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 ∗∗Evaluation of the Built Environment for Sustainability∗∗ V. Bentivegna, P.S. Brandon and P. Lombardi Hb: 0-419-21990-0 Spon Press ∗∗Geothermal Energy for Developing Countries∗∗ D. Chandrasekharam and J. Bundschuh Hb: 9058095223 Spon Press ∗∗Building Energy Management Systems, 2nd ed∗∗ G. Levermore Hb: 0-419-26140-0 Pb: 0-419-22590-0 Spon Press ∗∗Cutting the Cost of Cold: Affordable Warmth for Healthier Homes∗∗ F. Nicol and J. Rudge Pb: 0-419-25050-6 Spon Press 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 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.” 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 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