Renewable Energy Resources

625 Pages·2006·10.51 MB·English

Renewable Energy Resources

Renewable Energy Resources is a numerate and quantitative text covering subjects
of proven technical and economic importance worldwide. Energy supplies from
renewables (such as solar, thermal, photovoltaic, wind, hydro, biofuels, wave, tidal,
ocean and geothermal sources) are essential components of every nation’s energy
strategy, not least because of concerns for the environment and for sustainability.
In the years between the first and this second edition, renewable energy has come
of age: it makes good sense, good government and good business.
This second edition maintains the book’s basis on fundamentals, whilst includ-
ing experience gained from the rapid growth of renewable energy technologies as
secure national resources and for climate change mitigation, more extensively illus-
trated with case studies and worked problems. The presentation has been improved
throughout, along with a new chapter on economics and institutional factors. Each
chapter begins with fundamental theory from a scientific perspective, then considers
applied engineering examples and developments, and includes a set of problems and
solutions and a bibliography of printed and web-based material for further study.
Common symbols and cross referencing apply throughout, essential data are tabu-
lated in appendices. Sections on social and environmental aspects have been added
to each technology chapter.
Renewable Energy Resources supports multi-disciplinary master degrees in sci-
ence and engineering, and specialist modules in first degrees. Practising scientists
and engineers who have not had a comprehensive training in renewable energy will
find this book a useful introductory text and a reference book.

John Twidell has considerable experience in renewable energy as an academic pro-
fessor, a board member of wind and solar professional associations, a journal editor
and contractor with the European Commission. As well as holding posts in the UK,
he has worked in Sudan and Fiji.

Tony Weir is a policy adviser to the Australian government, specialising in the
interface between technology and policy, covering subjects such as energy supply
and demand, climate change and innovation in business. He was formerly Senior
Energy Officer at the South Pacific Forum Secretariat in Fiji, and has lectured and
researched in physics and policy studies at universities of the UK, Australia and the
Pacific.

Also available from Taylor & Francis

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∗∗Geothermal Energy for Developing Countries∗∗

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Information and ordering details

For price availability and ordering visit our website www.sponpress.com
Alternatively our books are available from all good bookshops.

Renewable Energy
Resources

Second edition

John Twidell and Tony Weir

First published 1986
by E&FN Spon Ltd
Second edition published 2006
by Taylor & Francis
2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN

Simultaneously published in the USA and Canada
by Taylor & Francis
270 Madison Ave, New York, NY 10016, USA

Taylor & Francis is an imprint of the Taylor & Francis Group

© 1986, 2006 John W. Twidell and Anthony D. Weir
All rights reserved. No part of this book may be reprinted or
reproduced or utilised in any form or by any electronic, mechanical, or
other means, now known or hereafter invented, including photocopying
and recording, or in any information storage or retrieval system, without
permission in writing from the publishers.

The publisher makes no representation, express or implied, with regard
to the accuracy of the information contained in this book and cannot
accept any legal responsibility or liability for any errors or
omissions that may be made.

British Library Cataloguing in Publication Data
A catalogue record for this book is available
from the British Library

Library of Congress Cataloging in Publication Data
Twidell, John.
Renewable energy resources / John Twidell and
Anthony Weir. — 2nd ed.
p.
cm.
Includes bibliographical references and index.
ISBN 0–419–25320–3 (hardback) — ISBN 0–419–25330–0 (pbk.)
1. Renewable energy sources.
I. Weir, Anthony D.
II. Title.

TJ808.T95 2005
621.042—dc22
2005015300

ISBN10: 0–419–25320–3
ISBN13: 9–78–0–419–25320–4 Hardback
ISBN10: 0–419–25330–0
ISBN13: 9–78–0–419–25330–3 Paperback

This edition published in the Taylor & Francis e-Library, 2006.

“To purchase your own copy of this or any of Taylor & Francis or Routledge’s
collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.”

Contents

Preface
xi
List of symbols
xvii

1
Principles of renewable energy
1

1.1 Introduction 1
1.2 Energy and sustainable development 2
1.3 Fundamentals 7
1.4 Scientific principles of renewable energy 12
1.5 Technical implications 16
1.6 Social implications 22
Problems 24
Bibliography 25

2
Essentials of fluid dynamics
29

2.1 Introduction 29
2.2 Conservation of energy: Bernoulli’s equation 30
2.3 Conservation of momentum 32
2.4 Viscosity 33
2.5 Turbulence 34
2.6 Friction in pipe flow 35
2.7 Lift and drag forces: fluid and turbine machinery 39
Problems 41
Bibliography 44

3
Heat transfer
45

3.1 Introduction 45
3.2 Heat circuit analysis and terminology 46
3.3 Conduction 49

vi
Contents

3.4 Convection 51
3.5 Radiative heat transfer 61
3.6 Properties of ‘transparent’ materials 73
3.7 Heat transfer by mass transport 74
3.8 Multimode transfer and circuit analysis 77
Problems 80
Bibliography 82

4
Solar radiation
85

4.1 Introduction 85
4.2 Extraterrestrial solar radiation 86
4.3 Components of radiation 87
4.4 Geometry of the Earth and Sun 89
4.5 Geometry of collector and the solar beam 93
4.6 Effects of the Earth’s atmosphere 98
4.7 Measurements of solar radiation 104
4.8 Estimation of solar radiation 107
Problems 110
Bibliography 112

5
Solar water heating
115

5.1 Introduction 115
5.2 Calculation of heat balance: general remarks 118
5.3 Uncovered solar water heaters – progressive analysis 119
5.4 Improved solar water heaters 123
5.5 Systems with separate storage 129
5.6 Selective surfaces 134
5.7 Evacuated collectors 137
5.8 Social and environmental aspects 140
Problems 141
Bibliography 145

6
Buildings and other solar thermal applications
146

6.1 Introduction 146
6.2 Air heaters 147
6.3 Energy-efficient buildings 149
6.4 Crop driers 157
6.5 Space cooling 161
6.6 Water desalination 162

Contents
vii

6.7
Solar ponds 164
6.8
Solar concentrators 166
6.9
Solar thermal electric power systems 170
6.10 Social and environmental aspects 173
Problems 175
Bibliography 179

7
Photovoltaic generation
182

7.1
Introduction 182
7.2
The silicon p–n junction 184
7.3
Photon absorption at the junction 193
7.4
Solar radiation absorption 197
7.5
Maximising cell efficiency 200
7.6
Solar cell construction 208
7.7
Types and adaptations of photovoltaics 210
7.8
Photovoltaic circuit properties 220
7.9
Applications and systems 224
7.10 Social and environmental aspects 229
Problems 233
Bibliography 234

8
Hydro-power
237

8.1
Introduction 237
8.2
Principles 240
8.3
Assessing the resource for small installations 240
8.4
An impulse turbine 244
8.5
Reaction turbines 249
8.6
Hydroelectric systems 252
8.7
The hydraulic ram pump 255
8.8
Social and environmental aspects 257
Problems 258
Bibliography 261

9
Power from the wind
263

9.1
Introduction 263
9.2
Turbine types and terms 268
9.3
Linear momentum and basic theory 273
9.4
Dynamic matching 283
9.5
Blade element theory 288

viii
Contents

9.6
Characteristics of the wind 290
9.7
Power extraction by a turbine 305
9.8
Electricity generation 307
9.9
Mechanical power 316
9.10 Social and environmental considerations 318
Problems 319
Bibliography 322

10
The photosynthetic process
324

10.1
Introduction 324
10.2
Trophic level photosynthesis 326
10.3
Photosynthesis at the plant level 330
10.4
Thermodynamic considerations 336
10.5
Photophysics 338
10.6
Molecular level photosynthesis 343
10.7
Applied photosynthesis 348
Problems 349
Bibliography 350

11
Biomass and biofuels
351

11.1
Introduction 351
11.2
Biofuel classification 354
11.3
Biomass production for energy farming 357
11.4
Direct combustion for heat 365
11.5
Pyrolysis (destructive distillation) 370
11.6
Further thermochemical processes 374
11.7
Alcoholic fermentation 375
11.8
Anaerobic digestion for biogas 379
11.9
Wastes and residues 387
11.10 Vegetable oils and biodiesel 388
11.11 Social and environmental aspects 389
Problems 395
Bibliography 397

12
Wave power
400

12.1
Introduction 400
12.2
Wave motion 402
12.3
Wave energy and power 406
12.4
Wave patterns 412
12.5
Devices 418

Contents
ix

12.6 Social and environmental aspects 422
Problems 424
Bibliography 427

13
Tidal power
429

13.1 Introduction 429
13.2 The cause of tides 431
13.3 Enhancement of tides 438
13.4 Tidal current/stream power 442
13.5 Tidal range power 443
13.6 World range power sites 447
13.7 Social and environmental aspects of tidal range power 449
Problems 450
Bibliography 451

14
Ocean thermal energy conversion (OTEC)
453

14.1 Introduction 453
14.2 Principles 454
14.3 Heat exchangers 458
14.4 Pumping requirements 464
14.5 Other practical considerations 465
14.6 Environmental impact 468
Problems 469
Bibliography 469

15
Geothermal energy
471

15.1 Introduction 471
15.2 Geophysics 472
15.3 Dry rock and hot aquifer analysis 475
15.4 Harnessing Geothermal Resources 481
15.5 Social and environmental aspects 483
Problems 487
Bibliography 487

16
Energy systems, storage and transmission
489

16.1 The importance of energy storage and distribution 489
16.2 Biological storage 490
16.3 Chemical storage 490
16.4 Heat storage 495
16.5 Electrical storage: batteries and accumulators 499
16.6 Fuel cells 506

x
Contents

16.7
Mechanical storage 507
16.8
Distribution of energy 509
16.9
Electrical power 513
16.10 Social and environmental aspects 520
Problems 521
Bibliography 524

17
Institutional and economic factors
526

17.1
Introduction 526
17.2
Socio-political factors 526
17.3
Economics 530
17.4
Some policy tools 534
17.5
Quantifying choice 536
17.6
The way ahead 545
Problems 550
Bibliography 550

Appendix A
Units and conversions
553
Appendix B
Data
558
Appendix C
Some heat transfer formulas
564
Solution guide to problems
568
Index
581

Preface

Our aim

Renewable Energy Resources is a numerate and quantitative text covering
subjects of proven technical and economic importance worldwide. Energy
supply from renewables is an essential component of every nation’s strat-
egy, especially when there is responsibility for the environment and for
sustainability.
This book considers the timeless principles of renewable energy tech-
nologies, yet seeks to demonstrate modern application and case studies.
Renewable Energy Resources supports multi-disciplinary master degrees in
science and engineering, and also specialist modules in science and engineer-
ing first degrees. Moreover, since many practising scientists and engineers
will not have had a general training in renewable energy, the book has wider
use beyond colleges and universities. Each chapter begins with fundamental
theory from a physical science perspective, then considers applied exam-
ples and developments, and finally concludes with a set of problems and
solutions. The whole book is structured to share common material and to
relate aspects together. After each chapter, reading and web-based material
is indicated for further study. Therefore the book is intended both for basic
study and for application. Throughout the book and in the appendices, we
include essential and useful reference material.

The subject

Renewable energy supplies are of ever increasing environmental and eco-
nomic importance in all countries. A wide range of renewable energy tech-
nologies are established commercially and recognised as growth industries
by most governments. World agencies, such as the United Nations, have
large programmes to encourage the technology. In this book we stress the
scientific understanding and analysis of renewable energy, since we believe
these are distinctive and require specialist attention. The subject is not easy,
mainly because of the spread of disciplines involved, which is why we aim
to unify the approach within one book.

xii
Preface

This book bridges the gap between descriptive reviews and specialised
engineering treatises on particular aspects. It centres on demonstrating how
fundamental physical processes govern renewable energy resources and their
application. Although the applications are being updated continually, the
fundamental principles remain the same and we are confident that this new
edition will continue to provide a useful platform for those advancing the
subject and its industries. We have been encouraged in this approach by the
ever increasing commercial importance of renewable energy technologies.

Why a second edition?

In the relatively few years between the first edition, with five reprinted
revisions, and this second edition, renewable energy has come of age; its
use makes good sense, good government and good business. From being
(apart from hydro-power) small-scale ‘curiosities’ promoted by idealists,
renewables have become mainstream technologies, produced and operated
by companies competing in an increasingly open market where consumers
and politicians are very conscious of sustainability issues.
In recognition of the social, political and institutional factors which con-
tinue to drive this change, this new edition includes a new final chapter
on institutional and economic factors. The new chapter also discusses and
demonstrates some tools for evaluating the increasingly favourable eco-
nomics of renewable energy systems. There is also a substantial new section
in Chapter 1 showing how renewable energy is a key component of sus-
tainable development, an ideal which has become much more explicit since
the first edition. Each technology chapter now includes a brief concluding
section on its social and environmental impacts.
The book maintains the same general format as the first edition, but
many improvements and updates have been made. In particular we wish
to relate to the vibrant developments in the individual renewable energy
technologies, and to the related commercial growth. We have improved the
presentation of the fundamentals throughout, in the light of our teaching
experience. Although the book continues to focus on fundamental physi-
cal principles, which have not changed, we have updated the technological
applications and their relative emphases to reflect market experience. For
electricity generation, wind-power and photovoltaics have had dramatic
growth over the last two decades, both in terms of installed capacity and
in sophistication of the industries. In all aspects of renewable energy, com-
posite materials and microelectronic control have transformed traditional
technologies, including hydro-power and the use of biomass.
Extra problems have been added at the end of each chapter, with hints
and guidance for all solutions as an appendix. We continue to emphasise
simplified, order-of-magnitude, calculations of the potential outputs of the
various technologies. Such calculations are especially useful in indicating

Preface
xiii

the potential applicability of a technology for a particular site. However we
appreciate that specialists increasingly use computer modelling of whole,
complex systems; in our view such modelling is essential but only after
initial calculation as presented here.

Readership

We expect our readers to have a basic understanding of science and tech-
nology, especially of physical science and mathematics. It is not necessary
to read or refer to chapters consecutively, as each aspect of the subject is
treated, in the main, as independent of the other aspects. However, some
common elements, especially heat transfer, will have to be studied seriously
if the reader is to progress to any depth of understanding in solar energy.
The disciplines behind a proper understanding and application of renew-
able energy also include environmental science, chemistry and engineering,
with social science vital for dissemination. We are aware that readers with
a physical science background will usually be unfamiliar with life science
and agricultural science, but we stress the importance of these subjects with
obvious application for biofuels and for developments akin to photosynthe-
sis. We ourselves see renewable energy as within human-inclusive ecology,
both now and for a sustainable future.

Ourselves

We would like our readers to enjoy the subject of renewable energy, as
we do, and to be stimulated to apply the energy sources for the benefit
of their societies. Our own interest and commitment has evolved from the
work in both hemispheres and in a range of countries. We first taught,
and therefore learnt, renewable energy at the University of Strathclyde in
Glasgow (JWT) and the University of the South Pacific in Fiji (ADW and
JWT). So teaching, together with research and application in Scotland and
the South Pacific, has been a strong influence for this book. Since the first
edition we have made separate careers in universities and in government
service, whilst experiencing the remarkable, but predicable, growth in rele-
vance of renewable energy. One of us (JWT) became Director of the Energy
Studies Unit, in the Faculty of Engineering at the University of Strathclyde
in Glasgow, Scotland, and then accepted the Chair in Renewable Energy
at the AMSET Centre, De Montfort University, Leicester, England. He is
editor of the academic journal Wind Engineering, has been a Council and
Board member of the British Wind Energy Association and the UK Solar
Energy Society, and has supervised many postgraduates for their disserta-
tions. The AMSET Centre is now a private company, for research, education
and training in renewables; support is given to MSc courses at Reading
University, Oxford University and City University, and there are European

xiv
Preface

Union–funded research programmes. TW was for several years the Senior
Energy Officer of the South Pacific Forum Secretariat, where he managed
a substantial program of renewable energy pilot projects. He then worked
for the Australian Government as an adviser on climate change, and later
on new economy issues.
We do not see the world as divided sharply between developed industri-
alised countries and developing countries of the Third World. Renewables
are essential for both, and indeed provide one way for the separating con-
cepts to become irrelevant. This is meaningful to us personally, since we
wish our own energies to be directed for a just and sustainable society,
increasingly free of poverty and the threat of cataclysmic war. We sincerely
believe the development and application of renewable energy technology
will favour these aspirations. Our readers may not share these views, and
this fortunately does not affect the content of the book. One thing they will
have to share, however, is contact with the outdoors. Renewable energy is
drawn from the environment, and practitioners must put on their rubber
boots or their sun hat and move from the closed environment of buildings
to the outside. This is no great hardship however; the natural environment
is the joy and fulfilment of renewables.

Suggestions for using the book in teaching

How a book is used in teaching depends mainly on how much time is
devoted to its subject. For example, the book originated from short and
one-semester courses to senior undergraduates in Physics at the University
of the South Pacific and the University of Strathclyde, namely ‘Energy
Resources and Distribution’, ‘Renewable Energy’ and ‘Physics and Ecology’.
When completed and with regular revisions, the book has been mostly used
worldwide for MSc degrees in engineering and science, including those on
‘renewable energy’ and on ‘energy and the environment’. We have also
taught other lecture and laboratory courses, and have found many of the
subjects and technologies in renewable energy can be incorporated with
great benefit into conventional teaching.
This book deliberately contains more material than could be covered in
one specialist course. This enables the instructor and readers to concentrate
on those particular energy technologies appropriate in their situation. To
assist in this selection, each chapter starts with a preliminary outline and
estimate of each technology’s resource and geographical variation, and ends
with a discussion of its social and environmental aspects.
The chapters are broadly grouped into similar areas. Chapter 1 (Principles
of Renewable Energy) introduces renewable energy supplies in general, and
in particular the characteristics that distinguish their application from that
for fossil or nuclear fuels. Chapter 2 (Fluid Mechanics) and Chapter 3 (Heat
Transfer) are background material for later chapters. They contain nothing