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8/2/2019 Photo Voltaic Cells and Batteries

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PracticalapplicationsSolar cells have become cheaper and more efficient in recent years, as researchers have

looked to themasa longtermalternativeenergysource.Solarpanelsareused insatellites.

Theycanbeused inconjunctionwithrechargeablebatteries,suchasthe leadacidornickel

cadmiumtypes,toprovidepowerindependentofthecommercialutilities.

A completely independent solar/battery power system is called a standalone sys tem. It

generallyuseslargesolarpanels,largecapacityleadacidorNICADbatteries,powerconverters

toconvertthedc intoac,andarathersophisticatedchargingcircuit.Thesesystemsarebest

suitedtoenvironmentswherethereissunshineahighpercent ageofthetime.

Solarcells,eitheraloneorsupplementedwithrechargeablebatteries,canbeconnectedintoa

homeelectricsystem inan interactivearrangementwiththeelectricutilities.Whenthesolar

powersystemcantprovide for theneedsof thehouseholdallby itself, theutilitycompany

cantakeuptheslack.Conversely,whenthesolarpowersys temsuppliesmorethanenough

fortheneedsofthehome,theutilitycompanycanbuytheexcess.

Howlargeofabattery?Youmightget the ideathatyoucanconnecthundreds,oreven thousands,ofcells inseries

andobtainbatterieswithfantasticallyhighEMFs.Whynotput1,000zinccarboncellsinseries,

forexample,andget1.5 kV?Orput2,500 solar cells in seriesand get1.25kV?Maybe its

possibletoputabillionsolarcells inseries,out insomevastsunscorcheddesertwasteland,

anduse the resulting500MV (megavolts) to feed the greatesthightensionpower line the

worldhaseverseen.

There are several reasons why these schemes arent good ideas. First, high voltages for

practicalpurposes canbe generated cheaplyandefficientlybypower converters thatwork

from117

V

or

234

V

utility

mains.

Second,

it

would

be

difficult

to

maintain

abattery

of

thousands, millions or billions of cells in series. Imagine a cell holder with 1,000 sets of

contacts.Andnotoneofthemcanopenup, lestthewholebatterybecomeuseless,because

allthecellsmustbeinseries.(Solarpanels,atleast,canbepermanentlywiredtogether.Not

sowithbatteriesthatmustoftenbereplaced.)Andfinally,theinternalresistancesofthecells

wouldaddupand limit thecurrent,aswellas theoutputvoltage, thatcouldbederivedby

connecting so many cells in series. This is not so much of a problem with seriesparallel

combinations,asinsolarpanels,aslongasthevoltagesarereasonable.Butitisabigfactorif

allthecellsare inseries,withthe intentofgettingahugevoltage.Thiseffectwilloccurwith

anykindofcell,whetherelectrochemicalorphotovoltaic.

InthedaysoftheSecondWorldWar,portabletwowayradioswerebuiltusingvacuumtubes.

Thesewerepoweredbybatteries supplying103.5V.Thebatterieswere several inches long

andaboutaninchindiameter.Theyweremadebystackingmanylittlezinccarboncellsontop

ofeachother,andenclosing thewholeassembly inasinglecase.Youcouldgetanastyjolt

fromoneofthosethings.Theyweredownrightdangerous!Afresh103.5Vbatterywouldlight

upa15Whouseholdincandescentbulbtoal mostfullbrilliance.Butthe117Voutletwould

workbetter,andforalotlonger.

Nowadays, handheld radio transceiverswillwork fromNICAD battery packsor batteries of

ordinarydrycells,providing6V,9V,or12V.Even thebiggestpower transistors rarelyuse

highervoltages.

Automotive

or

truck

batteries

can

produce

more

than

enough

power

for

almost anymobile or portable communications system.And if a really substantial setup is

8/2/2019 Photo Voltaic Cells and Batteries

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