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Technology/Alternative & Renewable Energy

g Easier!
Making Everythin

Are you looking to secure a job in the exciting field of photovoltaic design and installation? This hands-on, friendly guide
covers the workings of residential and small commercialsized photovoltaic systems and gives you the essentials you
need to safely install a system from start to finish.
• Shed some light on PV systems — get the scoop on electricity
basics and how the sun-earth relationship affects where a PV
system will (or won’t) work
• Dig into the nitty-gritty of components — understand the
technologies used in all types of PV systems, from modules and
batteries to charge controllers, inverters, and more
• Know that size matters — discover how to properly size a griddirect system, a battery-based system, wiring, and safety devices

Open the book and find:
• Advice on figuring out which
system type is right for you
• Plain-English explanations of
electricity basics
• How to properly select a site for
a PV system
• The lowdown on PV modules,
batteries, and other system
components
• Guidance for sizing the most
common PV systems, as well as
wiring and safety devices
• Pointers for permitting,
commissioning, inspection,
and maintenance

Photovoltaic
Design & Installation

Get a grip on
photovoltaic design
and installation



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Phot
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I
Design &

• Safety first — follow helpful guidance for staying safe anytime
you work on a PV system, from general construction and battery
safety to working on ladders and roofs
• Break ground — learn how to assemble mechanical parts and
integrate electrical elements to put together your PV system

Learn to:
• Design and install photovoltaic systems

Go to Dummies.com®
for videos, step-by-step examples,
how-to articles, or to shop!

• Follow processes for permitting,
commissioning, and inspection
• Grasp electrical concepts in plain
English
• Expand your skill set for “green collar”
jobs

$24.99 US / $29.99 CN / £16.99 UK

Ryan Mayfield is President of Renewable Energy Associates, a consulting
firm providing design, support, and educational services for commercial
photovoltaic systems. He is also Photovoltaic Systems Technical Editor for
SolarPro magazine, where he also regularly contributes feature articles.

ISBN 978-0-470-59893-1

Ryan Mayfield
Mayfield

President, Renewable Energy Associates

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To access the Cheat Sheet created specifically for this book, go to

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www.dummies.com/cheatsheet/photovoltaicdesigninstallation

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Photovoltaic
Design & Installation
FOR

DUMmIES



by Ryan Mayfield

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Photovoltaic Design & Installation For Dummies®
Published by
Wiley Publishing, Inc.
111 River St.
Hoboken, NJ 07030-5774
www.wiley.com
Copyright © 2010 by Wiley Publishing, Inc., Indianapolis, Indiana
Published simultaneously in Canada
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, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written
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or its affiliates in the United States and other countries, and may not be used without written permission.
NFPA 70®, National Electrical Code®, and NEC® are registered trademarks of the National Fire Protection
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Publishing, Inc., is not associated with any product or vendor mentioned in this book.
LIMIT OF LIABILITY/DISCLAIMER OF WARRANTY: THE PUBLISHER AND THE AUTHOR MAKE NO
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THE CONTENTS OF THIS WORK AND SPECIFICALLY DISCLAIM ALL WARRANTIES, INCLUDING WITHOUT LIMITATION WARRANTIES OF FITNESS FOR A PARTICULAR PURPOSE. NO WARRANTY MAY BE
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AUTHOR SHALL BE LIABLE FOR DAMAGES ARISING HEREFROM. THE FACT THAT AN ORGANIZATION OR WEBSITE IS REFERRED TO IN THIS WORK AS A CITATION AND/OR A POTENTIAL SOURCE
OF FURTHER INFORMATION DOES NOT MEAN THAT THE AUTHOR OR THE PUBLISHER ENDORSES
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MAY MAKE. FURTHER, READERS SHOULD BE AWARE THAT INTERNET WEBSITES LISTED IN THIS
WORK MAY HAVE CHANGED OR DISAPPEARED BETWEEN WHEN THIS WORK WAS WRITTEN AND
WHEN IT IS READ.
For general information on our other products and services, please contact our Customer Care
Department within the U.S. at 877-762-2974, outside the U.S. at 317-572-3993, or fax 317-572-4002.
For technical support, please visit www.wiley.com/techsupport.
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may
not be available in electronic books.
Library of Congress Control Number: 2010932457
ISBN: 978-0-470-59893-1
Manufactured in the United States of America. This book is printed on recycled paper.
10 9 8 7 6 5 4 3 2 1

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About the Author
Ryan Mayfield discovered his passion for renewable energy shortly after
beginning college at Humboldt State University in Arcata, California. While
pursuing his degree in environmental resources engineering, Ryan was
exposed to the exciting possibilities of solar power by his professors and the
university’s Campus Center for Appropriate Technology. This desire to learn
more about and be involved in the solar industry only increased as Ryan continued his studies.
After getting his hands on an actual installation during a class with Solar
Energy International, Ryan knew exactly where he wanted to spend his workdays. Early in his career, he worked as an installer, provided technical support for a renewable energy retailer, and moved up to Engineering Manager
at a national wholesale renewable energy distributor. It was during his time
at the distributor when Ryan’s knowledge of PV systems grew exponentially.
During this time, he read every Home Power magazine he could get his hands
on from cover to cover.
Now, Ryan lives in Corvallis, Oregon, with his wife and two children. He is a
Certified Affiliated Master Trainer for the PV Design and Installation courses
he teaches at Lane Community College in Eugene, Oregon. He’s also a North
American Board of Certified Energy Practitioners (NABCEP)-Certified PV
Installer. Ryan is one of a handful of people who hold both certifications. In
the state of Oregon, Ryan holds a Limited Renewable Energy Technician’s
license and chairs the apprenticeship committee for that license, helping to
bring up the next group of licensed PV installers in the Beaver State.
Ryan is currently the President of Renewable Energy Associates, a consulting
firm that provides design, support, and educational services for architectural
and engineering firms, contractors, and government agencies. The courses he
teaches take him across the United States working with various individuals
looking to increase their knowledge of PV systems.
In the spirit of going full circle, Ryan also serves as Photovoltaic Systems
Technical Editor for SolarPro magazine and regularly authors feature articles
in SolarPro and Home Power magazines. Occasionally, he’s able to go back
and teach with Solar Energy International, the same organization that got his
hands on some equipment and provided his first true installation experience.

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Dedication
I would like to dedicate this book to my children, Aidan and Lauren, in hopes
that I can make the world just a little bit better for them while giving them
the opportunity to make a positive impact themselves; my dear wife, Amy,
who’s my biggest fan and supporter; my parents and sister for guiding me to
become the person I am; and all of my friends and colleagues — your support
to me personally and your contributions to the solar industry are invaluable,
and I thank each and every one of you.

Author’s Acknowledgments
I feel very fortunate for the people who have come into my life. On a professional level, I would like to make special recognition of the following people:
Bob Maynard, who opened up so many doors for me and allowed me to flourish; Joe Schwartz, whose work was highly influential to me long before we
met and began collaborating; David Brearley, a true friend who always has a
good answer for any question I have — solar or otherwise; Roger Ebbage, for
giving me the opportunity to discover my passion for teaching; Paul Farley,
for always keeping me on my toes and reminding me to have fun; and Eric
Maciel, for giving me a chance to get started in the industry.
There are so many more people that have influenced and helped guide me
over the years. Without their help, lessons, and guidance, I’d still be walking
around bright-eyed and clueless: John Berdner, Bill Brooks, Justine Sanchez,
Tobin Booth, Kirpal Khalsa, Christopher Dymond, Christopher Freitas, Jon
Miller, Jsun Mills, John Wiles, Carol Weis, Wes Kennedy, Jason Sharpe, and
Glenn Harris — just to name a few.
I have to give recognition to the solar pioneers that made all of this possible for so many, some of whom I’ve never met personally but want to
thank anyway: Richard Perez, Bob-O Schultze, Windy Dankoff, Allan Sindelar,
Michael Welch, and Johnny Weiss.
Thanks to all the wonderful people at Solar Energy International, Home
Power, and SolarPro. The work you do to spread the word to so many never
ceases to amaze me.
My editors at Wiley, Mike Baker, Erin Calligan Mooney, and Jen Tebbe, helped
turn an idea into reality. Georgette Beatty earns a special thank you for her
ability to keep me on task; without her input and perspective, I couldn’t have
written this book. Thanks to all the people behind the scenes at Wiley,

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especially the folks in the composition department. Thanks to Alex Jarvis for
the insightful technical review and to Precision Graphics for taking ideas and
turning them into works of art.
On a personal level, my extended family, friends, and heroes also deserve a
special nod: Grandma Eva, your lessons continue to direct me to this day;
Grandma Joan, for your never-ending support; Matt Minkoff, for helping me
discover who I am; Beth Baugh, thanks for all you do for us; Jim Meyer and
Luke Nersesian, I wish I could have just a moment to share this with you two;
Jennifer Fisher for her always-unique perspective; John Panzak, world’s greatest teacher; Jeff Lebowski, hey, that’s your name, Dude; and the Oregon State
Beavers and the Milwaukee Brewers, who make rooting so much more fun.
Given the long list of people I’ve mentioned as directly supporting and influencing me on this project and in life, I can only take partial credit for the
pages in this book, yet I’ll take all the blame. If there are any errors or omissions, that’s due to an oversight on my part, and I regret any errors.

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Publisher’s Acknowledgments
We’re proud of this book; please send us your comments at http://dummies.custhelp.com.
For other comments, please contact our Customer Care Department within the U.S. at 877-762-2974,
outside the U.S. at 317-572-3993, or fax 317-572-4002.
Some of the people who helped bring this book to market include the following:
Acquisitions, Editorial, and Media
Development

Composition Services

Senior Project Editor: Georgette Beatty

Project Coordinator: Patrick Redmond

Senior Acquisitions Editor: Mike Baker

Layout and Graphics: Ashley Chamberlain,
Nikki Gately, Joyce Haughey

Copy Editor: Jennifer Tebbe

Special Art: Precisiongraphics.com

Assistant Editor: Erin Calligan Mooney

Proofreader: Bonnie Mikkelson

Senior Editorial Assistant: David Lutton

Indexer: BIM Indexing & Proofreading Services

Technical Editor: Alexander D. Jarvis

Special Help
Caitlin Copple

Editorial Manager: Michelle Hacker
Editorial Assistant: Jennette ElNaggar
Art Coordinator: Alicia B. South
Cover Photo: © Getty/Dreamlight
Cartoons: Rich Tennant
(www.the5thwave.com)

Publishing and Editorial for Consumer Dummies
Diane Graves Steele, Vice President and Publisher, Consumer Dummies
Kristin Ferguson-Wagstaffe, Product Development Director, Consumer Dummies
Ensley Eikenburg, Associate Publisher, Travel
Kelly Regan, Editorial Director, Travel
Publishing for Technology Dummies
Andy Cummings, Vice President and Publisher, Dummies Technology/General User
Composition Services
Debbie Stailey, Director of Composition Services

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Contents at a Glance
Introduction ................................................................ 1
Part I: Here Comes the Sun: Shedding
Some Light on PV Systems ............................................ 7
Chapter 1: The Photovoltaic Revolution ........................................................................ 9
Chapter 2: Checking Out Common Components and Systems .................................. 21
Chapter 3: Powering through Electricity Basics .......................................................... 35
Chapter 4: Warming Up to the Solar Resource ............................................................ 57
Chapter 5: Properly Selecting a Site for a PV System.................................................. 79

Part II: Digging into Complete System Details ............. 99
Chapter 6: PV Modules: From Sand to Electricity ..................................................... 101
Chapter 7: The Basics of Batteries .............................................................................. 121
Chapter 8: Keeping Current and Voltage in Check: Charge Controllers ................. 139
Chapter 9: Inverters: AC (From) DC ............................................................................ 149
Chapter 10: Staying Secure: Wiring and Safety Components ................................... 163

Part III: Sizing a PV System ..................................... 177
Chapter 11: Sizing a Grid-Direct System ..................................................................... 179
Chapter 12: Sizing a Battery-Based System ................................................................ 203
Chapter 13: Sizing Conductors, Conduit, and Safety Components ......................... 229

Part IV: Installing a PV System ................................ 247
Chapter 14: The Permitting Process ........................................................................... 249
Chapter 15: Staying Safe Anytime You Work on a PV System.................................. 261
Chapter 16: Assembling the Mechanical Parts .......................................................... 279
Chapter 17: Integrating the Electrical Elements ........................................................ 301
Chapter 18: Commissioning, Inspecting, and Maintaining a PV System ................. 319

Part V: The Part of Tens ........................................... 341
Chapter 19: Ten Ways to Avoid Common Code Mistakes ........................................ 343
Chapter 20: Ten Ways to Maximize Energy Production for Your Clients ............... 349

Index ...................................................................... 355

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Table of Contents
Introduction ................................................................. 1
About This Book .............................................................................................. 1
Conventions Used in This Book ..................................................................... 2
What You’re Not to Read ................................................................................ 3
Foolish Assumptions ....................................................................................... 3
How This Book Is Organized .......................................................................... 3
Part I: Here Comes the Sun: Shedding Some Light on PV Systems .... 4
Part II: Digging into Complete System Details .................................... 4
Part III: Sizing a PV System ................................................................... 4
Part IV: Installing a PV System ............................................................. 4
Part V: The Part of Tens ........................................................................ 5
Icons Used in This Book ................................................................................. 5
Where to Go from Here ................................................................................... 6

Part I: Here Comes the Sun: Shedding
Some Light on PV Systems ............................................ 7
Chapter 1: The Photovoltaic Revolution. . . . . . . . . . . . . . . . . . . . . . . . . . .9
Peeking into the Past, Present, and Future of PV Installations.................. 9
Acquainting yourself with typical PV applications ......................... 10
Checking out PV pros and cons ......................................................... 10
Looking into the future of PV ............................................................. 11
Introducing PV Components and Systems ................................................. 11
Knowing Your Electricity A-B-Cs ................................................................. 12
Solar Resource 101 ........................................................................................ 13
Surveying a PV System Site .......................................................................... 13
Delving into PV System Details .................................................................... 14
PV modules ........................................................................................... 14
Batteries ................................................................................................ 14
Charge controllers ............................................................................... 15
Inverters ................................................................................................ 15
Wiring and safety devices ................................................................... 15
Sizing a PV System ......................................................................................... 16
Grid-direct systems ............................................................................. 16
Battery-based systems ........................................................................ 16
Conductors and safety devices .......................................................... 17
Bringing a PV System to Life ........................................................................ 17
Permitting ............................................................................................. 17
Staying safe ........................................................................................... 17
Putting together the mechanical parts ............................................. 18

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x

Photovoltaic Design & Installation For Dummies
Adding the electrical parts ................................................................. 18
Commissioning, inspecting, and maintaining a system .................. 19
Introducing the Sections of Code You Need to Know............................... 20

Chapter 2: Checking Out Common Components and Systems . . . . . . .21
Introducing the Components That Make Up PV Systems ........................ 21
PV modules and racking ..................................................................... 22
Battery bank ......................................................................................... 22
Charge controller ................................................................................. 23
Inverter .................................................................................................. 24
Loads ..................................................................................................... 25
Load centers ......................................................................................... 25
Disconnects and overcurrent protection ......................................... 26
Utility interconnection ........................................................................ 27
Differentiating between PV System Types ................................................. 28
Grid-direct systems ............................................................................. 28
Battery-based systems ........................................................................ 30
Figuring Out the Right System Type for Any Situation ............................. 32
The customer is connected to the grid ............................................. 33
The customer isn’t connected to the grid ........................................ 33

Chapter 3: Powering through Electricity Basics . . . . . . . . . . . . . . . . . .35
Going with the Flow: Current ....................................................................... 35
Understanding amps ........................................................................... 36
Distinguishing between direct current
and alternating current ................................................................... 36
Measuring current with a meter ........................................................ 37
May the (Electromotive) Force Be with You: Voltage .............................. 41
Grasping the concept of voltage ........................................................ 41
Getting a grip on nominal voltage and operating voltage .............. 41
Measuring voltage................................................................................ 42
Making a Stop: Resistance ............................................................................ 44
Introducing ohms................................................................................. 45
Measuring resistance .......................................................................... 45
Connecting Current, Voltage, and Resistance with Ohm’s Law .............. 47
Pondering Power and Energy....................................................................... 48
Recognizing the differences between power and energy ............... 48
Relating power to current, voltage, and resistance
with the power equation ................................................................. 49
Calculating energy in terms of watt-hours ....................................... 51
Introducing amp-hours, a companion to watt-hours ...................... 51
Wrapping Together Current, Voltage, Resistance,
Power, and Energy ..................................................................................... 52
Another Electricity Concept: Circuit Configurations ................................ 53
Series ..................................................................................................... 54
Parallel................................................................................................... 55
Series-parallel ....................................................................................... 56

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Table of Contents

xi

Chapter 4: Warming Up to the Solar Resource . . . . . . . . . . . . . . . . . . . .57
High (Or Low) Energy: Solar Radiation....................................................... 57
Distinguishing between direct radiation and diffuse radiation ..... 58
Determining the intensity of solar radiation: Irradiance ................ 59
Calculating solar radiation energy: Irradiation ................................ 62
Just for a day: Peak sun hours ........................................................... 63
Examining the Effects of the Sun’s Path on the Earth ............................... 67
Getting a grip on seasonal effects ...................................................... 68
Understanding the sun’s relationship to your
location: Altitude and azimuth ....................................................... 70
Ticking off solar time ........................................................................... 72
Interpreting sun charts ....................................................................... 72
Opening up to the solar window ........................................................ 74
Positioning PV Modules to Make the Most of the Solar Resource .......... 75
Introducing tilt angle ........................................................................... 75
Orienting your array to the azimuth ................................................. 77

Chapter 5: Properly Selecting a Site for a PV System . . . . . . . . . . . . . .79
Setting the Stage for a Site Survey ............................................................... 79
Putting aside enough time .................................................................. 80
Creating a standard site-survey form ................................................ 80
Toting a site-survey bag ...................................................................... 81
Picture This: Documenting Your Entire Site Survey
with Digital Photos..................................................................................... 82
Collecting Basic Information during a Site Survey .................................... 83
General site information ..................................................................... 84
Structural and mechanical information ............................................ 85
Electrical information .......................................................................... 86
Measuring Information in Degrees .............................................................. 88
Understanding magnetic declination ................................................ 88
Calculating the array’s tilt angle and azimuth ................................. 90
Exploring Shading-Analysis Tools ............................................................... 93
Interpreting the Data and Bringing It All Together ................................... 95
Analyzing reports from your shading-analysis tool ........................ 95
Considering the total solar resource factor ..................................... 96
Using other collected information to
plan out the design and installation .............................................. 98

Part II: Digging into Complete System Details .............. 99
Chapter 6: PV Modules: From Sand to Electricity. . . . . . . . . . . . . . . . .101
Creating Solar Electricity: It All Starts with a Cell ................................... 102
Getting a grip on cell construction and manufacturing ................ 102
Connecting cell construction to the photovoltaic effect .............. 104

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xii

Photovoltaic Design & Installation For Dummies
Reviewing Common Types of PV Modules ............................................... 104
Checking out crystalline modules ................................................... 105
Looking at thin film modules ............................................................ 107
Pointing Out Electrical Specifications on PV Modules ........................... 109
Current specifications ....................................................................... 110
Voltage specifications ....................................................................... 111
Maximum power point ...................................................................... 112
Voltage temperature coefficient ...................................................... 113
Power tolerance ................................................................................. 114
Series fuse rating................................................................................ 114
Surveying Test Conditions for PV Modules ............................................. 114
Standard test conditions................................................................... 115
Environmental effects on standard test conditions ...................... 116
Relating Current and Voltage in IV Curves ............................................... 118
An IV curve with varying temperature ............................................ 119
An IV curve with varying irradiance ................................................ 120

Chapter 7: The Basics of Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121
The Fundamentals of Battery Anatomy and Operation .......................... 122
Constructing a battery, from cell to bank....................................... 122
Discovering how batteries charge and discharge ......................... 124
Comparing Different Types of Batteries ................................................... 126
Lead-acid batteries ............................................................................ 127
Lead-calcium batteries ...................................................................... 129
Nickel-cadmium batteries ................................................................. 130
Comprehending Battery Capacity ............................................................. 130
Considering the C rate for capacity................................................. 131
Recognizing factors that affect capacity ......................................... 132
Specifying Batteries ..................................................................................... 134
Specifying the type of battery to use .............................................. 134
Specifying the battery bank size ...................................................... 135

Chapter 8: Keeping Current and Voltage in Check:
Charge Controllers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .139
The Essentials of Charge Controllers........................................................ 140
Seeing how a charge controller works in stages............................ 140
Surveying special effects provided by some charge controllers ..... 143
Maximum Power Point Tracking Technology .......................................... 144
How MPPT works ............................................................................... 145
The pros and cons of MPPT controllers ......................................... 146
Pulse-Width Modulation Technology........................................................ 147
How PWM works ................................................................................ 147
The pros and cons of PWM controllers .......................................... 147
Specifying a Charge Controller .................................................................. 148

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Table of Contents

xiii

Chapter 9: Inverters: AC (From) DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149
Getting the Goods on Grid-Direct Inverters ............................................. 149
Basic operation .................................................................................. 150
Standard features............................................................................... 151
Power output sizes ............................................................................ 153
The importance of transformers...................................................... 154
Investigating Battery-Based Inverters....................................................... 155
Utility-interactive inverter operation .............................................. 156
Stand-alone inverter operation ........................................................ 158
Standard features for all battery-based inverters ......................... 158
Sizes of battery-based inverters ...................................................... 159
Low-frequency transformer technology ......................................... 159
Specifying Any Inverter............................................................................... 160
Grid-direct ........................................................................................... 160
Battery-based ..................................................................................... 161

Chapter 10: Staying Secure: Wiring and Safety Components . . . . . .163
Defining the Circuits in a PV System ......................................................... 163
Checking Out Types of Conductors .......................................................... 165
USE-2 .................................................................................................... 166
PV wire ................................................................................................ 166
Building wiring ................................................................................... 167
Battery wiring ..................................................................................... 167
Ground wiring..................................................................................... 168
Considering Kinds of Conduit .................................................................... 168
Metallic conduit ................................................................................. 169
Nonmetallic conduit .......................................................................... 170
Delving into Disconnects ............................................................................ 171
Perusing Overcurrent Protection Devices ............................................... 172
Circuit breakers ................................................................................. 172
Fuses .................................................................................................... 173
Focusing on Ground Fault Protection ....................................................... 174
Looking at the Basics of Labels ................................................................. 175

Part III: Sizing a PV System ...................................... 177
Chapter 11: Sizing a Grid-Direct System . . . . . . . . . . . . . . . . . . . . . . . .179
First Things First: Evaluating the Budget
and the Available Array Area ................................................................. 180
Estimating the Site’s Annual Energy Production ..................................... 181
Sizing the Array to Meet Your Client’s Energy Consumption ................ 182
Determining annual energy consumption ...................................... 183
Looking at contract options with the utility................................... 183
Using consumption and contract options
to select an array’s needed power value .................................... 184

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Getting Ready to Match an Inverter to an Array ..................................... 185
Matching Power Values for an Array and an Inverter ............................ 186
Coming Up with the Right Voltage Values
for Your Array and Inverter .................................................................... 188
Establishing the inverter’s AC voltage ............................................ 189
Defining the inverter’s DC voltage window .................................... 190
Calculating the modules’ maximum DC voltage contribution ..... 191
Figuring out the modules’ minimum DC voltage contribution..... 196
Bringing It All Together: Combining Your Power
and Voltage Information ......................................................................... 201
One Last Check: The Inverter’s Maximum Current Input....................... 202

Chapter 12: Sizing a Battery-Based System . . . . . . . . . . . . . . . . . . . . .203
Get Loaded: Looking at Loads in a Battery-Based System ..................... 204
Evaluating the loads that the battery bank must serve ................ 204
Calculating the energy required during an
outage for utility-interactive systems .......................................... 206
Determining the average daily energy
consumption for stand-alone systems ........................................ 207
Sizing the Battery Bank ............................................................................... 209
Inverter efficiency .............................................................................. 210
The days of autonomy....................................................................... 210
The temperature used for battery operation ................................. 211
The depth of discharge ..................................................................... 211
Nominal voltages ............................................................................... 213
Figuring out the battery capacity you need ................................... 213
Strung along: Wiring the battery bank ............................................ 215
Sizing the PV Array ...................................................................................... 216
Sizing the array in a utility-interactive system............................... 216
Sizing the array in a stand-alone system ........................................ 217
Sizing the Charge Controller ...................................................................... 219
Voltage specifications ....................................................................... 220
Power or amperage specifications .................................................. 221
A check before you move on: Comparing
the array size to the battery capacity ......................................... 223
Sizing the Inverter ....................................................................................... 223
Viewing voltage output ..................................................................... 224
Calculating the power draw.............................................................. 224
Staying in charge ................................................................................ 225
Looking at surge ratings.................................................................... 225
Evaluating inverter and array power output .................................. 226
Incorporating a Generator .......................................................................... 226
Generator features ............................................................................. 227
Generator sizing ................................................................................. 227

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Chapter 13: Sizing Conductors, Conduit,
and Safety Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .229
Conductor Sizing 101 .................................................................................. 229
Defining the PV circuits’ maximum
and continuous current ................................................................. 230
Calculating non-PV circuits’ maximum current ............................. 231
Considering conditions of use with some handy tables ............... 232
Putting together the details to determine conductor sizing ........ 236
Accounting for voltage drop after you size your conductors ...... 238
Sizing Conduit .............................................................................................. 243
Sizing Overcurrent Protection Devices and Disconnects ...................... 244
Beginning with a few basics.............................................................. 244
Placing protection on PV circuits .................................................... 245
Protecting inverter circuits .............................................................. 246

Part IV: Installing a PV System ................................. 247
Chapter 14: The Permitting Process . . . . . . . . . . . . . . . . . . . . . . . . . . . .249
Obtaining Permits before You Install a PV System ................................. 249
In the beginning: Having the right licenses and certifications ..... 250
Home grown: Permitting for residential systems .......................... 251
Big business: Permitting for commercial systems ........................ 255
Not Just Pretty Pictures: Creating Drawing Sets ..................................... 258
Calling out components clearly ....................................................... 259
Depicting equipment locations ........................................................ 259
Showing conductor-sizing calculations .......................................... 259
Jotting down job notes ...................................................................... 260

Chapter 15: Staying Safe Anytime You Work on a PV System . . . . . .261
Getting a Grip on General Construction Site Safety ................................ 262
Identifying job-site obstacles and putting on
protective gear right away ............................................................ 262
Safely working alone and with others ............................................. 263
Taking in tips for tool safety............................................................. 264
Limiting your exposure to the elements ......................................... 264
Stowing a first-aid kit on the job site ............................................... 265
Looking at Ladder Safety ............................................................................ 265
Selecting your stash of ladders ........................................................ 265
Properly setting up any ladder ........................................................ 267
Raising the Issue of Rooftop Safety ........................................................... 268
Restraining yourself with fall protection ........................................ 269
Storing your tools .............................................................................. 269
Maintaining safe walkways ............................................................... 271

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Examining Electrical Safety ........................................................................ 271
Staying aware of general shock hazards ......................................... 271
Working with circuits ........................................................................ 272
Charging Ahead with Battery Safety ......................................................... 276

Chapter 16: Assembling the Mechanical Parts . . . . . . . . . . . . . . . . . .279
Surveying PV Array Mounting Methods ................................................... 280
Roof mounting .................................................................................... 281
Ground mounting ............................................................................... 285
Top-of-pole mounting ........................................................................ 287
Building-integrated mounting........................................................... 289
Considering Loading When You Mount an Array on a Roof .................. 290
Following building codes .................................................................. 291
Accounting for additional dead load ............................................... 291
Looking at live loads .......................................................................... 293
Properly Attaching an Array to a Roof ..................................................... 294
Making attachments with lag screws .............................................. 294
Sealing roof penetrations with flashing .......................................... 296
Supporting Ground and Top-of-Pole Mounting........................................ 298

Chapter 17: Integrating the Electrical Elements. . . . . . . . . . . . . . . . . .301
Location Is Everything: Knowing Where
to Place Electrical Equipment ................................................................ 301
Manufacturers’ requirements for equipment locations................ 302
Locations for disconnecting means................................................. 303
Combiner boxes and junction boxes and wiring, oh my! ............. 304
Working on Wiring ....................................................................................... 305
Seeing red (and green and white): Color-coding ........................... 305
Managing wires on PV modules ....................................................... 307
Protecting wires with conduit .......................................................... 308
Bonding Yourself to Grounding ................................................................. 308
Equipment grounding ........................................................................ 309
System grounding .............................................................................. 312
Connecting to the Utility............................................................................. 314
Determining the utility’s requirements ........................................... 314
Making a load side or line side connection .................................... 315

Chapter 18: Commissioning, Inspecting,
and Maintaining a PV System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .319
Making a List and Checking It Twice: Preparing for Commissioning .... 320
Mechanical elements? Check!........................................................... 320
Electrical elements? Check! .............................................................. 321
Start ’Er Up: The Commissioning Process ................................................ 325
Putting safety first.............................................................................. 325
Gathering the gear you need ............................................................ 326
Commissioning different types of systems..................................... 326
Verifying that the system is working ............................................... 330

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Arming Yourself for Inspection Issues ...................................................... 332
Not having “a neat and workmanlike manner” .............................. 333
Forgetting about aesthetics .............................................................. 333
Failing to manage conductors on the array.................................... 334
Neglecting to label the system ......................................................... 334
Surveying System Maintenance ................................................................. 336
Mechanical maintenance .................................................................. 337
Electrical maintenance ...................................................................... 337
Maintenance on a higher level: Taking care of battery banks ..... 338

Part V: The Part of Tens ............................................ 341
Chapter 19: Ten Ways to Avoid Common Code Mistakes . . . . . . . . . .343
Providing Proper Working Clearance ....................................................... 344
Supplying the Right Structural Support.................................................... 344
Keeping Water out of Buildings with Flashing ......................................... 345
Ensuring All Conductors Have the Necessary Ratings ........................... 345
Managing the Conductors on Modules ..................................................... 346
Selecting the Correct Conduit .................................................................... 346
Locating the Disconnects ........................................................................... 347
Grounding the Equipment .......................................................................... 347
Grounding the System................................................................................. 347
Labeling the System Properly .................................................................... 348

Chapter 20: Ten Ways to Maximize Energy
Production for Your Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .349
Select the Right Site..................................................................................... 349
Orient the Array Correctly ......................................................................... 350
Configure the Array Properly ..................................................................... 350
Work within the Limits of the Utility Voltage .......................................... 351
Choose the Correct Inverter ...................................................................... 351
Size Conductors Appropriately ................................................................. 352
Keep the Components Cool........................................................................ 352
Advise Clients to Monitor Their System ................................................... 353
Clean the Array Periodically ...................................................................... 353
Inspect the Array Annually......................................................................... 354

Index ....................................................................... 355

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Introduction

S

olar electricity is one of the most accessible forms of renewable energy
available, and it can be adapted to fit anyone’s specific needs. The
source of it, sunlight, allows photovoltaic (PV) modules to produce electricity and perform useful work, such as running electrical loads or putting
energy back into the utility grid.
Globally, there has been an incredible increase in demand for solar modules
and PV systems since the turn of the 21st century. No longer is PV technology limited to NASA spacecraft and backwoods cabins. Nowadays, PV systems are within reach for many people. This global demand and increased
accessibility and affordability have helped transform the PV industry from a
small cottage industry into a worldwide megabusiness.
As a renewable energy educator, advocate, and user, my primary goal is to
see the solar industry grow successfully and sustainably — two things that
require consistent high-level performance from the people “in the trenches”
or, more appropriately, “on the roofs.” PV system designers and installers
are tasked with providing high-quality systems that can benefit clients for
more than 20 years. If you follow the information, advice, and tips I present
in this book, you’ll be well on your way to completing this task with the best
of them. (Of course, no perfect power source is out there. To be a good PV
system designer and installer, you have to realize the limitations of PV systems, which is why I help you consider those limitations in this book, too.)

About This Book
As the PV industry expands and captures the attention of more and more
individuals, so does the amount of information about these systems.
Photovoltaic Design & Installation For Dummies adds to this ever-expanding
mass of information, but it stands out in its ability to provide you with practical, hands-on specifics. My intention with this book is twofold: to give you
the ability to jump headfirst into the PV industry and to arm you with the
knowledge you need to competently install a system (more or less) on your
own. I use my real-world experience and desire to see every roof holding a
well-designed and properly installed PV system to help you.

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Photovoltaic Design & Installation For Dummies
My approach is to give you the information you need in easy-to-understand
sections that are relevant to the work you’ll be expected to perform as a PV
designer and installer. (I don’t expect you to read this book from cover to
cover, but if you do, I’ll take it.)
Note: This book is focused on the applications used to power homes and
small businesses — with or without the electrical utility present — but you
can take the principles and guidelines I present and adapt them for just about
any application you need.

Conventions Used in This Book
Even though the title of this book has the word photovoltaic in it, most folks
in the industry don’t throw that word around day in and day out. Instead, we
prefer to say PV — it’s simpler, and it creates far fewer tied-up tongues.
Also, throughout this book you’ll see references to PV array and PV system.
The former term refers to the collection of PV modules that makes up the
PV array, and the latter term refers to the PV array and all the associated
components (disconnects, inverters, batteries, and so on) that make it operational and useful.
In addition, all time references throughout this book are based off solar time
(which I cover in Chapter 4). Solar noon is the time of day exactly between
sunrise and sunset, when the sun is at its highest point in the sky that day.
Your longitude, the time of year, and whether you’re subjected to daylight
saving time influence the relationship between your clock and solar time.
Last but not least, the following conventions help you more easily sort
through all the new ideas I throw at you:
✓ The key words in bulleted lists and the action steps I ask you to follow in
a specific order appear in boldface.
✓ New terms that are important for your understanding of PV systems are
in italics, as are words I choose to emphasize.
✓ Web addresses appear in monofont. (Note that when this book was
printed, some Web addresses may have needed to break across two
lines of text. There’s no extra punctuation, though, so just type in
exactly what you see, pretending as though the line break doesn’t exist.)

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Introduction

3

What You’re Not to Read
So many interesting side notes about PV technology, politics, and installation techniques exist that I could easily use all the pages of this book for
nothing but various tangents. I think I’ve done a good job of sticking to the
main points to give you the most important information you need, but some
stories and bits of knowledge are just too good to keep to myself. These stories and tidbits are included in the gray-shaded boxes (sidebars) and paragraphs marked with the Technical Stuff icon. Don’t feel bad for skipping over
this text if that’s what you choose to do; you aren’t going to miss out on the
essential information a PV system designer and installer needs to know.

Foolish Assumptions
Simply by picking this book up, you’ve already proven my first assumption,
that you have an interest in finding out more about PV systems, to be true. I
also make some other assumptions about you; here they are, for your viewing pleasure:
✓ You’re one of the many individuals ready to make a career move that
includes PV design and installation; you’re either already a buildingtrade professional or you’re enrolled in classes and want to secure an
entry-level position in the PV industry.
✓ Perhaps you’re a homeowner looking for a better understanding of PV
systems; you’re thinking about having one installed and want to be as
knowledgeable as possible when working with a PV system designer and
installer.
✓ You’re interested in technically challenging projects, and you can accept
that good designs and installations don’t happen overnight. You want to
prepare yourself and gain some knowledge first.

How This Book Is Organized
Photovoltaic Design & Installation For Dummies is arranged in five different
parts. Each part can stand alone or be read in conjunction with the others.
If one of the following parts (or a particular chapter within that part) excites
you more than the others, by all means, head there first.

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Photovoltaic Design & Installation For Dummies

Part I: Here Comes the Sun: Shedding
Some Light on PV Systems
Get ready to discover the fundamentals of PV design and installation in this
part. Here, I introduce you to the major components used in the systems
you’ll most likely be working with. And in case you need a refresher course
on (or an introduction to) the fundamental electrical principles, this part has
you covered. It also explains the specific relationship between the sun and
the earth and how this relationship affects where you should position a PV
installation.

Part II: Digging into Complete
System Details
Everything you ever wanted to know about the major components of PV
systems can be found in Part II. If you’ve been wondering how a PV module
works and how the acid inside a battery can make electricity, here’s your
chance to find out those things. This part also covers the basic functions of
the other major components of PV systems: charge controllers, inverters, and
wiring. And because safety should always be your top priority, I also get you
acquainted with essential safety devices (think fuses and circuit breakers).

Part III: Sizing a PV System
In this part, I walk you through the different methods for sizing your PV systems (figuring out how many PV modules you need), whether they’re griddirect or battery-based, and the necessary wiring and safety devices. Sizing is
the area that can make or break your system. If you properly size and specify
(select) all the system components, your system will likely pass inspection
much faster, and your client will be left with a safe, efficient way of capturing
and using solar energy. If, however, you make major errors in your preparation and design, fixing those errors after the system is already installed can
be a difficult (and sometimes dangerous) task.

Part IV: Installing a PV System
Part IV is where I cover the physical installation process, as well as the
activities that precede and follow it. I kick things off by walking you through
the permitting process so you have the permission you need to install the

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Introduction

5

system. Next, I cover the safety considerations you need to have in mind
when you’re out installing systems. (After all, PV construction sites offer a
number of hazards for everyone on-site; by preparing for these hazards, you
can avoid them altogether.) After that, I break the installation process into
the mechanical and electrical portions. Then I give you a process to follow
when you’re ready to commission (turn on) the system and get the modules
working prior to the mandatory building department inspection. Finally, I
address proper PV system maintenance.

Part V: The Part of Tens
The Part of Tens is designed to give you small chunks of information for a
quick and easy read. Prepare to find out some of the common mistakes made
in PV installations so you can do your best to avoid them, as well as some
quick tips on how to keep the PV systems you design and install working as
well as they should.

Icons Used in This Book
Throughout this book, I use the following icons to bring your attention to
interesting, important, or even downright critical information.
Although I’d love it if you remembered everything in this book, I know that’s
practically impossible. That’s why I mark ideas I want you to keep in mind no
matter what with this icon.

Every now and then I tend to “nerd out” on you with interesting but nonessential information. I promise to keep these asides (relatively) short and to warn
you that they’re coming with this icon.

This little bull’s-eye brings your attention to information that may make your
job a little easier.

Don’t let anyone fool you. PV systems pose real dangers. This icon alerts you
to a situation that requires special attention and caution.

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Photovoltaic Design & Installation For Dummies

Where to Go from Here
Wondering where to start reading? If it were me, I’d jump to Chapter 6; this is
where I get into the PV modules themselves — far and away the most interesting part of PV systems (in my humble opinion). If you’d rather choose
the approach my children take — which is to decide what you think is best
despite my advice — flip to the table of contents. There you can breeze
through all the chapters and see what jumps out at you.
After you get what you want out of this book, I strongly suggest you find a
way to put that knowledge into action. Numerous organizations that provide hands-on training and experience are available, and these classes are
an excellent way to get your hands on some equipment and have access to
individuals who are knowledgeable and eager to help you master PV systems.
Then, if you have the means, install a PV system on your own home. Doing so
lets you run the show and gives you some personal insight into what it takes
to install PV systems (plus it provides you with a slightly less stressful situation for your first solo installation because you don’t have a client or supervisor looking over your shoulder).
Wherever you end up going first in this book, realize that you’re jumping into
an exciting and rapidly evolving technology and industry. No matter where
you go within the pages of Photovoltaic Design & Installation For Dummies,
you’ll be well on your way to becoming involved with one of the most
dynamic and exciting industries you can imagine.

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Part I

Here Comes the Sun:
Shedding Some
Light on PV Systems

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U

In this part . . .

nderstanding the fundamentals of photovoltaic (PV)
systems is the key to designing and installing highquality systems that’ll perform beyond your (and your clients’) expectations. That’s why this part provides the
foundation you need to move forward with designing and
installing PV systems.
Chapter 1 gives you an understanding of where PV systems started, where they are now, and where they’re
headed; Chapter 2 gives you a feel for the major components used in all types of PV systems and how they relate
to each other. Chapter 3 provides an overview of the electrical fundamentals that drive system designs and installations, and Chapter 4 outlines the relationship between the
sun and the earth and guides you on assessing the solar
resource. Rounding out the bunch, Chapter 5 walks you
through the process of selecting where on a client’s property to install a PV system; it also helps you quantify the
solar resource at a particular location.

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Chapter 1

The Photovoltaic Revolution
In This Chapter
▶ Taking a look at the PV timeline
▶ Refreshing yourself on the basics of electricity and the solar resource
▶ Selecting a site for a PV system and outlining the different system components
▶ Making the sun work on your client’s behalf with proper system sizing and installation
▶ Getting to know Code

I

n recent years, photovoltaic (PV) systems have popped up on people’s
homes and businesses all over the United States. Believe it or not, this
desire to use the sun to power people’s electricity needs is anything but new.
Ever since scientists discovered materials that can produce electrical current
by simply being exposed to light, people have been excited about this energy
source. Get ready to dive into the exciting and ever-expanding world of solar
power with the overview I provide in this chapter.

Peeking into the Past, Present, and
Future of PV Installations
To truly appreciate PV, it helps to have an understanding of where the technology came from, where it’s at now, and where it’s going.
The operating principles for modern PV cells were first discovered in 1839 by
a French physicist named A.E. Becquerel. After that, a number of scientists
played with and improved on Becquerel’s original discovery. In the 1950s,
Bell Labs created the first piece of PV technology designed for use in space.
This technology soon found its way back down to earth for use in telecommunications applications in remote areas. In the 1970s and 1980s, people began
using PV modules to charge batteries and then used those batteries to run
various lights and appliances in their remote homes. These early PV pioneers
helped set the stage for today’s PV industry.

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Part I: Here Comes the Sun: Shedding Some Light on PV Systems
The first PV cells weren’t very efficient or widely used outside of space
programs. They were also quite costly. Yet over the years, researchers and
manufacturing companies increased efficiencies and reliability and managed
to drive down costs drastically. All of these contributions have led to the
widespread use of solar modules and their availability to you and me. In the
following sections, I describe some common PV applications, a few brief pros
and cons of PV systems, and the future of the PV industry.

Acquainting yourself with
typical PV applications
Modern PV systems can be found in a wide variety of applications. They
power calculators, pump water, help offset the energy used by floodlights
along highways, and, of course, power homes and businesses.
For you and me, electricity is available nearly everywhere we go, and PV systems are able to integrate with the existing utility grid. In remote, developing
areas, PV systems provide valuable energy for powering lighting systems,
running refrigerators, and helping deliver clean drinking water.

Checking out PV pros and cons
PV systems have some serious advantages on their side. Producing electricity from the sun has environmental benefits because the power source is an
abundant renewable resource that’s available every day (even though PV
systems aren’t as effective during cloudy weather, they still produce a small
amount of power on those days). PV is also a highly adaptable power source.
You can use individual cells to power small electronics and individual panels
to power specific loads. You can build small arrays to power homes, or you
can build utility-scale projects to send massive amounts of power into the utility grid. And after PV systems are installed, they can provide many years of
clean, reliable power at virtually any location on earth.
On homes and businesses connected to the utility, PV systems are considered distributed generation, a power source that produces electricity close to
the location where the power is used. They’re able to offset the requirements
on the central power plants sending out the electricity most people use.
PV systems aren’t the right answer for all applications. They have some disadvantages too. For example:

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Chapter 1: The Photovoltaic Revolution

11

✓ The sun isn’t a continuous power source. At night, the PV modules
can’t produce power, so in some scenarios, you have to use a method to
store the energy for later use (adding cost and complexity to the system
design and installation).
✓ The amount of area required to produce power is large in comparison
to other sources of power. For large-scale projects, significant portions
of land or roof space are necessary. Not every homeowner or business
owner has access to such space.

Looking into the future of PV
Most people accept that “alternatives” to the “conventional” power sources
acquired by burning fossil fuels must be developed, and so, to use a really
bad pun, the solar industry has a bright future ahead of it. The worldwide
demand for solar electricity continues to grow on a global level, and the
amount of time, effort, and money being put into the industry is amazing.
Many research and development projects are underway that will help drive
down costs further, increase efficiency, and deliver better PV systems.
I’m reluctant to make any bold predictions about the future of PV technology;
ideas I had just a few years ago that I wrote off as too far-fetched and nearly
impossible are proving to be real solutions in the PV industry. However, I am
comfortable saying that the overall acceptance of PV systems and their integration into the built environment will do nothing but increase in the years to
come. Solar power is no silver bullet, though. It’ll take a movement on many
fronts to make the global shift away from over-reliance on fossil fuels.

Introducing PV Components and Systems
PV systems can be ridiculously simple (connect a module to a load and use
the load as you wish), but they can also seem overwhelming when you first
look at them. Every time I go to design and install a PV system, I look at the
whole process as a real-life puzzle that must be arranged and put together
just so. Each project is unique in its own way, and that’s part of the fun.
Yet despite the differences in the details, the PV systems you connect to
homes and small businesses have some specific and very necessary components (all of which have an important role to play in the system).

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Part I: Here Comes the Sun: Shedding Some Light on PV Systems
✓ PV modules: The individual units that you place in the sun to produce
electricity from the sun are called PV modules. A number of modules
connected together in different configurations form a PV array.
✓ Battery bank: Batteries provide a way of storing the energy produced
by the PV array. Individual batteries connected together make up a PV
system’s battery bank.
✓ Inverters: Devices that take power from the PV array or the battery bank
and turn it into AC power used to operate loads are inverters.
✓ Disconnects and overcurrent protection: These components are necessary for ensuring the safety of the system and the people who come into
contact with it.
Grid-direct PV systems, which send power back to the utility grid, have
become the most popular type of PV system at locations where the utility grid
is present. They offer increased efficiency and reduced maintenance as well
as decreased costs compared to their battery-based counterparts. What they
give up, though, is the ability to use the PV array whenever the utility power
goes out. Luckily for most people who have utility power present, utility outages are relatively rare; when they happen, they’re generally short-lived.
Battery-based systems operate independently from the grid (stand-alone) or
as a backup to the grid (utility-interactive).
In Chapter 2, I run through all the major components you need to install in
a PV system — whether it’s a grid-direct one or a battery-based one — and
what their relationship is to the other pieces of the puzzle. There, I also
explain how to determine which type of system is best for any given client.

Knowing Your Electricity A-B-Cs
A good understanding of electrical concepts and fundamental equations is
vital to designing and installing PV systems correctly. My goal is to have you
feeling comfortable and confident in your understanding of the basic electrical terms and equations (don’t worry — no calculus here). If you design and
install PV systems long enough, I guarantee you’ll find yourself using these
concepts on a daily basis.
If you’ve never opened an electrical box for fear of the unknown monsters
lurking behind the cover, or if you just need a refresher on all the terminology, check out the information I present in Chapter 3. The jargony, industryspecific terms that the PV world is filled with (many of which are born from
the electrical trade) will be much clearer if you do.

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Solar Resource 101
The solar resource is defined as the amount of solar energy received at a particular site. Following are some of the terms used to describe the intensity
of the sunlight striking the earth (these terms are used pretty frequently in
PV system design, so I suggest getting familiar with them; for specifics on the
relationship between the sun and the earth, see Chapter 4):
✓ Azimuth describes the position of the sun (and the modules) in terms of
how many degrees the sun or the array is from north.
✓ Irradiance describes how intense the sunlight is at a particular moment
in time.
✓ Irradiation refers to the quantity of solar energy received for a given
amount of time (a day is a typical time frame).
✓ Solar window refers to the portion of the sky where the sun appears at
a particular location on earth. The solar window varies based on your
latitude. You want to do your best to keep any obstructions out of the
PV array’s solar window.
✓ Tilt describes the number of degrees that the PV modules are off of the
horizontal surface.
But that’s not all you need to know about the solar resource. A PV system’s
location on the earth has a definite effect on the overall system installation.
Also in Chapter 4, I help you look out at the sky and see the big window that
must be kept open for your PV system to perform as well as it possibly can; I
also describe the specific effects of the sun’s path on the earth.

Surveying a PV System Site
PV systems are wonderful, magical things, but they can’t perform miracles all
on their own. You have to give them a fighting chance for them to knock your
client’s socks off. In other words, you have to survey the area where the array
will be located and make sure nothing will block sunlight’s path to the array.
Shade is your enemy, so take a critical look at the potential PV location when
you conduct your site survey. A tiny bit of shade on the array may be unavoidable at certain parts of the year, but it’s your job to predict and limit these
scenarios to the best of your ability.
In Chapter 5, I show you what to keep an eye out for and how to properly
assess your site’s potential. I also outline the most common tools you should
have on hand in order to perform a successful site survey.

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Part I: Here Comes the Sun: Shedding Some Light on PV Systems

Delving into PV System Details
PV systems use a number of interesting components that can leave even the
most seasoned electrician gawking in amazement. I walk you through the
major components in the sections that follow. My goal is to boost your comfort level with the capabilities, limitations, and basic construction of all the
major pieces of a PV system. I strongly encourage you to read these sections
(rather than skip over them) so you can acquire some basic understanding;
without it, any system you design is just a bunch of parts and boxes that
likely won’t get the job done.

PV modules
PV modules are truly where all the magic of PV systems begins. They produce voltage and current, and, when wired correctly, they perform useful
work. (To me, that’s more magical than making entire bridges disappear.) In
Chapter 6, I show you the module specifications you’ll refer back to many,
many times during the system design and installation processes. I also show
you how the modules are at the mercy of their surrounding environment and
will react to whatever sunlight and temperatures they’re exposed to.

Batteries
When you need to store the energy produced by a PV array and use it at a
later time, you need batteries. I list your many options and go over the basic
construction and operation of batteries in Chapter 7. (This information will
prove invaluable when you start specifying [selecting] batteries for your
battery-based PV systems.)
Whenever you need to incorporate batteries in a PV system, you need to
define the following parameters:
✓ The amount of energy the client needs daily
✓ The number of days the client wants to be able to go without having to
recharge the batteries
✓ The amount of solar energy that’s available for charging the batteries
✓ The temperature at which the batteries are stored

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Charge controllers
When you use batteries, you have to make sure they’re properly charged
by the PV array — that’s where a charge controller comes in. In Chapter 8, I
show you how to evaluate the different charge controller technologies that
are used most often and explain how the different technologies interact with
the array and batteries to deliver the maximum amount of energy to the batteries. I also outline the different feature sets commonly found on charge controllers and introduce the specifications to consider when selecting a charge
controller for a battery-based PV system.

Inverters
Because PV arrays and battery banks produce and store DC electricity, you
almost always need to include an inverter in a PV system (or more than one,
depending on the size of the array). An inverter takes DC electricity and turn
it into the AC power used by most electrical loads in homes and businesses.
I go over the inverter categories used in PV systems in Chapter 9, but in general, you can classify inverters as either grid-direct or battery-based:
✓ All grid-direct inverters are also classified as utility-interactive (meaning
they can take power from the PV array and send it into the grid).
✓ Battery-based inverters, on the other hand, can be classified as utilityinteractive or stand-alone (meaning they can’t send power into the grid
and are meant for off-grid applications).

Wiring and safety devices
Safety is one of the most important considerations you make during the
design and installation process. To achieve proper equipment safety, you
need to install a number of safety devices, not least of which is the right
wiring. In Chapter 10, I introduce you to the different types of conductors
(wires), the conduit that protects those conductors from damage, and the
overcurrent protection devices you have to use to protect the conductors
from having too much current flowing through them.
Another important piece of safety equipment is the disconnect switch that
allows you to (no surprise here) disconnect the PV array from the inverter.
When a disconnect switch is in the off position, you can safely access the
components of a PV system for servicing.

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Part I: Here Comes the Sun: Shedding Some Light on PV Systems
Because other people (such as emergency personnel) may come into contact
with the system, you need to make sure it’s safe for them by installing labels
that explain how to quickly and safely access the system.
As a final note on safety precautions, you need to keep in mind that at some
point the wiring in the PV system may become damaged and pose a risk.
Ground fault protection (GFP) devices help protect against fire hazards in the
case of damaged conductors. In grid-direct inverters, this protection is preinstalled; for battery-based systems, you must install GFP separately.

Sizing a PV System
In order to have a PV system operate properly and meet your client’s expectations, you need to spend some time in the design phase evaluating the
individual components of the system and their interaction with all the other
pieces. During this sizing process (which is when you determine the number
of modules to use in a particular system), you have to consider the client’s
available budget for the project, the PV array location, and the specifications
for the individual pieces of equipment.
In this section, I explain the basics of sizing and installing the two main system
types and talk about sizing the safety equipment used in your systems.

Grid-direct systems
Grid-direct systems offer more design flexibility than battery-based systems
because you don’t have to worry about storing any energy; the grid will usually be there to make sure all the loads can run when the user wants them
to. Even with this flexibility, you need to carefully consider the PV array you
design and the components you connect to it. In Chapter 11, I show you what
you need to consider in the sizing and design process, from evaluating the
energy consumption at the site to the utility requirements for connecting to
the grid to the calculations used when matching a PV array to an inverter.

Battery-based systems
Before you can size a battery-based system (either utility-interactive or standalone), you must evaluate the energy consumption used by the loads that will
be powered via the battery bank. After you complete this step, you’re ready
to move on to sizing the different system components, specifically the battery
bank, the PV array, the charge controller, and the inverter. Chapter 12 has the
how-to on sizing these components. (If you need to incorporate a generator
into any battery-based system design, Chapter 12 has you covered as well.)

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Conductors and safety devices
PV systems have some rather unique properties that need your attention
when sizing wiring and safety components. The conductors are exposed to
some extremely high temperatures, the current values passing through those
conductors are at the mercy of the sun, and on top of all that, the DC current
passing through the system requires you to seek out components that are
specially listed for the application. Never fear. I walk you through the processes of properly choosing and sizing conductors, conduit, and overcurrent
protection devices in Chapter 13.

Bringing a PV System to Life
After you spend all the required time designing a PV system, you’re ready for
the real fun: going out in the sun and putting the modules to work. The next
sections are dedicated to the different portions of the installation process
to help get you up to speed. Of course, every situation you encounter will
be slightly different from the last, but the fundamental ideas and processes
behind PV system installation remain constant.

Permitting
An important activity takes place before a PV system is ever installed: permitting. The local building department is responsible for providing permits for
any PV installation. You must apply for this permit, just like you would if you
were doing any other major construction project.
Generally, you need to have two permits issued to you: an electrical permit
and a building permit. The electrical permit is required so that the building
department can ensure that the electrical portion of the system is safe, and
the building permit helps keep the building safe from mechanical failure. (For
full coverage of the permitting process, turn to Chapter 14.)

Staying safe
The safety of all individuals on the job site should be the most important
factor during any installation — period. When you’re installing a PV system,
you’ll be on a construction site with numerous hazards. The Occupational
Safety and Health Administration (OSHA) rules regarding constructionrelated trades will be in full effect, and you need to be sure to address these
requirements. The OSHA Web site, www.osha.gov, is full of information and
resources to help you make your work sites as safe as possible.

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Part I: Here Comes the Sun: Shedding Some Light on PV Systems
Just because PV systems deal with solar power doesn’t mean they don’t possess the same electrical hazards associated with any other electrical system.
Always keep this fact in mind. Also, because PV systems run on energy they
obtain from the sun, you’re going to be working on ladders, accessing roofs,
and working in locations that are fully exposed to the elements — all of which
add even more safety hazards you need to be aware of. (For a review of the
major safety elements you need to consider, as well as methods you can use to
keep yourself and others safe during a system installation, turn to Chapter 15.)
It takes a single accident to not only seriously injure an individual but also
cripple an entire business. So do whatever you have to do to keep safety top
of mind during each and every installation job.

Putting together the mechanical parts
For many PV system installers, the truly difficult part of any PV installation
is the mechanical portion, which includes setting up the rack to hold the
modules and evaluating the interaction between the PV array and the building. Depending on the location of the array (on a roof or on the ground), the
installation of the mechanical components can represent a large portion of
the time spent on the job site. Refer to Chapter 16 for a complete rundown
of the issues you’ll face as you install the mechanical components of a PV
system, as well as effective solutions for them.
A number of PV installations occur on rooftops, especially for residential systems. Whenever you’re working with a rooftop system, you need to carefully
consider the methods used to attach the racking system to the roof. For
ground-mounted systems (including top-of-pole mounting), you have to evaluate how you plan to keep the array in place without overtaxing the racking
system or constructing a structure that can support a small country.

Adding the electrical parts
The electrical installation is always the portion of PV systems that receives
the most attention — and rightly so given the numerous regulations you
must comply with. The majority of these regulations are spelled out in the
PV-specific portion of the National Electrical Code® (NEC®), specifically Article
690. I point out the highlights of Article 690 later in this chapter; consider this
information a primer on the NEC®, not a complete review of the Code. (Note:
Some local building departments may have additional requirements, so be
sure to check in with the local office to make sure you’re on the same page.)

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As I walk you through the different portions of the electrical installation in
Chapter 17, I refer to the NEC® and point out specific requirements. I cover the
required locations for different electrical components such as disconnects
and overcurrent protection, and I guide you through the ever-fun topic of
grounding the PV system (as well as grounding methods that are commonly
used throughout the United States). I also note the requirements you need to
follow when connecting the PV system to the local utility grid.
You don’t have to memorize specific passages of the NEC®, but you do have to
be knowledgeable about the layout and format of the Code so you can effectively refer to it while designing and installing your systems.

Commissioning, inspecting,
and maintaining a system
After you install the system, you’re ready to commission it (in other words,
you’re ready to flip the switch and release the magical electrons from the PV
modules and put them to work). Before you get too excited, though, you need
to take some time and make sure the system has been installed properly so
you don’t have to spend the next three weeks on-site fixing a problem that
could’ve been discovered earlier. I walk you through this self-inspection, as
well as the commissioning process, in Chapter 18.
When you know for sure that the system works, you need to turn it off and
await the official inspection from the local building department. You must set
up an appointment for an inspector to come out and look everything over.
The inspector’s job is to make sure you followed the basic requirements and
installed the components you said you would. If he sees any major problems,
he’ll document them and require you to fix them before he’ll pass the system
and allow you to turn it on. Turn to Chapter 18 for the full scoop on inspection requirements and common problem areas in PV installations.
To avoid getting hung up for too long in the inspection process, speak with an
inspector early in the process (even as early as when you apply for the permits). This way you can make sure you’re clear on the local building department’s guidelines and get initial approval on things like grounding and labeling
while you’re in the design phase (when it’s easier to make changes).
Don’t think you’re done as soon as the system receives approval from the
inspector. No matter how low maintenance it may be, every PV system still
requires maintenance now and then. I outline the common maintenance
issues you need to be aware of and share advice on how to approach them
(as well as who’s responsible for them) in Chapter 18.

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Introducing the Sections of
Code You Need to Know
As you begin to install PV systems, including the electrical elements, you
need to make sure you’re familiar and comfortable with the National Electrical
Code® (NEC®), also referred to as NFPA 70®. I reference the NEC® (also known
simply as the Code) throughout this book, directing you to specific sections
and applications.
Here are some basics related to the NEC® that you may find helpful:
✓ If you’ve never referenced the NEC® or look at it only on rare occasions, I suggest you purchase a copy the NEC® Handbook. It contains the
entire NEC®, along with some pretty pictures and helpful explanations
that make the Code easier to understand. Perhaps the easiest way to
obtain a copy of the handbook is to head to the National Fire Protection
Association’s Web site (www.nfpa.org) and click the Buy NFPA codes
& standards link on the left-hand side of the page. From there, just
search for the NEC® Handbook. The handbook is a little pricey, and
you’ll have to keep purchasing new editions periodically. Rest assured,
though, that the cost is worth it.
✓ Always make sure you’re using the correct version of the handbook for
your area. The NEC® Handbook is released every three years, but the
local jurisdiction (the office that issues building permits) may not be
using the most current version. To find out which version the jurisdiction in your client’s area is using, call the local building department.
✓ As you work more and more with the Code, you’ll realize that people
interpret the same section differently. The powers that be who author
Code sections try for concrete language, but there’s no way to achieve
total clarity with a document like this. If you ever have a question, your
best bet is to research your question and maybe even consult with your
electrical inspector to make sure you’re on the same page as he is (literally and figuratively). Note: The local authority having jurisdiction (AHJ) —
in other words, the electrical inspector — has the final ruling on the Code
interpretation; the Code is there as a guideline, but the enforcement is up
to the AHJ.
✓ Although a specific section in the NEC® covers PV systems, you don’t
get to ignore the other sections. The entire NEC® applies to PV systems,
so reference the other sections as appropriate. However, there may be
situations where the requirements set in Article 690 are different than in
other sections. In this situation, Article 690 supersedes the other Code
sections because it relates to PV installations.

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Chapter 2

Checking Out Common
Components and Systems
In This Chapter
▶ Identifying the major parts of a PV system
▶ Distinguishing between battery-based and battery-less systems
▶ Helping your customers select the correct system for their needs

T

his chapter may seem trivial and worth skipping when all you want to
do is dive into a new-to-you technology and design systems that’ll be
the envy of your peers (not to mention major moneymakers). My advice to
you? Remember that it’s all about the details. Before you can design and
install that envy-inducing, moneymaking PV system, you need to have a grasp
on exactly what goes into a PV system. Each component has a unique and
important role in the whole system. You, the designer and installer, have
to understand these components and their purpose, as well as how they fit
together as a whole, in order to help your customers select the best system
for their needs. This chapter gives you the knowledge base you need to start
working with and recommending PV systems.

Introducing the Components
That Make Up PV Systems
Even though you and I probably drive a different kind of vehicle, the major
components inside each one are identical. Both vehicles have an engine,
some wheels, and a steering wheel to help us navigate, although your vehicle
may have a bigger engine than mine, and my vehicle may have bigger wheels
and a smaller steering wheel than yours. You can look at PV systems in a similar manner. The basic components, such as the PV modules and the inverter,
are the same even though the types of components differ based on the user’s
needs and what the local regulations require. In the following sections, I take
a look at the major components of a typical PV system and explain how each
component relates to the others.

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Part I: Here Comes the Sun: Shedding Some Light on PV Systems
Note: The following information isn’t all-inclusive. Rather, it’s a primer
designed to help you understand PV systems as a whole. Each of these components receives much more attention in later chapters, so please don’t feel
overwhelmed with the descriptions I provide here.

PV modules and racking
PV modules are the source of power in a PV system. They produce DC electricity, which is easily stored in battery banks but needs to become AC power
via an inverter for use in homes. (I present the features and limitations of different types of PV modules in Chapter 6.)
Racking components hold the PV array to the location where you choose
to place the modules. One typical way to mount the entire array is on the
roof of the structure you’re working with. Other options include buildingintegrated mounting (where the PV array becomes a substitute for the roofing
or window materials) and mounting the array on a racking system down at
ground level. Another common option is mounting the PV array on top of a
pole rack. I give you the scoop on mounting methods and considerations in
Chapter 16.
No matter where they’re mounted, PV modules are always connected to
these particular components: disconnects, inverters, and charge controllers.
The terms PV module and PV panel are often used interchangeably (I’ve been
fighting myself for years on getting it straight when talking to people). You
also see and hear PV array quite a bit. The fact is, different definitions describe
these terms. If you’re discussing modules, panels, and arrays with someone,
you need to make sure you’re both talking the same language.
✓ A module is a single unit consisting of PV cells contained in an environmentally secure package.
✓ A panel is a group of modules fastened and wired together.
✓ An array is all the modules (and panels) and racking components used
to produce DC electricity.

Battery bank
For systems that require energy storage (namely, any system that needs to
operate without the utility grid; see the later “Battery-based systems” section
for more information), a battery bank, multiple batteries wired together to
achieve the specific voltage and energy capacity desired, is the best option.

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The battery bank is typically housed in a container to keep the batteries safe.
The PV array connects to it in order to provide charging, with a charge controller located somewhere in between. The battery bank is also connected
to the inverter to provide power for the AC loads. If the system also uses DC
loads, the battery bank is wired to a DC load center. (Don’t know what loads
and load centers are? I cover both later in this chapter.)
Just like your car’s fuel gauge tells you when you need to fill up, a battery
monitor tells you how full the battery is. In battery-based systems, a monitoring system is very important in keeping track of the battery level.
I describe the different battery technologies in detail in Chapter 7, but the
most common batteries used for the typical PV system are as follows:
✓ Sealed batteries: These come in a sealed container that requires a
reduced amount of maintenance by the end user.
✓ Flooded batteries: These come in an open (or flooded) container that
requires a higher level of user interaction.
Sealed batteries are often referred to as “maintenance-free batteries.” Don’t
believe the hype! Sealed batteries are indeed a reduced-maintenance option
compared to flooded batteries, but they still need some attention. If you don’t
advise your clients to monitor and properly maintain a battery bank, the batteries will die prematurely. Relatively simple battery monitoring can not only
keep the system owner updated on the batteries’ status but it can also keep
her from experiencing poor results when using the batteries. (Chapter 18 has
details on the maintenance required for battery-based systems.)
All batteries give off gas when they’re charging, releasing hydrogen. Sealed
batteries release minuscule levels of hydrogen; flooded batteries can give off
substantial levels of it. A wise choice (actually a requirement in most locations) is to keep all batteries inside a protective container that vents to the
outside to avoid the possibility of hydrogen buildup and an explosion hazard.

Charge controller
A charge controller is a piece of electronics that’s placed between the PV
array and the battery bank. As you can probably guess, its primary function in life is to control the charge coming into the battery bank from the PV
array. Charge controllers can vary from a small unit intended to connect a
single PV module to a single battery all the way to a controller designed to
connect a multiple-kilowatt PV array to a large battery bank.
Flip to Chapter 8 for more information about charge controllers, including
their features, technology, and sizing.

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Part I: Here Comes the Sun: Shedding Some Light on PV Systems

Inverter
Inverters turn the DC power produced by PV arrays or stored by battery
banks (in battery-based systems) into the AC power used in homes and businesses. They come in many different shapes and sizes. An inverter can be as
small as the 100-watt unit you plug into the DC plug in your car or as large
as a megawatt unit installed in conjunction with a utility-scale PV project. (I
delve into the details of inverter specifications in Chapter 9.)
If the PV system is only going to supply power for DC loads such as lighting,
water pumping, or small electronics, an inverter isn’t a requirement. DC loads
in standard residential applications don’t show up much anymore, but they’re
common in recreational vehicles.
The inverters in PV applications fall into two major categories:
✓ Utility-interactive: These inverters can connect to a utility and either
supply power to the connected loads or send electricity back into the
grid, essentially running the meter backward.
✓ Stand-alone: These inverters aren’t designed to interact with the utility
and work by supplying power to loads.
Utility-interactive and stand-alone inverters have a similar appearance. If you
were to look at two inverters from the same manufacturer, you wouldn’t be
able to tell the difference because manufacturers try to put multiple inverters
in the same chassis, or outer shell, to reduce the number of parts they have to
use and cut costs. The only way to know for sure which inverter is which is to
look at the label on the side of each inverter.
Utility-interactive inverters come in two flavors:
✓ Grid-direct: These are primarily used in systems for homes and businesses with utility power present. They don’t provide the user with
any energy storage, which means if the utility power isn’t present, the
inverter can’t work. In grid-direct inverter systems, the PV array is connected to the inverter on the DC side, and the inverter is connected to
the utility grid on the AC side.
✓ Battery-based: These require a stable voltage source of power, typically
a battery bank, to keep the inverter running. A PV system using this
inverter requires more components and is generally more complicated,
but it allows the user to have backup power for times when the utility
goes out. Battery-based inverters use a PV array and charge controller
on the DC side and connect to the utility on the AC side.
Stand-alone inverters are quite similar to utility-interactive, battery-based
inverters. The main difference is the source of AC power. In a typical standalone system you have an AC engine generator to supply power to the loads

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and allow for battery charging when the PV array can’t keep up with the
user’s energy consumption. On the DC side, a stand-alone inverter is connected to the same components as its utility-interactive, battery-based counterpart, but on the AC side, the inverter sends power only to AC loads.

Loads
Loads are all the pieces of electrical equipment people want to use in their
homes and offices. You can have DC loads or AC loads (and sometimes even
both). You just have to make sure you supply the correct type of power to the
load. For instance, you can’t use a DC light bulb when AC power is provided.
Loads are served differently depending on the system used (you can find out
more about different systems later in this chapter).
✓ In grid-direct systems, loads are primarily served by the utility. The PV
system can send power directly to the loads or back into the utility grid.
✓ In battery-based systems, the inverters are designed to directly run the
loads connected to the inverter in the load center. This requires sizing
the inverters differently based on the inverter technology used. Note:
Occasionally, DC loads are present in battery-based systems; when they
are, they receive their power from the battery bank via a DC load center.
In a utility-interactive, battery-based system, the system owner defines the
exact loads that get backed up. Although people would like to back up their
entire suburban home, that’s a very difficult task. Bring them back to reality
with this list of loads that can be backed up with success: refrigeration, well
pumps, lighting, and computer equipment.

Load centers
A load center is the place where electrical loads (see the preceding section)
receive their power. In a typical scenario where the utility is present, the utility
sends power to a building at a single location. The utility’s wires are connected
to a meter; from that meter, a connection is made to the main distribution panel
(MDP; also called a main load center). The individual wires running throughout
the building are ultimately connected to the MDP via a circuit breaker.
When a number of electrical circuits are connected within a building, or if a
detached structure is present, such as a garage, often an AC subpanel is used
to help reduce the number of wires running all the way across the house.
Figure 2-1 is an example of how a main panel and subpanel can be laid out in
a residential setting. Usually, a circuit breaker in the MDP sends electricity to
the subpanel. The subpanel then uses multiple circuit breakers to send electricity to loads and outlets that are physically close to the subpanel.

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Part I: Here Comes the Sun: Shedding Some Light on PV Systems

Utility
service

PV array

Utility
meter
Inverter

Figure 2-1:
A main
distribution
panel and a
subpanel in
a residence.

Subpanel
MDP

So how do load centers come into play in a PV system? One possibility is to
connect a grid-direct inverter to the AC subpanel, as long as the NEC® and utility requirements are met. In a utility-interactive, battery-based system, the AC
subpanel can serve as the backup load center, allowing the loads connected to
this panel to remain powered up during an outage. For stand-alone inverters,
because no utility power is present, the inverter supplies the AC power and is
connected to the MDP.

Disconnects and overcurrent protection
A number of safety and servicing requirements exist for PV systems, including disconnects (the switches that can turn everything off, much like a big
version of a light switch) and overcurrent protection devices (the pieces of
equipment, typically a fuse or circuit breaker, that automatically turn a load
off if it’s drawing too much current). The requirements for the exact components and their locations vary depending on the specifics of your installation
and the requirements of the local utility and electrical inspector, but here are
the main considerations:
✓ Disconnects are placed in locations for system maintenance and to isolate the PV array and inverter.
✓ Overcurrent protection is placed in the system to protect the conductors
(wires) from becoming too hot and starting a fire.

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Chapter 2: Checking Out Common Components and Systems

27

Making the utility interconnection with
net metering and the FIT program
Net metering, which is when the utility has to
credit the system owner with retail rates for
PV-generated energy (within some limits),
makes utility-interconnected PV systems a reality. Under net metering, the utility is required
to pay the system owner retail energy rates
for every kilowatt-hour of energy put into the
grid, meaning the system owner is credited at
the same rate at which she is charged. The
catch comes when the system generates more
energy than its owner can consume. Each utility has its own way of handling this situation; it
can credit the account or take the credit itself.
Remember: The key is to know what the netmetering rules are with the utility and make
sure the energy production and consumption
at the site match well with those rules. A great
place to find specific rules for your client’s

location is the Database of State Incentives for
Renewables & Efficiency; you can access the
database online at www.dsireusa.org.
Another popular method for connecting to the
utility and maximizing the investment is known as
a feed-in tariff (FIT). The idea is relatively simple:
Governments and utilities recognize that energy
produced from renewable sources such as PV
has a higher monetary value than energy from
fossil fuels. Therefore, the PV system is interconnected to the utility and metered separately
from the building. The energy created from the
PV system is bought by the utility at a higher rate
than the standard retail rate, and the energy
used in the building is charged at the standard
retail rate. This system encourages customers to
install high-quality systems that produce as much
energy as possible to maximize their payments.

Disconnects and overcurrent protection are commonly combined in a single
enclosure in the form of a fusible disconnect.
The NEC® sets the basic requirements that most inspectors follow, yet the
NEC® is only a guide. Local inspectors are generally given the ability to enforce
more requirements as they deem necessary. The NEC® has specific requirements for disconnects and overcurrent protection; I cover these requirements
in detail in Chapters 10 and 17. However, many utilities have requirements
that may exceed those found in the NEC®, so you need to understand those
requirements and how they affect your installation.

Utility interconnection
The point at which a PV system interconnects with a utility grid is often
referred to as the point of common connection (POCC). This is an electrical connection that can take various forms depending on the size of the PV
system and the electrical equipment already located on-site.
When connecting an inverter to the utility, you need to let the utility know
what you’re doing in order to get its approval. Most utilities require that the
system owner review the interconnection requirements and sign a document

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Part I: Here Comes the Sun: Shedding Some Light on PV Systems
stating that she will adhere to the rules. As PV systems have become more
popular, these documents are generally easy to obtain from the utilities and
have standard language for all customers to follow. Thankfully, the requirements of most utilities aren’t hard to incorporate into the system. Flip to
Chapter 17 for more information on connecting to the utility.
The most straightforward way of making the POCC is to attach the inverter
to a circuit breaker in the existing MDP on-site. Specific requirements for this
type of connection need to be met, but that isn’t a difficult task in most cases.
If you need to connect to the utility in any method other than through an existing MDP, communicate this need to the utility early in the process. You may
need to coordinate a time for it to purposely disconnect the building from its
power lines in order to make the connection safely. Also, the utility may have
additional requirements for safety equipment.

Differentiating between PV System Types
You know the saying “the whole is greater than the sum of its parts”? It
applies to PV systems too. After you have a picture of the major components
of a PV system, you’re ready to focus on the two main types of systems: griddirect and battery-based. The sections that follow help you create a mental
picture of both systems; they also get you ready to differentiate between the
two for scenarios you’re bound to encounter.

Grid-direct systems
For those folks with access to the utility grid, a grid-direct system is the most
common type of PV system being installed today. A grid-direct (sometimes
referred to as battery-less) PV system requires the least number of components
and is typically the most efficient in converting the sun’s radiation into usable
AC electricity for loads. These systems have the added benefit of requiring
very little human interaction because the inverter is able to automatically control the flow of electricity from the PV array to the grid. In the following sections, I describe the configuration of a grid-direct system and explain its pros
and cons.

The configuration
Grid-direct systems, like the one pictured in Figure 2-2, have a relatively
straightforward configuration. The PV array is connected to the inverter,
which in turn is connected to the utility. Grid-direct systems typically use
✓ A PV array with racking
✓ A junction box to get the wires in the building
✓ A DC disconnect

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Chapter 2: Checking Out Common Components and Systems

29

✓ An inverter (or more than one, depending on the size of the PV array
and/or whether you have multiple arrays)
✓ An AC disconnect
✓ A meter to record the energy produced by the PV array
✓ A utility interconnection across a circuit breaker inside the MDP
As I explain in Chapter 17, the exact locations of all the equipment vary and
are dependent on the specific system. However, Figure 2-2 is a good representation of the components most grid-direct systems use.

Array
Junction
box
– +

– +

– +

– +

– +

– +

DC
disconnect
AC
disconnect

Figure 2-2:
A typical
grid-direct
PV system.



+

L1

Meter

MDP

L2

Inverter
Note: Grounding not shown for clarity.

The pros and cons
Since 2001, the grid-direct system has been the most popular type of PV
system installed in the United States. Why? Because 2001 is when manufacturers started selling reliable grid-direct inverters. It’s also when rebate programs came along.
The pros of installing and operating a grid-direct system rather than a batterybased one are as follows:
✓ You have fewer components to work with.
✓ The design and installation are more simplistic (meaning less expensive).

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