diy power solar 1

7/30/2019 DIY Power Solar 1

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IntroductionInthisguidewewillbetakingalookattheeverevolvingworldofsolar

photovoltaics,orPV for short. Inessence,wewillbeexamininghow

we have learned to take the suns energy and convert that into

electricity. Thesunhasanenormousamountofenergy,evidentbythe

sunburnswehaveallputourselvesthrough. Humanshave learnedto

passively harness this energy for thousands of years, using the suns

raystowarmtheirhomesordrytheirfoodandclothing. Notuntilthe

latter part of the 19th century, however, did we discover how to

convertthosepowerfulraysofsunlight intousableenergy intheform

ofdirectcurrent (DC)electricity. This importantbreakthroughwillbe

discussed, with the various types of solar cells that have been

developedandtheprosandconsofeach. Themaincomponentsofa

solarelectric

system

will

be

identified

and

discussed,

and,

finally,

we

willdiscussthestepstowardsconstructingyourownsolarPVpanelto

harnessthesunsfullpotential.


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PVHistoryTherootsofphotovoltaicscanbetracedallthewaybackto1839when

19yearoldphysicistAlexandreEdmondBecquerelwasexperimenting

withanelectrolyticcellmadeupoftwometalelectrodesandstumbled

uponthe

photovoltaic

concept.

Forty

years

later,

in

1873,

Willoughby

Smith discovered the photoconductivity of selenium and in 1883

Charles Fritts, an American inventor, describes the first solar cell

derivedfromseleniumwafers.

Even Nikola Tesla and Albert Einstein got into the concept of

photovoltaicsintheearlyyears,withTeslareceivingaUSpatentforthe

"method of utilizing, and apparatus for the utilization of, radiant

energy"andEinsteinreceivingtheNobelprizefora1904paperonthe

photoelectriceffect. Then, in1954BellLabsexhibits firsthighpower

silicon PV cell. Based upon the momentum of the photovoltaic

sciences, theNewYorkTimes forecasts that solarcellswilleventually


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leadtoasourceof"limitlessenergyofthesun". This,consideringthat

the cellsback thenwereonlyabout5.5%efficientcompare that to

the20%+

efficient

cells

now!

From

there

the

commercial

age

of

photovoltaicsbeganand someof thenamesyouhearnow, including

NASA,SiemensandSharpgotinvolvedandtherestishistory.

TheScienceofSolarandElectricityThesunsraysarecomprisedofmanytinyphotonsoflight. These

photons,whiletechnicallymatterless,dopossessenergy. Theselittle

ballsofenergymultipliedmanytimesoverstrikethesurfaceofthe

solarpanelandcausethenecessarycommotiontoknocktheelectron

freeinthesolarcell. Solarcellsaretypicallymadeupofhighgrade

siliconasthesemiconductor,butdotoitschemistrythisaloneisnot

sufficienttocreateanefficientsolarcell. However,ifadopingagentis

introduced,commonlyboronandphosphorus,itcausesanunbalanced

chemicalstructure,withasurplusofelectronsinthesiliconphosphorus


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layeronthefrontsurfaceofthecells. Thiscreatesanegativecharge

andisreferredtoastheNlayer. Boronisoftenaddedtothebacklayer

ofthe

cells,

creating

asilicon

boron

mixture

that

has

apositive

charge

andcaneasilyacceptextraelectrons,oftenreferredtoasthePlayer.

Inbetweenthetwoisapositive/negativejunction,orP/Njunction.

Thismiddlejunctionbetweentheothertwolayershasaneutralcharge

andwillonlyallowtheflowofelectronsinonedirection;fromtheP

layertotheNlayer. Inherently,electronsliketomovefromnegativeto

positivecharges,andtheonlypathwayfortheelectronstoreturnto

thePlayerfromtheNlayeristhroughtheconductor,whichoffers

themverylittleresistanceandallowsthemtoflowoutofthesurfaceof

thesolarcell. Itthenreturnstothesolarcellthroughthecompleted

circuitintothePlayer. Bytakingthisflowofelectrons,orelectricity,

andattachingaloadtoitscircuityoumaketheelectronsdoworkand

haveusable,renewableenergy.


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Wheneachphotonhitsthecell itcarriesenoughenergyfromthesun

withittoexciteoneelectroninthecellintothemovementthatcreates

the electricity. That is where the importance of the sun comes in.

Without an outside energy source, the circuit would not flow.

However,whenthereisenoughsunlight,theelectronsfromthePlayer

leave theirunbalancedatomand leaveholesbehind,whichareeasily

filledbynewelectrons intheNlayerreturningfromtheirwork inthe


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circuit. Thisprocesshappensuntil the sun sets for thedayand then

theylayinwaitforanewday. Ablockingdiodeonthepositiveleadout

ofthe

panel

prevents

any

current

from

flowing

back

into

the

cells

at

nightanddraining thebatteries. Whenwired together thesolarcells

formasolarpanel. Whensolarpanelsarewiredtogethertheyforma

solararray.

Solar cells are typically comprised of one of three solid types:

monocrystalline, polycrystalline and amorphous cells. While many

differentmaterialsareusedtomakethesolarcells,themostcommon

elementusedforthemono andpolycrystallinecellsissilicon. Silicon,

whilethesecondmostabundantelementontheEarthscrust,mustbe

of thehighest grade to beused in solar cellproduction. Itmustbe

cleanedofany impuritiesandsuperheatedtoformthe ingotsthatare

thenthinlycut intothecrystallinesolarcells. Amorphousorthin film

cellsare comprisedofmanydifferentelements, commonly cadmium,

tellurideorindium,amongothers. Thesecellsaretypicallyappliedtoa


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flexible substrate such as aluminum, certainplasticsoreven glassby

evermoretechnicallyadvancedmethods.

Of the three, monocrystalline cells are the most efficient, while

polycrystalline cells are a close second. Amorphous cells, while

considerably less efficient tend to cost only a fraction of what the

crystalline cellsdo. Thecrystalline cells comprise thepanels thatare

typically used in residential installation. Because they are so much

moreefficientthattheamorphouscellsyoudonotneedasmuchroof

orground space toprovideenoughenergy tooffseta typicalhomes

usage. However,duetoamorphouspanels lowcoststheytendtobe

preferredformanycommercialapplications,sincespaceisnotanissue

inmanycases.

Solarcellsoutputpowerthatcanbemeasured involtsandamps. To

comparethis

concept

to

water,

the

voltage

of

adevice

can

be

related

tothepressureofthewater,whiletheamps (measured inamps)can


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be compared to the amount ofwater flowing. This is an important

concepttoremember.

Whenyouknowboththevoltageandcurrent(oramps)ofasolarcell

youcanmultiplythemtogethertofind itsrating inwatts. Completed

solar panels are rated in watts, so its important to understand this

formula. Knowingjusttwopartsoftheformula,youcanalsoderivethe

third component. For example, understanding the basic formula V

(volts)xA(amps)=W(watts)allowsustoderivetheampsfroma100

watt18voltpanel.

VxA

=W

or

W/V=A

100w/18v=5.55ampsthatthepanelwilldeliver


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Thebest

way

to

measure

this

output

from

the

cells

is

to

use

a

multimeter and touch thepositive andnegative leads to thepositive

and negative conductors on the solar cell under full sun. Once you

know the voltage and amperageof your solar cells you canbegin to

wirethemtogethertoformthesolarpanel.


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And since the solar cells physical size determines the current output

(assumingthesametypeofcellsarebeingused)wecanparallelcells,

orstrings

of

cells,

together

to

achieve

the

proper

current.

For

example,

ifyouhaveasolarcellwith3.5ampsandyouwire20oftheminseries

thiswouldgiveusabout10voltswhenexposedtothesun,whilestill

outputting theoriginal3.5amps. On theotherhand, ifyou take this

samecellwith .5voltsand3.5ampsandwire20ofthem together in

parallelyouwouldhaveapanelwith35ampsbutstilljust.5volts.

Thesameconceptapplieswhenwiringmultiplepanelstogether. Many

largersolar invertershaveavoltagewindow,usuallybetweenabout

150450 volts (dependingon the inverter size andmanufacturer). In

order to kick the inverter on we would have to wire enough solar

panels together to raise the voltage high enough for the inverter to

operate properly. You can wire multiple solar panels together to

achieve a higher current, too, but beware to get this too high as it


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becomesdangerousandyoumayhaveahard time finding fuses that

canhandletoomuchcurrent.

SolarElectricSystemComponentsTherearethreemaintypesofsolarelectricsystems:offgrid,gridtied

or gridtied with battery backup. Off grid systems typically use

batteries as their form of energy storage and have been around for

manydecades. Thesesystemstypicallyrelyonabackuppowersource

like a generator forwhen the sun does not come out for prolonged

periods. Gridtiedsystemshaveonlygainedpopularityinrecentyears,

asutility,stateandfederalincentiveshavemadethesolarsystemmuch

morecostcompetitivewith itsdirtyrivals:thefossilfuels. Thesegrid

tiedsystemsusetheutilitygrid (thenetworkofwiresandcables that

span every city and town in the US) to store their energy, sending

excessenergy intothegridduringthedayandpullingfrom itatnight.


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Agoodresourcetochecktoseewhat incentivesareavailable inyour

localityiswww.dsireusa.org.

Every solar system, no matter which type, will always start at the solar

panel. This is where the energy starts, and from there it must enter some

conductor to reach its destination. This conductor is typically an

insulated copper wire. The amount of energy and the distance of the

wire will determine what size wire to use. Inelectricalcircuits,Ohm's

lawstatesthatthecurrentthroughaconductorbetweentwopointsis

directlyproportionaltothepotentialdifferenceorvoltageacrossthe

twopoints,andinverselyproportionaltotheresistancebetweenthem.

Themathematicalequationthatdescribesthisrelationshipis:

Visthepotentialdifferencemeasuredacrosstheresistanceinunits

ofvolts;Iisthecurrentthroughtheresistanceinunitsofamperes

(amps)andRistheresistanceoftheconductorinunitsofohms. A


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morethoroughdiagramtoexpresstherelationshipbetweenthese

unitsisshownbelow.

Typically youwillwant nomore than 2% loss through yourDCwire

runs. Thereareseveralonlinecalculatorsfordeterminingthis,oryou

maychoosetodothemathyourselfusingthetablebelow.


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Vol tage Drop Per 100 FT Run o f Pa ired W i re

For

example:

Given a load current of 4 amps, andusing 14AWGwire,howmuch

voltagedropcanweexpectattheloadendfora250footrunofpaired

wire?

Using thechart,wematch therow for14AWGand thecolumn for4

ampsanddetermine that voltagedropper100 feet is2.02Volts.By


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dividingthepairedwire lengthby100,wegetthefactorbywhichwe

needtomultiplyvoltagedropper100 feettodeterminetotalvoltage

drop.Therefore,

250

feet

divided

by

100

equals

2.5.

Multiply

2.5

by

2.02 voltsdropper100 feet toget your total voltagedrop.Thus the

totalvoltagedropis2.5times2.02,or5.05voltagedropfor250feet.If

yoursystemvoltage is250voltsormorethismaybeacceptable loss.

Note that the higher the voltage the lower the current, as they are

inverselyrelated. Ifyouhavealongwireandhavelowsystemvoltage

youhave3mainchoices. The first istobuyverythickwire,although

the cost of copper these days may prohibit this. The second is to

reduce thewire runby situatingyour solararray closer toyour load.

The third option is to increase the voltage bywiringmore panels in

seriesorby invertingtheDCpowertoACpoweratthesite insteadof

the point of contact with the load. This may require putting the

batteries closer to the array in an enclosure separate from your

residence,butcanresult insomebigsavingssinceyouwillberunning

AC power at 120 or 240 volts instead of 12 volts.


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regulatestheflowofenergytothebatteryanddetermineshowmuch

energy is being pulled from the batteries at nighttime or in cloudy

weather.Depending

on

the

size

of

the

solar

array

you

may

spend

anywherefromabout$25toover$100foryourchargecontroller(s).

Controllersare

available

in

avariety

of

sizes

and

appearances.

Thebatteriesareacrucialcomponentofyouroffgridsystem. This is

what will be powering your appliances when the sun goes down or

behindclouds. Mostbatteriesnowareleadacidbatteries,althoughas


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more funding isbeingput into theR&Dofbatteries thechemistry is

constantly evolving and becoming more efficient. Batteries are also

availablein

unsealed

and

sealed

types.

The

unsealed

types

are

much

more common due to their lower cost. However, they do require

weeklymaintenance to keep theirelectrolyte levels above theplates

insidethebattery. Thesealedbatteriescomeatapremium,butdonot

require the maintenance, since the electrolyte is usually in a gel

substance. Foreitherbatteryyouwillwant tokeep themaway from

anypotentialheatorfiresources. Ashedorawellventedroominyour

home will work best. Try to avoid temperature extremes for your

batterybank,asthiswillaffecttheperformancenegatively.

The charge controller can be programmed to stop flow from the

batteries when they reach a certain depth of discharge (DOD). The

DODistypicallynolessthan50%ofthebatteryscapacity. Thefurther

youdischargeabatteryonaregularbasistheshorterthelifespanofa


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batterywillbe. Forsolarapplicationsyouwillwanttousedeepcycle

batteries. Wiredtogether,theyformabatterybank.

These may look very similar to car batteries but are only similar in

appearanceandgreatlydiffer in their requirements.Carbatteriesare

meantto

be

fully

discharged

and

then

rapidly

recharged.

Solar

deep

cycle batteries are slowly charged throughout the day and then

dischargedslowlyatnight. Theirenergyinputwillvarythroughoutthe


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dayandthedischargewillbesporadicatnight,too. Acarbatteryused

for a solar applicationwouldnotbe expected to last evenone year,

whileawell

maintained

deep

cycle

battery

can

be

expected

to

last

6

yearsormore,dependingonthedepthofdischargelevelyouhaveset

andhowoftenyoukeeptheelectrolytelevelsmaintained.

If you are usingjust direct current (DC) loads you will not need an

inverterandcanjustcharge the loads from thebattery,assumingthe

voltagesmatchup. However,thecostandavailabilityofDCappliances

remains an impediment to the solely DC home. Alternating current

(AC)appliancesdominatethehomeappliancelandscapeandrequirean

invertertochangetheDCcurrentfromthesolararraytoACcurrentfor

your refrigerator,TV, lights,etc. You shouldexpect to spendaround

$0.50/watt or more depending on the size of the inverter needed.

Typically,allbutthe largestresidentialsolarsystemswillwork fineon

oneinverter.


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Inverters, like the charge controllers, will vary in shape and size

dependingupontheinvertersoutputratingandmanufacturer.

Youmaybeabletosavesomemoneyonlargersystemsbypurchasing

an inverter thathasachargecontroller inside itscircuitry. Check the

spec sheets to determine this. Many of the largermanufacturersof

invertershave

solar

string

sizing

programs

available

for

free

on

their

website, so you may want to reference this to determine what size

inverter to use. The inverters input voltage window is the main

determinationtodeterminehowmanypanelsyoucanwiretogetherin

aseries

string,

which

is

why

they

are

often

called

string

inverters.

You can get bywith an inverter that is rated below the name plate

ratingofthearray. Forexample,asolararraywithanameplaterating


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of 3,300 watts (3.3 kilowatts) will workjust fine with a 3,000 watt

inverter,sinceyouwilltypicallyloseupto20%oftheoutputfromthe

panelsfrom

many

factors.

Among

them,

voltage

losses

in

the

wires,

panel mismatch, dirt or pollen on the panels and the DC to AC

inversion.

Disconnectswitchesareoftentimesbuilt intothe inverters,butmany

municipalities require a separatedisconnect switch for either theDC

sideortheACside,orboth. Ifyouareplanningongettingyoursystem

inspectedbya licensed inspectororaregoingtoconnectyoursystem

tothegridcheckwithyour local lawstodeterminewhichdisconnects

youwillneedto install. TheNationalElectricalCode(NEC)book,too,

has set laws on mounting the equipment, such as how high off the

ground, distance from batteries and other components, etc.

Disconnectswitches,dependingonhowmanystringsofpanelsyouare

creatingmayneedtohavean integratedfuse. Thesedisconnectscan

bepurchasedatalocalelectricalsupplyorhardwarestore.


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maxcontinuousoutputoftheinverterisfoundinthespecsheetorby

contacting themanufacturer. Reference theNational Electrical Code

(NEC)book

for

the

latest

requirements

when

sizing

an

electrical

array.

Gridtied systems substitute the utility grid for the batteries. Most

homesthatareconnectedtothegridoptforthisservice. Ifgoingthis

route,youwillwantyourutilityprovidertoinstallanetmeterforyou.

Thismeterrecordstheflowofelectricityinbothdirections,essentially

crediting your account for sending excess electricity into the grid.

When the sun is out and your panels are producingmore electricity

thanyourhomeneeds,yourmeterwillspinbackwards. Whenthesun

goesdownandthelightscomeonyoubegintopullelectricityfromthe

grid and your meter spins forwards again. Most states have now

adoptednetmeteringforrenewableenergysystems. Ifyoudontgeta

net meter your old meter may actually charge you for energy

consumedandenergyproduced!


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It is important tonote thatwhen you losepower from thegrid, you

wontbeabletousethepowerfromyoursolararray. This isasafety

featurebuilt

into

the

inverters

so

that

ifyou

have

autility

lineman

workingon thepower lines in your front yard they canbe confident

there is no current in the lines. If your array were in the backyard

feeding the grid and hewas working in the front he would run the

chanceofhavingabadelectricshock.

Asmallpercentageofhomeownersoptforagridtiedsolarsystemwith

battery backup. This is more common in places with an unreliable

utility connection like very remote areas or places with inclimate

weather. Asidefromtheextramaintenanceandintroducingmoretoxic

chemicals intoyourhomeand theenvironment,you couldpayup to

50%moreon the total costof an installed systemby addingbattery

backup. There are inverters out there that have gridtied/battery

backup capabilities, but youmay need two inverters for this option.

Having a crucial load subpanel is a goodoption forwhen thepower


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goesdownandyouaredrawingfromthebatteries. Thisisolatessome

ofyourelectricloadsonaseparatebreakerpanelsothatyouwontpull

downthe

batterys

storage

too

fast

by

running

unnecessary

loads.

SiteDeterminationThebiggestfactorwhendeterminingthe location isaccesstothesun.

Theway

the

panels

are

wired

together,

it

is

very

important

that

your

panelswillgetatleast6hoursofunobstructedsunperday. Thissolar

windowistypicallyfrom9amto6pm,butmayadjusttoearlierorlater

in the day depending on the orientation of the panels. The optimal

pitchfor

the

panels

is

equal

to

your

latitude,

although

in

many

locations

with cloudywinters, itmaybeoptimal to subtract about15degrees

fromyour latitudeforoptimalpitch. AsolarpathfinderoraSolmetric

Sun Eye are two popular options for determining the sites sun

potential.They

are

useful

tools

that

will

show

what

shade

issues

you

willhavewithaparticularspotatalltimesoftheyearandevenwhat

timeoftheday. Shade istobeavoidedatallcostssincethecellsand


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panelsaremainlywiredinseries,andshadingevenonecellofapanel

canwipeoutaportionoftheentirearray.

TheNationalRenewable Energy Laboratories (NREL)hasdeveloped a

veryusefulonlineresourcetodetermine thepotentialoutputofyour

array. Theprogram iscalledPVWattsand isfreetouseonline. Itcan

befoundonlineat:http://www.nrel.gov/rredc/pvwatts/. Simply input

yourarraysizeinkilowatts,theorientationandangleofyourpaneland

your zip code and theprogramwill give you yourestimated kilowatt

hour (kWh)output foreachmonthof theyear. Ifyoucannotmount

the panel to your roof, another consideration for site selection is to

keepthearrayasclosetoyourhomeasreasonablypossible,sincelong

wirerunswillhavehigherpower lossesandwillrequirethickerwires,

increasingthecostofyoursystemandrequiringlongertrenches.

Onceyou

have

determined

the

necessary

size

of

you

solar

array

and

whichcomponentstogowith itbaseduponyourneedsyouareready


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to begin the final steps of completing the installation and wiring

everythingtogethertobeginproducingenergyrightinyourbackyard.

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