Solar Electricity HandbookA simple, practical guide to solarenergy: how to design and install

photovoltaic solar electric systems

2012 EditionMichael Boxwell

www.GreenstreamPublishing.com

Greenstream Publishing12 Poplar Grove, Ryton onDunsmore, Warwickshire, CV83QE. United Kingdom

Copyright Michael Boxwell20092012

Published by GreenstreamPublishing 2012

Smashwords Edition: ISBN 978-1-907670-23-7

Kindle Edition: ISBN 978-1-907670-22-0

First Edition published April2009

Second Edition publishedNovember 2009

Third Edition published March2010

Fourth Edition published January2011

Fifth Edition published October2011

Sixth Edition published February2012

Editor: Sheila GlasbeyMichael Boxwell asserts the moralright to be identified as the author

of this work.A catalogue record for this book isavailable from the British Library.

Whilst we have tried to ensure theaccuracy of the contents in thisbook, the author or publishers

cannot be held responsible for anyerrors or omissions found therein.All rights reserved. No part of this

publication may be reproduced,stored in a retrieval system, or

transmitted, in any form or by anymeans, electronic, mechanical,

photocopying, recording orotherwise, without the priorpermission of the publishers.

Table of Contents

Table of ContentsIntroducing Solar Energy

Who this book is aimed atThe rapidly changing world ofsolar energySolar electricity and solar heatingThe source of solar powerThe principles of solar electricityUnderstanding the terminologySetting expectations for solarelectricityWhy choose a solar electricsystem?Cost-justifying solar

Solar power and wind powerFuel cellsGrid-tied solar electric systemsSolar electricity and theenvironment

Environmental efficiency:comparing supply and demand

In conclusionA Brief Introduction to Electricity

Dont panicA brief introduction to electricityHow to measure electricityThe relationship between volts,amps, ohms, watts and watt-hours

VoltsPower

EnergyA word for non-electriciansIn conclusion

The Four Configurations for SolarPower

Stand-alone/off-gridExamples of simple stand-alonesystems

Grid-tieAn example of a grid-tie system

Grid-tie with power backup (gridinteractive)

An example of a grid interactivesystem

Grid fallbackAn example of a grid fallback

systemGrid failover

How grid-tie systems differ fromstand-aloneIn conclusion

Components of a Solar ElectricSystem

Solar panelsBatteriesControllerInverterElectrical devicesConnecting everything together

A stand-alone systemA grid-tie system using a singlecentral inverterA grid-tie system using multiple

micro-invertersIn conclusion

The Design ProcessShort-cutting the design workSolar energy and emotionsIn conclusion

Scoping the ProjectDesigning grid-tie or grid fallbacksystems

Comparing supply with demandFleshing out the scopeProducing a power analysis

A word of warningWhen you are ready to proceedCalculating inefficiencies

Adding the inefficiencies to our

power analysisWhen do you need to use the solarsystem?Keeping it simpleImproving the scopeIn conclusion

Calculating Solar EnergyWhat is solar energy?

Why is this useful?Calculating solar irradianceCapturing more of the sunsenergyThe impact of tilting solarpanels on solar irradianceCalculating the optimum tilt forsolar panelsGetting the best from solar

panels at different times of theyearPositioning your solar panelsUsing solar irradiance to workout how much energy a solarpanel will generateUsing solar irradiance to giveyou an approximate guide for therequired power capacity of yoursolar array

Solar panels and shadeSolar array power pointefficienciesThe effects of temperature onsolar panels

Temperature impact on solarperformance in Austin, Texas

during the summer monthsWorking out an approximate cost

What if the figures do not addup?

Working out dimensionsIn conclusion

Surveying Your SiteWhat we want to achieve

What you will needFirst impressions

Drawing a rough sketch of thesite

Positioning the solar arrayRoof-mountingGround-mountingPole-mountingSplitting the solar array into

several smaller arraysIdentifying the path of the sunacross the skyShading

Professional tools for obstacleanalysisCell phone applicationsUsing paper and pencil

Future proof your systemWhat if there are shadingobstructions?

Positioning batteries, controllersand invertersCablingSite survey for the holiday homeIn conclusion

Understanding the ComponentsHow to use these chapters

Common components for allsystemsSolar panels

Amorphous solar panelsPolycrystalline solar panelsMonocrystalline solar panelsWhich solar panel technology isbest?What to look for when choosinga solar panelBuying cheap solar panelsSecond-hand solar PV panelsFresnel lenses and mirrors

Solar panel mountingsSolar trackers

Solar array cablesFuses and isolation switchesGround fault protection

Components for Grid-Tie systemsHigh voltage in-seriesLow voltage systemsMicro-inverter systems

Grid-tie solar panelsGrid-tie inverters

Input voltagePower ratingPower trackingMultiple stringsDiagnostics and reportinginformationBuilt-in safety

Installation options andoperating environmentBuying from eBay

Components for Stand-AloneSystems

Calculate your optimum voltageVoltages and currentsWhat voltages can I run at?How to work out what voltageyou should be running at

How to calculate your currentCalculating cable thicknesses

Converting wire sizes:Mixing and matching solar panelsBatteries

Types of batteries

Battery configurationsBattery lifespanHoldoverCalculating how long a set ofbatteries will lastSecond-hand batteriesBuilding your battery bankBattery safety

Solar controllerBalancing the batteriesAllow for expansionMaximum power point trackingGround fault protectionBackup powerUsing multiple controllers

InvertersBattery bank voltage

Power ratingWaveformInstallation options andoperating environmentGround fault protection

CablesBattery cablesAppliance cabling

Plugs and socketsAppliances

LightingRefrigerationMicrowave ovensTelevisions, DVDs, computergames consoles and musicMusic systemsDishwashers, washing machines

and tumble dryersAir conditioning systems

Reputable brand namesSolar panel manufacturers andbrandsSolar controller and invertermanufacturers and brandsBattery manufacturers andbrands

Shopping list for the holiday homeIn conclusion

Planning, regulations and approvalsNational and internationalstandards for solar componentsInstallation regulationsGetting your electricity supplierinvolved

Solar grants and selling yourpower

General information aboutgrants, tax credits and feed-intariffs

In conclusionDetailed Design

Safety is designed inWhat is the worst that canhappen with a solar installation?Grounding your electricsDC ElectricsAC electricsHigh temperaturesThink safety

Solar array design

Solar array design stand-alonesystemsSolar array design grid-tiesystems with micro-invertersSolar array design grid-tiesystems with a single inverter

BatteriesControllerInverterDevices

Specifics for a grid fallbacksystemCircuit protection

Earthing (grounding)DC circuit protectionAC circuit protection

Cable sizing and selection

Sizing your cablesProtecting cable runsDesigning your system to keepyour cables runs as short aspossibleSelecting solar cableController cableBattery interconnection cables

Some sample wiring diagramsThe holiday home wiringdiagram

The next stepSolar frame mountingPositioning batteriesPlanning the installationIn conclusion

InstallationHave you read the instructions?Safety

Your First Aid kitChemical clean-up kitConsidering the general publicWorking at heightHandlingWorking with batteriesGlovesElectrical safety

Assembling your toolkitPreparing your siteTesting your solar panelsInstalling the solar array

Cleaning the panelsAssembly and connections

Roof-mounting a solar arrayFinal wiring

Installing the batteriesPre-installationPositioning the batteriesVentilationAccessInsulationConnections

Installing the control equipmentInstalling a grid-tie systemCommissioning the system

Programming your solarcontrollerTesting your system

Charging up your batteriesConnecting your devices

In conclusionTroubleshooting

Keep safeCommon faultsExcessive power usage

SolutionsInsufficient power generation

SolutionsDamaged wiring/ poorconnectionsWeak battery

Changing batteriesInverter issues

Maintaining Your SystemAs requiredEvery month

Every three monthsEvery six monthsEvery yearAt the start of each winter

Internet SupportTools available on the website

Online project analysisMonthly insolation figuresSolar angle calculatorSolar resourcesQuestions and answersAuthor online!Solar articles

A Final WordAppendix A Crystalline SolarPanels and Shading

Types of obstructionDesigning shade-tolerant solarsystems

Track the shadeIncreasing the number of solarpanelsPanel orientationChoice of solar panelUse micro-invertersDesign a parallel solar arrayDesign a multi-string solar array

Other optionsIf all else fails...In conclusion

Appendix B Solar InsolationUnderstanding this information

Solar insolation values AustraliaSolar insolation values CanadaSolar insolation values IrelandSolar insolation values NewZealandSolar insolation values UnitedKingdomSolar insolation values UnitedStates of America

Appendix C Typical PowerRequirements

Household and officeGarden and DIYCaravans, boats and recreational

vehiclesAppendix D Living Off-Grid

A solar electric system inconjunction with grid electricity

Appendix E Other Solar ProjectsGrid fallback system/ gridfailover systemPortable solar power unitSolar boatSolar shed lightSolar electric bikes

Appendix F Building Your OwnSolar Panels (and Why YouShouldnt)

Introducing SolarEnergy

Ninety-three million miles fromEarth, our sun is 333,000 times thesize of our planet. It has a diameterof 865,000 miles, a surfacetemperature of 5,600C and a coretemperature of 15,000,000C. It is ahuge mass of constant nuclearactivity.Directly or indirectly, our sunprovides all the power we need toexist and supports all life forms.The sun drives our climate and our

weather. Without it, our worldwould be a frozen wasteland of ice-covered rock.Solar electricity is a wonderfulconcept. Taking power from the sunand using it to power electricalequipment is a terrific idea. Thereare no ongoing electricity bills, noreliance on a power socket: a freeand everlasting source of energythat does not harm the planet!Of course, the reality is a littledifferent from that. Yet generatingelectricity from sunlight alone is apowerful resource, withapplications and benefits throughout

the world.But how does it work? For what isit suitable? What are thelimitations? How much does itcost? How do you install it? Thisbook answers all these questionsand shows you how to use thepower of the sun to generateelectricity yourself.Along the way, I will also expose afew myths about some of the wilderclaims made about solar energy andI will show you where solar powermay only be part of the solution.Although undoubtedly there aresome significant environmental

benefits of solar electricity, I willalso be talking about where itsenvironmental credentials havebeen oversold.I will keep the descriptions asstraightforward as possible. Thereis some mathematics and scienceinvolved. This is essential to allowyou to plan a solar electricinstallation successfully. However,none of it is complicated and thereare plenty of short-cuts to keepthings simple.The book includes a number ofexample projects to show how youcan use solar electricity. Some of

these are very straightforward, suchas providing electrical light for ashed or garage, for example, orfitting a solar panel to the roof of acaravan or boat. Others are morecomplicated, such as installingphotovoltaic solar panels to ahouse.I also show some rather moreunusual examples, such as thepossibilities for solar electricmotorbikes and cars. These areexamples of what can be achievedusing solar power alone, along witha little ingenuity and determination.I have used one main example

throughout the book: providingsolar-generated electricity for aholiday home which does not haveaccess to an electricity supply fromthe grid. I have created this exampleto show the issues and pitfalls thatyou may encounter along the way,based on real life issues andpractical experience.A website accompanies this book.It has lots of useful information,along with lists of suppliers and asuite of online solar energycalculators that will simplify thecost analysis and design processes.The website is at

www.SolarElectricityHandbook.com

Who this book is aimedatIf you simply want to gain anunderstanding about how solarelectricity works then this handbookwill provide you with everythingyou need to know.If you are planning to install yourown stand-alone solar powersystem, this handbook is acomprehensive source ofinformation that will help youunderstand solar and guide you inthe design and installation of yourown solar electric system.

Solar has a big application forintegrating into electrical products:mobile phones, laptop computers,portable radios. Even light electriccars can use solar energy to providesome or all of their powerrequirements, depending on theapplication. If you are a designer,looking to see how you canintegrate solar into your product,this book will give you a groundingin the technology that you will needto get you started.If you are specifically looking toinstall a grid-tie system, i.e. a solarenergy system that will feed

electricity back into your localpower grid, this book will provideyou with a good foundation and willallow you to carry out the design ofyour system. You will still need tocheck the local planning laws andany other local legislationsurrounding the installation of solarenergy systems, and you will haveto understand the building ofelectrical systems. In somecountries, you specifically need tobe certified in order to carry out thephysical installation of a grid-tiesystem.If you are planning to install larger,commercialsize systems, or if you

are hoping to install grid-tie solarsystems professionally, then thisbook will serve as a goodintroduction, but you will need togrow your knowledge further. Thisbook gives you the foundations youneed in order to build thisknowledge, but there are specialskills required when designing andimplementing larger scale solarsystems that go far beyond what isrequired for smaller systems andare beyond the scope of this book.If you are planning your own solarinstallation, it will help if you havesome DIY skills. Whilst I include a

chapter that explains the basics ofelectricity, a familiarity with wiringis also of benefit for smallerprojects and you will require athorough understanding of electricalsystems if you are planning a largerproject such as powering a housewith solar.

The rapidly changingworld of solar energyI wrote the first edition of this bookearly in 2009. It is not a long timeago. Yet this 2012 issue is the sixthedition. In every edition, I have hadto rewrite significant sections of thebook and significantly update thewebsite in order to keep up with therapid pace of change.The rapid improvement in thetechnology and the freefall in costssince early 2009 have transformedthe industry. Systems that werecompletely unaffordable orimpractical just two or three years

ago are now cost-effective andachievable.Solar panels available today aresmaller, more robust and bettervalue for money than ever before.For many more applications, solaris now the most cost-effective wayto generate electricity.Over the coming years, all the signsare that the technology and theindustry will continue to evolve at asimilar pace. By 2015, solar willbe the cheapest form of electricitygenerator, undercutting traditionallylow-cost electricity generators suchas coal-fired power stations. We

are likely to see solar energyincorporated into more everydayobjects such as laptop computers,mobile phones, backpacks andclothing. Meanwhile, solar energyis causing a revolution for largeareas of Asia and Africa, whereentire communities are now gainingaccess to electricity for the firsttime.As an easy-to-use and low-carbonenergy generator, solar is withoutequal. Its potential for changing theway we think about energy in thefuture is huge. For families andbusinesses in rural African andAsian villages, it is creating a

revolution.

Solar electricity and solarheatingSolar electricity is produced fromsunlight shining on photovoltaicsolar panels. This is different tosolar hot water or solar heatingsystems, where the power of the sunis used to heat water or air.Solar heating systems are beyondthe remit of this book. That said,there is some useful information onsurveying and positioning yoursolar panels later on that is relevantto both solar photovoltaics andsolar heating systems.

If you are planning to use solarpower to generate heat, solarheating systems are far moreefficient than solar electricity,requiring far smaller panels togenerate the same amount of energy.Solar electricity is often referred toas photovoltaic solar, or PV solar.This describes the way thatelectricity is generated in a solarpanel.For the purposes of this book,whenever I refer to solar panels Iam talking about photovoltaic solarpanels for generating electricity,and not solar heating systems.

The source of solarpowerDeep in the centre of the sun,intense nuclear activity generateshuge amounts of radiation. In turn,this radiation generates light energycalled photons. These photons haveno physical mass of their own, butcarry huge amounts of energy andmomentum.Different photons carry differentwavelengths of light. Some photonswill carry non-visible light (infra-red and ultra-violet), whilst otherswill carry visible light (whitelight).

Over time, these photons push outfrom the centre of the sun. It cantake one million years for a photonto push out to the surface from thecore. Once they reach the sunssurface, these photons rush throughspace at a speed of 670 millionmiles per hour. They reach earth inaround eight minutes.On their journey from the sun toearth, photons can collide with andbe deflected by other particles, andare destroyed on contact withanything that can absorb radiation,generating heat. That is why youfeel warm on a sunny day: your

body is absorbing photons from thesun.Our atmosphere absorbs many ofthese photons before they reach thesurface of the earth. That is one ofthe two reasons that the sun feels somuch hotter in the middle of theday. The sun is overhead and thephotons have to travel through athinner layer of atmosphere to reachus, compared to the end of the daywhen the sun is setting and thephotons have to travel through amuch thicker layer of atmosphere.This is also one of the two reasonswhy a sunny day in winter is so

much colder than a sunny day insummer. In winter, when yourlocation on the earth is tilted awayfrom the sun, the photons have totravel through a much thicker layerof atmosphere to reach us.

(The other reason that the sun ishotter during the middle of the daythan at the end is because theintensity of photons is much higher

at midday. When the sun is low inthe sky, these photons are spreadover a greater distance simply bythe angle of your location on earthrelative to the sun.)

The principles of solarelectricityA solar panel generates electricityusing the photovoltaic effect, aphenomenon discovered in the early19th century when scientistsobserved that certain materialsproduced an electric current whenexposed to light.Two layers of a semi-conductingmaterial are combined to create thiseffect. One layer has to have adepleted number of electrons. Whenexposed to sunlight, the layers ofmaterial absorb the photons. This

excites the electrons, causing someof them to jump from one layer tothe other, generating an electricalcharge.The semi-conducting material usedto build a solar cell is silicon, cutinto very thin wafers. Some of thesewafers are then doped tocontaminate them, thereby creatingan electron imbalance in the wafers.The wafers are then alignedtogether to make a solar cell.Conductive metal strips attached tothe cells take the electrical current.When a photon hit the solar cell, itcan do one of three things: it can be

absorbed by the cell, reflected offthe cell or pass straight through thecell.It is when a photon is absorbed bythe silicon that an electrical currentis generated. The more photons (i.e.the greater intensity of light) that areabsorbed by the solar cell, thegreater the current generated.Solar cells generate most of theirelectricity from direct sunlight.However, they also generateelectricity on cloudy days and somesystems can even generate verysmall amounts of electricity onbright moonlit nights.

Individual solar cells typically onlygenerate tiny amounts of electricalenergy. To make useful amounts ofelectricity, these cells areconnected together to make a solarmodule, otherwise known as a solarpanel or, to be more precise, aphotovoltaic module.

Understanding theterminologyIn this book, I use various termssuch as solar electricity, solarenergy and solar power. Here iswhat I mean when I am talkingabout these terms:Solar power is a general term forgenerating power, whether heat orelectricity, from the power of thesun.Solar energy refers to the energygenerated from solar power,whether electrical or as heat.Solar electricity refers to

generating electrical power usingphotovoltaic solar panels.Solar heating refers to generatinghot water or warm air using solarheating panels or ground-sourceheat pumps.

Setting expectations forsolar electricitySolar power is a useful way ofgenerating modest amounts ofelectricity, so long as there is agood amount of sunlight availableand your location is free fromobstacles such as trees and otherbuildings that will shade the solarpanel from the sun.Solar experts will tell you that solarelectricity is normally onlycost-effective where there is noother source of electricityavailable.

Whilst this is often the case, thereare plenty of exceptions to this rule.Often solar electricity can beextremely practical and can saveyou money over the more traditionalalternatives. Some examples mightinclude:

Installing a light or a powersource somewhere where it istricky to get a standardelectricity supply, such as inthe garden, shed or remotegarage

Creating a reliable andcontinuous power sourcewhere the standard electricity

supply is unreliable becauseof regular power cuts

Building a mobile powersource that you can take withyou, such as a power sourcefor use whilst camping,working on outdoor DIYprojects or working on abuilding site

Creating green energy foryour own use and sellingsurplus energy productionback to the electricitysuppliers through a feed-intariff

The amount of energy you need to

generate has a direct bearing on thesize and cost of a solar electricsystem. The more electricity youneed, the more difficult and moreexpensive your system willbecome.If your requirements for solarelectricity are to run a few lights, torun some relatively low-powerelectrical equipment such as alaptop computer, a small TV, acompact fridge and a few othersmall bits and pieces, then if youhave a suitable location you canachieve what you want with solar.On the other hand, if you want to

run high-power equipment such asfan heaters, washing machines andpower tools, you are likely to findthat the costs will rapidly get out ofcontrol.As I mentioned earlier, solarelectricity is not well suited togenerating heat: heating rooms,cooking and heating water all takeup significant amounts of energy.Using electricity to generate thisheat is extremely inefficient. Insteadof using solar electricity to generateheat, you should consider a solarhot water heating system, andheating and cooking with gas orsolid fuels.

It is possible to power the averagefamily home purely on solarelectricity without making any cutsin your current electricityconsumption. However, it is notcheap, and you will need a lot ofroof space to fit all the panels! It isusually a good idea to carefullyevaluate your electricity usage andmake savings where you can beforeyou proceed.Most households and businesses arevery inefficient with their electricalusage. Spending some time firstidentifying where electricity iswasted and eliminating this waste is

an absolute necessity if you want toimplement solar electricitycost-effectively.This is especially true if you live incooler climates, such as NorthernEurope or Canada, where thewinter months produce much lowerlevels of solar energy. In the UnitedKingdom, for instance, the roof ofthe average-sized home is not largeenough to hold all the solar panelsthat would be required to providethe electricity used by the averagehousehold throughout the year. Inthis instance, making energy savingsis essential.

For other applications, a solarelectric installation is much morecost-effective. For instance, nomatter which country you live in,providing electricity for a holidayhome is well within the capabilitiesof a solar electric system, so longas heating and cooking are cateredfor using gas or solid fuels and thesite is in a sunny position with littleor no shade. In this scenario, a solarelectric system may be morecost-effective than installing aconventional electricity supply ifthe house is off-grid and is notclose to a grid electricityconnection.

If your requirements are moremodest, such as providing light fora lock-up garage, for example, thereare off-the-shelf packages to do thisfor a very reasonable cost. Around70100 ($110$160) willprovide you with a lighting systemfor a shed or small garage, whilst200 ($300) will provide you witha system big enough for lightinglarge stables or a workshop.This is far cheaper than installing aconventional electricity supply intoa building, which can be expensiveeven when a local supply isavailable just outside the door.

Low-cost solar panels are alsoideal for charging up batteries incaravans and recreational vehiclesor on boats, ensuring that thebatteries get a trickle chargebetween trips and keeping thebatteries in tip-top condition whilstthe caravan or boat is not in use.

Why choose a solarelectric system?There are a number of reasons toconsider installing a solar electricsystem:

Where there is no othersource of electrical poweravailable, or where the costof installing conventionalelectrical power is too high

Where other sources ofelectrical power are notreliable. For example, whenpower cuts are an issue and asolar system can act as a

cost-effective contingency

When a solar electricsystem is the most convenientand safest option. Forexample, installing lowvoltage solar lighting in agarden or providing courtesylighting in a remote location

You can become entirelyself sufficient with your ownelectrical power

Once installed, solar powerprovides virtually free powerwithout damaging theenvironment

Cost-justifying solarCalculating the true cost ofinstalling a solar electric systemdepends on various factors:

The power of the sun atyour location at differenttimes of the year

How much energy you needto generate

How good your site is forcapturing sunlight

Compared to other power sources,solar electric systems typicallyhave a comparatively high capitalcost, but a low ongoing maintenance

cost.To create a comparison withalternative power sources, you willoften need to calculate a payback ofcosts over a period of a few yearsin order to justify the initial cost ofa solar electric system.On all but the simplest ofinstallations, you will need to carryout a survey on your site and carryout some of the design work beforeyou can ascertain the total cost ofinstalling a photovoltaic system. Donot panic: this is not as frighteningas it sounds. It is not difficult and Icover it in detail in later chapters.

We can then use this figure to puttogether a cost-justification on yourproject to compare with thealternatives.

Solar power and windpowerWind turbines can be a goodalternative to solar power, butprobably achieve their best whenimplemented together with a solarsystem: a small wind turbine cangenerate electricity in a breeze evenwhen the sun is not shining.Small wind turbines do have somedisadvantages. Firstly, they are verysite-specific, requiring higher thanaverage wind speeds and minimalturbulence. They must be higherthan surrounding buildings andaway from tall trees. If you live on

a windswept farm or close to thecoast, a wind turbine can workwell. If you live in a built-up areaor close to trees or main roads, youwill find a wind turbine unsuitablefor your needs.Compared to the large windturbines used by the powercompanies, small wind turbines arenot particularly efficient. If you areplanning to install a small windturbine in combination with a solarelectric system, a smaller windturbine that generates a few watts ofpower at lower wind speeds isusually better than a large wind

turbine that generates lots of powerat high wind speeds.

Fuel cellsFuel cells can be a good way tosupplement solar energy, especiallyfor solar electric projects thatrequire additional power in thewinter months, when solar energy isat a premium.A fuel cell works like a generator.It uses a fuel mixture such asmethanol, hydrogen or zinc to createelectricity.Unlike a generator, a fuel cellcreates energy through chemicalreactions rather than throughburning fuel in a mechanical engine.These chemical reactions are far

more carbon-efficient than agenerator.Fuel cells are extremely quiet,although rarely completely silent,and produce water as their onlyemission. This makes them suitablefor indoor use with little or noventilation.

Grid-tied solar electricsystemsGrid-tied solar electric systemsconnect directly into the electricitygrid. When the sun is shining duringthe day, excess electricity feeds intothe grid. During the evening andnight, when the solar panels are notproviding sufficient power,electricity is taken from the grid asrequired.Grid-tied solar electric systemseffectively create a micro powerstation. Electricity can be used byother people as well as yourself. Insome countries, owners of grid-tied

solar electric systems receivepayment for each kilowatt of powerthey sell to the electricityproviders.Because a grid-tied solar electricsystem becomes part of the utilitygrid, the system will switch off inthe event of a power cut. It does thisto stop any current flowing backinto the grid, which could be fatalfor engineers repairing a fault.

Solar electricity and theenvironmentOnce installed, a solar electricsystem is a low-carbon electricitygenerator: the sunlight is free andthe system maintenance is extremelylow.There is a carbon footprintassociated with the manufacture ofsolar panels, and in the past thisfootprint has been quite high,mainly due to the relatively smallvolumes of panels beingmanufactured and the chemicalsrequired for the doping of thesilicon in the panels.

Thanks to improved manufacturingtechniques and higher volumes, thecarbon footprint of solar panels isnow much lower. You can typicallyoffset the carbon footprint ofbuilding the solar panels by theenergy generated within 25 years,and some of the very latestamorphous thin-film solar panelscan recoup their carbon footprint inas little as six months.Therefore, a solar electric systemthat runs as a complete stand-alonesystem can reduce your carbonfootprint, compared to taking thesame power from the grid.

Grid-tied solar systems are slightlydifferent in their environmentalbenefit, and their environmentalpayback varies quite dramaticallyfrom region to region, depending ona number of factors:

How grid electricity isgenerated by the powercompanies in your area (coal,gas, nuclear, hydro, wind orsolar)

Whether or not yourelectricity generationcoincides with the peakelectricity demand in yourarea (such as air conditioning

usage in hot climates, or highelectrical usage by nearbyheavy industry)

It is therefore much more difficult toput an accurate environmentalpayback figure on grid-tied solarsystems.It is undeniably true that somepeople who have grid-tied solarpower actually make no differenceto the carbon footprint of theirhome. In colder climates, themajority of electricity consumptionis in the evenings and during thewinter. If you have grid-tie solarbut sell most of your energy to the

utility companies during the day inthe summer and then buy it back toconsume in the evenings and in thewinter, you are making little or nodifference to the overall carbonfootprint of your home. In effect,you are selling your electricitywhen there is a surplus and buyingit back when there is high demandand all the power stations areworking at full load.In warmer climates, solar energycan make a difference. In a hot area,peak energy consumption tends tooccur on sunny days as people try tokeep cool with air conditioning. Inthis scenario, peak electricity

demand occurs at the same time aspeak energy production from a solararray, and a grid-tie solar systemcan be a perfect fit.If you live in a colder climate, thisdoes not mean that there is no pointin installing a grid-tie solar system.It does mean that you need to take agood hard look at how and whenyou consume electricity. Do not justassume that because you can havesolar panels on the roof of yourhouse, you are automaticallyhelping the environment.From an environmental perspective,if you wish to get the very best out

of a grid-tie system, you should tryto achieve the following:

Use the power you generatefor yourself

Use solar energy for highload applications such asclothes washing

Reduce your own powerconsumption from the gridduring times of peak demand

Environmental efficiency:comparing supply anddemandThere is an online calculator that

will allow you to map yourelectricity usage over a period of ayear and compare it with the amountof sunlight available to your home.Designed specifically for grid-tieinstallations, this calculator allowsyou to see how close a fit solarenergy is in terms of supply anddemand.Whilst this online calculator is nosubstitute for a detailed electricalusage survey and research into theexact source of the electricitysupplied to you at your location, itwill give you a good indication ofthe likely environmentalperformance of a solar energy

system.To use this online calculator, youwill need to collate informationabout your electricity usage foreach month of the year. You willusually find this information on yourelectricity bill or by contacting yourelectricity provider. Then visitwww.SolarElectricityHandbook.comfollow the links to the Grid-TieSolar Calculator in the OnlineCalculators section and fill in theonline questionnaire.

In conclusion Solar electricity can be a

great source of power whereyour power requirements aremodest, there is no othersource of electricity easilyavailable and you have agood amount of sunshine

Solar electricity is not thesame as solar heating

Solar panels absorb photonsfrom sunlight to generateelectricity

Direct sunlight generates themost electricity. Dull days

still generate some power

Solar electricity is unlikelyto generate enough electricityto power the average familyhome, unless majoreconomies in the householdpower requirements are madefirst

Larger solar electricsystems have a comparativelyhigh capital cost, but theongoing maintenance costsare very low

Smaller solar electricsystem can actually beextremely cost-effective to

buy and install, even whencompared to a conventionalelectricity supply

It can be much cheaperusing solar electricity at aremote building, rather thanconnecting it to aconventional grid electricitysupply

Stand-alone solar energysystems can have a bigenvironmental benefit if theynegate the need for aconnection to grid power

Grid-tie solar energysystems have an

environmental benefit insunny climates where typicalelectricity usage patterns aresimilar to the supply ofsunlight

In colder regions, whereelectricity usage is highestwhen sunlight is in shortsupply, the environmentalbenefits are less certain

A Brief Introductionto Electricity

Before we can start playing withsolar power, we need to talk aboutelectricity. To be more precise, weneed to talk about voltage, current,resistance, power and energy.Having these terms clear in yourhead will help you to understandyour solar system. It will also giveyou confidence that you are doingthe right thing when it comes todesigning and installing yoursystem.

Dont panicIf you have not looked at electricssince you were learning physics atschool, some of the principles ofelectricity can be a bit daunting tostart with. Do not worry if you donot fully grasp everything on yourfirst read through.

There are a few calculations thatI show on the next few pages, but Iam not expecting you to rememberthem all! Whenever I use thesecalculations later on in the book, Ishow all my workings and, ofcourse, you can refer back to thischapter as you gain more

knowledge on solar energy.Furthermore, the website thataccompanies this book includes anumber of online tools that you canuse to work through most of thecalculations involved in designing asolar electric system. You will notbe spending hours with a slide-ruleand reams of paper working all thisout by yourself.

A brief introduction toelectricityWhen you think of electricity, whatdo you think of? Do you think of abattery that is storing electricity?Do you think of giant overheadpylons transporting electricity? Doyou think of power stations that aregenerating electricity? Or do youthink of a device like a kettle ortelevision set or electric motor thatis consuming electricity?The word electricity actuallycovers a number of differentphysical effects, all of which arerelated but distinct from each other.

These effects are electric charge,electric current, electric potentialand electromagnetism:

An electric charge is abuild-up of electrical energy.It is measured in coulombs. Innature, you can witness anelectric charge in staticelectricity or in a lightningstrike. A battery stores anelectric charge

An electric current is theflow of an electric charge,such as the flow of electricitythrough a cable. It ismeasured in amps

An electric potential refersto the potential difference inelectrical energy betweentwo points, such as betweenthe positive tip and thenegative tip of a battery. It ismeasured in volts. Thegreater the electric potential(volts), the greater capacityfor work the electricity has

Electromagnetism is therelationship betweenelectricity and magnetism,which enables electricalenergy to be generated frommechanical energy (such as in

a generator) and enablesmechanical energy to begenerated from electricalenergy (such as in an electricmotor)

How to measureelectricityVoltage refers to the potentialdifference between two points. Agood example of this is an AAbattery: the voltage is the differencebetween the positive tip and thenegative end of the battery. Voltageis measured in volts and has thesymbol V.Current is the flow of electrons in acircuit. Current is measured inamps (A) and has the symbol I. Ifyou check a power supply, it willtypically show the current on thesupply itself.

Resistance is the opposition to anelectrical current in the material thecurrent is flowing through.Resistance is measured in ohms andhas the symbol R.Power measures the rate of energyconversion. It is measured in watts(W) and has the symbol P. Youwill see watts advertised whenbuying a kettle or vacuum cleaner:the higher the wattage, the morepower the device consumes and thefaster (hopefully) it does its job.Energy refers to the capacity forwork: power multiplied by time.Energy has the symbol E. Energy

is usually measured in joules (ajoule equals one watt-second), butelectrical energy is usually shownas watt-hours (Wh), or kilowatt-hours (kWh), where 1 kWh = 1,000Wh.

The relationship betweenvolts, amps, ohms, wattsand watt-hoursVolts

Current x Resistance = VoltsI x R = V

Voltage is equal to currentmultiplied by resistance. Thiscalculation is known as OhmsLaw. As with power calculations,you can express this calculation indifferent ways. If you know voltsand current, you can calculateresistance. If you know volts and

resistance, you can calculatecurrent:

Volts Resistance = CurrentV R = I

Volts Current = ResistanceV I = R

PowerVolts x Current = Power

V x I = PPower is measured in watts. Itequals volts times current. A 12-volt circuit with a 4-amp currentequals 48 watts of power (12 x 4 =48).

Based on this calculation, we canalso work out voltage if we knowpower and current, and current ifwe know voltage and power:

Power Current = VoltsP I = V

Example: A 48-watt motor with a4-amp current is running at 12 volts.

48 watts 4 amps = 12 voltsCurrent = Power Volts

I = P VExample: a 48-watt motor with a12-volt supply requires a 4-ampcurrent.

48 watts 12 volts = 4 ampsPower (watts) is also equal to thesquare of the current multiplied bythe resistance:

Current x Resistance = PowerI x R = P

EnergyEnergy is a measurement of powerover a period of time. It shows howmuch power is used, or generated,by a device, typically over a periodof an hour. In electrical systems, itis measured in watt-hours (Wh) andkilowatt-hours (kWh).A device that uses 50 watts of

power, has an energy demand of50Wh per hour. A solar panel thatcan generate 50 watts of power perhour, has an energy creationpotential of 50Wh per hour.However, because solar energygeneration is so variable, based ontemperature, weather conditions,the time of day and so on, a newfigure is now often shownspecifically for solar systems: awatt-peak (Wp) rating.A watt-peak rating shows howmuch power can be generated by asolar panel at its peak rating. It hasbeen introduced to highlight the fact

that the amount of energy a solarpanel can generate is variable andto remind consumers that a solarpanel rated at 50 watts is not goingto be producing 50 watt-hours ofenergy every single hour of everysingle day.

A word for non-electriciansRealistically, if you are new toelectrical systems, you should notbe planning to install a big solarenergy system yourself. If you wanta low-voltage system to mount tothe roof of a boat, garden shed orbarn, or if you want to play with thetechnology and have some fun, thengreat: this book will tell youeverything you need to know.However, if the limit of yourelectrical knowledge is wiring aplug or replacing a fuse, you shouldnot be thinking of physically wiring

and installing a solar energy systemyourself without learning moreabout electrical systems andelectrical safety first.Furthermore, if you are planning toinstall a solar energy system to theroof of a house, be aware that inmany parts of the world you need tohave electrical qualifications inorder to carry out even simplehousehold wiring.That does not mean that you cannotspecify a solar energy system,calculate the size you need and buythe necessary hardware for a bigproject. It does mean that you are

going to need to employ a specialistto check your design and carry outthe installation.

In conclusion Understanding the basic

rules of electricity makes itmuch easier to put together asolar electric system

As with many things in life,a bit of theory makes a lotmore sense when you startapplying it in practice

If this is your firstintroduction to electricity,you may find it useful to runthrough it a couple of times

You may also find it usefulto bookmark this section and

refer back to it as you read on

You will also find that,once you have learned a bitmore about solar electricsystems, some of the termsand calculations will start tomake a bit more sense.

If you are not an electrician,be realistic in what you canachieve. Electrics can bedangerous and you do notwant to get it wrong. You cando most of the design workyourself, but you are going toneed to get a specialist in tocheck your design and carry

out the installation.

The FourConfigurations for

Solar Power

There are four differentconfigurations you can choose fromwhen creating a solar electricityinstallation. These are stand-alone(sometimes referred to as off-grid),grid-tie, grid-tie with power backup(also known as grid interactive)and grid fallback.Here is a brief introduction to thesedifferent configurations:

Stand-alone/off-gridWorldwide, stand-alone solarphotovoltaic installations are themost popular type of solarinstallation there is. It is what solarphotovoltaics were originallycreated for: to provide power at alocation where there is no othersource easily available.Whether it is powering a shed light,providing power for a pocketcalculator or powering a completeoff-grid home, stand-alone systemsfundamentally all work in the sameway: the solar panel generatespower, the energy is stored in a

battery and then used as required.In general, stand-alone systems arecomparatively small systems,typically with a peak powergeneration of under one kilowatt.Almost everyone can benefit from astand-alone solar system forsomething, even if it is something asmundane as providing an outsidelight somewhere. Even if you areplanning on something much biggerand grander, it is often a good ideato start with a very small andsimple stand-alone system first.Learn the basics and then progressfrom there.

Examples of simple stand-alone systemsThe vending machineByBox is a manufacturer ofelectronic lockers. These aretypically used for left luggage atrailway stations or at airports, orsituated at shopping malls or fuelstations and used as part of adelivery service for people tocollect internet deliveries, so theydo not need to wait at home.One of the biggest issues withelectronic lockers has often beenfinding suitable locations to placethem where a power source is

available. ByBox overcame thisissue by building an electroniclocker with a solar roof to providepermanent power to the locker.The solar roof provides power to aset of batteries inside the locker.When not in use, the locker itself isin standby mode, thereby consumingminimal power. When a customerwishes to use the locker, they pressthe START button and use thelocker as normal.The benefit to ByBox has beentwofold: they can install a lockerbank in any location, without anydependence on a power supply.

Secondly, the cost of the solarpanels and controllers is often lessthan the cost of installing a separateelectricity supply, even if there isone nearby.Recreational vehiclesHolidaying with recreationalvehicles or caravans is on theincrease, and solar energy ischanging the way people are goingon holiday.In the past, most RV owners electedto stay on larger sites, whichprovided access to electricity andother facilities. As recreationalvehicles themselves become more

luxurious, however, people are nowchoosing to travel to more remotelocations and live entirely off-grid, using solar energy to provideelectricity wherever they happen tobe. Solar is being used to provideall the comforts of home, whilstoffering holidaymakers the freedomto stay wherever they want.

Grid-tieGrid-tie is gaining popularity inEurope and the United States. Thisis due to the availability of grants toreduce the installation costs and theability to earn money by sellingelectricity back into the electricitycompanies through a feed-in tariff.Feed-in tariff schemes vary aroundthe world and are not availableeverywhere. Where they exist, yourlocal electricity company buyselectricity from solar producers atan agreed rate per kilowatt-hour. Insome countries, this price has beenset at an inflated rate by government

in order to encourage people toinstall solar. In other countries andregions, the price is agreed by theelectricity companies themselves.In a grid-tie system, your home runson solar power during the day. Anysurplus energy that you produce isthen fed into the grid. In theevenings and at night, when yoursolar energy system is notproducing electricity, you then buyyour power from the electricitycompanies in the usual way.The benefit of grid-tie solarinstallations is that they reduce yourreliance on the big electricity

companies and ensure that more ofyour electricity is produced in anenvironmentally efficient way.One disadvantage of most grid-tiesystems is that if there is a powercut, power from your solar array isalso cut.Grid-tie can work especially wellin hot, sunny climates, where peakdemand for electricity from the gridoften coincides with the sun shining,thanks to the high power demand ofair conditioning units. Grid-tie alsoworks well where the owners usemost of the power themselves.

An example of a grid-tiesystemSi Gelatos is a small Florida-basedice-cream manufacturer. In 2007,they installed solar panels on theroof of their factory to providepower and offset some of the energyused in running their cold storagefacility.Running industrial freezers isextremely expensive and consumesa lot of power, explains DanFoster of Si Gelatos. Realistically,we could not hope to generate all ofthe power from solar, but we felt itwas important to reduce our overall

power demand and solar allowedus to do that.Cold storage facilities consumemost of their power during the dayin the summer, when solar isrunning at its peak. Since installingsolar power, Si Gelatos has seen itsoverall energy consumption drop by40% and now hardly takes anypower from the utilities during peakoperating times.Solar has done three things for ourbusiness, says Dan. Firstly, it is avery visible sign for our staff thatwe are serious about theenvironment. This in turn has made

our employees more aware that theyneed to do their bit by making surelights and equipment are switchedoff when they are not needed.Secondly, it shows our customersthat we care for the environment,which has definitely been good forgoodwill and sales. Thirdly, andmost importantly, were genuinelymaking a real contribution to theenvironment, by reducing ourelectricity demand at the time ofday when everyone elses demandfor electricity is high as well.

Grid-tie with powerbackup (grid interactive)Grid-tie with power backup alsoknown as a grid interactive system combines a grid-tie installationwith a bank of batteries.As with grid-tie, the concept is thatyou use power from your solararray when the sun shines and sellthe surplus to the power companies.Unlike a standard grid-tie system,however, a battery bank providescontingency for power cuts so thatyou can continue to use power fromyour system.

Typically, you would set upprotected circuits within yourbuilding that will continue toreceive power during a poweroutage. This ensures that essentialpower remains available forrunning lights, refrigeration andheating controllers, for example,whilst backup power is not wastedon inessential items such astelevisions and radios.If there is a potential for mainpower to be lost for several days, itis also possible to design a systemto incorporate other powergenerators into a grid interactive

system, such as a generator. Thiswould allow a grid interactivesystem to work as a highly efficientuninterruptable power supply(UPS) for extended periods of time.The cost of a grid-tie system withpower backup is higher than astandard grid-tie system, because ofthe additional cost of batteries andbattery controllers. Typically,having power backup will add1220% of additional costs over astandard grid-tie system.As with normal grid-tie systems, itis possible to sell surplus powerback to the utility companies in

some countries, allowing you toearn an income from your solarenergy system.

An example of a gridinteractive systemGrid interactive systems are gainingpopularity with rural farms in theUnited Kingdom, where even shortpower blackouts can causesignificant disruption.Traditionally, farms have counteredthis by using generators to providelight and power. However, between2009 and 2011, when the UKGovernment were offering large

incentives for installing solarpower, many farmers fitted gridinteractive systems onto theirbuildings, providing themselveswith an income by sellingelectricity to the electricity utilitycompanies and giving themselvesbackup power in case of a powerblackout.The additional cost of installing agrid interactive system over astandard grid-tie system is morethan offset by the low running costsand ease of use of the system.Farmers do not need to buy and rungenerators and the system is almostentirely maintenance-free. This is a

big contrast with generator systems,which need to be tested and runregularly in order to ensure they areworking effectively.

Grid fallbackGrid fallback is a lesser-knownsystem that makes a lot of sense forsmaller household solar powersystems. For most household solarinstallations where solar is beinginstalled for technical orenvironmental reasons, gridfallback is my preferred solution.Operationally it is effective, it iscost-effective and it isenvironmentally extremely efficient.With a grid fallback system, thesolar array generates power, whichin turn charges a battery bank.Energy is taken from the battery and

run through an inverter to powerone or more circuits from thedistribution panel in the house.When the batteries run flat, thesystem automatically switches backto the grid power supply. The solararray then recharges the batteriesand the system switches back tosolar power.With a grid fallback system, you donot sell electricity back to theelectricity companies. All thepower that you generate, you useyourself. This means that some ofthe grants that are available forsolar installations in some countries

may not be available to you. It alsomeans that you cannot benefit fromselling your electricity back to theelectricity companies.For this reason, grid fallback makesmore sense in countries where thereis no feed-in tariff available, suchas India, or in countries likeAustralia that have financialincentives available for both grid-tied and off-grid systems.Grid fallback systems provide mostof the benefits of a grid interactivesystem, with the additional benefitthat you use your own power whenyou need it, rather than when the sun

is shining. This reduces yourreliance on external electricitysupplies during peak load periods,which ensures that your system hasan overall environmental benefit.The other significant benefit of agrid fallback system is cost: youcan genuinely build a useful gridfallback system to power one ormore circuits within a house for avery small investment and expand itas budget allows. I have seen gridfallback systems installed for under400 ($680), providing a usefulamount of power for a home. Incomparison, even a very modestgrid-tie system costs several

thousands of pounds.There is a crossover point where agrid-tie system works out morecost-effective than a grid fallbacksystem. At present, that crossoverpoint is around the 1kWh mark: ifyour system is capable ofgenerating more than 1kW ofelectricity per hour, a grid-tiesystem may be more cost-effective.If your system generates less than1kW of electricity per hour, a gridfallback system is almost certainlycheaper.Unless you are looking to invest asignificant amount of money on a

larger grid-tie system in order toproduce more than 1 kW of powerper hour, or if you want to takeadvantage of feed-in tariffs, a gridfallback solution is certainly worthinvestigating as an alternative.

An example of a grid fallbacksystemBack in 2001, Colin Metcalfeinstalled a solar panel onto the roofof his garage, in order to charge anold car battery, which in turnpowered a single light and a smallinverter. After a power cut thatwinter, Colin decided to expand hissystem in order to provide basic

power to his house.I wanted to ensure I always hadenough power in my home to powerlights and to ensure my heatingsystem would work, explainedColin. I have gas heating, but thecontrollers are all electric, whichmeans that if there is a power cut, Ihave no heating at all. In addition, Iliked the idea of free electricity thatwas generated in anenvironmentally friendly way.Colin upgraded his system bit bybit, as funds allowed. Anelectrician fitted a new distributionpanel (consumer unit) for my

essential circuits, and this wasconnected up to the main panel viaan automatic transfer switch. Then Iadded additional solar panels andbatteries over the years as I couldafford them.This automatic transfer switchmeant the essential circuits wouldreceive power from the solar arrayor the batteries while power wasavailable, but switch back to utilitypower when the batteries ran flat.Originally, the system providedaround half the power he needed,but as he has added to the system,more and more of his power nowcomes from his solar array. Today

I have around 1.4kW of solarpanels on the roof of my garage,says Colin. They look a bit odd asno two panels are alike, as I havebought them bit by bit as fundsallow, but they now provide all thepower I need around the year for allmy essential circuits.

Grid failoverAlternatively, you can configure agrid fallback system as a gridfailover system.A grid failover system kicks inwhen there is a power failure fromyour main electricity supply. In

effect, it is an uninterruptablepower supply, generating its powerfrom solar energy.The benefit of this configuration isthat if you have a power cut, youhave contingency power. Thedisadvantage of this configuration isthat you are not using solar powerfor your day-to-day use.Although rare in Europe andAmerica, grid failover systems usedto be more common in countrieswhere power failures arecommonplace. In Africa and inmany parts of Asia, grid failoversystems reduce the reliance on

power generators for lighting andbasic electricity needs.However, in most cases, customershave found that a grid fallback orgrid interactive system is moresuitable for their needs. I am awareof two grid failover systems thathave been installed in the past: bothof these have since beenreconfigured as grid fallbacksystems.

How grid-tie systemsdiffer from stand-aloneGenerally, stand-alone and smallergrid fallback systems run at lowvoltages, typically between 12 and48 volts. This is because batteriesare low-voltage units and sobuilding a stand-alone system at alow voltage is a simple, flexibleand safe approach.Grid-tie systems tend to be largerinstallations, often generatingseveral kilowatts of electricity eachhour. As the electricity is requiredas a high-voltage supply, it is moreefficient to connect multiple solar

panels together to produce a highvoltage circuit, rather than use aninverter to step up the voltage. Thishigh-voltage DC power is thenconverted into an AC current by asuitable grid-tie inverter.Grid-tie systems either link multiplesolar panels together to produce asolar array voltage of severalhundred volts before running to theinverter, or have a small inverterconnected to each solar panel tocreate a high-voltage AC supplyfrom each panel.The benefit of this high voltage isefficiency. There is less power loss

running high-voltage, low-currentelectricity through cables from thesolar array.For stand-alone battery-basedsystems, low-voltage is the bestsolution, as the battery banks tend towork better as low-voltage energystores. For grid-tie systems wherethe energy is not being stored in abattery bank, the higher-voltagesystems are the best solution.Neither approach is inherentlybetter: it all depends on the typeof system you are designing.

In conclusion Solar can be used in a

number of different ways andfor many differentapplications

Stand-alone systems are thesimplest and easiest tounderstand. They tend to becomparatively small systems,providing power where noother power source is easilyavailable

With grid-tie, your solarenergy system generateselectricity that is then used

normally. Any excesselectricity production isexported onto the grid

Grid-tie with power backup(also known as gridinteractive) provides youwith the benefits of a grid-tiesystem with the added benefitthat power remains availableeven if electricity to your areais cut off

Grid fallback systems havemore in common with stand-alone systems than grid-tiesystems. In design they arevery similar to stand-alone

systems, with an inverterrunning from a bank ofbatteries and an automatictransfer switch to switchpower between the solarenergy system and the gridpower supply

Grid failover systems arecomparatively rare now, butprovide uninterruptablepower supplies using solar asthe backup source

Grid-tie systems have adifferent design to stand-alone systems. They tend tobe high-voltage systems,

whereas stand-alone systemsrun at much lower voltages

Components of aSolar Electric System

Before I get into the detail aboutplanning and designing solarelectric systems, it is worthdescribing all the differentcomponents of a system andexplaining how they fit together.Once you have read this chapter,you will have a reasonable grasp ofhow a solar energy system fitstogether.I deliberately do not go into muchdetail at this stage: all I am doing is

providing an overview for now.The detail can come later.

Solar panelsThe heart of a solar electric systemis the solar panel itself. There arevarious types of solar panel and Iwill describe them all in detail lateron.Solar panels or, more accurately,photovoltaic solar panels, generateelectricity from the sun. The morepowerful the suns energy, the morepower you get, although solarpanels continue to generate smallamounts of electricity in the shade.Most solar panels are made up ofindividual solar cells, connectedtogether. A typical solar cell will

only produce around half a volt, soby connecting them together inseries inside the panel, a moreuseful voltage is achieved.Most solar panels are rated as 12-volt solar panels, althoughhigher-voltage panels are alsoavailable. A 12-volt solar panelproduces around 1418 volts whenput under load. This allows a singlesolar panel to charge up a 12-voltbattery.Incidentally, if you connect avoltmeter up to a solar panel whenit is not under load, you may wellsee voltage readings of up to 26

volts. This is normal in an opencircuit on a solar panel. As soon asyou connect the solar panel into acircuit, this voltage level will dropto around 1418 volts.Solar panels can be linked togetherto create a solar array. Connectingmultiple panels together allows youto produce a higher current or to runat a higher voltage:

Connecting the panels inseries allows a solar array torun at a higher voltage.Typically, 24 volts or 48volts in a stand-alone system,or up to several hundred volts

in a grid-tie system

Connecting the panels inparallel allows a solar arrayto produce more power whilemaintaining the same voltageas the individual panels

When you connect multiplepanels together, the power ofthe overall system increases,irrespective of whether theyare connected in series or inparallel

In a solar array where the solarpanels are connected in series (asshown in the following diagrams),you add the voltages of each panel

together and add the wattage ofeach panel together to calculate themaximum amount of power andvoltage the solar array willgenerate.

A solar array madeof four solar panelsconnected in series.If each individualpanel is rated as a

12-volt, 12-wattpanel, this solar

array would be ratedas a 48-volt, 48-wattarray with a 1 amp

current.In a solar array where the panelsare connected in parallel (as shownin the diagram below), you take theaverage voltage of all the solarpanels and you add the wattage ofeach panel to calculate themaximum amount of power thesolar array will generate.

A solar array madeof four solar panels

connected inparallel. With eachpanel rated as a 12-volt, 12-watt panel,

this solar arraywould be rated as a

12-volt, 48-wattarray with a 4 amp

current.I will go into more detail laterabout choosing the correct voltagefor your system.

BatteriesExcept in a grid-tie system, wherethe solar array connects directly toan inverter, solar panels rarelypower electrical equipmentdirectly. This is because the amountof power the solar panel collectsvaries depending on the strength ofsunlight. This makes the powersource too variable for mostelectrical equipment to cope with.In a grid-tie system, the inverterhandles this variability: if demandoutstrips supply, you will get powerfrom both the grid and your solarsystem. For a stand-alone or a grid

fallback system, batteries store theenergy and provide a constantpower source for your electricalequipment.Typically, this energy is stored indeep cycle lead acid batteries.These look similar to car batteriesbut have a different internal design.This design allows them to beheavily discharged and rechargedseveral hundred times over.Most lead acid batteries are 6-voltor 12-volt batteries and, like solarpanels, these can be connectedtogether to form a larger batterybank. Like solar panels, multiple

batteries used in series increase thecapacity and the voltage of a batterybank. Multiple batteries connectedin parallel increase the capacitywhilst keeping the voltage the same.

ControllerIf you are using batteries, your solarelectric system is going to require acontroller in order to manage theflow of electricity (the current) intoand out of the battery.If your system overcharges thebatteries, this will damage andeventually destroy them. Likewise,if your system completelydischarges the batteries, this willquite rapidly destroy them. A solarcontroller prevents this fromhappening.There are a few instances where asmall solar electric system does not

require a controller. An example ofthis is a small battery top-up solarpanel that is used to keep a carbattery in peak condition when thecar is not being used. These solarpanels are too small to damage thebattery when the battery is fullycharged.In the majority of instances,however, a solar electric systemwill require a controller in order tomanage the charge and discharge ofbatteries and keep them in goodcondition.

InverterThe electricity generated by a solarelectric system is direct current(DC). Electricity from the grid ishigh-voltage alternating current(AC).If you are planning to run equipmentthat runs from grid-voltageelectricity from your solar electricsystem, you will need an inverter toconvert the current from DC to ACand convert the voltage to the samevoltage as you get from the grid.Traditionally, there is usually onecentral inverter in a solar system,either connecting directly to the

solar array in a grid-tie system, orto the battery pack in an off-gridsystem. A more recent invention hasbeen the micro inverter.Micro-inverters are connected toindividual solar panels so that eachindividual panel provides ahigh-voltage alternating current.Solar panels with micro-invertersare typically only used with grid-tiesystems and are not suitable forsystems with battery backup. Forgrid-tie systems, they do offer somesignificant benefits over the moretraditional big box inverter,although the up-front cost iscurrently higher.

Inverters are a big subject all ontheir own. I will come back todescribe them in much more detaillater on in the book.

Electrical devicesThe final element of your solarelectric system is the devices youplan to power. Theoretically,anything that you can power withelectricity can be powered by solar.However, many electrical devicesare very power hungry, whichmakes running them on solar energyvery expensive!Of course, this may not be so muchof an issue if you are installing agrid-tie system: if you have veryenergy-intensive appliances thatyou only use for short periods, theimpact to your system is low. In

comparison, running high-powerappliances on an off-grid systemmeans you have to have a morepowerful off-grid solar energysystem to cope with the peakdemand.Low-voltage devicesMost off-grid solar systems run atlow voltages. Unless you areplanning a pure grid-tie installation,you may wish to consider running atleast some of your devices directlyfrom your DC supply rather thanrunning everything through aninverter. This has the benefit ofgreater efficiency.

Thanks to the caravanning andboating communities, lots ofequipment is available to run from a12-volt or 24-volt supply: lightbulbs, refrigerators, ovens, kettles,toasters, coffee machines,hairdryers, vacuum cleaners,televisions, radios, air conditioningunits, washing machines and laptopcomputers are all available to runon 12-volt or 24-volt power.In addition, thanks to the recentuptake in solar installations, somespecialist manufacturers arebuilding ultra low-energyappliances, such as refrigerators,

freezers and washing machines,specifically for people installingsolar and wind turbine systems.You can also charge up mostportable items such as MP3 playersand mobile phones from a 12-voltsupply.High-voltage devicesIf running everything at low voltageis not an option, or if you are usinga grid-tie system, you use aninverter to run your electricaldevices.

Connecting everythingtogetherA stand-alone system

The simplified block diagramabove shows a simple stand-alone

solar electric system. Whilst thedetail will vary, this design formsthe basis of most stand-alonesystems and is typical of theinstallations you will find incaravans, boats and buildings thatdo not have a conventional powersupply.This design provides bothlow-voltage DC power for runningsmaller electrical devices andappliances such as laptopcomputers and lighting, plus ahigher-voltage AC supply forrunning larger devices such aslarger televisions and kitchenappliances.

In this diagram, the arrows showthe flow of current. The solarpanels provide the energy, which isfed into the solar controller. Thesolar controller charges thebatteries. The controller alsosupplies power to the low-voltagedevices, using either the solarpanels or the batteries as the sourceof this power.The AC inverter takes its powerdirectly from the battery andprovides the high-voltage ACpower supply.

A grid-tie system using a

single central inverter

This simplified block diagramshows a simple grid-tie system,typical of the type installed in manyhomes today. The solar panels areconnected to the grid-tie inverter,

which feeds the energy into themain supply. Electricity can be usedby devices in the building or fedback out onto the grid, depending ondemand.The grid-tie inverter monitors thepower feed from the grid. If itdetects a power cut, it also cutspower from the solar panels toensure that no energy is fed back outonto the grid.The grid-tie meter monitors howmuch energy is taken from the gridand how much is fed back into thegrid using the solar energy system.

A grid-tie system usingmultiple micro-invertersA grid-tie system using micro-inverters is similar to the oneabove, except that each solar panelis connected to its own inverter,and the inverters themselves aredaisy-chained together, convertingthe low-voltage DC power fromeach solar panel into a high-voltageAC power supply.

In conclusion There are various

components that make up asolar electric system

Multiple solar panels canbe joined together to create amore powerful solar array.

In a stand-alone system, theelectricity is stored inbatteries to provide an energystore and provide a moreconstant power source. Acontroller manages thebatteries, ensuring thebatteries do not get

overcharged by the solararray and are notover-discharged by thedevices taking current fromthem

An inverter takes the DCcurrent from the solar energysystem and converts it into ahigh-voltage AC current thatis suitable for runningdevices that require gridpower

Generally, it is moreefficient to use the electricityas a DC supply than an ACsupply

The Design Process

No matter what your solar energysystem is for, there are seven stepsin the design of every successfulsolar electric installation:

Scope the project Calculate the amount of

energy you need

Calculate the amount ofsolar energy available

Survey your site Size up the solar electric

system

Select the right componentsand work out full costs

Produce the detailed designThe design process can be mademore complicated, or simplified,based on the size of the project. Ifyou are simply installing an off-the-shelf shed light, for instance, youcan probably complete the wholedesign in around twenty minutes. If,on the other hand, you are lookingto install a solar electric system in abusiness to provide emergency sitepower in the case of a power cut,your design work is likely to takeconsiderably more time.

Whether your solar electric systemis going to be large or small,whether you are buying anoff-the-shelf solar lighting kit ordesigning something from scratch, itis worth following this basic designprocess every time. This is trueeven if you are installing an off-the-shelf system. This ensures that youwill always get the best from yoursystem and will provide you withthe reassurance that your solarenergy system will achieveeverything you need it to do.

Short-cutting the designworkHaving said that doing the designwork is important, there are someuseful online tools to help make theprocess as easy as possible.Once you have scoped your project,the Solar Electricity Handbookwebsite(www.SolarElectricityHandbook.comincludes a number of online toolsand calculators that will help youcarry out much of the design work.The solar irradiance tables andsolar angle calculators will allow

you to work out how much solarenergy is available at your location,whilst the off-grid project analysisand grid-tie project analysisquestionnaires will each generateand e-mail to you a full report foryour proposed system, includingcalculating the size of system yourequire and providing a costestimate.Of course, there is a limit to howmuch a set of online solar tools canhelp you in isolation, so you willstill need to carry out a site surveyand go through componentsselection and detailed designyourself, but these tools will allow

you to try several differentconfigurations and play out whatif scenarios quickly and easily.Incidentally, whilst some of thesetools ask you for an e-mail address(in order to send you your report),your e-mail address is not storedanywhere on the system. Other thanthe report that you request, you willnever receive unsolicited e-mailsbecause of entering your e-mailaddress.

Solar energy andemotionsDesign can often seem to be apurely analytical and rationalprocess. It should not be. All greatdesigns start with a dream.For many people, choosing solarenergy is often an emotionaldecision: they want a solar energysystem for reasons other than justthe purely practical. Some peoplewant solar energy because theywant to do their bit for theenvironment, others want the verylatest technology, or want to usesolar simply because it can be

done. Others want solar energybecause they see the opportunity toearn money. I suspect that for mosthomeowners, the reasons are acombination of the above.It is so important that the emotionalreasons for wanting something arenot ignored. We are not robots. Ouremotions should be celebrated, notsuppressed: the Wright brothersbuilt the first aircraft because theywanted to reach the sky. NASA senta man to the moon because theywanted to go further than anyonehad ever done before. Neitherundertaking could be argued as

purely rational; they were theresults of big dreams.It is important to acknowledge thatthere are often hidden reasons forwanting solar energy. Sadly, thesereasons often do not make it downonto a sheet of paper in a designdocument or onto a computerspreadsheet. Sometimes, the personmaking the decision for buyingsolar energy is secretly worried thatif they voice their dreams, they willappear in some way irrational.The reality is that it is often a goodthing if there is an emotionalelement to wanting a solar energy

system. By documenting thesereasons, you will end up with abetter solution. For instance, if theenvironmental benefits are top ofyour agenda, you will use yoursolar energy system in a differentway to somebody who is looking atsolar purely as a businessinvestment.By acknowledging these reasonsand incorporating them into thedesign of your system, you will endup with a far better system. Notonly will you have a system thatworks in a practical sense, it willalso achieve your dream.

In conclusion No matter how big or small

your project, it is important todesign it properly

There are online toolsavailable to help you with thecalculations and to speed upthe work

Do not ignore the emotionalreasons for wanting a solarenergy system. You are ahuman being: you are allowedto dream

Scoping the Project

As with any project, before youstart, you need to know what youwant to achieve. In fact, it is one ofthe most important parts of thewhole project. Get it wrong and youwill end up with a system that willnot do what you need it to.

It is usually best to keep yourscope simple to start with. You canthen flesh it out with more detaillater.

Here are some examples of asuitable scope:

To power a light and aburglar alarm in a shed on anallotment

To provide power forlighting, a kettle, a radio andsome handheld power tools ina workshop that has noconventional electricalconnection

To provide enough powerfor lighting, refrigeration anda TV in a holiday caravan

To provide lighting andpower to run four laptopcomputers and the telephone

system in an office during apower cut

To charge up an electricbike between uses

To provide an off-gridholiday home with its entireelectricity requirements

To reduce my carbonfootprint by producingelectricity for all my homerequirements

To run an electric carentirely on solar energy

From your scope, you can startfleshing this out to provide some

initial estimates on powerrequirements.

As mentioned in the previouschapter, I have created two onlineSolar Project Analysis tools, onefor grid-tie systems and one for off-grid systems. You can find both ofthese tools on my websitewww.SolarElectricityHandbook.comYou will still need to collect thebasic information to work with, butall the hard work is done for you.This tool will produce a completeproject scope, work out the likelyperformance of your solar energysystem and provide some ballparkcost estimates.

For the purpose of these next fewchapters, I am going to use theexample of providing a small off-grid holiday home with its entireelectricity requirements.This is a big project. In reality ifyou have little or no experience ofsolar electric systems or householdelectrics you would be best startingwith something smaller. Goingcompletely off-grid is an ambitiousproject, but for the purposes ofteaching solar electric systemdesign, it is a perfect example: itrequires a detailed design thatcovers all of the aspects of

designing a solar energy system.

Designing grid-tie or gridfallback systemsFor our sample project, grid-tie isnot an option as we are using solarpower as an alternative toconnecting our site to the electricitygrid.However, grid-tie is becoming apopular option, especially in thesouthern states of the United Statesand in European countries likeSpain, Germany and the UnitedKingdom where generousgovernment subsidies and feed-intariffs are available.

In terms of scoping the project, itmakes little difference whether youare planning a grid-tie or gridfallback system or not: the steps youneed to go through are the same.The only exception, of course, isthat you do not need to take intoaccount battery efficiencies withgrid-tie.The biggest difference with a grid-tie or grid fallback system is thatyou do not have to rely on yoursolar system providing you with allyour electricity requirements: youwill not be plunged into darkness ifyou use more electricity than you

generate.This means that you can start with asmall grid-tie or grid fallbacksystem and expand it later on asfunds allow.Despite that, it is still a good ideato go through a power analysis aspart of the design. Even if you donot intend to produce all the poweryou need with solar, having apower analysis will allow you tobenchmark your system and willhelp you size your grid-tie system ifyou aim to reduce your carbonfootprint by providing theelectricity companies with as much

power as you buy back.Most grid-tie systems are sized toprovide more power than you needduring the summer and less than youneed during the winter. Over aperiod of a year, the aim is togenerate as much power as you use,although on a month-by-month basisthis may not always be the case.Many solar companies claim thatthis then provides you with acarbon neutral system: you areselling your excess power to theelectricity companies and thenbuying the same amount ofelectricity back when you need it.

If this is what you are planning todo with your grid-tie system, yourscope is much simpler. You need toget your electricity bills for the pastyear and make a note of how muchelectricity you have used over theyear. Then divide this figure by thenumber of days in the year to workout a daily energy usage and ensureyour system generates this as anaverage over the period of a year.Because you are not generatingenough electricity during the wintermonths in a carbon neutral grid-tiesystem, you need fewer solar panelsthan you would need to create an

entirely stand-alone system.

Comparing supply withdemandIf you are designing a grid-tiesystem, it can be interesting tocompare the supply of solar energywith your electricity usage pattern.By comparing supply with demand,you can see how closely solarenergy production matches yourown usage and this, in turn, can beused as an indicator to identify howenvironmentally beneficial solarenergy is for you.To do this, you will need to

ascertain your monthly electricityusage for each month of the year.Your electricity supplier mayalready provide you with thisinformation on your electricity bill.If not, you should be able to requestthis from them.Once you have this information,visitwww.SolarElectricityHandbook.comand fill in the Grid-Tie SolarProject Analysis, including yourindividual monthly consumptionfigures. In the report that is e-mailed to you, you will see a chartthat allows you to see how closelyyour electricity usage maps onto

solar energy production.This report will also provide youwith an approximate estimate forthe carbon footprint for eachkilowatt-hour of electricity youproduce from your solar array,based on the production andinstallation of your solar array andthe likely amount of energy that itwill generate during its lifetime.Based on this, it is possible to seewhether installing solar energy islikely to produce real-worldenvironmental savings.

Fleshing out the scopeNow we know the outline scope ofour project, we need to quantifyexactly what we need to achieveand work out some estimates forenergy consumption.Our holiday home is a small two-bedroom cottage with a solid fuelcooker and boiler. The cost ofconnecting the cottage to the grid is4,500 (around $7,200) and Isuspect that solar electric powercould work out significantlycheaper.The cottage is mainly used in thespring, summer and autumn, with

only a few weekend visits duringthe winter.Electricity is required for lightingin each room, plus a courtesy lightin the porch, a fridge in the kitchenand a small television in the sittingroom. There also needs to besurplus electricity for charging up amobile phone or MP3 player andfor the occasional use of a laptopcomputer.Now we have decided whatdevices we need to power, we needto find out how much energy eachdevice needs, and estimate the dailyusage of each item.

In order to keep efficiency high andcosts low, we are going to workwith low-voltage electricswherever possible. The benefits ofusing low-volt devices rather thanhigher grid-voltage are twofold:

We are not losing efficiencyby converting low-volt DCelectrics to grid-voltage ACelectrics through an inverter.

Many electronic devicesthat plug into a grid-voltagesocket require a transformerto reduce the power backdown to a low DC current,thereby creating a second

level of inefficiencyMany household devices, likesmaller televisions, music systems,computer games consoles andlaptop computers, have externaltransformers. It is possible to buytransformers that run on 12-volt or24-volt electrics rather than the ACvoltages we get from grid power,and using these is the most efficientway of providing low-voltagepower to these devices.There can be disadvantages oflow-voltage configurations,however, and they are not the rightapproach for every project:

If running everything at1224 volts requires asignificant amount ofadditional rewiring, the costof carrying out the rewiringcan be much higher than thecost of an inverter and aslightly larger solar array

If the cable running betweenyour batteries and yourdevices is too long, you willget greater power lossesthrough the cable at lowervoltages than you will athigher voltages

If you already have wiring in place

to work at grid-level voltages, it isoften more appropriate to run asystem at grid voltage using aninverter, rather than running thewhole system at low voltage. If youhave no wiring in place, running thesystem at 12 or 24 volts is oftenmore suitable.

Producing a poweranalysisThe next step is to investigate yourpower requirements by carrying outa power analysis, where youmeasure your power consumption inwatt-hours.

You can find out the wattage ofhousehold appliances in one of fourways:

Check the rear of theappliance, or on the powersupply

Check the product manual

Measure the watts using awatt meter

Find a ballpark figure forsimilar items

Often a po