbines made of?
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

56
 Wind Energy
4.8 WIND ENERGY FOR WATER PUMPING AND
OFF-GRID POWER GENERATION

Water-pumping windmills, aerogenerators (small wind electric generators), and

wind-solar hybrid systems have been found to be useful for meeting
water-pumping and small-power requirements in a decentralized mode in rural
and remote windy areas of the country.
The MNRE is implementing a programme on ‘Small Wind Energy and Hybrid
Systems’ to promote utilization of water-pumping wind mills, aerogenerators, and
wind-solar hybrid systems for water pumping and power generation. The source
of information given in this unit is MNRE annual reports.
4.8.1 Water-pumping Windmill
A water-pumping windmill pumps water from wells, ponds, and bore wells for
drinking, minor irrigation, salt farming, fish farming, etc. Available windmills are
of two types, namely direct drive and gear type.
The most commonly used windmill has a horizontal axis rotor of 3-5.5 m
diameter, with 12-24 blades mounted on the top of a 10-20 m high mild steel
tower. The rotor is coupled with a reciprocating pump of 50-150 mm diameter
through a connecting rod.
Such windmills start lifting water when wind speed approaches 8–10 Km/hour.
Normally, a windmill is capable of pumping water in the range of 1000 to 8000
litres per hour, depending on the wind speed, the depth of water table, and the
type of windmill.
Windmills are capable of pumping water from depths of 60 m. Water-pumping
windmills have an advantage in that no fuel is required for their operation, and
thus they can be installed in remote windy areas where other conventional means
of water pumping are not feasible.
However, water-pumping windmills have limitations too. They can be operated
satisfactorily only in medium wind regimes (12-18 Km/hour. Further, special care
is needed at the time of site selection as the sites should be free from obstacles
such as buildings and trees in the surrounding areas. The cost of the system being
high, many individual users do not find them affordable.
The cost of a water-pumping windmill varies from Rs. 45000 to Rs. 150000,
depending on the type. In addition, Rs. 10000-Rs. 20000 is required for the
foundation, storage tank, and the installation of the windmill. As the system
involves moving parts, it requires frequent maintenance. The repair and
maintenance cost of a windmill is about Rs. 2000 per year.
The MNRE provides a subsidy of up to 50% of the ex-works cost of
water-pumping windmills, subject to ceilings of Rs. 20000, Rs. 30000, and Rs.
45000 in the case of direct drive, gear type, and AV-55 Auroville models,
respectively. For non-electrified islands, subsidy of up to 90% of the ex-works
cost is provided for the above types of windmills, subject to ceilings of Rs. 30000,
Rs. 45000, and Rs. 80000, respectively.
4.8.2 Aerogenerator
An aerogenerator is a small wind electric generator having a capacity of up to
30 KW. Aerogenerators are installed either in stand-alone mode or along with
solar photovoltaic (SPV) systems to form a wind-solar hybrid system for
decentralized power generation. An aerogenerator is suitable for power generation
57
Renewable Energy
Resources
in un-electrified areas having adequate wind speeds. It consists of a rotor of
1-10 m diameter having 2-3 blades, permanent magnet generator, control devices,
yaw mechanism, tower, storage battery, etc. The aerogenerator rotor starts
moving at a wind speed of 9-12 Km per hour. However, it produces optimum
power at the rated wind speed of 40-45 Km per hour. The limitation of not being
able to provide power as and when it is required is overcome by storing it in a
battery bank.
Aerogenerators cost about Rs. 2.00-2.50 lakhs per KW. In addition, the cost of
installation including civil works is estimated at Rs. 5000 per KW. The repair and
maintenance cost is about Rs. 2000 per KW per annum.
4.8.3 Wind-solar Hybrid Systems
When an aerogenerator and an SPV system are interfaced, the power generation
from these is mutually supplemented, and the resultant hybrid system offers a
reliable and cost-effective electric supply in a decentralized mode. The wind-solar
hybrid system mainly consists of one or two aerogenerators along with SPV
panels of suitable capacity, connected with charge controller, inverter, battery
bank, etc. to supply AC power. The major advantage of the system is that it meets
the basic power requirements of non-electrified remote areas, where grid power
has not yet reached. The power generated from both wind and solar components
is stored in a battery bank for use whenever required. The cost of the system
varies from Rs. 2.50 lakhs to Rs. 3.50 lakhs per KW depending on the ratio of
wind and solar components.
The approximate cost of installation, including civil works, is about Rs. 10000 per
KW. Repair and maintenance cost is about Rs. 3000 per KW per annum. Subsidy
of up to 50% of ex-works cost of the system is provided, subject to a maximum of
Rs. 1.25 lakhs per KW to individuals, industries, and R&D and academic
institutions. The MNRE provides a subsidy for community use and direct use by
central/state government departments and defense and para-military forces of up
to 75% of the ex-works cost of the system subject to a maximum of Rs. 2 lakhs
per KW. For non-electrified islands, subsidy of up to 90% of ex-works cost
subject to a maximum of Rs. 2.4 lakhs per KW is available.
4.8.4 System Availability and Repair/Servicing Facility
Water-pumping windmills, aerogenerators, and wind-solar hybrid systems are
installed through state nodal agencies using central subsidy.
The state nodal agencies are responsible for providing repair/service facilities
through the respective manufacturers.
4.8.5 Potential and Achievement
Water-pumping windmills require only medium wind regimes. Considering the
availability of required wind speeds and the level of the prevailing water table,
potential exists for installing water-pumping windmills in almost all states, except
in hilly and rocky regions.
Aerogenerators and wind-solar hybrid systems require high wind speeds and good
solar radiation. Potential exists for their installation in Andhra Pradesh, Gujarat,
Karnataka, Kerala, Madhya Pradesh, Maharashtra, Orissa, Rajasthan, Tamil
Nadu, Uttaranchal, Uttar Pradesh, West Bengal, and the windy regions of Jammu
and Kashmir and all northeastern states. So far, about 1000 water-pumping
windmills and 380 KW aggregate capacity of aerogenerators/wind-solar hybrid
systems have been installed in the country.
58
 Wind Energy
4.8.6 Success Stories
Water-pumping Windmills
Three water-pumping windmills of AV-55 type installed in and around Auroville
have become the exclusive source of drinking water for the community, which is
fully dependent on the water lifted by these windmills. The maximum number of
water-pumping windmills have been installed in Gujarat, for irrigation and
drinking water purposes.
Aerogenerators
The West Bengal Renewable Energy Development Agency (WBREDA) has
installed six aerogenerators of 3-KW capacity each in the existing SPV power
plants at Sagar and Mousani islands. A number of aerogenerators have been
installed by the Maharashtra Energy Development Agency (MEDA), and are
working satisfactorily. An aerogenerator of 3.2-KW capacity, installed at the
Manashakti Research Centre, Lonawala, is supplying electricity to illuminate
22 streetlights on the road connecting the centre’s hostel to the highway. The
aerogenerator is visible from the Mumbai-Pune highway.
Wind-solar Hybrid Systems
Wind-solar hybrid systems have been installed for a variety of applications. Some
of them have been installed on islands and in coastal areas. One notable project is
a 5 KW capacity wind-solar hybrid system installed on Vagator beach in Goa,
which has become a destination point for tourists. The system illuminates
60 CFLs (compact fluorescent lamps) of 18 W rating each. These CFLs are the
only source of illumination on the beach. A 15 KW wind-solar hybrid system has
recently been installed at the famous pilgrimage site of Bhimashanker
Deosthan, in Pune district, Maharashtra. This system provides electricity to meet
the needs of the entire temple complex. It has become a point of attraction for a
large number of devotees visiting the temple complex. A large number of
wind-solar hybrid systems have been installed in Maharashtra by MEDA,
including a unit that provides power to the local area network of computers and
other needs in their own office complex in Pune.

4.9 LET US SUM UP

Let us summaries what we have learnt in this unit. We begin our discussion with
introduction of wind energy. Wind is a form of solar energy. Winds are caused by
the uneven heating of the atmosphere by the sun, the irregularities of the earth’s
survice and rotation of the earth. We are using the wind flow for many purposes.
We can also generate electricity by using wind energy. Basically it converts the
kinetic energy of wind to some other forms of energy like mechanical energy on
electrical energy as per our needs. India ranks 5th in the world for using wind
energy for power generation. We have also discussed different types of wind
machines.

4.10 KEY WORDS

Aerogenerator
An aerogenerator is a small wind electric generator having a capacity of up
to 30 KW. Aerogenerators are installed either in stand-alone mode or along
with solar photovoltaic (SPV) systems to form a wind–solar hybrid system
for decentralized power generation.
59
Renewable Energy
Resources
Wind Energy
Wind energy is the kinetic energy associated with the movement of
atmospheric air. Wind energy system covert the kinetic energy to more
useful forms of power.
Wind Generator
It describe the process by which the wind is use to generate mechanical
power on electricity. Wind turbines converts the kinetic energy in the wind
into mechanical power can be used for specific tasks for generating
electricity.

4.11 ANSWERS TO SAQs

SAQ 1
(a) The terms "wind energy" or "wind power" describe the process by
which the wind is used to generate mechanical power or electricity.
Wind turbines convert the kinetic energy of the wind into mechanical
power. This mechanical power can be used for specific tasks (such as
grinding grain or pumping water) or a generator can convert this
mechanical power into electricity to power homes, businesses,
schools, and the like.
(b) Wind turbines, like aircraft propeller blades, turn in the moving air
and power an electric generator that supplies an electric current.
Modern wind turbines are horizontal-axis variety, like the traditional
farm windmills used for pumping water. Wind turbines are often
grouped together into a single wind power plant, also known as a
wind farm, and generate bulk electrical power. Electricity from these
turbines is fed into a utility grid and distributed to customers just as it
is with conventional power plants.
(c) Wind turbines are available in a variety of sizes, and therefore power
ratings. Typical commercial wind facilities are 1.5 MW. The largest
machine has blades that span more than the length of a football field,
stands 20 building stories high, and produces enough electricity to
power 1,400 homes. A small home-sized wind machine has rotors
between 8 and 25 feet in diameter, stands upwards of 30 feet, and can
supply the power needs of an all-electric home or small business.
(d) All electric-generating wind turbines, no matter their size, are
comprised of a few basic components: a rotor (the part that actually
rotates in the wind), an electrical generator, a speed-control system,
and a tower.

60
 Other Forms of Renewable
UNIT 5 OTHER FORMS OF RENEWABLE Energy

ENERGY

Structure

5.1 Introduction
Objectives
5.2 Geothermal Energy
5.2.1 Use of Geothermal Energy
5.2.2 Geothermal Power Plants and Environment
5.3 Ocean and Tidal Energy
5.3.1 Ocean Thermal Energy
5.3.2 Tidal Energy
5.3.3 Advantages and Disadvantages of Tidal Energy
5.4 Hydrogen and Fuel Cells
5.4.1 Hydrogen as Fuel
5.4.2 Hydrogen as Energy Carrier
5.4.3 Hydrogen Fuel Cells Produce Electricity
5.4.4 Hydrogen Use in Vehicles
5.4.5 Fuel Cells
5.4.6 Fuel Cell Components
5.4.7 Advantages of Fuel Cells
5.5 Biofuels
5.5.1 1st-Generation Biofuels
5.5.2 2nd-Generation Biofuels
5.6 Hydropower
5.6.1 Hydropower and Environmental Impacts
5.7 Animal Energy
5.8 Let Us Sum Up
5.9 Key Words
5.10 Answers to SAQs

5.1 INTRODUCTION
You have already studied important sources of renewable energy like solar
thermal energy, biogas, biomass, solar PV, wind energy, etc. There are other
renewable energy sources which are not so popular but are now gaining
importance. The other sources of renewable energy are mainly geothermal, ocean,
hydrogen and fuel cells. These have immense potential, although tapping this
potential for power generation and other applications calls for development of
suitable technologies. You will learn these renewable energy sources in this unit.
We begin our discussion with geothermal energy.
61
Renewable Energy
Resources Objectives
After studying this unit, you will be able to learn other forms of renewable
energies. More preciously, you will be able to
· understand hydel power,
· understand geothermal power,
· understand ocean and tidal energy,
· understand fuel cell, and
· understand hydrogen energy.

5.2 GEOTHERMAL ENERGY

There are two large sources of energy. One is sun which is above the earth and
other is geothermal energy beneath the earth. The word geothermal comes from
the Greek words geo (earth) and therme (heat). Therefore, geothermal energy is
heat from within the Earth. We can recover this heat as steam or hot water and
use it for various applications like power generation and direct heat applications.
Geothermal energy is a renewable energy source because the heat is continuously
produced inside the Earth. Today we have recognized that this resource has
potential for much broader application. In India, Northwest Himalayas and the
west coast are considered geothermal areas. The Geological Survey of India has
already identified more than 350 hot spring sites, which can be explored as areas
to tap geothermal energy.
You might have heard the names like volcanoes and fumaroles (holes where
volcanic gases are released), hot springs and geysers. These are the visible forms
of geothermal energy. However, the geothermal energy inside the earth may be
utilized to heat buildings and to produce electricity by digging deep wells and
pumping the heated underground water or steam to the surface.
Geothermal energies are of two types; the high grade and low the grade
geothermal energies. The high-grade geothermal energy is the heat due to the
earth’s pressure that turns water into steam. The low-grade geothermal energy is
the heat within the earth’s crust. This heat is actually stored solar energy.
5.2.1 Use of Geothermal Energy
You may be familiar with some uses of geothermal energy like bathing and
cooking in hot springs. The main areas where geothermal energy is being used
are :
· Direct use as heating systems : Geothermal energy is used to heat
water from springs or reservoirs near the surface.
· Electricity generation by power plants : This application requires
water or steam at very high temperature.
· Geothermal heat pumps : The geothermal energy is used where
stable ground or water temperatures near the Earth's surface are
available to control temperatures in a buildings above ground. A heat
pump is a mechanical device used for heating and cooling purposes.
The heat pump operates on the principle that heat can be extracted
from a warmer temperature to a cooler temperature. A geothermal
heat pump uses the earth to warm us in the winter and cool us in the
summer. You may be familiar with one of the most widely used heat
62
 Other Forms of Renewable
pump in your home. It is your refrigerator. It extracts the heat from Energy
the items put inside the refrigerator and throws it outside which you
can feel if you put your hand behind it. The geothermal heat pumps
are energy efficient, environmentally clean, and cost effective systems
for temperature control.
5.2.2 Geothermal Power Plants and Environment
Since geothermal power plants do not burn fossil fuels to generate electricity,
harmful emission levels are negligible. The geothermal power plants release less
than 1% of the CO2 emissions as compared to a fossil fuel plant. Another
interesting fact is that geothermal plants emit about 97% less acid rain-causing
sulphur compounds than are emitted by fossil fuel plants. After the steam and
water from a geothermal reservoir have been used, they are injected back into the
Earth.

SAQ 1
Define geothermal energy.
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

SAQ 2
What is geothermal heat pump?
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

5.3 OCEAN AND TIDAL ENERGY

Ocean thermal and tidal energies are two main ocean renewable energies. The
other ocean renewable energies are wave energy, ocean current energy, offshore
wind and ocean thermal gradient energy.
The vast potential of energy of the seas and oceans which cover about three fourth
of our planet, can make a significant contribution to meet our energy needs.
Ocean energy can be used to generate electricity in an environment-friendly
manner.
Waves are caused by the wind blowing over the surface of the ocean. There is
tremendous energy in the ocean waves. The wave energy converters are used to
extract the power of ocean waves and convert it into electricity. Typically, these
systems use either a water column or some type of surface to capture the wave
power.
63
Renewable Energy
Resources 5.3.1 Ocean Thermal Energy
Ocean thermal energy conversion (OTEC) systems exploit temperature
differences between warmer, surface layers and colder, deep layers of the ocean.
All OTEC designs require a large-diameter intake pipe to pump cold water to the
surface. They employ a variety of heat-exchange cycles to drive a turbine and
generate electricity.
5.3.2 Tidal Energy
Tides are caused by the gravitational pull of the moon and sun, and the rotation of
the Earth. Thus, tidal energy is the utilization of the moon and sun's gravitational
forces – as tides are formed by the gravitational pull of the moon and sun on the
oceans of the rotating earth. Near shore, water levels can vary up to 40 feet due to
tides. A flood tide is one that is coming in or rising and an ebb tide is one that is
going out. Thus, tidal energy takes advantage of the daily ebb and flow of tides
and of localized examples of water in motion. The gravitational pull of the moon
drives tidal flows. Tidal energy is one of the oldest forms of energy used as
evidence of tide mills from before 1100AD has been found along the coast of
France, Spain and the UK.
The process of generating electricity from the tidal energy may be understood by
the following steps :
· When the tide comes in, water flows through a sluice into a storage
pond
· When the tides go back out, the water flows back into the sea by
passing through a turbine generating electricity.
5.3.3 Advantages and Disadvantages of Tidal Energy
Advantages
The important advantages of tidal energy are :
· Tidal energy does not require any fuel.
· The economic life of a tidal plant is about 75 to 100 years as
compared to about 35 years of a conventional fossil fuel plant.
· Tidal energy is clean and renewable.
· Tidal energy is non-polluting. A tidal barrage can prevent
approximately one million tons of CO2 per TWH generated.
Disadvantages
The important disadvantages are :
· Tidal energy affects the ecosystem.
· Tidal energy leads to damages like reduced flushing and erosion
which ultimately affects the vegetation of the area and disrupt
the balance.
· The alteration of tidal currents also affects the habitat of the
seabirds and the fish.
SAQ 3
What is ocean renewable energy?
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
64
 Other Forms of Renewable
SAQ 4 Energy
What is ocean thermal energy conversion systems?
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

5.4 HYDROGEN AND FUEL CELLS

In the case of Hydrogen energy, electricity is produced through an
electro-chemical reaction between hydrogen and oxygen. Hydrogen gas is the
primary fuel for fuel cells also. Hydrogen can be produced from the electrolysis
of water using solar energy. It can also be extracted from sewage gas, natural gas,
naptha or biogas. Fuel cells can be very widely used for a wide range of
applications once they become commercially viable.
5.4.1 Hydrogen as Fuel
You may be aware that hydrogen (H2) as a gas is not found by itself on Earth.
This is because Hydrogen gas is so much lighter than air that it rises fast and is
quickly ejected from the atmosphere. Hydrogen is found only in compound form
with other elements. You are familiar with one such compound which is water
(H2O) and is the result of Hydrogen combining with oxygen. Hydrogen when
combined with carbon forms different compounds like methane (CH4), coal, and
petroleum. Hydrogen is also available in biomass.

Point to Remember :
1. Hydrogen has the highest energy content of any common fuel by weight
(about three times more than gasoline)
2. Hydrogen has the lowest energy content by volume (about four times less than
gasoline).

5.4.2 Hydrogen as Energy Carrier

You have seen that electricity is the most well-known energy carrier. Like
electricity, hydrogen is an energy carrier and must be produced from another
substance. Hydrogen is not currently widely used, but it has tremendous potential
as an energy carrier in the future. Hydrogen can be separated from water,
biomass, or natural gas molecules. One of the widely known methods for
producing hydrogen is electrolysis. Electrolysis is a process that splits hydrogen
from water. It results in no emissions, but it is an expensive process at present.
5.4.3 Hydrogen Fuel Cells Produce Electricity
Hydrogen fuel cells (batteries) are being used as a source of electricity. They are
very efficient, but expensive to build. Small fuel cells can power electric cars
while large fuel cells can provide electricity in remote areas where there is no
power.
5.4.4 Hydrogen Use in Vehicles
Hydrogen has an excellent potential as fuel for vehicles. Hydrogen may be stored
as gas or liquid on board and converted in to electricity. The vehicles may also
burn the hydrogen directly with no pollution.
65
Renewable Energy
Resources 5.4.5 Fuel Cells
Fuel cells are based on the electrochemical reaction between hydrogen and
oxygen to produce electricity, water vapor, and heat. The byproducts of the
reaction can be re-utilized by the fuel cell system. Fuel cells are efficient,
environmentally friendly and reliable for power production. The use of fuel cells
has been demonstrated for stationary/portable power generation and other
applications.
Fuel cells are different from electrochemical cell batteries in that they consume
reactant from an external source, which must be replenished. By contrast batteries
store electrical energy chemically and hence represent a closed system.
Many combinations of fuel and oxidant are possible. A hydrogen cell uses
hydrogen as fuel and oxygen (usually from air) as oxidant. Other fuels include
hydrocarbons and alcohols. Other oxidants include chlorine and chlorine dioxide.
Fuel cells are simple, low-cost device and can produce an average of 10 watts of
power.
A battery chemically stores and releases electricity while a fuel cell produces
energy by reacting a fuel with air. A battery may run out of power if not
recharged. A fuel cell, however, will continue to function and produce power as
long as the fuel and oxygen are supplied to it.
5.4.6 Fuel Cell Components
There are three main components of a fuel cell system. These are :
(1) hydrogen source
(2) fuel cell stacks
(3) power inverter
The hydrogen can be produced through electrolysis of water by using renewable
energy sources like solar panels or wind generators. The fuel cell stack converts
the hydrogen and oxygen into electricity, water vapor and heat. An inverter
converts the DC electricity from the fuel cell into AC electricity that most
equipment requires.
5.4.7 Advantages of Fuel Cells
Fuel cells have a number of advantages over other technologies for power
generation. Some of the important advantages are :
· use less fuel as compared to other competing technologies.
· emit no pollution when used.
· quiet operation without noise pollution.

SAQ 5
Explain the process of producing electricity by Fuel Cells.
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

66
 SAQ 6 Other Forms of Renewable
Energy
Write down the main components of Fuel Cells.
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

SAQ 7
Fuel cells are renewable sources of energy. Do you agree?
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

5.5 BIOFUELS
Biofuels are liquid or gaseous fuels. They are manufactured from biomass, such
as agricultural crops and the biodegradable parts of waste. Biofuels can replace
fossil fuels, such as petrol or diesel, either totally or partially. The biofuels have
been used in combustion engines way back over 100 years ago.
There are many types of biofuels. The well known biofuels are biodiesel,
bioethanol and biogas. Ethanol is generally produced from sugar cane or grain. In
Brazil, ethanol is manufactured from sugar cane and is available at almost all
filling stations, either in pure form or blended with conventional petrol. Ethanol is
an alcohol that can be blended (up to 5%) with petrol, without any engine
modifications required. Biofuels are classified as 1st-generation and
2nd generation biofules.
5.5.1 1st-Generation Biofuels
The biofules are defined based on the biomass from which these are produced.
The biofuels produced from sugar, starch or oil-based crops or residues are
known as 1st-generation biofuels. The examples include biodiesel from rapeseed
oil or sunflower oil, and alcohol from sugar beets or corn. Majority of
1st-generation biofuels achieve CO2 emission reductions of around 30-50%
compared to fossil fuels.
5.5.2 2nd-Generation Biofuels
The biofuels produced from the woody parts of plants or trees are known as
2nd-generation biofuels. These biofuels can achieve CO2 emissions reductions of
around 90%.
Biofuels are attractive alternatives to petrol and diesel for use in automobiles. The
Government of India has now permitted the use of 5% ethanol blended petrol.
Ethanol produced from molasses/cane juice, when used as fuel will reduce the
dependence on crude oil and help in reducing pollution.

67
Renewable Energy
Resources
Most of the fossil fuels which are used are biological in nature. Biofuel does not
add to the carbon dioxide in the atmosphere. These are plant forms that, typically,
remove carbon dioxide from the atmosphere, and give up the same amount when
burnt. This is why the biofuels are considered to be "CO2 neutral". The type of
biofuel used will depend on a number of factors, like available feedstock and the
energy that can be used locally.

5.6 HYDROPOWER

Hydropower is one of the oldest sources of energy. It was used thousands of years
ago to turn a paddle wheel for purposes such as grinding grain.
Hydropower is the renewable energy source. The original source of hydropower
is the Sun. You can understand the hydropower by looking over the following
observations :
· Solar energy heats water on the surface, causing it to evaporate.
· This water vapor condenses into clouds and falls back onto the
surface as precipitation (rain, snow, etc.).
· The water flows through rivers back into the oceans, where it can
evaporate and begin the cycle over again.
· The water at high levels is collected in dams. The amount of available
energy in moving water is determined by its flow or fall. Thus when
the water stored in the dam is released; it runs turbines for generating
electricity. The flowing rivers on higher levels like mountains etc are
also put to run turbines.

SAQ 8
Define ist-generation and 2 nd-generation biofules.
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………

5.6.1 Hydropower and Environmental Impacts

Hydropower is a clean source and does not pollute the water or the air. However,
hydropower facilities can have large environmental impacts by changing the
environment and affecting land use, homes, and natural habitats in the dam area.

5.7 ANIMAL ENERGY

Domesticated animals are used in drawing heavy loads. Draft animals were in
common use in Mesopotamia before 3000 BC for farm work and for pulling
wheeled vehicles. Their use spread to the rest of the world over the following
2,500 years. While cattle, usually in teams, have been used most often as draft
animals, horses and donkeys have supplemented them in many areas. Some
horses such as the Belgian horse, the Clydesdale, the Suffolk, the Shire, and the
Percheron have been bred to serve as draft animals; they weigh more than 725 Kg
68
 Other Forms of Renewable
and stand at least 16 hands high. The Asian water buffalo, however, is probably Energy
the most important draft animal in the world today. Many of the some 165 million
domesticated water buffalo worldwide are used as draft animals, particularly in
tropical Asia, where they assist in the production of rice. The role of draft animals
in agriculture in less-developed regions of the world continues because of the
advantages they offer: their feed is easily grown and commonly available; little
maintenance of the animals is required; their manure is a valuable resource for the
farmer; and the animal itself may become a source of food or other products at the
end of its useful life.
A draught or draft animal is an animal used for its physical (i.e. muscular) power,
as in transport and haulage, such as pulling carts or sleds, ploughing fields and
hauling goods. Animals are also used for animal-powered transport, for
movement of people and goods. People ride some animals directly as mounts, use
them as pack animals to carry goods, or harness one or a team to pull vehicles.
Such animals are sometimes known as beasts of burden.
Pack Animals
These often belong to the same species as mounts or harness animals, though
animals such as horses, mules, donkeys, or the Arabian camel may be of
specialized breeding for packing. Other species are only used to carry loads,
including llamas in the Andes, and the Bactrian camel in Central Asia.
Bovines include water buffalo (as distinct from bison and the extremely
dangerous African Cape buffalo both of which cannot be domesticated, oxen,
bullocks, and yaks (the latter adapted to extreme conditions in the Himalayas).
Other species include dogs, reindeer and goats.
Other Draught Animals
Animal power is also used to drive machines and devices, and for ploughing,
especially oxen. Water buffalo in tropical or very wet subtropical, areas help in
rice-growing. Elephants are still used for logging in South-east Asia.
Animal Used for different Purpose
As predatory species are naturally equipped to catch prey, this is a further use for
animals and birds. This can be done either for sustenance or sport, to reduce the
population of undesired animals (pests) that are considered harmful to crops,
livestock or the environment.
Hounds and other dogs are used to kill and fetch prey. Certain breeds have been
bred for this task. Mousers (domestic cats used for hunting small rodents and
birds) are one of the oldest working animals having protected food supplies from
pests since the foundation of human agriculture. Ferrets prey on creatures living
in burrows, such as rabbits and hares.
Dogs, with their highly developed sense of smell, are used to catch human 'prey',
such as escaped prisoners or people lost in remote areas. They are used also to
find people who are trapped, such as in avalanches or collapsed buildings.
Horses are used in remote areas to help human searchers cover large areas of
rugged terrain. Their natural awareness of their surroundings will often alert
human handlers to the presence of anything unusual, including lost hikers, hunters
or other. Like some dogs, some horses are trained to follow scent.
The best-known example is the guide dog or seeing eyes dog for blind people.
Miniature horses are also occasionally used for this purpose as well.

69
Renewable Energy
Resources 5.8 LET US SUM UP
Geothermal energy is a renewable energy source because the heat is continuously
produced inside the Earth. There are two types of geothermal energies; the high
grade and low grade geothermal energies. The high-grade geothermal energy is
the heat of the earth’s pressure that turns water into steam. The low-grade
geothermal energy is the heat within the earth’s crust. This heat is actually stored
solar energy.
Ocean thermal and tidal energies are referred to as ocean renewable energies.
Ocean energy can be used to generate electricity in an environment friendly
manner. Ocean thermal energy conversion (OTEC) systems exploit temperature
differences between warmer, surface layers and colder, deep layers of the ocean.
Tides are caused by the gravitational pull of the moon and sun, and the rotation of
the Earth. Tidal energy is one of the oldest forms of energy.
The tidal energy does not require any fuel and the economic life of a tidal plant is
about 75 to 100 years as compared to about 35 years of a conventional fossil fuel
plant. The tidal energy is clean and renewable and tidal energy is non-polluting.
A tidal barrage can prevent approximately one million tons of CO 2 per TWH
generated.
Hydrogen energy is used in producing electricity through an electro-chemical
reaction between hydrogen and oxygen. Hydrogen gas is the primary fuel for fuel
cells also. Hydrogen has the highest energy content of any common fuel by
weight but the lowest energy content by volume (about four times less than
gasoline). Hydrogen fuel cells (batteries) are being used as a source of electricity.
They are very efficient, but expensive to build.
Fuel cells are based on the electrochemical reaction between hydrogen and
oxygen to produce electricity, water vapor, and heat. Fuel cells are efficient,
environmentally friendly and reliable for power production. The use of fuel cells
has been demonstrated for stationary/portable power generation and other
applications.
Biofuels are liquid or gaseous fuels. They are manufactured from biomass, such
as agricultural crops and the biodegradable parts of waste. The well known
biofuels are biodiesel, bioethanol and biogas. Ethanol is generally produced from
sugar cane or grain. The biofuels produced from sugar, starch or oil-based crops
or residues are known as 1st-generation biofuels. The biofuels produced from the
woody parts of plants or trees are known as 2nd-generation biofuels.
The original source of hydropower is the Sun. Hydropower is a clean source and
does not pollute the water or the air. However, hydropower facilities can have
large environmental impacts by changing the environment and affecting land use,
homes, and natural habitats in the dam area.

5.9 KEY WORDS

Biomass
A renewable source of energy derived from organic matter like wood,
agriculture waste; also include algae, sewage and other organic substances
that may be used to make energy through chemical processes
Bio-fuels
Fuels made from biomass; include ethanol, biodiesel and methanol
70
 Other Forms of Renewable
Biogas Energy
A combustible gas derived from decomposing biological waste; normally
consists of 50 to 60 percent methane
Fuel Cell
An electrochemical device with no moving parts that converts the chemical
energy of a fuel, such as hydrogen, and an oxidant, such as oxygen, directly
into electricity.
Geothermal Energy
Energy from hot water or steam available deep inside the earth's crust
Geothermal heat pumps
The geothermal energy is used where stable ground or water temperatures
near the Earth's surface are available to control building temperatures above
ground. A heat pump is a mechanical device used for heating and cooling.

5.10 ANSWERS TO SAQs

SAQ 1
There are two types of geothermal energies :
1. High grade
2. Low grade
The high-grade geothermal energy is the heat of the earth’s pressure that
turns water into steam. The low-grade geothermal energy is the heat within
the earth’s crust. This heat is actually stored solar energy.
SAQ 2
A heat pump is a mechanical device used for heating and cooling.
It operates on the principle that heat can be extracted from a warmer
temperature to a cooler temperature. A geothermal heat pump uses the earth
to warm us in the winter and cool us in the summer.
SAQ 3
Ocean renewable energy includes all forms of renewable energy derived
from the sea. This includes tidal energy, wave energy, ocean current energy
and ocean thermal gradient energy. The ocean renewable energy is also
known as marine renewable energy.
SAQ 4
Ocean thermal energy conversion generates electricity from the temperature
differential of cold subsurface sea water and warmer surface waters.
SAQ 5
Fuel cells produce electricity through electrochemical reaction. This
combines hydrogen and oxygen to form water vapor, heat and electricity.
The byproducts of the reaction can be re-utilized by the fuel cell system.
The heat can be used for space heating, water vapor may be used as
re-supply for additional hydrogen. The electricity is directed to an external
circuit for using.
71
Renewable Energy
Resources SAQ 6
There are three main components of a fuel cell system. These are :
(1) The hydrogen source
(2) The fuel cell stacks
(3) A power inverter
The potential sources hydrogen are fossil fuels and electrolysis of
water. The function of fuel cell stack is to convert the hydrogen and oxygen
into electricity, water vapor and heat. An inverter converts the DC
electricity from the fuel cell into AC electricity that most equipment
requires.
SAQ 7
Fuel cells use a fuel to produce power and are not a power source on their
own. If this fuel is obtained from renewable sources, then fuel cells can be
treated as renewable source and become an important part of the energy
chain.
SAQ 8
1st-generation biofuels : The biofuels made from sugar, starch or oil-based
crops or residues are known as 1st-generation biofuels.
2nd-generation biofuels : Biofuels that are produced from the woody parts
of plants or trees are known as 2nd-generation biofuels.

REFERENCES
http://www.eia.doe.gov/kids/energyfacts/renewable/geothermal.html.

72