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Library of Congress Cataloguing-in-Publication Data

Häberlin, Heinrich.

Photovoltaics: system design and practice / Heinrich Häberlin; translated by Herbert Eppel.

p. cm.

Includes bibliographical references and index.

ISBN 978-1-119-99285-1 (cloth)

1. Photovoltaic power systems–Design and construction. 2. Photovoltaic power systems–Standards. 3. Photovoltaic power generation. I. Title.

TK1087.H33 2012

621.31′244–dc23

2011032983

A catalogue record for this book is available from the British Library.

Print ISBN: 9781119992851

To my wife Ruth and my children Andreas and Kathrin, who, while I was writing this book, weren't able to spend as much time with me as they would have liked – and to all those who want to see our society transition to sustainable and responsible electricity generation.

Foreword

Energy and the concerns it raises for individuals, society at large and the environment, is a more burning issue today than ever before. Evolutions such as climate change, energy security issues, energy market deregulation, energy price fluctuations and the like have made energy the centre of a multi-faceted debate where the need for sustainable energy and improved energy efficiency are taking centre stage as never before. The European Commission's objectives for 2020 in this regard are both courageous and pioneering.

The Stern Report issued by the British government in 2006 noted that global warming and its worldwide economic repercussions constitute the widest-ranging failure of free market mechanisms that the world has ever seen. This report also quantified the economic costs of this evolution. The “business as usual” attitude that unfortunately still prevails in the business and political communities is going to cost us dearly; and the longer we wait to act, the higher the cost will be. A growing number of politicians, business leaders, and consumers have come to the realization that action must be taken, and that such action will not come cheap.

The timing of this book's publication could not be better. Admittedly photovoltaics is no magic bullet solution for the myriad problems we face but photovoltaics is one of the key technologies that will bring us closest to a sustainable energy supply in the foreseeable and distant future. Many technical and other obstacles remain to be surmounted before photovoltaics can do this, however, the undeniable fact of the matter is that photovoltaics is now the subject of feverish and rapid worldwide development on an industrial scale. The annual growth rates of upwards of 40 percent registered by the photovoltaics industry are all the more remarkable in light of the recent financial crisis, not to mention past economic recessions.

The term photovoltaics is often associated primarily with solar cells and solar modules. As these are the core elements of photovoltaic technology, this mindset makes perfect sense. However, it does not go far enough when it comes to characterizing the energy production of a solar power installation. Only if we regard photovoltaics as an energy system can we begin to make accurate statements concerning its contribution to the energy supply. Moreover, regarding a phenomenon as a system often allows us to connect the dots between theory and practice, paradigm and experience.

As growing numbers of PV installations are put into operation, questions are increasingly being raised concerning their quality and reliability. Only a PV installation that works properly can genuinely contribute to the energy supply. Hence such issues are looming ever larger worldwide. One of the great virtues of the present book is that it places tremendous emphasis on the system related aspects of photovoltaics.

Over the course of his many years of research on the system related aspects of photovoltaics, Prof. Hberlin has accumulated unparalleled experience that is richly detailed in his numerous publications on the subject. He has now made this experience available to a wider public, via this book, which in using its author's experience as a springboard, provides a wealth of insights and highly practical information concerning the design and operation of PV installations. In so doing, this book also addresses an increasingly pressing problem, namely that rapid growth in the photovoltaics industry and other renewable energy sectors will increase the need for qualified individuals in this domain. Thus education and training are a matter of growing importance in this regard.

I would like to on one hand express my gratitude to Prof. Hberlin for having written this book, and on the other congratulate him on his willingness to share his photovoltaics expertise with a wider audience via this book, which I feel will make a significant contribution to the advancement of photovoltaic technology. I am confident that this richly detailed and very complete book will enable numerous photovoltaics engineers, researchers and other professionals to gain greater insight into photovoltaics, and particularly into the practical aspects of this intriguing field.

Stefan Nowak, Ph.D.
Chairman of the International Energy Agency Photovoltaics Power Systems
Programme (IEA PVPS)
St. Ursen, Switzerland

Preface

The PV industry has experienced an exponential growth since the appearance of the first edition of this book in German in 2007 and ever-larger PV installations are being realized in an ever-growing number of countries. The tremendous interest shown in the first edition of this book, as well as the extensive positive feedback it elicited, show that photovoltaics, which is discussed comprehensively and in all its complexity in this book, is a topic of tremendous importance nowadays.

Therefore the second edition published also in German in 2010 goes into even greater depth on a number of matters and also explores some aspects of and insights into photovoltaics that were not contained in the first edition. For this second edition, I have extensively revised, updated and expanded the material from the first edition in such a way that, using the information in this book, designers can make very close sizing and yield estimates for PV installations at any site worldwide between 40 °S and 60 °N. In addition to updating my own extremely extensive PV installation monitoring data, I have also included energy yield figures from other countries, thanks to the generosity of the relevant operators who kindly provided data concerning their installations.

Considering the success of the two German books and the expressed interest also from many English speaking PV engineers, it was decided to translate this book into English to make my extended PV experience available also to them. The present book is an exact translation into English of the extended second German edition published in 2010.

Since the finalisation of the German book and the translation, prices for PV modules have considerably dropped further especially in 2011. For large quantities of crystalline modules prices of 1 per Wp or even somewhat less were offered in autumn 2011, i.e. even less than the lowest values indicated in the book. Therefore the price of PV electricity is now already very close to competiveness with conventional electricity in many countries.

Heinrich Häberlin
Ersigen
October 2011

About the Author

After earning a Masters degree in electrical engineering from ETH Zurich, Heinrich Häberlin became a staff researcher at the ETH Microwave Lab. During this time he developed hardware, software and numerous learning applications for a computerized teaching and learning system that was used at ETH until 1988. He earned a doctorate in 1978, based on the thesis he wrote concerning this system.

From 1979 to 1980, Dr. Häberlin headed a team at the Zellweger Company that worked on the development of hardware and software for microprocessor-based control of a complex short-wave radio system. In late1980 he was appointed a professor to the engineering school in Burgdorf, Switzerland, where from 1980 to 1988 besides electrical engineering he also taught computer science.

Prof. Häberlin has been actively involved in photovoltaics since 1987. In 1988 he established the Bern University of Applied Sciences Photovoltaics Lab, where he and his staff mainly investigate the behaviour of grid-connected systems. Since 1989 he has also been operating his own PV installation. In 1988 he began testing various PV inverters and in 1990 he initiated a series of lab experiments concerning PV installation lightning protection. Prof. Häberlin's PV Lab has, since 1992, also been continuously monitoring more than 70 PV installations, mainly under the auspices of research projects commissioned by Switzerland's Federal Office for Energy. His lab also carries out specialized measurements of PV installation components for the relevant manufacturers and also works on various EU projects.

Prof. Häberlin has been teaching photovoltaics at Bern University of Applied Sciences since 1989. He is a member of Electrosuisse, ETG, the Swiss TK82 panel of experts on PV installations, and the IEC's International Photovoltaics Standards Committee TC82.

Acknowledgements

I would like to thank all of the private and public sector organizations that kindly provided photos, graphics, data and other documentation for this book. Without these elements, I would not have been able to provide such a detailed and in-depth account of the relevant issues.

I would also like to express my heartfelt gratitude to my past and current assistants, who carried out investigations and analyses in connection with numerous research projects and whose work products I have used in this book. I also owe a debt of gratitude to the following organizations that commissioned and financed the aforementioned research projects: the Swiss Ministry of Energy; the Swiss Ministry of Science and Education; the Bern Canton Office of Water and Energy Resource Management; and various power companies (namely, Localnet, Bernische Kraftwerke, Gesellschaft Mont Soleil, Elektra Baselland and Elektrizitätswerk der Stadt Bern).

My former assistants Christoph Geissbühler, Martin Kämpfer and Urs Zwahlen, and my current assistants Luciano Borgna and Daniel Gfeller, read the manuscript for the first edition of this book in German and pointed out errors and elements that were unclear. My colleagues Dr Urs Brugger and Michael Höckel read certain sections of the first-edition manuscript and provided helpful suggestions.

The manuscript for the second book in German was read by my current assistants Daniel Gfeller, David Joss, Monika Münger and Philipp Schärf, who likewise pointed out errors and elements that were unclear.

I would like to express my gratitude to all of these individuals for their assistance.

Heinrich Häberlin
Ersigen
January 2010

Note on the Examples and Costs

Many of the chapters in this book contain examples whose numbers were in many cases calculated using spreadsheet programs that round off the exact numbers that were originally input. On the other hand, for reasons of space many of the numbers in the tables in Appendix A have been rounded off to two decimal places. Hence, when used for actual calculations, these rounded-off numbers may under certain circumstances differ slightly from the counterpart numbers indicated in the examples.

In several sections of this book, costs of PV modules or PV systems or feed-in tariffs are given in euros. In some cases or examples, especially where the situation in Switzerland is discussed, costs in Swiss francs (SFr) are expressed as their equivalent in euros (). The exchange rate used in this case was the exchange rate during the finalization of the German book, i.e. 1 Swiss franc is equivalent to about 0.67 euros. Due to the problems on the financial markets, there were extreme variations of this exchange rate in 2010 and 2011 (variation between about 1 SFr 0.67 and 1 SFr 1 ). For actual values in Swiss francs the actual exchange rate has to be used.

List of Symbols

Symbol	Name	Metric
a	Depreciation rate	%
aA	Battery depreciation rate	%
aE	Depreciation rate for electronic installations	%
AG	Total surface area of a solar generator field (aggregate module surface area)
aG	Solar generator depreciation rate	%
AL	Space required for a ground-based or rooftop solar generator field	m2
AM	Air mass number	––
aMB	Relative number of shaded modules per string	––
aMM	Relative number of modules per string that exhibit power loss	––
AZ	Solar cell surface area	m2
C	Battery capacity	F
C	Capacitance	F
CE	Solar generator earthing capacitance	F
CF	Capacity factor	––
cT	Temperature coefficient for a solar generator's MPP output	K−1
di/dtmax	Maximum current curve in a lightning leader stroke	kA/μs
dV	Relative voltage rise at the grid link point	––
e	Electron charge (scope of an electron or proton charge) (e = 1.602·10−19 A s)	A s
e	Basis for natural logarithms: e = 2.718 281 828	––
E	Energy (in general)	kWh, MJ
eA	PV installation surface-related grey energy	kWh/m2 MJ/m2
EAC	PV installation AC power output	kWh
ED	Mean daily DC power used by a stand-alone installation	Wh/d
EDC	PV installation DC power output	kWh
EDC-S	Mean DC power output per day and string for a stand-alone installation with MPT	Wh/d
EF	Yield factor = L/ERZ	––
EG	Band gap energy (usually expressed in eV; 1 eV = 1.602·10−19 J)	eV
EH	Mean daily energy yield of a hybrid generator	Wh/d
EL	Total energy produced by a PV installation during its service life	kWh, MJ
eP	Peak-power-related grey energy in PV installations	kWh/W, MJ/W
ERZ	Energy payback time (time needed to produce grey energy)	a
f	Frequency	Hz
FF	Filling factor for a solar cell, solar module or solar generator	––
FFi	Idealized filling factor	––
G	Global irradiance (power/surface), usually indicated for the horizontal plane	W/m2
GB	Direct beam irradiance, usually indicated for the horizontal plane	W/m2
GD	Diffuse irradiance, usually indicated for the horizontal plane	W/m2
GE	Grey energy	kWh, MJ
Gex	Extraterrestrial irradiance	W/m2
GG	Global irradiance on the solar generator plane	W/m2
Go, GSTC	Irradiance under STC: Go = 1 kW/m2	W/m2
H	Total irradiation (energy/area), usually indicated for the horizontal plane	kWh/m2 (MJ/m2)
HB	Total irradiation; direct beam irradiation (usually indicated for the horizontal plane)	kWh/m2 (MJ/m2)
HD	Total irradiation; diffuse irradiation (usually indicated for the horizontal plane)	kWh/m2 (MJ/m2)
Hex	Total extraterrestrial irradiation on a plane parallel to the horizontal plane outside of the Earth's atmosphere	kWh/m2 (MJ/m2)
HG	Total irradiation, irradiation on the solar generator plane (energy/area)	kWh/m2 (MJ/m2)
I	Electric current (general)	A
iA	Lightning current in a down-conductor	A
iAmax	Peak lightning current in a down-conductor	A
IDceff	Figure for the DC input current of a stand-alone inverter	A
IF	Passband current	A
IL	Charging current	A
imax	Peak lightning current voltage	A
IMPP	MPP current	A
IPV	Solar generator current	A
IR	Solar module reverse current (= passband current in a solar cell diode)	A
IS	Saturation current of a diode or solar cell	A
ISC	Short-circuit current of a solar cell, solar module or solar generator	A
ISC-STC	Short-circuit current under STC	A
ISN	Nominal string fuse voltage	A
iSo	Short-circuit current induced by lightning current in a conductor loop	A
iSomax	Peak induced short-circuit current in a conductor loop	A
iV	Displacement current induced in a PV installation by a distant lightning strike	A
iV	Varistor current induced by lightning current	A
IV8/20	Requisite nominal varistor current (for an 8/20 μs waveform)	A
Jmax	Peak current density	A/m2
JS	Saturation current density	A/m2
k	Boltzmann's constant = 1.38·10−23 J/K	J/K
KA	Battery costs for stand-alone installations	euros
kB	Annual operating costs	euros/year
kB	Shading correction factor (1 for no shading, 0 for full shading)	––
kC	Proportion of lightning current in a down-conductor	––
KE	Costs for electronic components such as inverters	euros
kG	Solar generator correction factor	––
KG	Costs attributable to a solar generator, site modification, wiring, and so on	euros
kI	Total harmonic current distortion	––
KJ	Total annual PV installation operating costs	euros/year
kMR	Correction factor for deriving MMi from MMR for a module frame	––
KN	Usable battery capacity	Ah
KS	Cost savings for roof tiles and the like for PV installations that are integrated into buildings	euros
kT	Temperature correction factor	––
Kx	Battery discharge capacity expressed as x number of hours (Kx = f(x))	Ah
L	Inductance (in general)	H
L	Installation lifetime (in years)	a
LC	Capture losses	h/d
LCM	Miscellaneous capture losses	h/d
lCM	Standardized miscellaneous non-capture losses: lCM = yT − yA	––
LCT	Thermal capture losses	h/d
lCT	Standardized thermal capture losses: lCT = yR − yT	––
LS	Conductor loop inductance	H
lS	Standardized system capture losses: lS = yA − yF	––
LS, LBOS	Balance of system losses	h/d
M	Mutual inductance (in general)	H
Mi	Effective mutual inductance, based on total lightning current i	H
MMi	Effective mutual inductance of a module (based on total lightning current i)	H
MMR	Module frame mutual inductance (based on iA = kC·i)	H
nAP	Number of parallel-connected batteries	––
nAS	Number of series-connected batteries	––
ND	Mean annual number of direct lightning strikes	––
Ng	Number of lightning strikes per square kilometre and year	––
nI	Inverter efficiency (energy efficiency)	––
nMP	Number of parallel-connected modules in a solar generator	––
nMS	Number of series-connected modules in a string	––
nMSB	Number of shaded modules per string	––
nMSM	Number of modules per string that exhibit power loss	––
nSP	Number of parallel-connected strings in a solar generator	––
nVZ	Full-cycle service life of a battery	––
nZ	Number of series-connected cells	––
nZP	Number of parallel-connected strings in a solar module	––
P	Effective power	W
p	Interest rate that is to be applied to depreciation	%
PA	Solar generator DC power output	W
PAo	Effective (measured) peak solar generator output under STC	W
PAC	AC-side output	W
PAC1	Maximum connectable single-phase nominal inverter output	W
PAC3	Maximum connectable triphase nominal inverter output	W
PACn	AC-side nominal output of an inverter or a PV installation	W
PDC	DC-side output	W
PDCn	DC-side nominal inverter output	W
PF	Packing factor	––
PGo	Nominal solar generator peak output under STC (aggregate PMo)	W
PGoT	Temperature-corrected nominal solar generator peak output	W
Pmax	Maximum output (equates to PMPP under STC)	W
PMo	Nominal module output under STC, according to the vendor's data	W
PMPP	MPP of a solar cell, solar module or solar generator	W
Puse	PV installation output power	W
PR	Performance ratio = YF/YR	––
pr	Instantaneous performance ratio = yF/yR	––
PRa	Annual performance ratio	––
pVTZ	Maximum allowable area-specific solar cell power loss	W/m2
Q	Watless power (> 0 when inductive)	var
QD	Mean daily load consumption for a stand-alone installation	Ah/d
QH	Mean daily hybrid solar generator charge for a stand-alone installation	Ah/d
QL	Lightning current charge (up to a few hundred milliseconds)	A s
QL	Mean daily charge consumption (> QD) for a stand-alone installation	Ah/d
QPV	Mean daily charge provided by a solar generator	Ah/d
QS	Lightning current charge (surge current of less than 1 ms duration)	As
QS	Mean daily string charge for a stand-alone installation	Ah/d
R	Resistance (in general); real component of a complex impedance Z	Ω
R1L	Real component of complex single-phase impedance in a conductor between a transformer and grid link point (for inverter connection purposes)	Ω
R1N	Real component of complex single-phase grid impedance (ohmic component)	Ω
R1S	Real component of complex single-phase interconnecting line impedance (with impedance ZS) between a grid link point and inverter	Ω
R3L	Real component of complex triphase impedance in a conductor between a transformer and grid link point (for inverter connection purposes)	Ω
R3N	Real component of complex triphase grid impedance (ohmic component)	Ω
R3S	Real component of complex triphase interconnecting line impedance (with impedance ZS) between a grid link point and inverter	Ω
R(β,γ)	Global radiation factor = HG/H	––
Ra(β,γ)	Annual global radiation factor = HGa/Ha (ratio of annual irradiance figures)	––
RB	Direct beam radiation factor = HGB/HB (as in the tables in Section A4)	––
rB	Lightning sphere radius	m
RD	Diffuse radiation factor = HGD/HD	––
RD	Ground resistance of a grounding installation	Ω
Ri	Inner resistance of a battery or the like	Ω
RL	Power lead resistance (real component of ZL)	Ω
RM	Shielding resistance; resistance in the cladding of a shielded conductor	Ω
RN	Inner grid resistance (real component of ZN)	Ω
RP	Parallel resistance	Ω
RR	Frame reduction factor	––
RS	Series resistance of a solar cell or conductor loop	Ω
RT	Medium-voltage transformer resistance (real component of ZT)	Ω
RV	Equivalent (linearized) resistance in a varistor replacement source	Ω
S	Apparent output	VA
S1KV	Single-phase grid short-circuit current at the grid link point	VA
SF	Voltage factor	––
SKV	Triphase grid short-circuit current at the grid link point	VA
smin	Minimum safety gap for hazardous proximities	m
SWR	Apparent triphase output of an inverter	VA
T	Absolute temperature	K
TC	Cell temperature (variant of TZ)	°C
To, TSTC	Reference STC temperature (25 °C)	°C
TU	Ambient temperature	°C
tV	AC full-load hours (installation full load PACn)	h
tVb	AC full-load hours for a PV installation whose power limitation is PAC-Grenz < PACmax	h
tVm	AC full load hours for a PV installation based on the installation's peak AC output PACmax (normally PACmax differs from PACn)	h
tVo	PV installation full-load hours, including peak output PGo (under STC)	h
TZ	Cell temperature	°C
tZ	Battery depth of discharge	––
TZG	Irradiance-weighted cell and module temperature	°C
V	Voltage (in general)	V
V1N	Grid phase voltage for a replacement source under open-circuit conditions	V
V1V	Phase voltage at the grid link point	V
V1WR	Phase voltage at the inverter connection point	V
VBA	Bypass diode voltage under avalanche conditions	V
VG	Battery charge limiting voltage (gassing voltage)	V
VL	Battery charging voltage; output voltage of an MPT charge controller	V
VM	Peak voltage induced by lightning current in a module	V
vmax	Maximum induced voltage	V
VMPP	MPP voltage	V
VMPPA-STC	PV installation or solar generator MPP voltage under STC	V
VN	Concatenated grid voltage for a replacement source under open-circuit conditions	V
VOC	Open-circuit voltage of a solar cell, solar module or solar generator	V
VOCA-STC	Open-circuit PV installation voltage under STC	V
VPh	Theoretical photovoltage = EG/e	V
VPV	Solar generator voltage	V
VR	Inverse voltage	V
VRRM	Diode inverse voltage	V
VS	PV installation system voltage	V
VS	Peak voltage induced by lightning current in a string	V
VV	Concatenated voltage at the grid link point	V
VV	Equivalent (linearized) voltage in a varistor replacement source	V
VV	Peak voltage induced by lightning current in wiring	V
VVDC	Varistor DC operating voltage specified by the vendor	V
VWR	Concatenated voltage at the inverter connection point	V
Vmax	Peak potential increase relative to remote ground	V
X	Reactance (in general); imaginary component of an impedance Z	Ω
X1L	Imaginary component of complex single-phase impedance in a conductor between a transformer and grid link point (for inverter connection purposes)	Ω
X1N	Imaginary component of complex single-phase grid impedance (reactance)	Ω
X1S	Imaginary component of complex single-phase interconnecting line impedance (with impedance ZS) between a grid link point and inverter	Ω
X3L	Imaginary component of complex triphase impedance in a conductor between a transformer and grid link point (for inverter connection purposes)	Ω
X3N	Imaginary component of complex triphase grid impedance (reactance)	Ω
X3S	Imaginary component of complex triphase interconnecting line impedance (with impedance ZS) between a grid link point and inverter	Ω
XL	Power lead reactance (imaginary component of ZL)	Ω
XN	Grid reactance (imaginary component of ZN)	Ω
XT	Medium-voltage transformer reactance (imaginary component of ZT)	Ω
YA	Array yield, i.e. full-load PGo hours	h/d
yA	Standardized solar generator power = PA/PGo	––
YF	Final yield, i.e. full-load PGo hours	h/d
yF	Standardized output power = Puse/PGo	––
YFa	Specific annual energy yield	kWh/kWp and h/a
YR	Reference yield, i.e. full-load solar hours	h/d
yR	Standardized irradiance = GG/Go	––
YT	Temperature-corrected reference yield	h/d
yT	Temperature-corrected standardized irradiance = yR·PGoT/PGo	––
Z	Complex impedance Z = R + jX (in general)	Ω
Z	Impedance amount (AC resistance)	Ω
Z1L	Complex single-phase line impedance at the transformer grid link point	Ω
Z1N	Complex single-phase grid impedance	Ω
Z3L	Complex triphase line impedance at the transformer grid link point	Ω
Z3N	Complex triphase grid impedance	Ω
ZL	Complex power lead impedance	Ω
ZN	Complex grid impedance	Ω
ZS	Complex grid impedance in the inverter interconnecting line	Ω
ZN	Amount of grid impedance	Ω
ZT	Complex medium-voltage transformer impedance	Ω
ZW	DC cable wave impedance	Ω
ΔVV	Voltage rise at the grid link point	V
ΔVWR	Voltage rise at the inverter connection point	V
α	Lightning protection angle	°
β	Solar generator angle of incidence	°
γ	Solar generator azimuth	°
δ	Solar declination	°
ηAh	Battery ampere-hour efficiency	––
ηE	PV installation energy efficiency	––
ηM	Solar module efficiency	––
ηMPPT	MPP tracking efficiency; degree of grid inverter adaptation	––
ηMPT	Global efficiency (tracking plus conversion) of an MPT charge controller	––
ηPV	Solar cell efficiency	––
ηS	Spectral efficiency	––
ηT	Theoretical efficiency	––
ηtot	Global efficiency = η·ηMPPT	––
ηWR	Mean inverter efficiency for PV installation sizing and yield calculation purposes (recommended: ηtot, if available)	––
η, ηUM	Conversion efficiency	––
	Phase angle between V and I	°
	Latitude (used to determine RB for irradiance calculations using the three-component method)	°
ν	Frequency (variant of f for very high frequencies, e.g. light frequency)	Hz
ρ	Specific resistance of a material (usually metal)	Ω mm2/m
ρ	Reflection factor of a surface for reflection radiation calculation purposes	––
ψ	Grid impedance angle (phase angle) for grid impedance ZN	°
ψ1	Phase angle for single-phase grid impedance Z1N	°
ψ3	Phase angle for triphase grid impedance Z3N	°