study on process and othe requirement for solar inverter

8/18/2019 Study on Process and Othe Requirement for Solar Inverter

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HYBRID 2000VA SOLAR POWER SUPPLY

Abstract:-

In this Project we design hybrid 2000va solar power supply. The main motive behind this project is to use natural power o sunlight and save electricity or uture saety. !e all"nown sunlight is unlimited i we are able generate power rom them our power shortage

problem will resolve. !e design this power in a hybrid model between three source solar#

mainline and battery. $irstly i give priority to sunlight or charging battery then mainsupply. I sunlight is not present then the battery will charge rom main supply. !hen

both sunlight and main line is not present then we ta"e output rom battery through

inverter. In case o normal inverter and battery system it will ta"e long time to charge adrain battery and ta"es more electricity or charging battery but in our project with

problem is resolved by using solar panels and a charge controller.

%loc" &iagram:-

'omponents used:-(2) (*0 Ah %attery 2 +os

(2*! ,olar Panel +os

(*0! ,olar Panel 2 +os2000)A Inverter ( +os

2A /'% 2+osmm !ire 'oil ( +os

2.*mm wire coil +os

Amp 'hange over ( +os

(


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Introduction:-

P) T1'+34356

Photovoltaic 7P)8 solar cells as they are oten reerred to# are semiconductor devices thatconvert sunlight into direct current 7&'8 electricity. 5roups o P) cells are electrically

conigured into modules and arrays# which can be used to charge batteries# operate

motors# and to power any number o electrical loads. !ith the appropriate power

conversion e9uipment# P) systems can produce alternating current 7A'8 compatiblewith any conventional appliances# and operate in parallel with and interconnected to the

utility grid.

I,T36 3$ P3T3)34TAI' The irst conventional photovoltaic cells were produced in the late (;*0s# and throughout

the (;0s were principally used to provide electrical power or earth-orbiting satellites.

In the (;


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,ince the top o the cell must be open to sunlight# a thin grid o metal is applied to the top

instead o a continuous layer. The grid must be thin enough to admit ade9uate amounts o

sunlight# but wide enough to carry ade9uate amounts o electrical energy.

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4ight# including sunlight# is sometimes described as particles called Cphotons.C Assunlight stri"es a photovoltaic cell# photons move into the cell.

!hen a photon stri"es an electron# it dislodges it# leaving an empty CholeC. The loose

electron moves toward the top layer o the cell. As photons continue to enter the cell#

electrons continue to be dislodged and move upwards.

I an electrical path e?ists outside the cell between the top grid and the bac" plane o thecell# a low o electrons begins. 4oose electrons move out the top o the cell and into the

e?ternal electrical circuit. 1lectrons rom urther bac" in the circuit move up to ill the

empty electron holes.


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/ost cells produce a voltage o about one-hal volt# regardless o the surace area o the

cell. owever# the larger the cell# the more current it will produce.

The resistance o the circuit o the cell will aect the current and voltage. The amount o available light aects current production. The temperature o the cell aects its voltage.

egardless o siDe# a typical silicon P) cell produces about 0.* E 0. volt &' under open-circuit# no-load conditions. The current 7and power8 output o a P) cell depends on its

eiciency and siDe 7surace area8# and is proportional to the intensity o sunlight stri"ing

the surace o the cell. $or e?ample# under pea" sunlight conditions a typical commercial

P) cell with a surace area o (0 cmF2 7G2* inF28 will produce about 2 watts pea"

power. I the sunlight intensity were 0 percent o pea"# this cell would produce about 0.=

watts.

$ig(..2

T6P1, 3$ P) '144,

The our general types o photovoltaic cells are:

• ,ingle-crystal silicon.

• Polycrystalline silicon 7also "nown as multicrystalline silicon8.

• ibbon silicon.

• Amorphous silicon 7abbreviated as Ca,i#C also "nown as thin ilm silicon8.


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Single-crystal silicon

/ost photovoltaic cells are single-crystal types. To ma"e them#silicon is puriied# melted# and crystalliDed into ingots. The ingots are sliced into thin waers to

ma"e individual cells. The cells have a uniorm color# usually blue or blac".

Polycrystalline silicon

Polycrystalline cells are manuactured and operate in a similar manner. The dierence is

that lower cost silicon is used. This usually results in slightly lower eiciency# but polycrystalline cell manuacturers assert that the cost beneits outweigh the

eiciency losses. The surace o polycrystalline cells has a random pattern o crystal borders instead o the solid color o single crystal cells.

Ri!!on silicon

5rowing a ribbon rom the molten silicon instead o an ingot ma"es ribbon-type

photovoltaic cells. These cells operate the same as single and polycrystal cells.

The anti-relective coating used on most ribbon silicon cells gives them a prismatic rainbow

appearance.

*


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A"or#$o%s or t$in &il" silicon:

The previous three types o silicon used or photovoltaic cells have a distinct

crystal structure. Amorphous silicon has no such structure. Amorphous silicon is

sometimes abbreviated Ca,iC and is also called thin ilm silicon.Amorphous silicon units are made by depositing very thin layers o vaporiDed silicon in a

vacuum onto a support o glass# plastic# or metal.

P3T3)3A4TAI' /3&@41,

$or almost all applications# the one-hal volt produced by a single cell is inade9uate.

Thereore# cells are connected together in series to increase the voltage. ,everal o these

series strings o cells may be connected together in parallel to increase the current aswell.

These interconnected cells and their electrical connections are then sandwiched between

a top layer o glass or clear plastic and a lower level o plastic or plastic and metal. An

outer rame is attached to increase mechanical strength# and to provide a way to mount

the unit. This pac"age is called a CmoduleC or CpanelC . Typically# a module is the basic building bloc" o photovoltaic systems.

5roups o modules can be interconnected in series andHor parallel to orm an Carray.C %y

adding Cbalance o systemC 7%3,8 components such as storage batteries# charge

controllers# and power conditioning devices# we have a complete photovoltaic system.

Descri!ing #$oto'oltaic "o(%le #er&or"ance

To insure compatibility with storage batteries or loads# it isnecessary to "now the electrical characteristics o photovoltaic modules.


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'onsider CIC is the abbreviation or current# e?pressed in amps. C)C is used or voltage in

volts# and CC is used or resistance in ohms.

A photovoltaic module will produce its ma?imum current when there is essentially noresistance in the circuit. This would be a short circuit between its positive and negative

terminals.

This ma?imum current is called the short circuit current# abbreviated I7sc8. !hen the

module is shorted# the voltage in the circuit is Dero.'onversely# the ma?imum voltage is produced when there is a brea" in the circuit. This is called the open circuit voltage#

abbreviated )7oc8. @nder this condition the resistance is ininitely high and there is no

current# since the circuit is incomplete.

These two e?tremes in load resistance# and the whole range o conditions in betweenthem# are depicted on a graph called a I-) 7current-voltage8 curve. 'urrent# e?pressed in

amps# is on the vertical 6-a?is. )oltage# in volts# is on the horiDontal -a?is 7$igure (8.

A typical current voltage curve

As you can see in $igure (# the short circuit current occurs on a point on the curve where

the voltage is Dero. The open circuit voltage occurs where the current is Dero.

The power available rom a photovoltaic module at any point along the curve ise?pressed in watts. !atts are calculated by multiplying the voltage times the current

7watts J volts ? amps# or ! J )A8.

At the short circuit current point# the power output is Dero# since the voltage is Dero.At theopen circuit voltage point# the power output is also Dero# but this time it is because the

current is Dero.


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There is a point on the C"neeC o the curve where the ma?imum power output is located.

This point on our e?ample curve is where the voltage is (< volts# and the current is 2.*

amps. Thereore the ma?imum power in watts is (< volts times 2.* amps# e9ualing 2.*watts.

The power# e?pressed in watts# at the ma?imum power point is described as pea"#ma?imum# or ideal# among other terms. /a?imum power is generally abbreviated as CI

7mp8.C )arious manuacturers call it ma?imum output power# output# pea" power# rated power# or other terms.

The current-voltage 7I-)8 curve is based on the module being under standard conditions

o sunlight and module temperature. It assumes there is no shading on the module.

,tandard sunlight conditions on a clear day are assumed to be (000 watts o solar energy per s9uare meter 7(000 !Hm2or l"!Hm28. This is sometimes called Cone sun#C or a Cpea"

sun.C 4ess than one sun will reduce the current output o the module by a proportional

amount. $or e?ample# i only one-hal sun 7*00 !Hm28 is available# the amount o outputcurrent is roughly cut in hal 7$igure 28

A Typical 'urrent-)oltage 'urve at 3ne ,un and 3ne-hal ,un

$or ma?imum output# the ace o the photovoltaic modules should be pointed as straight

toward the sun as possible.

%ecause photovoltaic cells are electrical semiconductors# partial shading o the module

will cause the shaded cells to heat up. They are now acting as ineicient conductors

instead o electrical generators. Partial shading may ruin shaded cells.

Partial module shading has a serious eect on module power output. $or a typicalmodule# completely shading only one cell can reduce the module output by as much as

=


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=0K 7$igure 8. 3ne or more damaged cells in a module can have the same eect as

shading.

A Typical 'urrent-)oltage 'urve or an @nshaded /odule and or a /odule with 3ne ,haded

'ell.

This is why modules should be completely unshaded during operation. A shadow across amodule can almost stop electricity production. Thin ilm modules are not as aected by

this problem# but they should still be unshaded.

/odule temperature aects the output voltage inversely. igher module temperatures

will reduce the voltage by 0.0 to 0.( volts or every one-'elsius degree rise in

temperature 70.0)H0' to 0.()H0'8. In $ahrenheit degrees# the voltage loss is rom 0.022to 0.0* volts per degree o temperature rise 7$igure 8.

A Typical 'urrent-)oltage 'urve or a /odule at 2* ฐ ' 7


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This is why modules should not be installed lush against a surace. Air should be

allowed to circulate behind the bac" o each module so itLs temperature does not rise and

reducing its output. An air space o - inches is usually re9uired to provide proper ventilation.

The last signiicant actor that determines the power output o a module is the resistanceo the system to which it is connected. I the module is charging a battery# it must supply

a higher voltage than that o the battery.

I the battery is deeply discharged# the battery voltage is airly low. The photovoltaic

module can charge the battery with a low voltage# shown as point M( in $igure *. As the battery reaches a ull charge# the module is orced to deliver a higher voltage# shown as

point M2. The battery voltage drives module voltage.

3perating )oltages &uring a %attery 'harging 'ycle

1ventually# the re9uired voltage is higher than the voltage at the moduleLs ma?imum

power point. At this operating point# the current production is lower than the current atthe ma?imum power point. The moduleLs power output is also lower.

To a lesser degree# when the operating voltage is lower than that o the ma?imum power

point 7point M(8# the output power is lower than the ma?imum. ,ince the ability o themodule to produce electricity is not being completely used whenever it is operating at a point airly ar rom the ma?imum power point# photovoltaic modules should be careully

matched to the system load and storage.

@sing a module with a ma?imum voltage# which is too high# should be avoided nearly as

much as using one with a ma?imum voltage# which is too low.

(0


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The output voltage o a module depends on the number o cells connected in series.

Typical modules use either 0# 2# # # or cells wired in series.

The modules with 0-2 cells are considered sel-regulating modules. cell modules arethe most common in the photovoltaic industry. Their slightly higher voltage rating# (.<

volts# allows the modules to overcome the reduction in output voltage when the modulesare operating at high temperatures.

/odules with - cells also have enough surplus voltage to eectively charge highantimony content deep cycle batteries. owever# since these modules can overcharge

batteries# they usually re9uire a charge controller. $inally# cell modules are available

with a rated output voltage o 20. volts. These modules are typically used only when asubstantially higher voltage is re9uired.

As an e?ample# i the module is sometimes orced to operate at high temperatures# it can

still supply enough voltage to charge (2-volt battery.

Another application or cell modules is a system with an e?tremely long wire run

between the modules and the batteries or load. I the wire is not large enough# it willcause a signiicant voltage drop. igher module voltage can overcome this problem.

It should be noted that this approach is similar to putting a larger engine in a car with

loc"ed bra"es to ma"e it move aster. It is almost always more cost eective to use an

ade9uate wire siDe# rather than to overcome voltage drop problems with more costly cell modules.

P3T3)34TAI' AA6,

In many applications the power available rom one module is inade9uate or the load.

Individual modules can be connected in series# parallel# or both to increase either output

voltage or current. This also increases the output power. !hen modules are connected in

parallel# the current increases. $or e?ample# three modules which produce (* volts and amps each# connected in parallel# will produce (* volts and ; amps 7$igure 8.

((


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Three /odules 'onnected in Parallel

I the system includes a battery storage system# a reverse low o current rom the batteries through the photovoltaic array can occur at night. This low will drain power

rom the batteries.A diode is used to stop this reverse current low. &iodes are electrical devices which only

allow current to low in one direction 7$igure


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I one module in a series string ails# it provides so much resistance that other modules in

the string may not be able to operate either. A bypass path around the disabled module

will eliminate this problem 7$igure =8. The bypass diode allows the current rom the other modules to low through in the CrightC direction.

/any modules are supplied with a bypass diode right at their electrical terminals. 4arger

modules may consist o three groups o cells# each with its own bypass diode.%uilt in bypass diodes are usually ade9uate unless the series string produces = volts or

higher# or serious shading occurs regularly.

'ombinations o series and parallel connections are also used in arrays 7$igure ;8. I parallel groups o modules are connected in a series string# large bypass diodes are

usually re9uired.

Three /odules 'onnected in ,eries with a %loc"ing &iode and %ypass &iodes

(


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Twelve /odules in a Parallel-,eries Array with %ypass &iodes and Isolation &iodes

T6P1, 3$ AA6,

)lat-#late stationary arrays

,tationary arrays are the most common. ,ome allow adjustments in their tilt angle romthe horiDontal. These changes can be made any number o times throughout the year#

although they are normally changed only twice a year. The modules in the array do notmove throughout the day 7$igure (08. Although a stationary array does not capture asmuch energy as a trac"ing array that ollows the sun across the s"y# and more modules

may be re9uired# there are no moving parts to ail. This reliability is why a stationary

array is oten used or remote or dangerous locations.

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Adjustable Array Tilted or ,ummer and !inter ,olar Angles

Porta!le arrays

A portable array may be as small as a one s9uare oot module easily carried by one

person to recharge batteries or communications or lashlights. They can be mounted onvehicles to maintain the engine battery during long periods o inactivity. 4arger ones can

be installed on trailers or truc" beds to provide a portable power supply or ield

operations 7$igures ((8

(*


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PV *ELLS

A solar cell is a device that converts the energy o sunlight directly into electricity by the

photovoltaic eect. ,ometimes the term solar cell is reserved or devices intended

speciically to capture energy rom sunlight such as solar panels and solar cells# while the

term photovoltaic cell is used when the light source is unspeciied. Assemblies o cellsare used to ma"e solar panels# solar modules# or photovoltaic arrays. Photovoltaic’s is the

ield o technology and research related to the application o solar cells in producingelectricity or practical use. The energy generated this way is an e?ample o solar energy7also "nown as solar power 8.

Photovoltaic cells are manuactured by using dierent materials with dierent process o

ma"ing. 1ach type has it>s own advantages and disadvantages # giving the end user a loto choices# so as to consider dierent parameters.

T6P1, 3$ P) '144,:

There are our types o photovoltaic cells: multicrystalline silicon# monocrystalline

silicon# ribbon silicon# and thin-ilm.

/3+3'6,TA44I+1 P) '144,

+A,U)A*URI,. PRO*ESS

The starting material is lumps o chemically pure polycrystalline silicon# o a 9uality

close to semiconductor-grade# produced by the ,iemens process. The traditional route or

monocrystalline waers is the 'Dochrals"i process in which a single crystal o up to about(*0mm diameter is pulled rom molten ,i held in a large heated 9uartD crucible. In the

more recently developed method# ,i is cast in a re-useable graphite mould to produce

bloc"s o multicrystalline silicon 7cubes o over 0.*m dimensions8. !hen sawn into barsand then waers 7just bigger than a compact disc8 using a wire saw# the cleaned product is

ready or cell manuacturing.,ingle crystal or monocrystalline waers are made using the 'Dochrals"i process.

*/oc$ralsi #rocess

igh-purity# semiconductor-grade silicon 7only a ew parts per million o impurities8 ismelted down in a crucible# which is usually made o 9uartD. &opant impurity atoms such

as boron or phosphorus can be added to the molten intrinsic silicon in precise amounts in

order to dope the silicon# thus changing it into n-type or p-type e?trinsic silicon. Thisinluences the electronic properties o the silicon. A precisely oriented seed crystal#

mounted on a rod# is dipped into the molten silicon. The seed crystalLs rod is very slowly

pulled upwards and rotated at the same time. %y precisely controlling the temperaturegradients# rate o pulling and speed o rotation# it is possible to e?tract a large# single-

crystal# cylindrical ingot rom the melt. Investigating and visualiDing the temperature and

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velocity ields during the crystal growth process can avoid occurrence o unwanted

instabilities in the melt. This process is normally perormed in an inert atmosphere# such

as argon# and in an inert chamber# such as 9uartD.

&ue to the eiciencies that can be gained by the adoption o common waer

speciications# the semiconductor industry has or some time used waers withstandardiDed dimensions. 'urrently# high-end device manuacturers use 200 mm and 00

mm diameter waers. The crystal ingots rom which these waers are sliced can be up to 2

meters in length# weighing several hundred "ilograms. 4arger waers allowimprovements in manuacturing eiciency# as more chips can be abricated on each

waer# so there has been a steady drive to increase silicon waer siDes. The ne?t step up#

*0 mm# is currently scheduled or introduction in 20(2. ,ilicon waers are typically

about 0.2E0.


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owever# o?ygen impurities can react with boron in an illuminated environment# such as

e?perienced by solar cells. This results in the ormation o electrically active boronE

o?ygen comple? that detracts rom cell perormance. /odule output drops byappro?imately K during the irst ew hours o light e?posure.

+ULI*YRSALLI,E PV *ELLS

Techni9ues or the production o multicrystalline silicon are more simple# and thereorecheaper# than those re9uired or single crystal material. owever# the material 9uality o

multicrystalline material is lower than that o single crystalline material due to the

presence o grain boundaries. 5rain boundaries introduce high localised regions o recombination due to the introduction o e?tra deect energy levels into the band gap# thus

reducing the overall minority carrier lietime rom the material. In addition# grain

boundaries reduce solar cell perormance by bloc"ing carrier lows and providingshunting paths or current low across the p-n junction.

+an%&act%ring Process

The eedstoc" 7made by puriication o silicon or by alternative reining methods8 is

charged in a silicon nitride coated 9uartD crucible and heated until all the silicon is

melted. eat is then e?tracted rom the bottom o the crucible by moving the heat Doneup compared to the crucible and H or cooling the bottom o the crucible. 3ten the

crucible is lowered away rom the heat Done and simultaneously the bottom is revealed to

a cooling source.

A temperature gradient is created in the melt and the solidiication will start at the bottom

and crystals will grow upwards# and grain boundaries will grow parallel to the

solidiication direction. To obtain a directional solidiication the solidiication heat must be transported through the steadily growing layer o solid silicon. It is necessary tomaintain a net heat lu? over the solid-li9uid interace and the temperature at the lower

part o the crucible must be decreased according to the increase in solid silicon thic"ness

to maintain a steady growth rate. The growth rate is proportional to the temperaturegradient dierence between the solid and the li9uid silicon.

Impurity &istribution in &irectionally ,olidiied Ingots:

&ue to the act that most elements are more soluble in li9uid than in solid silicon#impurities dissolved in the melt will segregate and the element concentration in the ingot

will in most cases increase upwards in the ingot ollowing ,cheil>s e9uation when the

melt solidiies rom the bottom and up.

The e?ponential distribution will create a heavily contaminated thin layer at the top o theresulting ingot.

The ,cheil e9uation assumes no diusion in the solid state# complete mi?ing in the li9uid

state and e9uilibrium at the solidHli9uid interace. I convection is not suicient to

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provide complete mi?ing in the li9uid phase# solute atoms are rejected by the advancing

solid at a greater rate than they can diuse into the bul" o the melt. A concentration

gradient is thus developed ahead o the solid. This enriched region will determine the rateo solute incorporation into the solid ront. This region is called a diusion boundary

layer. ,cheil>s e9uation is still valid i an eective distribution coeicient is used.

)or"ing o& Preci#itates

Precipitates may orm ater saturation is met# and ,cheil>s e9uation will no longer bevalid. The amount o super saturation needed or precipitates to orm will vary with the

chemical composition and the growth conditions in the system.

Di&&%sion o& I"#%rities:

In addition to the ,cheil distribution the impurity distribution will depend on diusion.

Impurities will diuse into the solidiied silicon rom the crucible walls and bottom as

well as rom the coating. %ac"-diusion can also occur as impurities diuse rom theheavily contaminated top layer bac" into the bul" material ater solidiication# or rom the

boundary layer during solidiication. %oth in-diusion rom the crucible and coating and bac"-diusion are temperature dependent and the impurity distribution varies with

varying temperature proile during growth and the subse9uent cooling.

Boron Do#e( Silicon

%oron is an acceptor in silicon# and multicrystalline silicon ingots made by directionalsolidiication are oten pre-doped with boron. A small amount o boron is added together

with the eedstoc" prior to melting and solidiication. %oron is most commonly used

because it is the doping element with the distribution coeicient closest to ( 7"0 J 0.=8.The distribution proile will thus not vary as much with height as the other dopingelements.

HI, )IL+ SOLAR *ELL

A thin-ilm solar cell 7T$,'8# also called a thin-ilm photovoltaic cell 7T$P)8# is a solar cell that is made by depositing one or more thin layers 7thin ilm8 o photovoltaic material

on a substrate. The thic"ness range o such a layer is wide and varies rom a ew

nanometers to tens o micrometers.

/any dierent photovoltaic materials are deposited with various deposition methods on avariety o substrates. Thin-ilm solar cells are usually categoriDed according to the

photovoltaic material used:

• Amorphous silicon 7a-,i8 and other thin-ilm silicon 7T$-,i8

• 'admium Telluride 7'dTe8

• 'opper indium gallium selenide 7'I, or 'I5,8

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• &ye-sensitiDed solar cell 7&,'8 and other organic solar cells

Design an( &a!rication

The silicon is mainly deposited by chemical vapor deposition# typically plasma-enhanced

7P1-')&8# rom silane gas and hydrogen gas. 3ther deposition techni9ues beinginvestigated include sputtering and hot wire techni9ues.

The silicon is deposited on glass# plastic or metal# which has been coated with a layer o

transparent conducting o?ide 7T'38.

Polysilicon deposition# or the process o depositing a layer o polycrystalline silicon on asemiconductor waer# is achieved by pyrolyDing silane 7,i8 at *=0 to *0 O'. This

pyrolysis process releases hydrogen.

Polysilicon layers can be deposited using (00K silane at a pressure o 2*E(0 Pa 70.2 to

(.0 Torr8 or with 20E0K silane 7diluted in nitrogen8 at the same total pressure. %oth o these processes can deposit polysilicon on (0E200 waers per run# at a rate o (0E

20 nmHmin and with thic"ness uniormities o *K. 'ritical process variables or

polysilicon deposition include temperature# pressure# silane concentration# and dopantconcentration. !aer spacing and load siDe have been shown to have only minor eects

on the deposition process. The rate o polysilicon deposition increases rapidly with

temperature# since it ollows Arrhenius behavior# that is deposition rate J AQe?p7E91aH"T8

where 9 is electron charge and " is the %oltDmann constant. The activation energy 71a8 or polysilicon deposition is about (.< e). %ased on this e9uation# the rate o polysilicon

deposition increases as the deposition temperature increases. There will be a minimum

temperature# however# wherein the rate o deposition becomes aster than the rate at

which unreacted silane arrives at the surace. %eyond this temperature# the deposition ratecan no longer increase with temperature# since it is now being hampered by lac" o silane

rom which the polysilicon will be generated. ,uch a reaction is then said to be Lmass-transport-limited.L !hen a polysilicon deposition process becomes mass-transport-

limited# the reaction rate becomes dependent primarily on reactant concentration# reactor

geometry# and gas low.

!hen the rate at which polysilicon deposition occurs is slower than the rate at whichunreacted silane arrives# then it is said to be surace-reaction-limited. A deposition

process that is surace-reaction-limited is primarily dependent on reactant concentration

and reaction temperature. &eposition processes must be surace-reaction-limited because

they result in e?cellent thic"ness uniormity and step coverage. A plot o the logarithm o the deposition rate against the reciprocal o the absolute temperature in the surace-

reaction-limited region results in a straight line whose slope is e9ual to E91aH".

At reduced pressure levels or )4,I manuacturing# polysilicon deposition rate below*


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pumping speed or changing the inlet gas low into the reactor. I the inlet gas is composed

o both silane and nitrogen# the inlet gas low# and hence the reactor pressure# may be

varied either by changing the nitrogen low at constant silane low# or changing both thenitrogen and silane low to change the total gas low while "eeping the gas ratio constant.

Polysilicon doping# i needed# is also done during the deposition process# usually byadding phosphine# arsine# or diborane. Adding phosphine or arsine results in slower

deposition# while adding diborane increases the deposition rate. The deposition thic"nessuniormity usually degrades when dopants are added during deposition.

&epending upon the eiciency re9uired# these dopants are removed using several

techni9ues.

A+ORPHOUS SILI*O, PV *ELLS

Amorphous ,ilicon cells use layers o a-,i only a ew micrometers thic"# attached to an

ine?pensive bac"ing such as glass# le?ible plastic# or stainless steel. This means thatthey use less than (K o the raw material 7silicon8 compared standard crystalline ,ilicon

7c-,i8 cells# leading to a signiicant cost saving.

+A,U)A*URI,. PRO*ESS:

Amorphous silicon is gradually degraded# by e?posure to light# by phenomena called the

,taebler-!rons"i 1ect 7,!18. ,!1 aects the power output o a-,i modules by as

much as (0K. This light induced degradation is reduced by depositing the layers o thecell using high hydrogen dilution and by ma"ing combinations 7alloys8 o dierent types

o cells. %ecause o ,!1# a-,i cells are rated in the stabiliDed condition# which occurs

ater about (00 hours e?posure to light.

@nli"e crystal silicon# in which atomic arrangements are regular# amorphous siliconeatures irregular atomic arrangements. As a result# the reciprocal action between

photons and silicon atoms occurs more re9uently in amorphous silicon than in crystal

silicon# allowing much more light to be absorbed. Thus# an ultra-thin amorphous siliconilm o less than (Rm can be produced and used or power generation. This ilm# because

it is not crystalline and is so thin# will not brea" when it is le?ed# thus allowing it to be

deposited on le?ible substrates. %ecause o the le?ability o the cell and the substratesa-,i producers are able to use automated Croll-to-rollC manuacturing processes in which

the substrate and deposited material move through the production process as one

continuous strip passing over several rolls in the process which maintain stability to the process as well as moving the product along its way.

Amorphous silicon ilms are abricated using plasma vapor deposition techni9ues to

apply silane 7,i8 to the substrate or other beneicial ilm# allowing large-area solar

cells to be abricated much more easily than with conventional c-,i. Three amorphoussilicon layers S p-layer# i-layer# and n-layer S are ormed consecutively on the

substrate. This p-i-n junction corresponds to the pHn junction o a c-,i solar cell.

2(


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ilm through its entire thic"ness# but not damage the substrate. Toward this end# a layer o

silicon dio?ide is sometimes added to act as a thermal barrier. This allows the use o

substrates that cannot be e?posed to the high temperatures o standard annealing# polymers or instance. Polymer-bac"ed solar cells are o interest or seamlessly integrated

power production schemes that involve placing photovoltaics on everyday suraces.

A third method or crystalliDing amorphous silicon is the use o thermal plasma jet. This

strategy is an attempt to alleviate some o the problems associated with laser processing E namely the small region o crystalliDation and the high cost o the process on a

production scale. The plasma torch is a simple piece o e9uipment that is used to

thermally anneal the amorphous silicon. 'ompared to the laser method# this techni9ue issimpler and more cost eective.

Plasma torch annealing is attractive because the process parameters and e9uipment

dimension can be changed easily to yield varying levels o perormance. A high level o

crystalliDation 7G;0K8 can be obtained with this method. &isadvantages include

diiculty-achieving uniormity in the crystalliDation o the ilm. !hile this method isapplied re9uently to silicon on a glass substrate# processing temperatures may be too

high or polymers.

SOLAR *HAR.E *O,ROLLER

IMPORTANCE OF SOAR C!AR"E CONTROER

The primary unction o a charge controller in a stand-alone P) system is to maintain the

battery at highest possible state o charge while protecting it rom overcharge by the arrayand rom overdischarge by the loads. Although some P) systems can be eectively

designed without the use o charge control# any system that has unpredictable loads# user intervention# optimiDed or undersiDed battery storage 7to minimiDe initial cost8 typically

re9uires a battery charge controller. The algorithm or control strategy o a battery charge

controller determines the eectiveness o battery charging and P) array utiliDation# andultimately the ability o the system to meet the load demands. Additional eatures such as

temperature compensation# alarms# meters# remote voltage sense leads and special

algorithms can enhance the ability

o a charge controller to maintain the health and e?tend the lietime o a battery# as wellas providing an indication o operational status to the system careta"er.

Important unctions o battery charge controllers and system controls are:

UPrevent %attery 3vercharge: to limit the energy supplied to the battery by the P) array

when the battery becomes ully charged.

UPrevent %attery 3ver discharge: to disconnect the battery rom electrical loads when the

battery reaches low state o charge.

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UProvide 4oad 'ontrol $unctions: to automatically connect and disconnect an electrical

load at a speciied time# or e?ample operating a lighting load rom sunset to sunrise.

O'erc$arge Protection

A remote stand-alone photovoltaic system with battery storage is designed so that it will

meet the system electrical load re9uirements under reasonably determined worst-case

conditions# usually or the month othe year with the lowest insolation to load ratio.!hen the array is operating under good-to-e?cellent weather conditions 7typically during

summer8# energy generated by the array oten e?ceeds the electrical load demand. To

prevent battery damage resulting rom overcharge# a charge controller is used to protect

the battery. A charge controller should prevent overcharge o a battery regardless o thesystem siDingHdesign and seasonal changes in the load proile# operating temperatures and

solar insolation.

'harge regulation is the primary unction o a battery charge controller# and perhaps thesingle most important issue related to battery perormance and lie. The purpose o a

charge controller is to supply power to the battery in a manner which ully recharges the battery without overcharging. !ithout charge control# the current rom the array will low

into a battery proportional to the irradiance# whether the battery needs charging or not. I

the battery is ully charged# unregulated charging will cause the battery voltage to reache?ceedingly high levels# causing severe gassing# electrolyte loss# internal heating and

accelerated grid corrosion. In most cases i a battery is not protected rom overcharge in

P) system# premature ailure

o the battery and loss o load are li"ely to occur.

'harge controllers prevent e?cessive battery overcharge by interrupting or limiting the

current low rom the array to the battery when the battery becomes ully charged. 'hargeregulation is most oten accomplished by limiting the battery voltage to a ma?imum

value# oten reerred to as the voltage reg#lation $%R& set point .

,ometimes# other methods such as integrating the ampere-hours into and out o the

battery are used. &epending on the regulation method# the current may be limited while

maintaining the regulation voltage# or remain disconnected until the battery voltage drops

to the array reconnect voltage $AR%& set point .

O'er (isc$arge Protection

&uring periods o below average insolation andHor during periods o e?cessive electrical

load usage# the energy produced by the P) array may not be suicient enough to "eep the

battery ully recharged. !hen a battery is deeply discharged# the reaction in the batteryoccurs close to the grids# and wea"ens the bond between the active materials and the

grids. !hen a battery is e?cessively discharged repeatedly# loss o capacity and lie will

eventually occur. To protect batteries rom overdischarge# most charge controllers includean optional eature to disconnect the system loads once the battery reaches a low voltage

or low state o charge condition.

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In some cases# the electrical loads in a P) system must have suiciently high enough

voltage to operate. I batteries are too deeply discharged# the voltage alls below theoperating range o the loads# and the loads may operate improperly or not at all. This is

another important reason to limit battery overdischarge in P) systems.

3verdischarge protection in charge controllers is usually accomplished by open-circuiting

the connection between the battery and electrical load when the battery reaches a pre-set

or adjustable low voltage loa' 'isconnect $%(& set point . /ost charge controllers alsohave an indicator light or audible alarm to alert the system userHoperator to the load

disconnect condition. 3nce the battery is recharged to a certain level# the loads are again

reconnected to a battery.

Non-critical system loads are generally always protected rom overdischarging the battery by connection to the low voltage load disconnect circuitry o the charge

controller. I the battery voltage alls to a low but sae level# a relay can open and

disconnect the load# preventing urther battery discharge. Critical loa's can be connected

directly to the battery# so that they are not automatically disconnected by the chargecontroller. owever# the danger e?ists that these critical loads might overdischarge the

battery. An alarm or other method o user eedbac" should be included to giveinormation on the battery status i critical loads are

connected directly to the battery.

egulation or limiting the P) array current to a battery in a P) system may be

accomplished by several methods. The most popular method is battery voltage sensing#

however other methods such as amp hour integration are also employed. 5enerally#

voltage regulation is accomplished by limiting the P) array current at a predeinedcharge regulation voltage. &epending on the regulation algorithm# the current may be

limited while maintaining the regulation voltage# or remain disconnected until the battery

voltage drops to the arrayreconnect set point.

!hile the speciic regulation method or algorithm vary among charge controllers# allhave basic parameters and characteristics. 'harge controller manuacturerLs data

generally provides the limits o controller application such as P) and load currents#

operating temperatures# parasitic losses# set points# and set point hysteresis values. In

some cases the set points may be dependent upon the temperature o the battery andHor controller# and the magnitude o the battery current.

'harge 'ontroller ,et Points

The battery voltage levels at which a charge controller perorms control or switchingunctions are called the controller set points. $our basic control set points are deined or

most charge controllers that have battery overcharge and over discharge protection

eatures. The voltage regulation 7)8 and the array reconnect voltage 7A)8 reer to thevoltage set points at which the array is connected and disconnected rom the battery. The

2*


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low voltage load disconnect 74)&8 and load reconnect voltage 74)8 reer to the voltage

set points at which the load is disconnected rom the battery to prevent over discharge.

$igure ( shows the basic controller set points on a simpliied diagram plotting batteryvoltage versus time or a charge and discharge cycle. A detailed discussion o each charge

controller set point ollows.

'ontroller set points

Voltage Reg%lation VR3 Set Point

The voltage reg#lation $%R& set point is one o the "ey speciications or charge

controllers. The voltage regulation set point is deined as the ma?imum voltage that thecharge controller allows the battery to reach# limiting the overcharge o the battery. 3nce

the controller senses that the battery reaches the voltage regulation set point# the

controller will either discontinue battery charging or begin to regulate 7limit8 the amounto current delivered to the battery. In some controller designs# dual regulation set points

may be used. $or e?ample# a higher regulation voltage may be used or the irst charge

cycle o the day to provide a little battery overcharge# gassing and e9ualiDation# while alower regulation voltage is used on subse9uent cycles through the remainder o the day to

eectively Vloat charge> the battery.

Proper selection o the voltage regulation set point may depend on many actors#including the speciic battery chemistry and design# siDes o the load and array with

respect to the battery# operating temperatures# and electrolyte loss considerations.

An important point to note about the voltage regulation set point is that the values

re9uired or optimal battery perormance in stand-alone P) systems are generally much

higher than the regulation or Vloat voltages> recommended by battery manuacturers.

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This is because in a P) system# the battery must be recharged within a limited time

period 7during sunlight hours8# while battery manuacturers generally allow or much

longer recharge times when determining their optimal regulation voltage limits. %y usinga higher regulation voltage in P) systems# the battery can be recharged in a shorter time

period# however some degree over overcharge and gassing will occur. The designer is

aced selecting the optimal voltage regulation set point that maintains the highest possible battery state o charge without causing signiicant overcharge.

Array Reconnect Voltage ARV3 Set Point

In interrupting 7on-o8 type controllers# once the array current is disconnected at the

voltage regulation set point# the battery voltage will begin to decrease. The rate at which

the battery voltage decreases depends on many actors# including the charge rate prior todisconnect# and the discharge rate dictated by the electrical load. I the charge and

discharge rates are high# the battery voltage will decrease at a greater rate than i these

rates are lower. !hen the battery voltage decreases to a predeined voltage# the array isagain reconnected to the battery to resume charging. This voltage at which the array is

reconnected is deined as the array reconnect voltage $AR%& set point .

I the array were to remain disconnected or the rest o day ater the regulation voltage

was initially reached# the battery would not be ully recharged. %y allowing the array to

reconnect ater the battery voltage reduces to a set value# the array current will Vcycle>

into the battery in an on-o manner# disconnecting at the regulation voltage set point# andreconnecting at the array reconnect voltage set point. In this way# the battery will be

brought up to a higher state o charge by Vpulsing> the array current into the battery.

It is important to note that or some controller designs# namely constant-voltage and

pulse-width-modulated 7P!/8 types# there is no clearly distinguishable dierence

between the ) and A) set points. In these designs# the array current is not regulated ina simple on-o or interrupting ashion# but is only limited as the battery voltage is held at

a relatively constant value through the remainder o the day.

Voltage Reg%lation Hysteresis VRH3

The voltage span or dierence between the voltage regulation set point and the array

reconnect voltage is oten called the voltage reg#lation hysteresis $%R!&. The ) is amajor actor# which determines the eectiveness o battery recharging or interrupting

7on-o8 type controllers. I the hysteresis is to great# the array current remains

disconnected or long periods# eectively lowering the array energy utiliDation and

ma"ing it very diicult to ully recharge the battery. I the regulation hysteresis is toosmall# the array will cycle on and o rapidly# perhaps damaging controllers# which use

electro-mechanical switching elements.

Lo1 Voltage Loa( Disconnect LVD3 Set Point

3verdischarging the battery can ma"e it susceptible to reeDing and shorten it>s operatinglie. I battery voltage drops too low# due to prolonged bad weather or e?ample# certain

2


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non-essential loads can be disconnected rom the battery to prevent urther discharge.

This can be done using a low voltage loa' 'isconnect $%(& device connected between

the battery and non-essential loads. The 4)& is either a relay or a solid-state switch thatinterrupts the current rom the battery to the load# and is included as part o most

controller designs. In some cases# the low voltage load disconnect unit may be a separate

unit rom themain charge controller.

In controllers or controls incorporating a load disconnect eature# the low voltage loa' 'isconnect $%(& set point is the voltage at which the load is disconnected rom the

battery to prevent overdischarge. The %( set point 'e)ines the act#al allowa*le

+a,i+#+ 'epth-o)-'ischarge an' availa*le capacity o) the *attery operating in a P%

syste+ The available capacity must be careully estimated in the P) system design andsiDing process using the actual depth o discharge dictated by the 4)& set point.

The proper 4)& set point will maintain a healthy battery while providing the ma?imum

battery capacity and load availability. To determine the proper load disconnect voltage#the designer must consider the rate at which the battery is discharged. %ecause the battery

voltage is aected by the rate o discharge# a lower load disconnect voltage set point isneeded or high discharge rates to achieve the same depth o discharge limit. In general#

the low discharge rates in most small stand-alone P) systems do not have a signiicant

eect on the battery voltage. Typical 4)& values used are between ((.0 and ((.* volts#which corresponds to about


29/58

S$%nt *ontroller Designs

,ince photovoltaic cells are current-limited by design 7unli"e batteries8# P) modules andarrays can be short-circuited without any harm. The ability to short-circuit modules or an

array is the basis o operation or shunt controllers.

$igure (2 shows an electrical design o a typical shunt type controller. The shunt

controller regulates the charging o a battery rom the P) array by short-circuiting the

array internal to the controller. All shunt controllers must have a bloc"ing diode in series between the battery and the shunt element to prevent the battery rom short-circuiting

when the array is regulating. %ecause there is some voltage drop between the array and

controller and due to wiring and resistance o the shunt element# the array is never

entirely shortcircuited# resulting in some power dissipation within the controller. $or thisreason# most shunt controllers re9uire a heat sin" to dissipate power# and are generally

limited to use in P) systems with array currents

less than 20 amps.

,hunt controller

The regulation element in shunt controllers is typically a power transistor or /3,$1T#

depending on the speciic design. There are a couple o variations o the shunt controller design. The irst is a simple interrupting# or on-o type controller design. The second

type limits the array current in a gradual manner# by increasing the resistance o the shunt

element as the battery reaches ull state o charge.

,hunt-Interrupting &esign

The shunt-interrupting controller completely disconnects the array current in an

interrupting or on-o ashion when the battery reaches the voltage regulation set point.

!hen the battery decreases to the array reconnect voltage# the controller connects thearray to resume charging the battery. This cycling between the regulation voltage and

array reconnect voltage is why these controllers are oten called Von-o> or Vpulsing>

controllers. ,hunt-interrupting controllers are widely available and are low cost# however theyare generally limited to use in systems with array currents less than 20 amps due to heat dissipation

re9uirements.

,hunt-4inear &esign

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3nce a battery becomes nearly ully charged# a shunt-linear controller maintains the

battery at near a i?ed voltage by gradually shunting the array through a semiconductor regulation element. In some designs# a comparator circuit in the controller senses the

battery voltage# and ma"es corresponding adjustments to the impedance o the shunt

element# thus regulating the array current. In other designs# simple Wener power diodesare used# which are the limiting actor in the cost and power ratings or these controllers.

There is generally more heat dissipation in shunt-linear controllers than in shunt-

interrupting types.

,eries 'ontroller &esigns

As the name implies# this type o controller wor"s in series between the array and battery#

rather than in parallel as or the shunt controller. There are several variations to the seriestype controller# all o which use some type o control or regulation element in series

between the array and the battery. !hile this type o controller is commonly used insmall P) systems# it is also the practical choice or larger systems due to the current

limitations o shunt controllers.

$igure ( shows an electrical design o a typical series type controller. In a series

controller design# a relay or solid-state switch either opens the circuit between the arrayand the battery to discontinuing charging# or limits the current in a series-linear manner to

hold the battery voltage at a high value. In the simpler series interrupting design# the

controller reconnects the array to the battery once the battery alls to the array reconnectvoltage set point. As these on-o charge cycles continue# the Von> time becoming shorter

and shorter as the battery becomes ully charged.

%ecause the series controller open-circuits rather than short-circuits the array as in shunt-

controllers# no bloc"ing diode is needed to prevent the battery rom short-circuiting when

the controller regulates.

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,eries controller

,eries-Interrupting &esign

The most simple series controller is the series-interrupting type# involving a one-step

control# turning the array charging current either on or o. The charge controller constantly monitors battery voltage# and disconnects or open-circuits the array in series

once the battery reaches the regulation voltage set point. Ater a pre-set period o time# or

when battery voltage drops to the array reconnect voltage set point# the array and batteryare reconnected# and the cycle repeats. As the battery becomes more ully charged# the

time or the battery voltage to reach the regulation voltage becomes shorter each cycle# so

the amount o array current passed through to the battery becomes less each time. In thisway# ull charge is approached gradually in small steps or pulses# similar in operation to

the shunt-interrupting type controller. The principle dierence is the series or shunt mode

by which the array is regulated.

,imilar to the shunt-interrupting type controller# the series-interrupting type designs are

best suited or use with looded batteries rather than the sealed )4A types due to the

way power is applied to the battery

,eries-Interrupting# 2-step# 'onstant-'urrent &esign

This type o controller is similar to the series-interrupting type# however when the voltageregulation set point is reached# instead o totally interrupting the array current# a limited

constant current remains applied to the battery. This Vtric"le charging> continues either or

a pre-set period o time# or until the voltage drops to the array reconnect voltage due toload demand. Then ull array current is once again allowed to low# and the cycle repeats.

$ull charge is approached in a continuous ashion# instead o smaller steps as described

above or the on-o type controllers.

,eries-4inear# 'onstant-)oltage &esign

In a series-linear# constant-voltage controller design# the controller maintains the battery

voltage at the voltage regulation set point. The series regulation element acts li"e avariable resistor# controlled by the controller battery voltage sensing circuit o the

controller. The series element dissipates the balance o the power that is not used to

charge the battery# and generally re9uires heat sin"ing. The current is inherentlycontrolled by the series element and the voltage drop across it.

,eries-linear# constant-voltage controllers can be used on all types o batteries. %ecause

they apply power to the battery in a controlled manner# they are generally more eective

at ully charging batteries than on-o type controllers.

,eries-Interrupting# Pulse !idth /odulated 7P!/8 &esign

This algorithm uses a semiconductor-switching element between the array and battery#

which is# switched onHo at a variable re9uency with a variable duty cycle to maintain

the battery at or very close to the voltage regulation set point. Although a series typeP!/ design is discussed here# shunt-type P!/ designs are also popular and perorm

battery charging in similar ways. ,imilar to the series-linear# constant-voltage algorithm

(


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in perormance# power dissipation within the controller is considerably lower in the series

interrupting P!/ design.

%y electronically controlling the high speed switching or regulation element# the P!/

controller brea"s the array current into pulses at some constant re9uency# and varies the

width and time o the pulses to regulate the amount o charge lowing into the battery.!hen the battery is discharged# the current pulse width is practically ully on all the time.

As the battery voltage rises# the pulse width is decreased# eectively reducing the

magnitude o the charge current.

The P!/ design allows greater control over e?actly how a battery approaches ull

charge and generates less heat. P!/ type controllers can be used with all battery type#

however the controlled manner in which power is applied to the battery ma"es them preerential or use with sealed )4A types batteries over on-o type controls. To limit

overcharge and gassing# the voltage regulation set points or P!/ and constant voltage

controllers are generally speciied lower than those or on-o type controllers.

!3BI+5 3$ ,3A4 'A51 '3+T3441

!hen connecting a solar panel to a rechargeable battery# it is usually necessary to

use a charge controller circuit to prevent the battery rom overcharging and to avoid

power wastage.

,olar charger controller is typically conigured or a three stage charging process# %ul"#

Absorption and $loat. The three-stage charge process provides a somewhat higher chargevoltage to charge the battery 9uic"ly and saely. 3nce the battery is ully charged a

somewhat lower voltage is applied maintain the battery in a ully charged state without

e?cessive water loss. The three stage charge process charges the battery as 9uic"ly as possible while minimiDing battery water loss and maintenance.

2


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$igure (: %ul" charge curve%ul" charge:!hen charge starts the ,olar charger controller attempts to apply the bul" charge voltage

to the battery. The system will switch to %ul" charge i the battery is suiciently

discharged andHor insuicient charge current is available to drive the battery up to the bul" voltage set point. &uring the %ul" charge stage the unit delivers as much charge

current as possible to rapidly recharge the battery. 3nce the charge control system enters

Absorption or $loat# the unit will again switch to %ul" charge i battery voltage drops

below the present charge voltage set point.Absorption charge:

&uring this stage# the unit changes to a constant voltage mode where the absorption

voltage is applied to the battery. !hen charge current decreases to the loat transitioncurrent setting# the battery is ully charged and the unit switches to the loat stage.

$loat charge:

&uring this stage# the loat voltage is applied to the battery to maintain it in a ully

charged state. !hen battery voltage drops below the loat setting or a cumulative period#a new bul" cycle will be triggered.

The above charging process ensures that the battery is not overcharged thus ensuring

long lie o operation. ecently developed charge controllers also use a new technology

called the ma?imum power point trac"ing that allows the charge controller to "eep o the

ma?imum power voltage as operation conditions change thus ma?imiDing the output. ,olar charge controller essentially uses the property o the P) cell being a constant

current type device as shown in ig 2.


34/58

'A51 '3+T3441 ,141'TI3+

The selection and siDing o charge controllers and system controls in P) systems involvesthe consideration o several actors# depending on the comple?ity and control options

re9uired. !hile the primary unction is to prevent battery overcharge# many other

unctions may also be used# including low voltage load disconnect# load regulation andcontrol# control o bac"up energy sources# diversion o energy to and au?iliary load# and

system monitoring. The designer must decide which options are needed to satisy the

re9uirements o a speciic application. The ollowing list some o the basic considerationsor selecting charge controllers or P) systems.

(. ,ystem voltage2. P) array and load currents

. %attery type and siDe. egulation algorithm and switching element design

*. egulation and load disconnect set points. 1nvironmental operating conditions


35/58

costs o service and replacement will be higher than what would have been spent on a

controller that was initially

3versiDed or the application.

Typically# we would e?pect that a P) module or array produces no more than its rated

ma?imum power current at (000 !Hm2 irradiance and 2* o' module temperature.owever# due to possible relections rom clouds# water or snow# the sunlight levels on

the array may be XenhancedY up to (. times the nominal (000 !Hm2 value used to rate

P) module perormance. The result is that pea" array current could be (. times thenominal pea" rated value i relection conditions e?ist. $or this reason# the pea" array

current ratings or charge controllers should be siDed or about (0K or the nominal pea"

ma?imum power current ratings or the modules or array.

The siDe o a controller is determined by multiplying the pea" rated current rom an array

times this XenhancementY saety actor. The total current rom an array is given by the

number o modules or strings in parallel# multiplied by the module current. To be

conservative# use the short-circuit current 7Isc8 is generally used instead o the ma?imum power current 7Imp8. In this way# shunt type controllers that operate the array at short-

circuit current conditions are covered saely.

U,-I,ERRUPIBLE POWER SUPPLY

@P,is designed to provide un-interruptible power supply to critical load. The system is

supplied with a single phase mains power supply# which is rectiied to nominal &'voltage and used to drive inverter and charge a battery. In the event o mains power

ailure# the battery will continue to supply the inverter or a period o time to the loadcurrent.

@n-interruptible power supply comprises mainly o

(. ectiier Z battery charger

2. %attery. Inverter

(. ectiier Z battery charger:

The rectiier Ebattery charger transorms the alternating voltage o the mains to &'

supply to eed the inverter and charging the battery.the level o the &' voltage is decidedupon the number o batteries connected and the charging current depends on the ampere

hour 7Ah8 capacity o the battery.

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2. %attery:

The battery stores &' energy and delivers the same to the inverter whenever the mainsupply ails. 1lectrical energy is converted on to a chemical energy and it is stored when

in charging. ,imilarly the stored chemical energy is converted into electrical energy while

discharging. The bac"up duration depends on the ampere hour capacity o the batteryand the connected load.

. Inverter:

The inverter charging changes the dc voltage rom the rectiier or rom the battery in a

single Ephase sinusoidal alternating 7A'8 voltage or eeding the e?ternal loads

connected to it.

BAERIES

51+1A4 &1,'IPTI3+

To properly select batteries or use in stand-alone P) systems# it is important that system

designers have a good understanding o their design eatures# perormance characteristicsand operational re9uirements. %ecause the demand or energy does not always coincide

with its production# electrical storage batteries are commonly used in P) systems. The

primary unctions o a storage battery in a P) system are to:

(. 1nergy ,torage 'apacity and Autonomy: to store electrical energy when it is produced by the P% array and to supply energy to electrical loa's as needed or on demand.

2. )oltage and 'urrent ,tabiliDation. to supply power to electrical loa's at stable voltages

and currents# by suppressing or Lsmoothing outL transients that may occur in P) systems.

. ,upply ,urge 'urrents: to supply surge or high pea" operating currents to electrical

loa's or appliances.

Battery Design an( *onstr%ction

%attery manuacturing is an intensive# heavy industrial process involving the use o haDardous and to?ic materials. %atteries are generally mass produced# combining several

se9uential and parallel processes to construct a complete battery unit. Ater production#initial charge and discharge cycles are conducted on batteries beore they are shipped to

distributors and consumers.

,ome important components o battery construction are described below.


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'ell:

The cell is the basic electrochemical unit in a battery# consisting o a set o positive and

negative plates divided by separators/ immersed in an electrolyte solution and enclosedin a case. In a typical lea'aci' battery# each cell has a no+inal voltage o about 2.( volts#

so there are series cells in a nominal (2 volt battery. $igure ( shows a diagram o a

basic lead-acid battery cell.

Active /aterial:

The active materials in a battery are the raw composition materials that orm the positiveand negative plates# and are reactants in the electrochemical cell . The amount o active

material in a battery is proportional to the capacity a battery can deliver. In lea'-aci'

batteries# the active materials are lea' 'io,i'e 7Pb328 in the positive plates and +etallic

sponge lea' 7Pb8 in the negative plates# which react with a s#l)#ric aci' 72,38solution during battery operation.

1lectrolyte:The electrolyte is a conducting medium# which allows the low o current through ionic

transer# or the transer o electrons between the plates in a battery. In a lead-acid battery#the electrolyte is a diluted s#l)#ric aci' solution# either in li9uid 7looded8 orm# gelled or

absorbed in glass mats. In looded nic"el cadmium cells# the electrolyte is an al"alinesolution o potassium hydro?ide and water. In most looded battery types# periodic water

additions are re9uired to replenish the electrolyte lost through gassing. !hen adding

water to batteries# it is very important to use distilled or de-mineraliDed water# as even theimpurities

in normal tap water can poison the battery and result in premature ailure.

5rid:

In a lead-acid battery# the grid is typically a lead alloy ramewor" that supports the active

+aterial on a battery plate# and which also conducts current. Alloying elements such asanti+ony and calci#+ are oten used to strengthen the lead grids# and have characteristic

eects on battery perormance such as cycle perormance and gassing . ,ome grids are

made by e?panding a thin lead alloy sheet into a lat plate web# while others are made o

long spines o lead with the active material plated around them orming tubes# or what arereerred to as t#*#lar plates.


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Plate: A plate is a basic battery component# consisting o a gri' and active +aterial/ sometimes

called an electro'e. There are generally a number o positive and negative plates in each battery cell # typically connected in parallel at a bus bar or inter-cell connector at the topo the plates. A pasted plate is manuactured by applying a mi?ture o lea' o,i'e# s#l)#ric

aci' # ibers and water on to the gri' . The thic"ness o the grid and plate aect the deep

cycle perormance o a battery. In automotive starting or ,4I type batteries# many thin

plates are used per cell. This results in ma?imum surace area or delivering highcurrents# but not much thic"ness and mechanical durability or deep and prolonged

discharges. Thic" plates are used or deep cycling applications such as or or"lits# gol

carts and other electric vehicles. Thethic" plates permit deep discharges over long periods# while maintaining good adhesion

o the active material to the grid# resulting in longer lie.

,eparator:

A separator is a porous# insulating divider between the positive and negative plates in a

battery# used to "eep the plates rom coming into electrical contact and short-circuiting#and which also allows the low o electrolyte and ions between the positive and negative

plates. ,eparators are made rom micro porous rubber# plastic or glass-wool mats. In

some cases# the separators may be li"e an envelope# enclosing the entire plate and

preventing shed materials rom creating short circuits at the bottom o the plates.

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1lement:

In element is deined as a stac" o positive and negative plate groups and separators#assembled together with plate straps interconnecting the positive and negative plates.

Terminal Posts: Terminal posts are the e?ternal positive and negative electrical connections to a battery.

A battery is connected in a P) system and to electrical loads at the terminal posts. In alead-acid battery the posts are generally lead or a lead alloy# or possibly stainless steel or

copper-plated steel or greater corrosion resistance. %attery terminals may re9uire

periodic cleaning# particularly or looded designs. It is also recommended that the

clamps or connections to battery terminals be secured occasionally as they may loosenover time.

'ell )ents:

&uring battery charging# gasses are produced within a battery that may be vented to the

atmosphere. In looded designs# the loss o electrolyte through gas escape rom the cellvents it a normal occurrence# and re9uires the periodic addition o water to maintain

proper electrolyte levels. In sealed# or valve-regulated batteries# the vents are designedwith a pressure relie mechanism# remaining closed under normal conditions# but opening

during higher than normal battery pressures# oten the result o overcharging or high

temperature operation. 1ach cell o a complete battery unit has some type o cell vent.

$lame arrestor vent caps are commonly supplied component on larger# industrial battery

systems. The venting occurs through a charcoal ilter# designed to contain a cell e?plosionto one cell# minimiDing the potential or a catastrophic e?plosion o the entire battery

ban".

'ase:

'ommonly made rom a hard rubber or plastic# the case contains the plates# separators

and electrolyte in a battery. The case is typically enclosed# with the e?ception o inter-cell

connectors which attach the plate assembly rom one cell to the ne?t# terminal posts# andvents or caps which allow gassing products to escape and to permit water additions i

re9uired. 'lear battery cases or containers allow or easy monitoring o electrolyte levels

and battery plate condition. $or very large or tall batteries# plastic cases are otensupported with an e?ternal metal or rigid plastic casing.

Battery y#es an( *lassi&ications

/any types and classiications o batteries are manuactured today# each with speciic

design and perormance characteristics suited or particular applications. 1ach battery

type or design has its individual strengths and wea"nesses. In P) systems# lea'-aci' batteries are most common due to their wide availability in many siDes# low cost and well

understood perormance characteristics. In a ew critical# low temperature applications

nic0el-ca'+i#+ cells are used# but their high initial cost limits their use in most P)

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systems. There is no Xperect batteryY and it is the tas" o the P) system designer to

decide which battery type is most appropriate or each application.

In general# electrical storage batteries can be divided into to major categories# pri+aryand secon'ary batteries.

Primary %atteries:

Primary batteries can store and deliver electrical energy# but cannot *e recharge' . Typicalcarbon-Dinc and lithium batteries commonly used in consumer electronic devices are

primary batteries. Primary batteries are not used in P) systems because they cannot be

recharged.,econdary %atteries:

A secondary battery can store and deliver electrical energy# and can also *e recharge' by

passing a current through it in an opposite direction to the discharge current. 'ommon

lea'-aci' batteries used in automobiles and P) systems are secondary batteries. Table (lists common secondary battery types and their characteristics which are o importance to

P) system designers.

Table (. ,econdary %attery Types and 'haracteristics

Lea(-Aci( Battery *lassi&ications

/any types o lead-acid batteries are used in P) systems# each having speciic design

and perormance characteristics. !hile there are many variations in the design and

perormance o lead-acid cells# they are oten classiied in terms o one o the ollowingthree categories.

SLI Batteries

,tarting# lighting and ignition 7,4I8 batteries are a type o lead-acid battery designed

primarily or shallow cycle service# most oten used to power automobile starters. These

batteries have a number o thin positive and negative plates per cell# designed to increase

the total plate active surace area. The large number o plates per cell allows the battery todeliver high discharge currents or short periods. !hile they are not designed or long lie

under deep cycle service# ,4I batteries are sometimes used or P) systems in developing

countries where they are the only type o battery locally manuactured. Although notrecommended or most P) applications# ,4I batteries may provide up to two years o

useul service in small stand-alone P) systems where the average 'aily depth o

discharge is limited to (0-20K# and the ma?imum allowa*le 'epth o) 'ischarge is limitedto 0-0K.

0


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/otive Power or Traction %atteries:

/otive power or traction batteries are a type o lead acid

battery designed or deep discharge cycle service# typically used in electrically operatedvehicles and e9uipment such as gol carts# or" lits and loor sweepers. These batteries

have a ewer number o plates per cell than ,4I batteries[ however the plates are much

thic"er and constructed more durably. igh content lea'-anti+ony gri's are primarilyused in motive power batteries to enhance deep cycle perormance. Traction or motive

power batteries are very popular or use in P) systems due to their deep cycle capability#

long lie and durability o design.,tationary %atteries:

,tationary batteries are commonly used in un-interruptible power

supplies 7@P,8 to provide bac"up power to computers# telephone e9uipment and other

critical loads or devices. ,tationary batteries may have characteristics similar to both ,4Iand motive power batteries# but are generally designed or occasional deep discharge#

limited cycle service. 4ow water loss lea'-calci#+ battery designs are used or most

stationary battery applications# as they are commonly loat charged continuously.

4ead-Acid %attery 'hemistry

+ow that the basic components o a battery have been described# the overallelectrochemical operation o a battery can be discussed. eerring to $igure (0-(# the

basic lead-acid battery cell consists o sets positive and negative plates# divided by

separators# and immersed in a case with an electrolyte solution. In a ully charged lead-acid cell# the positive plates are lead dio?ide 7Pb328# the negative plates are sponge lead

7Pb8# and the electrolyte is a diluted suluric acid solution. !hen a battery is connected to

an electrical load# current lows rom the battery as the active materials are converted to

lead sulate 7Pb,38.

4ead-Acid 'ell eaction

The ollowing e9uations show the electrochemical reactions or the lead-acid cell. &uring battery discharge# the directions o the reactions listed goes rom let to right. &uring

battery charging# the direction o the reactions are reversed# and the reactions go rom

right to let. +ote that the elements as well as charge are balanced on both sides o eache9uation.

At the positive plate or electrode:

Pb32 \ ,3- \ \ \ 2 e ]UPb,3 \23

3n the negative electrode

Pb \ ,3- ]UPb,3 \ \ \ 2 e-

3verall reaction:

Pb \ Pb32 \ 2 \ \ 2 ,3- ]U2 Pb,3 \ 2 23

(


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As the battery is discharged# the active materials Pb32 and Pb in the positive and

negative plates# respectively# combine with the suluric acid solution to orm Pb,3 and

water. +ote that in a ully discharged battery the active materials in both the positive andnegative plates are converted to Pb,3# while the suluric acid solution is converted to

water.

%attery ,trengths and !ea"nesses:

1ach battery type has design and perormance eatures suited or particular applications.

Again# no one type o battery is ideal or a P) system applications. The designer mustconsider the advantages and disadvantages o dierent batteries with respect to the

re9uirements o a particular application. ,ome o the considerations include lietime#

deep cycle perormance# tolerance to high temperatures and overcharge# maintenance and

many others. The ollowing table summariDes some o the "ey characteristics o thedierent battery types discussed in the preceding section.

%attery ,election 'riteria

A %attery system design and selection criterion involves many decisions and trade os.

'hoosing the right battery or a P) application depends on many actors. !hile no

speciic battery is appropriate or all P) applications# common sense and a careul review

2


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o the battery literature with respect to the particular application needs will help the

designer narrow the choice. ,ome decisions on battery selection may be easy to arrive at#

such as physical properties# while other decisions will be much more diicult and mayinvolve ma"ing tradeos between desirable and undesirable battery eatures. !ith the

proper application o this "nowledge# designers should be able to dierentiate among

battery types and gain some application e?perience with batteries they are amiliar with.Table summariDes some o the considerations in battery selection and design.

UType o system and mode o operation

U'harging characteristics[ internal resistance

Ue9uired days o storage 7autonomy8

UAmount and variability o discharge current

U/a?imum allowable depth o discharge

U&aily depth o discharge re9uirements

UAccessibility o location

UTemperature and environmental conditions

U'yclic lie andHor calendar lie in years

U/aintenance re9uirements

U,ealed or unsealed

U,el-discharge rate

U/a?imum cell capacity

U1nergy storage density

U,iDe and weight

U5assing characteristics

U,usceptibility to reeDing

U,usceptibility to sulation

U1lectrolyte concentration

UAvailability o au?iliary hardware

UTerminal coniguration

Ueputation o manuacturer

U'ost and warranty.

In the individual case# the selection o battery depends upon very many actors and will

be inluenced by system management and climatic conditions. The special re9uirements

made o the battery in operation can be broadly classiied according to the operating time

per year# the type o loads 7 high or low power drain8 and the number o cycles per wee".owever# it is still diicult to ma"e generaliDations about which battery type is best or

which typical applications# as the basic conditions 7such as cost# housing capabilities#

maintenance capabilities and reliability re9uirements8 can be deciding actors.

%atteries or use in a pv stand-alone system should have the ollowing eatures:

(. 5ood PriceH Perormance ratio

2. 4ow maintenance re9uirements

. ,uiciently long service lie

. 4ow sel-discharging and high energy eiciency


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*. 'an be charged with small charge currents

. igh energy and power density 7space re9uirement and weight 8


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grids# resulting in greater gassing and electrolyte loss. 4ower operating temperatures

generally increase battery lie. owever# the capacity is reduced signiicantly at lower

temperatures# particularly or lead-acid batteries. !hen severe temperature variationsrom room temperatures e?ist# batteries are located in an insulated or other temperature-

regulated enclosure to minimiDe battery temperature swings.

Temperature eects on battery lie

*orrosion

The electrochemical activity resulting rom the immersion o two dissimilar metals in an

electrolyte# or the direct contact o two dissimilar metals causing one material to undergoo?idation or lose electrons and causing the other material to undergo reduction# or gain

electrons. 'orrosion o the grids supporting the active material in a battery is an ongoing process and may ultimately dictate the batteryLs useul lietime. %attery terminals mayalso e?perience corrosion due to the action o electrolyte gassing rom the battery# and

generally re9uire periodic cleaning and tightening in looded lead-acid types. igher

temperatures and the low o electrical current between two dissimilar metals accelerates

the corrosionProcess.

Battery .assing

5assing occurs in a battery during charging when the battery is nearly ully charged. At

this point# essentially all o the active materials have been converted to their ully chargedcomposition and the cell voltage rises sharply. The gas products are either recombined

internal to the cell as in sealed or valve reg#late' batteries# or released through the cell

vents in looded batteries. In general# the overcharge or gassing reaction in batteries is

irreversible# resulting in water loss. owever in sealed lead-acid cells# an internalrecombinant process permits the reorming o water rom the hydrogen and o?ygen

gasses generated under normal charging conditions# allowing the battery to be sealed and

re9uiring no electrolyte maintenance. All gassing reactions consume a portion o the

*


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charge current which can not be delivered on the subse9uent discharge# thereby reducing

the battery charging eiciency.

The onset o gassing in a lead-acid cell is not only determined by the cell voltage# but the

temperature as well. As temperatures increase# the corresponding gassing voltage

decreases or a particular battery. egardless o the charge rate# the gassing voltage is thesame# however gassing begins at a lower battery state o charge at higher charge rates.

The grid design# whether lead-antimony or lead-calcium also aects gassing.

The charge regulation voltage# or the ma?imum voltage that a charge controller allows a

battery to reach in operation plays an important part in battery gassing. 'harge controllers

are used in photovoltaic power systems to allow high rates o charging up to the gassing

point# and then limit or disconnect the P) current to prevent overcharge. The highestvoltage that batteries are allowed to reach determines in part how much gassing occurs. I

charge regulation voltages in a typical P) system were set at the manuacturer>s

recommended loat voltage# the batteries would never be ully charged.

S%l&ation

,ulation is a normal process that occurs in lead-acid batteries resulting rom prolonged

operation at partial states o charge. 1ven batteries which are re9uently ully charged

suer rom the eects o sulation as the battery ages. The sulation process involves the

growth o le

study on process and othe requirement for solar inverter

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