Stand-alone solar electric systems : the Earthscan expert handbook for planning, design and installation

249 Pages·2010·10.35 MB·english

by  Mark Hankins

PPC 252x192mm , spine 21mm
(for 246x189mm cover)
EARTHSCAN EXPERT SERIES EARTHSCAN EXPERT SERIES
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- STAND-ALONE
‘One watt-peak in a German grid-connected system saves the equivalent of 5 litres of oil used in a thermal A
power station. One watt-peak in a stand-alone system in Africa saves more than 50 litres of oil from L
kerosene lamps. This is the right book at the right time.’ O
Professor Peter Adelmann, University of Applied Science, Germany, and Founder of Phocos AG N
E SOLAR ELECTRIC
‘Mark Hankins has done it again. Like his prior publications, this book is a practical, useful and easy-to-
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read design guide for anyone interested in off-grid solar electric systems.’
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Arne Jacobson, Associate Professor, Environmental Resources Engineering Co-Director,
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Schatz Energy Research Center, Humboldt State University, USA
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SYSTEMS
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One of the best ways to get power to remote, off-grid locations, whether in developed or developing E
countries, is through the use of solar electric systems. This practical guide describes how to plan, design L
and install solar electric systems in a manner that is hands-on, graphic and technically complete. Highly E
illustrated chapters cover: C
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• solar energy basics R
• components of solar electric systems (modules, batteries, regulators, inverters and appliances) I
C THE EARTHSCAN
• installation practice

• details on planning and servicing systems S EXPERT HANDBOOK
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• rural electrification
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• larger systems FOR PLANNING,
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• water pumping
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DESIGN AND
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This is the must-have guide for electric technicians and designers, development workers, and anyone who
wants to install their own off-grid system. S INSTALLATION

Mark Hankinshas over 20 years’ experience of designing photovoltaic systems, managing projects and teaching M
solar electricity in Africa. He also managed a Nairobi-based renewable energy consulting company for over 10 years, a
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and has written extensively on the subject. k
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Series Editor: Frank Jackson Building / Renewable Energy
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www.earthscan.co.uk
Mark Hankins
Earthscan strives to minimize its impact on the environment
Stand-Alone Solar Electric Systems

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Stand-Alone Solar
Electric Systems
The Earthscan Expert Handbook
for Planning, Design and Installation
Mark Hankins
series editor:
frank jackson

publishing for a sustainable future
London • Washington, DC
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First published in 2010 by Earthscan
Copyright © Mark Hankins 2010
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system,
or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording
or otherwise, except as expressly permitted by law, without the prior, written permission of the
publisher.
This book draws on some material that originally appeared in the author’s book Solar Electric
Systems for Africa, published by AGROTEC and Commonwealth Science Council in June 1995.
While the author and the publishers believe that the information and guidance given in this work
are correct, all parties must rely upon their own skill and judgement when making use of them – it
is not meant to be a replacement for manufacturer’s instructions and legal technical codes. Neither
the author nor the publisher assumes any liability for any loss or damage caused by any error or
omission in the work. Any and all such liability is disclaimed.
This book was written using principally metric units. However, for ease of reference by readers
more familiar with imperial units, the publisher has inserted these in the text in brackets after their
metric equivalents. Please note that some conversions may have been rounded up or down for the
purposes of clarity.
Earthscan Ltd, Dunstan House, 14a St Cross Street, London EC1N 8XA, UK
Earthscan LLC, 1616 P Street, NW, Washington, DC 20036, USA
Earthscan publishes in association with the International Institute for Environment
and Development
For more information on Earthscan publications, see www.earthscan.co.uk
or write to [email protected]
ISBN 978-1-84407-713-7
Typeset by Domex e-Data, India
Cover design by Yvonne Booth
A catalogue record for this book is available from the British Library
Library of Congress Cataloging-in-Pu blication Data
Hankins, Mark.
Stand-alone solar electric systems : the Earthscan expert handbook for planning, design, and
installation / Mark Hankins.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-84407-713-7 (hardback)
1. Photovoltaic power systems. I. Title.
TK1087.H36 2010
621.31'244--dc22
2009051707
At Earthscan we strive to minimize our environmental impacts and carbon footprint through
reducing waste, recycling and offsetting our CO emissions, including those created through
2
publication of this book. For more details of our environmental policy, see www.earthscan.co.uk.
Printed and bound in the UK by Scotprint,
an ISO 14001 accredited company. The paper used
is FSC certified and the inks are vegetable based.
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Contents
List of Figures, Tables and Boxes vii
Preface and Acknowledgements xiii
List of Abbreviations xv
1 How to Use this Book: An Overview of Solar Electric Technology 1
2 Fundamentals of Solar Energy 11
3 Solar Cell Modules 27
4 Batteries 41
5 Charge Controllers, Inverters and Load Management 61
6 Lamps and Appliances 79
7 Wiring and Fittings 97
8 Planning an Off-Grid Solar Electric System 117
9 Installing Solar Electric Systems 141
10 Managing, Maintaining and Servicing Off-Grid PV Systems 165
11 Basics of Large Off-Grid Systems 179

12 Off-Grid PV and Solar Energy Resources 201
Appendix 1 Energy, Power and Efficiency 211
Appendix 2 Basic Extra-Low-Voltage Direct Current (DC) Electricity 213
Glossary 217
Worksheets 221
Index 227
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list of figures, tables and boxes
Figures
1.1 World shipments of PV modules, 1993–2008 2
1.2 Common PV applications 3
2.1 The sun is the source of virtually all of our energy 13
2.2 Absorption and reflection of solar radiation by the Earth’s atmosphere 15
2.3 How much power is 1000W/m2? 15
2.4 Direct and diffuse radiation 16
2.5 Solar irradiance, in watts per square metre, received over time on a
flat surface in an Equatorial region 16
2.6 The solar incident angle 17
2.7 Mean daily insolation in four cities 18
2.8 Global insolation map 19
2.9 Mounting angles for fixed solar collectors 20
2.10 Simple manually turned pole-mounted solar tracker 20
2.11 Solar concentrators and reflectors 21
2.12 The greenhouse effect 22
2.13 Indirect solar drier 23
2.14 Solar water-heater in Maasai Mara, Kenya 23
2.15 Solar cooker in Kenya, combining features of box and concentrator units 24
3.1 The photo-electric effect 28
3.2 Various types of silicon solar cell 29
3.3 Solar cells, modules and arrays 32
3.4 The I-V curve 35
3.5 Effects of radiation intensity on module output 36

3.6 Effects of temperature on a typical monocrystalline module output 37
3.7 Four common types of solar modules and their I-V curves at STC 40
4.1 Energy input from the solar array must balance the energy use of the load 42
4.2 Rechargeable lithium ion and nickel metal hydride battery cells 44
4.3 Parts of a lead-acid battery 45
4.4 Charge, discharge and cycling 48
4.5 Measuring state of charge 50
4.6 Using hydrometers 50
4.7 Battery cycle life is greatly reduced with deep discharges 52
4.8 Gassing in a cell due to overcharging 54
4.9 Types of battery 55
5.1 The role of a charge controller in off-grid PV systems 62
5.2 LED indicators and features of a charge controller 62
5.3 Steca charge controller for a solar home system; Morning Star charge
controllers for larger systems, with system indicators; Phocos MPPT 65
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viii stand-alone solar electric systems
5.4 Charge controllers, MPPTs, main switches, inverters, fuse boards and
other accessories on wall-mounted panels 67
5.5 Battery monitor 69
5.6 Common inverter configuration 72
5.7 Common sine wave inverters used in PV systems 76
5.8 Voltage converter 77
6.1 Lamps produce both light and heat energy 80
6.2 Important points to consider when choosing lamps 80
6.3 Incandescent lamps 82
6.4 Halogen lamp in 12V reflector fitting 83
6.5 Fluorescent lamp: parts, housing and assembled fitting 84
6.6 ‘PL-type’ fluorescent lamp fittings with and without replaceable bulb 85
6.7 Range of ‘PL-type’ fluorescent lamp fittings from Steca 86
6.8 LED (light-emitting diode) lamps 87
6.9 Light travels in all directions from bulb source 88
6.10 Reflectors direct light to the place where it is needed 89
6.11 Lighting in a classroom 90
6.12 Solar lanterns 91
6.13 Typical applications often found in small PV systems 94
7.1 Common types of wiring cable 98
7.2 Common AC switches for lighting circuits 101
7.3 DC sockets and plug 102
7.4 Battery DC-rated fuses 105
7.5 Connector strips and junction boxes 106
7.6 Shoelace crimp terminals 106
7.7 Larger-diameter cables are needed to carry larger currents 107
7.8 Current flow in 240V AC and 12V DC systems 108
7.9 Voltage drop in a 12V DC system 109
7.10 Possible earthing arrangement for an off-grid PV system 114

7.11 Earth rod connection 115
8.1 Off-grid PV system sizing process 118
8.2 Arusha total daily energy demand calculation 124
8.3 Insolation data chart for solar resources 126
8.4 Using I-V curves to calculate module current output 129
8.5 Arusha insolation data entered in Worksheet 2 130
8.6 Calculating the system design charging current 131
8.7 Calculating battery capacity: Arusha example 135
8.8 Choosing a charge controller 138
8.9 Using floorplans 139
9.1 Digital multimeters 144
9.2 Cable plans and wiring diagrams are used by electricians to plan
wire layout 147
9.3 Crimping tools 149
9.4 Working on roofs 151
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list of figures, tables and boxes ix
9.5 Module on roofs 151
9.6 Array mount designs 152
9.7 Back of module showing leads from junction box 154
9.8 Modules charging batteries in parallel and series 155
9.9 The battery should be located in a place that is well-ventilated 156
9.10 Battery box, rack and shed 157
9.11 Battery terminal connections 158
9.12 24V parallel/series connection of batteries 159
9.13 Charge controller, main switch and monitor on sub-board 160
9.14 Connection terminals for modules, battery and loads on charge controller 162
10.1 Using a rotatable tracking mount 166
10.2 Seasonal angle adjustment of a fixed mount 167
10.3 The energy output to the loads must be balanced by the energy input
from the array 168
10.4 Remember to turn off lamps and appliances when not in use 169
10.5 Sample system log book 171
10.6 Reflector fitting 172
11.1 Top-opening solar refrigerator 182
11.2 Pie-chart of energy use in Karamugi Secondary School system 184
11.3 Karamugi Secondary School system schematic 185
11.4 Olonana design process 186
11.5 Pie-chart of energy use in Olonana system 187
11.6 Olonana system schematic 189
11.7 Schematic diagram for a hybrid system 190
11.8 Typical standby generator 192
11.9 Kamabuye system schematic 195
11.10 Designing solar PV pumping systems 196
11.11 Comparing water-pumping costs 197
11.12 Common pumping configurations 199

Tables
1.1 Solar electricity advantages and disadvantages 6
1.2 A summary of basic electric concepts 9
2.1 Insolation measurement 17
2.2 Examples of established uses of solar thermal energy 22
2.3 Solar energy technologies and approximate efficiencies 26
3.1 Commercially available solar cell module types 29
3.2 Features of selected common solar modules 39
4.1 Measuring state of charge for a typical 12V modified SLI-type battery 51
4.2 Expected cycle life of two battery types at various DoDs 53
5.1 Features of common charge controllers 70
5.2 Inverters for off-grid PV systems 75
6.1 Performance of typical 12V lamps 86
6.2 Lighting levels in standard situations 89
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